Hair

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Hair Hairs are elongated keratinized structures from epital epidermis invagination. Color, size, and distribution varies in nation, age, gender, and part of body. Hair is found in all of the body except palm of the hand, palm of the foot, lips, penis glands, clitoris and labira minora. Hair isn’t growth continuelly but they have growth moment that followed by rest phase. In certain regions of the body, hair provides some protection, such as those that guard the external anogenital orifices, the external auditory meatuses, nostrils, and eyes eyelashes!. In addition to these minor function, especially adapted for the modality of light touch. Hair Structure "eratin that contained in hair is a special protein, which is resistant to wear and tear. It is the protein that also makes up the nails. #ike other proteins in the body, keratin is also a large molecule made up of smaller units called amino acids. $he amino acids are %oined together in a chain, like beads on a string. $he diameter of a single hair fiber varies from person to person& but it is usually around '.'( to '.') millimeters. $he epidermis is the outermost layer of the skin. *ach hair arises from an indentation on the epidermis. $he hair has two parts+ the hair follicle and the hair shaft.

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Hair Follicle , leaf of hair growing from epidermal invagination is hair follicle, that have hair bulb. Hair bulb is expansion of the end part hair follicle. Hair follicle is a tiny cup-shaped pit buried in the fat of the scalp. ,ttached to the follicle is a sebaceous gland, a tiny sebum-producing gland found everywhere except on the palms, lips and soles of the feet. $he thicker the density of the hair, the more the number of sebaceous glands that are found.

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,lso attached to the follicle is a tiny bundle of muscle fiber called the arrector pili that is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, and causing the follicle to protrude slightly above the surrounding skin piloerection!. $his process results in goose bumps or goose flesh!. 5tem cells are located at the %unction of the arrector and the follicle, and are principally responsible for the ongoing hair production during a process known as the ,nagen stage. $he average growth rate of healthy hair follicles on the scalp is half an inch per month.

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Structure of Hair Follicle Papilla ,t the base of the follicle is a large structure that is called the papilla. $he papilla is made up mainly of connective tissue and a capillary loop. Cell division in the papilla is either rare or non-existent. Matrix ,round the papilla is the hair matrix, a collection of epithelial cells often interspