Cells
Content
Mitosis is a type of cellular reproduction where a cell will produce an identical replica of itself
with the same number and patterns of genes and chromosomes.
Meiosis, on the other hand, is a special process in cellular division where cells are created
containing gene patterns of different types and combinations with 50% of the number of
chromosomes of the original cell.
Meiosis is used in sexual reproduction of organisms to combine male and female, through the
spermazoa and egg, to create a new, singular biological organism. Mitosis is used by single
celled organisms to reproduce, or in the organic growth of tissues, fibers, and mibranes.
Comparison chart
Meiosis
Discovered by:
Type of
Reproduction:
Genetically:
Cytokenesis:
Number of
Divisions:
Pairing of
Homologues:
Oscar Hertwig
Mitosis
Walther Flemming
Sexual
Asexual
different
Occurs in Telophase I & Telohpase II
identical
Occurs in Telophase
2
1
Yes
No
Function:
sexual reproduction
Cellular Reproduction & general
growth and repair of the body
Reduced by half
Remains the same
Occurs in Interphase I
Mixing of chromosomes
The centromeres do not separate during
anaphase I, but during anaphase II
Occurs in Interphase
Does not occur
The centromeres split during
Anaphase
Yes
No
Humans, animals, plants, fungi
all organisms
4
2
Chromosome
Number:
Karyokenesis:
Crossing Over:
Centromeres
Split:
Occurrence of
Crossing Over:
Occurs in:
Number of
Daughter Cells
produced:
Creates:
Definition:
Sex cells only: Female egg cells or Male Makes everything other than sex
sperm cells
cells
A type of cellular reproduction in which A process of asexual reproduction in
the number of chromosomes are reduced which the cell divides in two
by half through the separation of
producing a replica, with an equal
homologous chromosomes in a diploid number of chromosomes in haploid
cell.
cell
Produces:
Steps:
Meiosis
four haploid daughter cells
The steps of meiosis are Interphase,
Prophase I, Metaphase I, Anaphase I,
Telophase I, Prophase II, Metaphase II,
Anaphase II and Telophase II.
Mitosis
two diploid daughter cells
The steps of mitosis are Interphase,
Prophase, Metaphase, Anaphase,
Telophase and Cytokinesis
Process Differences
Mitosis is a method of reproduction for single celled organisms that reproduce asexually. An
identical version of the organism is created through splitting of the cell in two. Meiosis may
result in millions of spermazoa and egg cells with unique genetic patterns. The mating of the two
cells formed by meiosis results in a unique genetic offspring of the same species. Meiosis is a
major factor in evolution, natural selection, and biodiversity. The processes of cellular division
shown in mitosis and meiosis are present in all manner of life forms including humans, animals,
plants, fungi, and single celled organisms and species. Essentially any cell based organism of
which all organic life is based will exhibit some form of mitosis and meiosis for growth and
reproduction of the individual and species.
Different Stages of Mitosis and Meiosis
The different phases of meiosis are: Prophase, Metaphase, Anaphase and Telophase.
An overview of the process and phases of meiosis
The stages of mitosis are: Interphase, Preprophase, Prophase, Prometaphase, Metaphase,
Anaphase, Telophase and Cytokinesis.
The process of mitosis
Differences in Purpose
Both Meiosis and Mitosis are found in complex organisms which reproduce sexually. Mitosis
may be used for human growth, the replenishment of depleted organs and tissues, healing, and
sustenance of the body. Identical versions of cells can be created to form tissues through Mitosis.
Meiosis is a special process reserved for the creation of the egg and sperm cells. The same
patterns may be found in many species of plant and animal cell reproduction.
Significance of Mitosis vs. Meiosis
The importance of mitosis is the maintenance of the chromosomal set; each cell formed receives
chromosomes that are alike in composition and equal in number to the chromosomes of the
parent cell.
Occurrence
Meiosis is found to occur in humans, animals and plants while mitosis is found in single-cell
species as well.
History
Meiosis was discovered and described for the first time in sea urchin eggs in 1876, by noted
German biologist Oscar Hertwig.
Walther Flemming discovered the process of Mitosis in 1882.
Evolution of mitosis vs. meiosis
Mitosis as a form of reproduction for single-cell organisms originated with life itself (around 4
billion years ago). Meiosis is thought to have appeared 1.4 billion years ago.
Chromosomal pattern comparison
In mitosis, each daughter cell ends up with two complete sets of chromosomes while in meiosis,
each daughter cell ends up with one set of chromosomes.
Both mitosis and meiosis are studied by scientists generally by using a microscope to identify
and classify chromosomal patterns and relationships within the cell’s structure. An understanding
of the way cells synthesize chromosomes for reproduction can be applied in bio-machines and
nano-technology. Transplantation of genes and chromosomes through injection and implantation
is used to experiment with bio-engineering and cloning. Understanding the process through
which cells replicate also has application in medicine and the study of health and disease.
The cell cycle
Actively dividing eukaryote cells pass through a series of stages known collectively as the cell
cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is
duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides.
G1 phase. Metabolic changes prepare the cell for division. At a certain point
- the restriction point - the cell is committed to division and moves into the S
phase.
S phase. DNA synthesis replicates the genetic material. Each chromosome
now consists of two sister chromatids.
G2 phase. Metabolic changes assemble the cytoplasmic materials necessary
for mitosis and cytokinesis.
M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis).
The period between mitotic divisions - that is, G1, S and G2 - is known as interphase.
Mitosis
Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same
genetic component as the parent cell. Chromosomes replicated during the S phase are divided in
such a way as to ensure that each daughter cell receives a copy of every chromosome. In actively
dividing animal cells, the whole process takes about one hour.
The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then
separates the sister chromatids to produce an even partitioning of the genetic material. This
separation of the genetic material in a mitotic nuclear division (or karyokinesis) is followed by a
separation of the cell cytoplasm in a cellular division (or cytokinesis) to produce two daughter
cells.
In some single-celled organisms mitosis forms the basis of asexual reproduction. In diploid
multicellular organisms sexual reproduction involves the fusion of two haploid gametes to
produce a diploid zygote. Mitotic divisions of the zygote and daughter cells are then responsible
for the subsequent growth and development of the organism. In the adult organism, mitosis plays
a role in cell replacement, wound healing and tumour formation.
Mitosis, although a continuous process, is conventionally divided into five stages: prophase,
prometaphase, metaphase, anaphase and telophase.
The phases of mitosis
Prophase
Prophase occupies over half of mitosis. The nuclear membrane breaks down to form a number of
small vesicles and the nucleolus disintegrates. A structure known as the centrosome duplicates
itself to form two daughter centrosomes that migrate to opposite ends of the cell. The
centrosomes organise the production of microtubules that form the spindle fibres that constitute
the mitotic spindle. The chromosomes condense into compact structures. Each replicated
chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held
together by a structure known as the centromere.
Prometaphase
The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the
cell - at right-angles to the axis formed by the centrosomes. This region of the mitotic spindle is
known as the metaphase plate. The spindle fibres bind to a structure associated with the
centromere of each chromosome called a kinetochore. Individual spindle fibres bind to a
kinetochore structure on each side of the centromere. The chromosomes continue to condense.
Metaphase
The chromosomes align themselves along the metaphase plate of the spindle apparatus.
Anaphase
The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each
chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by
spindle fibres attached to the kinetochore regions. The separated sister chromatids are now
referred to as daughter chromosomes. (It is the alignment and separation in metaphase and
anaphase that is important in ensuring that each daughter cell receives a copy of every
chromosome.)
Telophase
The final stage of mitosis, and a reversal of many of the processes observed during prophase.
The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the
chromosomes uncoil and become diffuse, and the spindle fibres disappear.
Cytokinesis
The final cellular division to form two new cells. In plants a cell plate forms along the line of the
metaphase plate; in animals there is a constriction of the cytoplasm. The cell then enters
interphase - the interval between mitotic divisions.
Meiosis
Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes (which
contain a single copy of each chromosome) from diploid cells (which contain two copies of each
chromosome). The process takes the form of one DNA replication followed by two successive
nuclear and cellular divisions (Meiosis I and Meiosis II). As in mitosis, meiosis is preceded by a
process of DNA replication that converts each chromosome into two sister chromatids.
Meiosis I
Meiosis I separates the pairs of homologous chromosomes.
In Meiosis I a special cell division reduces the cell from diploid to haploid.
Prophase I
The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.
Prophase I is divided into five phases:
Leptotene: chromosomes start to condense.
Zygotene: homologous chromosomes become closely associated (synapsis)
to form pairs of chromosomes (bivalents) consisting of four chromatids
(tetrads).
Pachytene: crossing over between pairs of homologous chromosomes to
form chiasmata (sing. chiasma).
Diplotene: homologous chromosomes start to separate but remain attached
by chiasmata.
Diakinesis: homologous chromosomes continue to separate, and chiasmata
move to the ends of the chromosomes.
Prometaphase I
Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.
Metaphase I
Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase
plate. The arrangement of the paired chromosomes with respect to the poles of the spindle
apparatus is random along the metaphase plate. (This is a source of genetic variation through
random assortment, as the paternal and maternal chromosomes in a homologous pair are similar
but not identical. The number of possible arrangements is 2n, where n is the number of
chromosomes in a haploid set. Human beings have 23 different chromosomes, so the number of
possible combinations is 223, which is over 8 million.)
Anaphase I
The homologous chromosomes in each bivalent are separated and move to the opposite poles of
the cell
Telophase I
The chromosomes become diffuse and the nuclear membrane reforms.
Cytokinesis
The final cellular division to form two new cells, followed by Meiosis II. Meiosis I is a reduction
division: the original diploid cell had two copies of each chromosome; the newly formed haploid
cells have one copy of each chromosome.
Meiosis II
Meiosis II separates each chromosome into two chromatids.
The events of Meiosis II are analogous to those of a mitotic division, although the number of
chromosomes involved has been halved.
Meiosis generates genetic diversity through:
the exchange of genetic material between homologous chromosomes during
Meiosis I
the random alignment of maternal and paternal chromosomes in Meiosis I
the random alignment of the sister chromatids at Meiosis II
Meiosis in females
BIOS 170
Cell Division: Mitosis and Meiosis
CHROMOSOME:
Between divisions the chromosome is a threadlike strand.
During interphase the chromosome replicates and becomes 2 thread like
strands.
Homologous Chromosomes:
Pairs of chromosomes similar in size, shape, & genetic information, but not
identical.
When both members of each pair are present, the cell is diploid (2n).
When only one member of the pair is present, the cell is haploid (n).
Humans:
o
diploid (2n) = 46
o
haploid (n) = 23
Recent cytokinesis
MITOSIS
The equal division of all cellular components to form two daughter cells that
are identical to the original cell.
Ensures the same number and kind of chromosomes as the original cell. This is
accomplished by replicating the DNA prior to cell division.
Original cell and daughter cells are all diploid.
Functions in asexual reproduction
Basis for growth in multi-celled organisms
Occurs in somatic cells found throughout the body.
MITOSIS (white fish)
MITOSIS (onion)
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Prophase
Metaphase
Anaphase
Telophase
MITOSIS
MEIOSIS
Functions in growth and Functions in sexual reproduction in multi-celled
asexual reproduction.
organisms.
Occurs in somatic cells
Occurs in germ cells, located in testes or ovaries.
found throughout the body.
Produces haploid cells, or gametes, with the genetic
Produces clones, or exact
material halved. When the gametes (eggs & sperm) fuse in
replicates of the cell.
fertilization the diploid # is restored.
Occurs in one division.
Requires two divisions.
Watch a NOVA Online Animation
How Cells Divide: Mitosis vs. Meiosis
Meiosis oogenesis in Ascaris
Primary oocyte with sperm nucleus
Secondary oocyte in late anaphase II or early
telophase II
Primary oocyte with intact
spermatozoan
Primary oocyte in metaphase I
Primary oocyte in late anaphase I
or early telophase I
Secondary oocyte in metaphase II
Secondary oocyte and first polar
body in metaphase II
Secondary oocyte in early anaphase
II
Ovum where two polar bodies are visible
Ovum with male and female pronuclei
Ovum with male and female pronuclei
beginning to unite chromosomes
Zygote undergoing mitosis in metaphase
Zygote undergoing mitosis in anaphase
Zygote undergoing mitosis in telophase
GENETICS & DEVELOPMENT - Cell Division
Physical Basis of Inheritability...
Key Concepts*
Mechanisms of Cell Reproduction... egg cells & sperm cells
cells reproduce identically, yet with variations (new traits)
"All living cells arise from pre-existing cells"
GENETICS
level
asks.... HOW? What are mechanisms at cellular & molecular
for physical basis of inheritability?
looks.... at mechanisms of the LIFE CYCLE of organisms
1. cellular mechanisms of reproduction in organisms
2. growth of organism..... zygote to adult
DEVELOPMENT
cell differentiation - how one cell becomes different
from another
times
differential gene activity - genes are active at different
totipotency & cloning - exact genetic copies of cells
METHODS of CELL REPRODUCTION include...
Fission* - binary = 2 equal halves
(bacteria & cyanobacteria
& protozoans)
Budding* - outgrowths detach = new organism
(unequal split)
(hydra)
Chapter 46.1 video: Video:
Hydra Budding
Mitosis* - asexually = identical genetic copies
[cytokinesis*]
genetically equal somatic cells
1.5 lung cell*
divisions
c7 fig
amoeba, sand dollar, bone marrow cell
Meiosis* - sexually produces sperm & egg cells with
1/2 chromosome number & new
gene combos
MITOSIS - Asexual Reproduction Cell Cycle...
results in copying & equal duplication of parental cell's DNA
and the equal division of chromosomes into two daughter cells
(rates = epithelial cells 1x/day - liver cells 1x/yr)
the Life cycle of a Cell... is known as the "CELL CYCLE"...
Concept Activity 12.2 -
Cell Cycle
[3 Stages] -
Cell Cycle
o
is depicted as a circle 360 fig 12.5*
The
[G1 - S - G2 -
M]
Interphase - period between successive divisions of a cell
period after
3 parts =
G1 - before, DNA synthesis (S),
MITOSIS* - nuclear division phase;
& G2
separation & duplication of chromosomes
Cytokenesis* - physical division of cell into two parts: animals/plants
How does one determine the times of the phases of Cell Cycle ?
fibroblast cell cultures*
S-phase: pulse chase*experiments*
Investigation 12.2 - How much time is spent in each
phase of cell cycle
Stages of Mitosis*-pics*
Sumanas, Inc. animation -
Mitosis
Prophase -
Concept activity
12.2 Mitosis and Cytokinesis Video
chromatin condenses into chromosomes animation* cartoon
Prometaphase chromosome MT's attach to kinetochores
fig
12.6*
each homolog has 2 chromatids
Metaphase -
Concept Activity 12.2
Mitosis & Cytokinesis Animation
chromosomes align at equator
fig
12.6*
homologs align independently of each other
Anaphase MT attached to kinetochore; chromatids
fig12.8
are pulled apart & poles move apart
Telophase - ex:
cells*
animal cells* & onion root tip
chromosomes at opposite poles; daughter cells
form by cytokinesis.
next
BioFlix animation of mitosis*view@home
Names and Numbers -
(to protect the innocent)
Structure of chromosomes*
Genes occur in chromatin of nucleus,
which condense into CHROMOSOMES
(colored bodies) visible only during
MITOSIS
animation of DNA coiling into
chromosomes
bacteria have about 3,000 genes
(DNA molecule only)
humans have some 20 to 25,000+ genes
&
1 chromosome
&
46 chromosomes
Humans have 46 chromosomes or 23 HOMOLOGOUS pairs
23 maternal chromosomes
23 paternal chromosomes
Control of Cell Division and the Cell Cycle
2001 Nobel prize
Regulated by "Growth Factors" - proteins that promote cell division,
such as...
MPF - mitotic promoting factor...
cyclin]
cycle
protein-P
[ complex* of two proteins cdk +
MPF is a kinase enzyme, one that switches on/off target cell
proteins by phosphorylating them.....
inactive cycle protein ---------------->
active-
ATP ---> ADP
MPF promotes entrance into mitosis from the G2 phase by
phosphorylating multiple
proteins during mitosis including one that leads to destruction of
cyclin itself
MPF - cdk - a cell division control protein - cyclin dependent kinase;
active only when bound to cyclin;
cyclin - a protein whose amount varies cyclically;
when in high concentrations*, binds to cdk
makes MPF...
[cyclin + cdk = MPF]... favors
Mitosis
Growth Factors regulate at critical points... Cell cycle checkpoints*
Many cells divide on a circadian rhythm*
Concept Activity - 12.1 - Roles of Cell Division &
eukaryotic cell
cycle regulation
SEXUAL CELL REPRODUCTION...
"MEIOSIS"
nuclear division phase of
sexually dividing cells
compare physical differences* between nuclear divisions
of MEIOSIS & MITOSIS
so the Distinct Differences are:
Key Concepts*
meiosis = 4 progeny cells [1 = 2 = 4]...
thus 2
divisions
mitosis = 2 daughter cells only...
thus 1 cell division
meiosis = one-half number of chromosomes
mitosis = same # of chromosomes as parent
cell
meiosis = new combinations of genes not in
parents &
chromosomes sort randomly of each
other
mitosis = daughter cells are genetically
identical
Sexual Cell Reproduction
(Meiosis)
Only specialized sex cells can undergo meiosis...
and where does meiosis occur during the sexual cell cycle ?
Meiosis ---> produces cells half chrm # = 23 (sperm & egg haploid)
only specialized cells - gametes - can undergo meiosis.
Fertilization (sperm + egg) --->
# = 46)
diploid life cycle* --->
(chrm
Alternation of Generations* & Human life Cycle*
Concept Activity 13.1 - Asexual and Sexual Life
Cycles
Stages of Sexual Cell Division
same 3 phases of cell cycle...
just as in asexual division
(Interphase, Nuclear Division, Cytokinesis)
but, 2 Divisions
Meiosis I
and Meiosis II
1 cell = 2 cell = 4 cells
Names of stages are same & have analogous functions
Meiosis I...
male grasshopper meiosis
Prophase I
tetrad
= chromosomes condense
SYNAPSIS - homologs PAIR together --->
CROSSOVER* - exchange occurs at a chiasma
Metaphase I = chromosomes align at
equator
Anaphase I = chromosomes migrate toward poles
Telophase I = chromosome at poles - cell domains separate
Meiosis I separates homologs of homologous pair* fig 13.7*
Meiosis II...
is just like mitosis [but without an S phase]
separates chromatids of one homolog of the
homologous pair
just as is done in mitosis
Comparison(fig 13.9)* of Mitosis/Meiosis - comparison animation*view @
home
Independent Assortment* - random alignment of homologous pairs
(fig)
Crossing Over - exchange of chromosome material
BioFlix animation of meiosis*view@home & another meiosis animation*
Concept Activity 13.3 - Meiosis Animation
of Meiosis*
Sumanas, Inc. animation
Summary of MEIOSIS
1. Nuclear division phase of sexual cell reproduction
cycle
2. Two successive divisions, results in 4 daughter
cells...
Meiosis 1 and Meiosis 2
3. Reduction/division occurs.... diploid ----> haploid
daughter cells ½ number of parent cell
chromosomes
4. Stages have same nomenclature as Mitosis
prophase, metaphase, anaphase, telophase,
M1 & M2
5. Only one S phase, where DNA is duplicated
often may be no interphase between M1 &
M2
6. Homologs separate in Meiosis 1
Chromatids separate in Meiosis 2 (mitoticlike)
7. Random Assortment occurs...... homologs align
at equitorial plates independent of each
other
8. Crossing over... may occur in Prophase I...
synapsis = close pairing homologs allows
exchange
chiasma = point exchange of sister
chromatids
[table
of differences]*
issue (biology)
From Wikipedia, the free encyclopedia
This article is about biological tissue. For other uses, see Tissue.
Cross section of sclerenchyma fibers in plant ground tissue
Microscopic view of a histologic specimen of human lung tissue stained with
hematoxylin and eosin.
Tissue is a cellular organizational level intermediate between cells and a complete organism. A
tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together
carry out a specific function. These are called tissues because of their identical functioning.
Organs are then formed by the functional grouping together of multiple tissues.
The study of tissue is known as histology or, in connection with disease, histopathology. The
classical tools for studying tissues are the paraffin block in which tissue is embedded and then
sectioned, the histological stain, and the optical microscope. In the last couple of decades,
developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections
have enhanced the detail that can be observed in tissues. With these tools, the classical
appearances of tissues can be examined in health and disease, enabling considerable refinement
of clinical diagnosis and prognosis.
Contents
1 Animal tissues
o 1.1 Connective tissue
o
1.2 Muscle tissue
o
1.3 Nervous tissue
o
1.4 Epithelial tissue
2 Plant tissues
o
2.1 Meristematic tissues
o
2.2 Permanent tissues
3 See also
2.2.1 Simple permanent tissues
2.2.1.1 Parenchyma
2.2.1.2 Collenchyma
2.2.1.3 Sclerenchyma
2.2.1.4 Epidermis
2.2.2 Complex permanent tissue
2.2.2.1 Xylem
2.2.2.2 Phloem
4 References
5 External links
Animal tissues
PAS diastase showing the fungus Histoplasma.
Animal tissues can be grouped into four basic types: connective, muscle, nervous, and epithelial.
Multiple tissue types comprise organs and body structures. While all animals can generally be
considered to contain the four tissue types, the manifestation of these tissues can differ
depending on the type of organism. For example, the origin of the cells comprising a particular
tissue type may differ developmentally for different classifications of animals. The epithelium in
all animals is derived from the ectoderm and endoderm with a small contribution from the
mesoderm which forms the endothelium. By contrast, a true epithelial tissue is present only in a
single layer of cells held together via occluding junctions called tight junctions, to create a
selectively permeable barrier. This tissue covers all organismal surfaces that come in contact
with the external environment such as the skin, the airways, and the digestive tract. It serves
functions of protection, secretion, and absorption, and is separated from other tissues below by a
basal lamina. Endothelium, which comprises the vasculature, is a specialized type of epithelium.
Connective tissue
Connective tissues are fibrous tissues. They are made up of cells separated by non-living
material, which is called extracellular matrix. Connective tissue gives shape to organs and holds
them in place. Both blood and bone are examples of connective tissue. As the name implies,
connective tissue serves a "connecting" function. It supports and binds other tissues. Unlike
epithelial tissue, connective tissue typically has cells scattered throughout an extracellular
matrix.
Muscle tissue
Muscle cells form the active contractile tissue of the body known as muscle tissue. Muscle tissue
functions to produce force and cause motion, either locomotion or movement within internal
organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle,
which is found in the inner linings of organs; skeletal muscle, in which is found attached to bone
providing for gross movement; and cardiac muscle which is found in the heart, allowing it to
contract and pump blood throughout an organism..
Nervous tissue
Cells comprising the central nervous system and peripheral nervous system are classified as
neural tissue. In the central nervous system, neural tissue forms the brain and spinal cord and, in
the peripheral nervous system forms the cranial nerves and spinal nerves, inclusive of the motor
neurons. Transmits communications.
Epithelial tissue
The epithelial tissues are formed by cells that cover organ surfaces such as the surface of the
skin, the airways, the reproductive tract, and the inner lining of the digestive tract. The cells
comprising an epithelial layer are linked via semi-permeable, tight junctions; hence, this tissue
provides a barrier between the external environment and the organ it covers. In addition to this
protective function, epithelial tissue may also be specialized to function in secretion and
absorption. Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid
loss.
Plant tissues
Cross-section of a flax plant stem with several layers of different tissue types:
hi 1. Pith,
2. Protoxylem,
3.
4.
5.
6.
7.
Xylem I,
Phloem I,
Sclerenchyma (bast fibre),
Cortex,
Epidermis
Examples of tissue in other multicellular organisms are vascular tissue in plants, such as xylem
and phloem. Plant tissues are categorized broadly into three tissue systems: the epidermis, the
ground tissue, and the vascular tissue. Together they are often referred to as biomass.
Epidermis - Cells forming the outer surface of the leaves and of the young
plant body.
Vascular tissue - The primary components of vascular tissue are the xylem
and phloem. These transport fluid and nutrients internally.
Ground tissue - Ground tissue is less differentiated than other tissues.
Ground tissue manufactures nutrients by photosynthesis and stores reserve
nutrients.
Plant tissues can also be divided differently into two types:
1. Meristematic tissues
2. Permanent tissues
Meristematic tissues
Meristematic tissue consists of actively dividing cells, and leads to increase in length and
thickness of the plant. The primary growth of a plant occurs only in certain, specific regions,
such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells
in these tissues are roughly spherical or polyhedral, to rectangular in shape, and have thin cell
walls. New cells produced by meristem are initially those of meristem itself, but as the new cells
grow and mature, their characteristics slowly change and they become differentiated as
components of the region of occurrence of meristimatic tissues, they are classified as:
a) Apical Meristem - It is present at the growing tips of stems and roots and
increases the length of the stem and root. They form growing parts at the
apices of roots and stems and are responsible for increase in length,also
called primary growth.This meristem is responsible for the linear growth of an
organ.
b) Lateral Meristem - This meristem consist of cells which mainly divide in
one plane and cause the organ to increase in diameter and growth. Lateral
Meristem usually occurs beneath the bark of the tree in the form of Cork
Cambium and in vascular bundles of dicots in the form of vascular cambium.
The activity of this cambium results in the formation of secondary growth.
c) Intercalary Meristem - This meristem is located in between permanent
tissues. It is usually present at the base of node, inter node and on leaf base.
They are responsible for growth in length of the plant.This adds growth in the
girth of stem.
The cells of meristematic tissues are similar in structure and have thin and elastic primary cell
wall made up of cellulose. They are compactly arranged without inter-cellular spaces between
them. Each cell contains a dense cytoplasm and a prominent nucleus. Dense protoplasm of
meristematic cells contains very few vacuoles. Normally the meristematic cells are oval,
polygonal or rectangular in shape.
Meristemetic tissue cells have a large nucleus with small or no vacuoles, they have no inter
cellular spaces.
Permanent tissues
The meristematic tissues that take up a specific role lose the ability to divide. This process of
taking up a permanent shape, size and a function is called cellular differentiation. Cells of
meristematic tissue differentiate to form different types of permanent tissue. There are 2 types of
permanent tissues:
1. simple permanent tissues
2. complex permanent tissues
Simple permanent tissues
These tissues are called simple because they are composed of similar types of cells which have
common origin and function. They are further classified into:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma
4. Epidermis
Parenchyma
It consists of relatively unspecialised cells with thin cell walls. They are live cells. They are
usually loosely packed, so that large spaces between cells(intercellular spaces)are found in this
tissue. This tissue provides support to plants and also stores food.In some situations , it contains
chlorophyll and performs photosynthesis, and then it is called chlorenchyma. In aquatic
plants,large air cavities are present in parenchyma to give support to them to float on water. Such
a parenchyma type is called aerenchyma.
Collenchyma
Cross section of collenchyma cells
Collenchyma is Greek word where "Collen" means gum and "enchyma" means infusion. It is a
living tissue of primary body like Parenchyma. Cells are thin-walled but possess thickening of
cellulose and pectin substances at the corners where number of cells join together. This tissue
gives a tensile strength to the plant and the cells are compactly arranged and do not have intercellular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and
in roots.
Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides
mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing
sugar and storing it as starch. It is present in margin of leaves and resist tearing effect of the
wind.
Sclerenchyma
Sclerenchyma is Greek word where "Sclrenes" means hard and "enchyma" means infusion. This
tissue consists of thick-walled, dead cells. These cells have hard and extremely thick secondary
walls due to uniform distribution of lignin. Lignin deposition is so thick that the cell walls
become strong, rigid and impermeable to water. Sclerenchymatous cells are closely packed
without inter-cellular spaces between them. Thus, they appear as hexagonal net in transverse
section. The cells are cemented with the help of lamella. The middle lamella is a wall that lies
between adjacent cells. Sclerenchymatous cells mainly occur in hypodermis, pericycle,
secondary xylem and phloem. They also occur in endocorp of almond and coconut. It is made of
pectin, lignin, protein. The cells of sclerenchymatous cells can be classified as :
1. Fibres- Fibres are long, elongated sclerenchymatous cells with pointed ends.
2. Sclerides- Sclerenchymatous cells which are short and possess extremely
thick, lamellated, lignified walls with long singular piths. They are called
sclerides.
The main function of Sclerenchymatous tissues is to give support to the plant.
Epidermis
The entire surface of the plant consists of a single layer of cells called epidermis or surface
tissue. The entire surface of the plant has this outer layer of epidermis. Hence it is also called
surface tissue. Most of the epidermal cells are relatively flat. the outer and lateral walls of the
cell are often thicker than the inner walls. The cells forms a continuous sheet without inter
cellular spaces. It protects all parts of the plant.
Complex permanent tissue
A complex permanent tissue may be classified as a group of more than one type of tissue having
a common origin and working together as a unit to perform a function. These tissues are
concerned with transportation of water, mineral, nutrients and organic substances. The important
complex tissues in vascular plants are xylem, phloem.
Xylem
Xylem is a chief, conducting tissue of vascular plants. It is responsible for conduction of water
and mineral ions.
Xylem is a very important plant tissue as it is part of the ‘plumbing’ of a plant. Think of bundles
of pipes running along the main axis of stems and roots. It carries water and dissolved substances
throughout and consists of a combination of parenchyma cells, fibers, vessels, tracheids and ray
cells. Long tubes made up of individual cells are the vessels, while vessel members are open at
each end. Internally, there may be bars of wall material extending across the open space. These
cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity.
Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end
openings such as the vessels. The tracheids ends overlap with each other, with pairs of pits
present. The pit pairs allow water to pass from cell to cell. While most conduction in the xylem is
up and down, there is some side-to-side or lateral conduction via rays. Rays are horizontal rows
of long-living parenchyma cells that arise out of the vascular cambium. In trees, and other woody
plants, ray will radiate out from the center of stems and roots and in cross-section will look like
the spokes of a wheel.
Phloem
Phloem is an equally important plant tissue as it also is part of the ‘plumbing’ of a plant.
Primarily, phloem carries dissolved food substances throughout the plant. This conduction
system is composed of sieve-tube member and companion cells, that are without secondary
walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually
also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members
laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end
walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous
connections are called sieve plates. In spite of the fact that their cytoplasm is actively involved in
the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the
companion cells that are nestled between sieve-tube members that function in some manner
bringing about the conduction of food. Sieve-tube members that are alive contain a polymer
called callose. Callose stays in solution as long at the cell contents are under pressure. As a repair
mechanism, if an insect injures a cell and the pressure drops, the callose will precipitate.
However, the callose and a phloem protein will be moved through the nearest sieve plate where
they will form a plug. This prevents further leakage of sieve tube contents and the injury is not
necessarily fatal to overall plant turgor pressure. Phloem transports food and materials in plants
in upwards and downwards as required.
Shapes of different cells in the body?
Hi!
I need some examples of different cells in the body, their shape, and what
organ/where they are found within our body.
Eg. Sperm cell / Found in the Testis/ Long.Elongated shape
Thanks in advance.
3 years ago
Report Abuse
♥
Best Answer - Chosen by Asker
Epithelial cells come in a wide variety of shapes.
1.Squamous epithelium (Flat cells.. looks like a sheet)
Simple squamous (one layer of cells): Lines the heart and blood vessels and the air
sacs of the lungs
Stratified squamous (multiple layers of cells): Superficial layer of the skin
2. Cuboidal epithelium (Cube shaped cells)
Found in the secreting part of the pancreas, the thryoid gland and sweat glands.
3. Columnar epithelium (Column shaped cells)
Lines the gastrointestinal tract
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ARTICLE FEED
SITE FEED
Tissues
Published: October 30, 2007, 4:03 pm
Updated: October 30, 2007, 4:03 pm
Topics
Ecotoxicology
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This article has been reviewed by the following Topic Editor: Emily Monosson
Table of Contents
1 Introduction
2 Epithelial tissue
3 Connective tissue
4 Muscular tissue
5 Nervous tissue
Introduction
Figure 1. Hierarchical role of tissues.
There are only four types of tissues that are dispersed throughout the body: epithelial tissue,
connective tissue, muscle tissue, and nerve tissue. A type of tissue is not unique for a particular
organ and all types of tissue are present in most organs, just as certain types of cells are found in
many organs. For example, nerve cells and circulating blood cells are present in virtually all
organs.
Tissues in organs are precisely arranged so that they can work in harmony in the performance of
organ function. This is similar to an orchestra that contains various musical instruments, each of
which is located in a precise place and contributes exactly at the right time to create harmony.
Like musical instruments that are mixed and matched in various types of musical groups, tissues
and cells also are present in several different organs and contribute their part to the function of
the organ and the maintenance of homeostasis.
The four types of tissues are similar in that each consists of cells and extracellular materials.
They differ, however, in that they have different types of cells and differ in the percentage
composition of cells and the extracellular materials. Figure 1 illustrates how tissues fit into the
hierarchy of body components.
Epithelial tissue
Figure 2. Classification of epithelial tissues.
(Source: V. C. Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd
edition. F. A. Davis, 1995)
Epithelial tissue is specialized to protect, absorb and secrete substances, as well as detect
sensations. It covers every exposed body surface, forms a barrier to the outside world and
controls absorption. Epithelium forms most of the surface of the skin, and the lining of the
intestinal, respiratory, and urogenital tracts. Epithelium also lines internal cavities and
passageways such as the chest, brain, eye, inner surfaces of blood vessels, and heart and inner
ear.
Epithelium provides physical protection from abrasion, dehydration, and damage by xenobiotics.
It controls permeability of a substance in its effort to enter or leave the body. Some epithelia are
relatively impermeable; others are readily crossed. This epithelial barrier can be damaged in
response to various toxins. Another function of epithelium is to detect sensation (sight, smell,
taste, equilibrium, and hearing) and convey this information to the nervous system. For example,
touch receptors in the skin respond to pressure by stimulating adjacent sensory nerves. The
epithelium also contains glands and secrets substances such as sweat or digestive enzymes.
Others secrete substances into the blood (hormones), such as the pancreas, thyroid, and pituitary
gland.
The epithelial cells are classified according to the shape of the cell and the number of cell layers.
Three primary cell shapes exist: squamous (flat), cuboidal, and columnar. There are two types of
layering: simple and stratified. These types of epithelial cells are illustrated in Figure 2.
Connective tissue
Figure 3. Connective tissues. (Source: V. C.
Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A.
Davis, 1995)
Figure 4. Connective tissues. (Source: V. C.
Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A.
Davis, 1995)
Connective tissues are specialized to provide support and hold the body tissues together (i.e.,
they connect). They contain more intercellular substances than the other tissues. A variety of
connective tissues exist, including blood, bone and cartilage, adipose (fat), and the fibrous and
areolar (loose) connective tissues that gives support to most organs (see Figure 3 and Figure 4).
The blood and lymph vessels are immersed in the connective tissue media of the body. The
blood-vascular system is a component of connective tissue. In addition to connecting the
connective tissue plays a major role in protecting the body from outside invaders. The
hematopoietic tissue is a form of connective tissue responsible for the manufacture of all the
blood cells and immunological capability. Phagocytes are connective tissue cells and produce
antibodies. Thus, if invading organisms or xenobiotics get through the epithelial protective
barrier, it is the connective tissue that goes into action to defend against them.
Muscular tissue
Muscular tissue is specialized for an ability to contract. Muscle cells are elongated and referred
to as muscle fibers. When a stimulus is received at one end of a muscle cell, a wave of excitation
is conducted through the entire cell so that all parts contract in harmony. There are three types of
muscle cells: skeletal, cardiac, and smooth muscle tissue (Figure 5). Contractions of the skeletal
muscles, which are attached to bones, cause the bones to move. Cardiac muscle contracts to force
blood out of the heart and around the body. Smooth muscle can be found in several organs,
including the digestive tract, reproductive organs, respiratory tract, and the lining of the bladder.
Examples of smooth muscle activity are: contraction of the bladder to force urine out, peristaltic
movement to move feces down the digestive system, and contraction of smooth muscle in the
trachea and bronchi which decreases the size of the air passageway.
Nervous tissue
Figure 5. Muscle tissues. (Source: V. C. Scanlon
and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A. Davis,
1995)
Figure 6. Nerve tissue of the central nervous
system. (Source: V. C. Scanlon and T. Sanders, Essentials of Anatomy and
Physiology, 2nd edition. F. A. Davis, 1995)
Nervous tissue is specialized with a capability to conduct electrical impulses and convey
information from one area of the body to another. Most of the nervous tissue (98%) is located in
the central nervous system, the brain and spinal cord. There are two types of nervous tissue—
neurons and neuroglia. Neurons actually transmit the impulses. Neuroglia provide physical
support for the neural tissue, control tissue fluids around the neurons, and help defend the
neurons from invading organisms and xenobiotics. Receptor nerve endings of neurons react to
various kinds of stimuli (e.g., light, sound, touch, and pressure) and can transmit waves of
excitation from the farthest point in the body to the central nervous system.
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with the same number and patterns of genes and chromosomes.
Meiosis, on the other hand, is a special process in cellular division where cells are created
containing gene patterns of different types and combinations with 50% of the number of
chromosomes of the original cell.
Meiosis is used in sexual reproduction of organisms to combine male and female, through the
spermazoa and egg, to create a new, singular biological organism. Mitosis is used by single
celled organisms to reproduce, or in the organic growth of tissues, fibers, and mibranes.
Comparison chart
Meiosis
Discovered by:
Type of
Reproduction:
Genetically:
Cytokenesis:
Number of
Divisions:
Pairing of
Homologues:
Oscar Hertwig
Mitosis
Walther Flemming
Sexual
Asexual
different
Occurs in Telophase I & Telohpase II
identical
Occurs in Telophase
2
1
Yes
No
Function:
sexual reproduction
Cellular Reproduction & general
growth and repair of the body
Reduced by half
Remains the same
Occurs in Interphase I
Mixing of chromosomes
The centromeres do not separate during
anaphase I, but during anaphase II
Occurs in Interphase
Does not occur
The centromeres split during
Anaphase
Yes
No
Humans, animals, plants, fungi
all organisms
4
2
Chromosome
Number:
Karyokenesis:
Crossing Over:
Centromeres
Split:
Occurrence of
Crossing Over:
Occurs in:
Number of
Daughter Cells
produced:
Creates:
Definition:
Sex cells only: Female egg cells or Male Makes everything other than sex
sperm cells
cells
A type of cellular reproduction in which A process of asexual reproduction in
the number of chromosomes are reduced which the cell divides in two
by half through the separation of
producing a replica, with an equal
homologous chromosomes in a diploid number of chromosomes in haploid
cell.
cell
Produces:
Steps:
Meiosis
four haploid daughter cells
The steps of meiosis are Interphase,
Prophase I, Metaphase I, Anaphase I,
Telophase I, Prophase II, Metaphase II,
Anaphase II and Telophase II.
Mitosis
two diploid daughter cells
The steps of mitosis are Interphase,
Prophase, Metaphase, Anaphase,
Telophase and Cytokinesis
Process Differences
Mitosis is a method of reproduction for single celled organisms that reproduce asexually. An
identical version of the organism is created through splitting of the cell in two. Meiosis may
result in millions of spermazoa and egg cells with unique genetic patterns. The mating of the two
cells formed by meiosis results in a unique genetic offspring of the same species. Meiosis is a
major factor in evolution, natural selection, and biodiversity. The processes of cellular division
shown in mitosis and meiosis are present in all manner of life forms including humans, animals,
plants, fungi, and single celled organisms and species. Essentially any cell based organism of
which all organic life is based will exhibit some form of mitosis and meiosis for growth and
reproduction of the individual and species.
Different Stages of Mitosis and Meiosis
The different phases of meiosis are: Prophase, Metaphase, Anaphase and Telophase.
An overview of the process and phases of meiosis
The stages of mitosis are: Interphase, Preprophase, Prophase, Prometaphase, Metaphase,
Anaphase, Telophase and Cytokinesis.
The process of mitosis
Differences in Purpose
Both Meiosis and Mitosis are found in complex organisms which reproduce sexually. Mitosis
may be used for human growth, the replenishment of depleted organs and tissues, healing, and
sustenance of the body. Identical versions of cells can be created to form tissues through Mitosis.
Meiosis is a special process reserved for the creation of the egg and sperm cells. The same
patterns may be found in many species of plant and animal cell reproduction.
Significance of Mitosis vs. Meiosis
The importance of mitosis is the maintenance of the chromosomal set; each cell formed receives
chromosomes that are alike in composition and equal in number to the chromosomes of the
parent cell.
Occurrence
Meiosis is found to occur in humans, animals and plants while mitosis is found in single-cell
species as well.
History
Meiosis was discovered and described for the first time in sea urchin eggs in 1876, by noted
German biologist Oscar Hertwig.
Walther Flemming discovered the process of Mitosis in 1882.
Evolution of mitosis vs. meiosis
Mitosis as a form of reproduction for single-cell organisms originated with life itself (around 4
billion years ago). Meiosis is thought to have appeared 1.4 billion years ago.
Chromosomal pattern comparison
In mitosis, each daughter cell ends up with two complete sets of chromosomes while in meiosis,
each daughter cell ends up with one set of chromosomes.
Both mitosis and meiosis are studied by scientists generally by using a microscope to identify
and classify chromosomal patterns and relationships within the cell’s structure. An understanding
of the way cells synthesize chromosomes for reproduction can be applied in bio-machines and
nano-technology. Transplantation of genes and chromosomes through injection and implantation
is used to experiment with bio-engineering and cloning. Understanding the process through
which cells replicate also has application in medicine and the study of health and disease.
The cell cycle
Actively dividing eukaryote cells pass through a series of stages known collectively as the cell
cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is
duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides.
G1 phase. Metabolic changes prepare the cell for division. At a certain point
- the restriction point - the cell is committed to division and moves into the S
phase.
S phase. DNA synthesis replicates the genetic material. Each chromosome
now consists of two sister chromatids.
G2 phase. Metabolic changes assemble the cytoplasmic materials necessary
for mitosis and cytokinesis.
M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis).
The period between mitotic divisions - that is, G1, S and G2 - is known as interphase.
Mitosis
Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same
genetic component as the parent cell. Chromosomes replicated during the S phase are divided in
such a way as to ensure that each daughter cell receives a copy of every chromosome. In actively
dividing animal cells, the whole process takes about one hour.
The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then
separates the sister chromatids to produce an even partitioning of the genetic material. This
separation of the genetic material in a mitotic nuclear division (or karyokinesis) is followed by a
separation of the cell cytoplasm in a cellular division (or cytokinesis) to produce two daughter
cells.
In some single-celled organisms mitosis forms the basis of asexual reproduction. In diploid
multicellular organisms sexual reproduction involves the fusion of two haploid gametes to
produce a diploid zygote. Mitotic divisions of the zygote and daughter cells are then responsible
for the subsequent growth and development of the organism. In the adult organism, mitosis plays
a role in cell replacement, wound healing and tumour formation.
Mitosis, although a continuous process, is conventionally divided into five stages: prophase,
prometaphase, metaphase, anaphase and telophase.
The phases of mitosis
Prophase
Prophase occupies over half of mitosis. The nuclear membrane breaks down to form a number of
small vesicles and the nucleolus disintegrates. A structure known as the centrosome duplicates
itself to form two daughter centrosomes that migrate to opposite ends of the cell. The
centrosomes organise the production of microtubules that form the spindle fibres that constitute
the mitotic spindle. The chromosomes condense into compact structures. Each replicated
chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held
together by a structure known as the centromere.
Prometaphase
The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the
cell - at right-angles to the axis formed by the centrosomes. This region of the mitotic spindle is
known as the metaphase plate. The spindle fibres bind to a structure associated with the
centromere of each chromosome called a kinetochore. Individual spindle fibres bind to a
kinetochore structure on each side of the centromere. The chromosomes continue to condense.
Metaphase
The chromosomes align themselves along the metaphase plate of the spindle apparatus.
Anaphase
The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each
chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by
spindle fibres attached to the kinetochore regions. The separated sister chromatids are now
referred to as daughter chromosomes. (It is the alignment and separation in metaphase and
anaphase that is important in ensuring that each daughter cell receives a copy of every
chromosome.)
Telophase
The final stage of mitosis, and a reversal of many of the processes observed during prophase.
The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the
chromosomes uncoil and become diffuse, and the spindle fibres disappear.
Cytokinesis
The final cellular division to form two new cells. In plants a cell plate forms along the line of the
metaphase plate; in animals there is a constriction of the cytoplasm. The cell then enters
interphase - the interval between mitotic divisions.
Meiosis
Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes (which
contain a single copy of each chromosome) from diploid cells (which contain two copies of each
chromosome). The process takes the form of one DNA replication followed by two successive
nuclear and cellular divisions (Meiosis I and Meiosis II). As in mitosis, meiosis is preceded by a
process of DNA replication that converts each chromosome into two sister chromatids.
Meiosis I
Meiosis I separates the pairs of homologous chromosomes.
In Meiosis I a special cell division reduces the cell from diploid to haploid.
Prophase I
The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.
Prophase I is divided into five phases:
Leptotene: chromosomes start to condense.
Zygotene: homologous chromosomes become closely associated (synapsis)
to form pairs of chromosomes (bivalents) consisting of four chromatids
(tetrads).
Pachytene: crossing over between pairs of homologous chromosomes to
form chiasmata (sing. chiasma).
Diplotene: homologous chromosomes start to separate but remain attached
by chiasmata.
Diakinesis: homologous chromosomes continue to separate, and chiasmata
move to the ends of the chromosomes.
Prometaphase I
Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.
Metaphase I
Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase
plate. The arrangement of the paired chromosomes with respect to the poles of the spindle
apparatus is random along the metaphase plate. (This is a source of genetic variation through
random assortment, as the paternal and maternal chromosomes in a homologous pair are similar
but not identical. The number of possible arrangements is 2n, where n is the number of
chromosomes in a haploid set. Human beings have 23 different chromosomes, so the number of
possible combinations is 223, which is over 8 million.)
Anaphase I
The homologous chromosomes in each bivalent are separated and move to the opposite poles of
the cell
Telophase I
The chromosomes become diffuse and the nuclear membrane reforms.
Cytokinesis
The final cellular division to form two new cells, followed by Meiosis II. Meiosis I is a reduction
division: the original diploid cell had two copies of each chromosome; the newly formed haploid
cells have one copy of each chromosome.
Meiosis II
Meiosis II separates each chromosome into two chromatids.
The events of Meiosis II are analogous to those of a mitotic division, although the number of
chromosomes involved has been halved.
Meiosis generates genetic diversity through:
the exchange of genetic material between homologous chromosomes during
Meiosis I
the random alignment of maternal and paternal chromosomes in Meiosis I
the random alignment of the sister chromatids at Meiosis II
Meiosis in females
BIOS 170
Cell Division: Mitosis and Meiosis
CHROMOSOME:
Between divisions the chromosome is a threadlike strand.
During interphase the chromosome replicates and becomes 2 thread like
strands.
Homologous Chromosomes:
Pairs of chromosomes similar in size, shape, & genetic information, but not
identical.
When both members of each pair are present, the cell is diploid (2n).
When only one member of the pair is present, the cell is haploid (n).
Humans:
o
diploid (2n) = 46
o
haploid (n) = 23
Recent cytokinesis
MITOSIS
The equal division of all cellular components to form two daughter cells that
are identical to the original cell.
Ensures the same number and kind of chromosomes as the original cell. This is
accomplished by replicating the DNA prior to cell division.
Original cell and daughter cells are all diploid.
Functions in asexual reproduction
Basis for growth in multi-celled organisms
Occurs in somatic cells found throughout the body.
MITOSIS (white fish)
MITOSIS (onion)
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Prophase
Metaphase
Anaphase
Telophase
MITOSIS
MEIOSIS
Functions in growth and Functions in sexual reproduction in multi-celled
asexual reproduction.
organisms.
Occurs in somatic cells
Occurs in germ cells, located in testes or ovaries.
found throughout the body.
Produces haploid cells, or gametes, with the genetic
Produces clones, or exact
material halved. When the gametes (eggs & sperm) fuse in
replicates of the cell.
fertilization the diploid # is restored.
Occurs in one division.
Requires two divisions.
Watch a NOVA Online Animation
How Cells Divide: Mitosis vs. Meiosis
Meiosis oogenesis in Ascaris
Primary oocyte with sperm nucleus
Secondary oocyte in late anaphase II or early
telophase II
Primary oocyte with intact
spermatozoan
Primary oocyte in metaphase I
Primary oocyte in late anaphase I
or early telophase I
Secondary oocyte in metaphase II
Secondary oocyte and first polar
body in metaphase II
Secondary oocyte in early anaphase
II
Ovum where two polar bodies are visible
Ovum with male and female pronuclei
Ovum with male and female pronuclei
beginning to unite chromosomes
Zygote undergoing mitosis in metaphase
Zygote undergoing mitosis in anaphase
Zygote undergoing mitosis in telophase
GENETICS & DEVELOPMENT - Cell Division
Physical Basis of Inheritability...
Key Concepts*
Mechanisms of Cell Reproduction... egg cells & sperm cells
cells reproduce identically, yet with variations (new traits)
"All living cells arise from pre-existing cells"
GENETICS
level
asks.... HOW? What are mechanisms at cellular & molecular
for physical basis of inheritability?
looks.... at mechanisms of the LIFE CYCLE of organisms
1. cellular mechanisms of reproduction in organisms
2. growth of organism..... zygote to adult
DEVELOPMENT
cell differentiation - how one cell becomes different
from another
times
differential gene activity - genes are active at different
totipotency & cloning - exact genetic copies of cells
METHODS of CELL REPRODUCTION include...
Fission* - binary = 2 equal halves
(bacteria & cyanobacteria
& protozoans)
Budding* - outgrowths detach = new organism
(unequal split)
(hydra)
Chapter 46.1 video: Video:
Hydra Budding
Mitosis* - asexually = identical genetic copies
[cytokinesis*]
genetically equal somatic cells
1.5 lung cell*
divisions
c7 fig
amoeba, sand dollar, bone marrow cell
Meiosis* - sexually produces sperm & egg cells with
1/2 chromosome number & new
gene combos
MITOSIS - Asexual Reproduction Cell Cycle...
results in copying & equal duplication of parental cell's DNA
and the equal division of chromosomes into two daughter cells
(rates = epithelial cells 1x/day - liver cells 1x/yr)
the Life cycle of a Cell... is known as the "CELL CYCLE"...
Concept Activity 12.2 -
Cell Cycle
[3 Stages] -
Cell Cycle
o
is depicted as a circle 360 fig 12.5*
The
[G1 - S - G2 -
M]
Interphase - period between successive divisions of a cell
period after
3 parts =
G1 - before, DNA synthesis (S),
MITOSIS* - nuclear division phase;
& G2
separation & duplication of chromosomes
Cytokenesis* - physical division of cell into two parts: animals/plants
How does one determine the times of the phases of Cell Cycle ?
fibroblast cell cultures*
S-phase: pulse chase*experiments*
Investigation 12.2 - How much time is spent in each
phase of cell cycle
Stages of Mitosis*-pics*
Sumanas, Inc. animation -
Mitosis
Prophase -
Concept activity
12.2 Mitosis and Cytokinesis Video
chromatin condenses into chromosomes animation* cartoon
Prometaphase chromosome MT's attach to kinetochores
fig
12.6*
each homolog has 2 chromatids
Metaphase -
Concept Activity 12.2
Mitosis & Cytokinesis Animation
chromosomes align at equator
fig
12.6*
homologs align independently of each other
Anaphase MT attached to kinetochore; chromatids
fig12.8
are pulled apart & poles move apart
Telophase - ex:
cells*
animal cells* & onion root tip
chromosomes at opposite poles; daughter cells
form by cytokinesis.
next
BioFlix animation of mitosis*view@home
Names and Numbers -
(to protect the innocent)
Structure of chromosomes*
Genes occur in chromatin of nucleus,
which condense into CHROMOSOMES
(colored bodies) visible only during
MITOSIS
animation of DNA coiling into
chromosomes
bacteria have about 3,000 genes
(DNA molecule only)
humans have some 20 to 25,000+ genes
&
1 chromosome
&
46 chromosomes
Humans have 46 chromosomes or 23 HOMOLOGOUS pairs
23 maternal chromosomes
23 paternal chromosomes
Control of Cell Division and the Cell Cycle
2001 Nobel prize
Regulated by "Growth Factors" - proteins that promote cell division,
such as...
MPF - mitotic promoting factor...
cyclin]
cycle
protein-P
[ complex* of two proteins cdk +
MPF is a kinase enzyme, one that switches on/off target cell
proteins by phosphorylating them.....
inactive cycle protein ---------------->
active-
ATP ---> ADP
MPF promotes entrance into mitosis from the G2 phase by
phosphorylating multiple
proteins during mitosis including one that leads to destruction of
cyclin itself
MPF - cdk - a cell division control protein - cyclin dependent kinase;
active only when bound to cyclin;
cyclin - a protein whose amount varies cyclically;
when in high concentrations*, binds to cdk
makes MPF...
[cyclin + cdk = MPF]... favors
Mitosis
Growth Factors regulate at critical points... Cell cycle checkpoints*
Many cells divide on a circadian rhythm*
Concept Activity - 12.1 - Roles of Cell Division &
eukaryotic cell
cycle regulation
SEXUAL CELL REPRODUCTION...
"MEIOSIS"
nuclear division phase of
sexually dividing cells
compare physical differences* between nuclear divisions
of MEIOSIS & MITOSIS
so the Distinct Differences are:
Key Concepts*
meiosis = 4 progeny cells [1 = 2 = 4]...
thus 2
divisions
mitosis = 2 daughter cells only...
thus 1 cell division
meiosis = one-half number of chromosomes
mitosis = same # of chromosomes as parent
cell
meiosis = new combinations of genes not in
parents &
chromosomes sort randomly of each
other
mitosis = daughter cells are genetically
identical
Sexual Cell Reproduction
(Meiosis)
Only specialized sex cells can undergo meiosis...
and where does meiosis occur during the sexual cell cycle ?
Meiosis ---> produces cells half chrm # = 23 (sperm & egg haploid)
only specialized cells - gametes - can undergo meiosis.
Fertilization (sperm + egg) --->
# = 46)
diploid life cycle* --->
(chrm
Alternation of Generations* & Human life Cycle*
Concept Activity 13.1 - Asexual and Sexual Life
Cycles
Stages of Sexual Cell Division
same 3 phases of cell cycle...
just as in asexual division
(Interphase, Nuclear Division, Cytokinesis)
but, 2 Divisions
Meiosis I
and Meiosis II
1 cell = 2 cell = 4 cells
Names of stages are same & have analogous functions
Meiosis I...
male grasshopper meiosis
Prophase I
tetrad
= chromosomes condense
SYNAPSIS - homologs PAIR together --->
CROSSOVER* - exchange occurs at a chiasma
Metaphase I = chromosomes align at
equator
Anaphase I = chromosomes migrate toward poles
Telophase I = chromosome at poles - cell domains separate
Meiosis I separates homologs of homologous pair* fig 13.7*
Meiosis II...
is just like mitosis [but without an S phase]
separates chromatids of one homolog of the
homologous pair
just as is done in mitosis
Comparison(fig 13.9)* of Mitosis/Meiosis - comparison animation*view @
home
Independent Assortment* - random alignment of homologous pairs
(fig)
Crossing Over - exchange of chromosome material
BioFlix animation of meiosis*view@home & another meiosis animation*
Concept Activity 13.3 - Meiosis Animation
of Meiosis*
Sumanas, Inc. animation
Summary of MEIOSIS
1. Nuclear division phase of sexual cell reproduction
cycle
2. Two successive divisions, results in 4 daughter
cells...
Meiosis 1 and Meiosis 2
3. Reduction/division occurs.... diploid ----> haploid
daughter cells ½ number of parent cell
chromosomes
4. Stages have same nomenclature as Mitosis
prophase, metaphase, anaphase, telophase,
M1 & M2
5. Only one S phase, where DNA is duplicated
often may be no interphase between M1 &
M2
6. Homologs separate in Meiosis 1
Chromatids separate in Meiosis 2 (mitoticlike)
7. Random Assortment occurs...... homologs align
at equitorial plates independent of each
other
8. Crossing over... may occur in Prophase I...
synapsis = close pairing homologs allows
exchange
chiasma = point exchange of sister
chromatids
[table
of differences]*
issue (biology)
From Wikipedia, the free encyclopedia
This article is about biological tissue. For other uses, see Tissue.
Cross section of sclerenchyma fibers in plant ground tissue
Microscopic view of a histologic specimen of human lung tissue stained with
hematoxylin and eosin.
Tissue is a cellular organizational level intermediate between cells and a complete organism. A
tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together
carry out a specific function. These are called tissues because of their identical functioning.
Organs are then formed by the functional grouping together of multiple tissues.
The study of tissue is known as histology or, in connection with disease, histopathology. The
classical tools for studying tissues are the paraffin block in which tissue is embedded and then
sectioned, the histological stain, and the optical microscope. In the last couple of decades,
developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections
have enhanced the detail that can be observed in tissues. With these tools, the classical
appearances of tissues can be examined in health and disease, enabling considerable refinement
of clinical diagnosis and prognosis.
Contents
1 Animal tissues
o 1.1 Connective tissue
o
1.2 Muscle tissue
o
1.3 Nervous tissue
o
1.4 Epithelial tissue
2 Plant tissues
o
2.1 Meristematic tissues
o
2.2 Permanent tissues
3 See also
2.2.1 Simple permanent tissues
2.2.1.1 Parenchyma
2.2.1.2 Collenchyma
2.2.1.3 Sclerenchyma
2.2.1.4 Epidermis
2.2.2 Complex permanent tissue
2.2.2.1 Xylem
2.2.2.2 Phloem
4 References
5 External links
Animal tissues
PAS diastase showing the fungus Histoplasma.
Animal tissues can be grouped into four basic types: connective, muscle, nervous, and epithelial.
Multiple tissue types comprise organs and body structures. While all animals can generally be
considered to contain the four tissue types, the manifestation of these tissues can differ
depending on the type of organism. For example, the origin of the cells comprising a particular
tissue type may differ developmentally for different classifications of animals. The epithelium in
all animals is derived from the ectoderm and endoderm with a small contribution from the
mesoderm which forms the endothelium. By contrast, a true epithelial tissue is present only in a
single layer of cells held together via occluding junctions called tight junctions, to create a
selectively permeable barrier. This tissue covers all organismal surfaces that come in contact
with the external environment such as the skin, the airways, and the digestive tract. It serves
functions of protection, secretion, and absorption, and is separated from other tissues below by a
basal lamina. Endothelium, which comprises the vasculature, is a specialized type of epithelium.
Connective tissue
Connective tissues are fibrous tissues. They are made up of cells separated by non-living
material, which is called extracellular matrix. Connective tissue gives shape to organs and holds
them in place. Both blood and bone are examples of connective tissue. As the name implies,
connective tissue serves a "connecting" function. It supports and binds other tissues. Unlike
epithelial tissue, connective tissue typically has cells scattered throughout an extracellular
matrix.
Muscle tissue
Muscle cells form the active contractile tissue of the body known as muscle tissue. Muscle tissue
functions to produce force and cause motion, either locomotion or movement within internal
organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle,
which is found in the inner linings of organs; skeletal muscle, in which is found attached to bone
providing for gross movement; and cardiac muscle which is found in the heart, allowing it to
contract and pump blood throughout an organism..
Nervous tissue
Cells comprising the central nervous system and peripheral nervous system are classified as
neural tissue. In the central nervous system, neural tissue forms the brain and spinal cord and, in
the peripheral nervous system forms the cranial nerves and spinal nerves, inclusive of the motor
neurons. Transmits communications.
Epithelial tissue
The epithelial tissues are formed by cells that cover organ surfaces such as the surface of the
skin, the airways, the reproductive tract, and the inner lining of the digestive tract. The cells
comprising an epithelial layer are linked via semi-permeable, tight junctions; hence, this tissue
provides a barrier between the external environment and the organ it covers. In addition to this
protective function, epithelial tissue may also be specialized to function in secretion and
absorption. Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid
loss.
Plant tissues
Cross-section of a flax plant stem with several layers of different tissue types:
hi 1. Pith,
2. Protoxylem,
3.
4.
5.
6.
7.
Xylem I,
Phloem I,
Sclerenchyma (bast fibre),
Cortex,
Epidermis
Examples of tissue in other multicellular organisms are vascular tissue in plants, such as xylem
and phloem. Plant tissues are categorized broadly into three tissue systems: the epidermis, the
ground tissue, and the vascular tissue. Together they are often referred to as biomass.
Epidermis - Cells forming the outer surface of the leaves and of the young
plant body.
Vascular tissue - The primary components of vascular tissue are the xylem
and phloem. These transport fluid and nutrients internally.
Ground tissue - Ground tissue is less differentiated than other tissues.
Ground tissue manufactures nutrients by photosynthesis and stores reserve
nutrients.
Plant tissues can also be divided differently into two types:
1. Meristematic tissues
2. Permanent tissues
Meristematic tissues
Meristematic tissue consists of actively dividing cells, and leads to increase in length and
thickness of the plant. The primary growth of a plant occurs only in certain, specific regions,
such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells
in these tissues are roughly spherical or polyhedral, to rectangular in shape, and have thin cell
walls. New cells produced by meristem are initially those of meristem itself, but as the new cells
grow and mature, their characteristics slowly change and they become differentiated as
components of the region of occurrence of meristimatic tissues, they are classified as:
a) Apical Meristem - It is present at the growing tips of stems and roots and
increases the length of the stem and root. They form growing parts at the
apices of roots and stems and are responsible for increase in length,also
called primary growth.This meristem is responsible for the linear growth of an
organ.
b) Lateral Meristem - This meristem consist of cells which mainly divide in
one plane and cause the organ to increase in diameter and growth. Lateral
Meristem usually occurs beneath the bark of the tree in the form of Cork
Cambium and in vascular bundles of dicots in the form of vascular cambium.
The activity of this cambium results in the formation of secondary growth.
c) Intercalary Meristem - This meristem is located in between permanent
tissues. It is usually present at the base of node, inter node and on leaf base.
They are responsible for growth in length of the plant.This adds growth in the
girth of stem.
The cells of meristematic tissues are similar in structure and have thin and elastic primary cell
wall made up of cellulose. They are compactly arranged without inter-cellular spaces between
them. Each cell contains a dense cytoplasm and a prominent nucleus. Dense protoplasm of
meristematic cells contains very few vacuoles. Normally the meristematic cells are oval,
polygonal or rectangular in shape.
Meristemetic tissue cells have a large nucleus with small or no vacuoles, they have no inter
cellular spaces.
Permanent tissues
The meristematic tissues that take up a specific role lose the ability to divide. This process of
taking up a permanent shape, size and a function is called cellular differentiation. Cells of
meristematic tissue differentiate to form different types of permanent tissue. There are 2 types of
permanent tissues:
1. simple permanent tissues
2. complex permanent tissues
Simple permanent tissues
These tissues are called simple because they are composed of similar types of cells which have
common origin and function. They are further classified into:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma
4. Epidermis
Parenchyma
It consists of relatively unspecialised cells with thin cell walls. They are live cells. They are
usually loosely packed, so that large spaces between cells(intercellular spaces)are found in this
tissue. This tissue provides support to plants and also stores food.In some situations , it contains
chlorophyll and performs photosynthesis, and then it is called chlorenchyma. In aquatic
plants,large air cavities are present in parenchyma to give support to them to float on water. Such
a parenchyma type is called aerenchyma.
Collenchyma
Cross section of collenchyma cells
Collenchyma is Greek word where "Collen" means gum and "enchyma" means infusion. It is a
living tissue of primary body like Parenchyma. Cells are thin-walled but possess thickening of
cellulose and pectin substances at the corners where number of cells join together. This tissue
gives a tensile strength to the plant and the cells are compactly arranged and do not have intercellular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and
in roots.
Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides
mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing
sugar and storing it as starch. It is present in margin of leaves and resist tearing effect of the
wind.
Sclerenchyma
Sclerenchyma is Greek word where "Sclrenes" means hard and "enchyma" means infusion. This
tissue consists of thick-walled, dead cells. These cells have hard and extremely thick secondary
walls due to uniform distribution of lignin. Lignin deposition is so thick that the cell walls
become strong, rigid and impermeable to water. Sclerenchymatous cells are closely packed
without inter-cellular spaces between them. Thus, they appear as hexagonal net in transverse
section. The cells are cemented with the help of lamella. The middle lamella is a wall that lies
between adjacent cells. Sclerenchymatous cells mainly occur in hypodermis, pericycle,
secondary xylem and phloem. They also occur in endocorp of almond and coconut. It is made of
pectin, lignin, protein. The cells of sclerenchymatous cells can be classified as :
1. Fibres- Fibres are long, elongated sclerenchymatous cells with pointed ends.
2. Sclerides- Sclerenchymatous cells which are short and possess extremely
thick, lamellated, lignified walls with long singular piths. They are called
sclerides.
The main function of Sclerenchymatous tissues is to give support to the plant.
Epidermis
The entire surface of the plant consists of a single layer of cells called epidermis or surface
tissue. The entire surface of the plant has this outer layer of epidermis. Hence it is also called
surface tissue. Most of the epidermal cells are relatively flat. the outer and lateral walls of the
cell are often thicker than the inner walls. The cells forms a continuous sheet without inter
cellular spaces. It protects all parts of the plant.
Complex permanent tissue
A complex permanent tissue may be classified as a group of more than one type of tissue having
a common origin and working together as a unit to perform a function. These tissues are
concerned with transportation of water, mineral, nutrients and organic substances. The important
complex tissues in vascular plants are xylem, phloem.
Xylem
Xylem is a chief, conducting tissue of vascular plants. It is responsible for conduction of water
and mineral ions.
Xylem is a very important plant tissue as it is part of the ‘plumbing’ of a plant. Think of bundles
of pipes running along the main axis of stems and roots. It carries water and dissolved substances
throughout and consists of a combination of parenchyma cells, fibers, vessels, tracheids and ray
cells. Long tubes made up of individual cells are the vessels, while vessel members are open at
each end. Internally, there may be bars of wall material extending across the open space. These
cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity.
Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end
openings such as the vessels. The tracheids ends overlap with each other, with pairs of pits
present. The pit pairs allow water to pass from cell to cell. While most conduction in the xylem is
up and down, there is some side-to-side or lateral conduction via rays. Rays are horizontal rows
of long-living parenchyma cells that arise out of the vascular cambium. In trees, and other woody
plants, ray will radiate out from the center of stems and roots and in cross-section will look like
the spokes of a wheel.
Phloem
Phloem is an equally important plant tissue as it also is part of the ‘plumbing’ of a plant.
Primarily, phloem carries dissolved food substances throughout the plant. This conduction
system is composed of sieve-tube member and companion cells, that are without secondary
walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually
also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members
laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end
walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous
connections are called sieve plates. In spite of the fact that their cytoplasm is actively involved in
the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the
companion cells that are nestled between sieve-tube members that function in some manner
bringing about the conduction of food. Sieve-tube members that are alive contain a polymer
called callose. Callose stays in solution as long at the cell contents are under pressure. As a repair
mechanism, if an insect injures a cell and the pressure drops, the callose will precipitate.
However, the callose and a phloem protein will be moved through the nearest sieve plate where
they will form a plug. This prevents further leakage of sieve tube contents and the injury is not
necessarily fatal to overall plant turgor pressure. Phloem transports food and materials in plants
in upwards and downwards as required.
Shapes of different cells in the body?
Hi!
I need some examples of different cells in the body, their shape, and what
organ/where they are found within our body.
Eg. Sperm cell / Found in the Testis/ Long.Elongated shape
Thanks in advance.
3 years ago
Report Abuse
♥
Best Answer - Chosen by Asker
Epithelial cells come in a wide variety of shapes.
1.Squamous epithelium (Flat cells.. looks like a sheet)
Simple squamous (one layer of cells): Lines the heart and blood vessels and the air
sacs of the lungs
Stratified squamous (multiple layers of cells): Superficial layer of the skin
2. Cuboidal epithelium (Cube shaped cells)
Found in the secreting part of the pancreas, the thryoid gland and sweat glands.
3. Columnar epithelium (Column shaped cells)
Lines the gastrointestinal tract
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ARTICLE FEED
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Tissues
Published: October 30, 2007, 4:03 pm
Updated: October 30, 2007, 4:03 pm
Topics
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Content Source: NLM
This article has been reviewed by the following Topic Editor: Emily Monosson
Table of Contents
1 Introduction
2 Epithelial tissue
3 Connective tissue
4 Muscular tissue
5 Nervous tissue
Introduction
Figure 1. Hierarchical role of tissues.
There are only four types of tissues that are dispersed throughout the body: epithelial tissue,
connective tissue, muscle tissue, and nerve tissue. A type of tissue is not unique for a particular
organ and all types of tissue are present in most organs, just as certain types of cells are found in
many organs. For example, nerve cells and circulating blood cells are present in virtually all
organs.
Tissues in organs are precisely arranged so that they can work in harmony in the performance of
organ function. This is similar to an orchestra that contains various musical instruments, each of
which is located in a precise place and contributes exactly at the right time to create harmony.
Like musical instruments that are mixed and matched in various types of musical groups, tissues
and cells also are present in several different organs and contribute their part to the function of
the organ and the maintenance of homeostasis.
The four types of tissues are similar in that each consists of cells and extracellular materials.
They differ, however, in that they have different types of cells and differ in the percentage
composition of cells and the extracellular materials. Figure 1 illustrates how tissues fit into the
hierarchy of body components.
Epithelial tissue
Figure 2. Classification of epithelial tissues.
(Source: V. C. Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd
edition. F. A. Davis, 1995)
Epithelial tissue is specialized to protect, absorb and secrete substances, as well as detect
sensations. It covers every exposed body surface, forms a barrier to the outside world and
controls absorption. Epithelium forms most of the surface of the skin, and the lining of the
intestinal, respiratory, and urogenital tracts. Epithelium also lines internal cavities and
passageways such as the chest, brain, eye, inner surfaces of blood vessels, and heart and inner
ear.
Epithelium provides physical protection from abrasion, dehydration, and damage by xenobiotics.
It controls permeability of a substance in its effort to enter or leave the body. Some epithelia are
relatively impermeable; others are readily crossed. This epithelial barrier can be damaged in
response to various toxins. Another function of epithelium is to detect sensation (sight, smell,
taste, equilibrium, and hearing) and convey this information to the nervous system. For example,
touch receptors in the skin respond to pressure by stimulating adjacent sensory nerves. The
epithelium also contains glands and secrets substances such as sweat or digestive enzymes.
Others secrete substances into the blood (hormones), such as the pancreas, thyroid, and pituitary
gland.
The epithelial cells are classified according to the shape of the cell and the number of cell layers.
Three primary cell shapes exist: squamous (flat), cuboidal, and columnar. There are two types of
layering: simple and stratified. These types of epithelial cells are illustrated in Figure 2.
Connective tissue
Figure 3. Connective tissues. (Source: V. C.
Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A.
Davis, 1995)
Figure 4. Connective tissues. (Source: V. C.
Scanlon and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A.
Davis, 1995)
Connective tissues are specialized to provide support and hold the body tissues together (i.e.,
they connect). They contain more intercellular substances than the other tissues. A variety of
connective tissues exist, including blood, bone and cartilage, adipose (fat), and the fibrous and
areolar (loose) connective tissues that gives support to most organs (see Figure 3 and Figure 4).
The blood and lymph vessels are immersed in the connective tissue media of the body. The
blood-vascular system is a component of connective tissue. In addition to connecting the
connective tissue plays a major role in protecting the body from outside invaders. The
hematopoietic tissue is a form of connective tissue responsible for the manufacture of all the
blood cells and immunological capability. Phagocytes are connective tissue cells and produce
antibodies. Thus, if invading organisms or xenobiotics get through the epithelial protective
barrier, it is the connective tissue that goes into action to defend against them.
Muscular tissue
Muscular tissue is specialized for an ability to contract. Muscle cells are elongated and referred
to as muscle fibers. When a stimulus is received at one end of a muscle cell, a wave of excitation
is conducted through the entire cell so that all parts contract in harmony. There are three types of
muscle cells: skeletal, cardiac, and smooth muscle tissue (Figure 5). Contractions of the skeletal
muscles, which are attached to bones, cause the bones to move. Cardiac muscle contracts to force
blood out of the heart and around the body. Smooth muscle can be found in several organs,
including the digestive tract, reproductive organs, respiratory tract, and the lining of the bladder.
Examples of smooth muscle activity are: contraction of the bladder to force urine out, peristaltic
movement to move feces down the digestive system, and contraction of smooth muscle in the
trachea and bronchi which decreases the size of the air passageway.
Nervous tissue
Figure 5. Muscle tissues. (Source: V. C. Scanlon
and T. Sanders, Essentials of Anatomy and Physiology, 2nd edition. F. A. Davis,
1995)
Figure 6. Nerve tissue of the central nervous
system. (Source: V. C. Scanlon and T. Sanders, Essentials of Anatomy and
Physiology, 2nd edition. F. A. Davis, 1995)
Nervous tissue is specialized with a capability to conduct electrical impulses and convey
information from one area of the body to another. Most of the nervous tissue (98%) is located in
the central nervous system, the brain and spinal cord. There are two types of nervous tissue—
neurons and neuroglia. Neurons actually transmit the impulses. Neuroglia provide physical
support for the neural tissue, control tissue fluids around the neurons, and help defend the
neurons from invading organisms and xenobiotics. Receptor nerve endings of neurons react to
various kinds of stimuli (e.g., light, sound, touch, and pressure) and can transmit waves of
excitation from the farthest point in the body to the central nervous system.
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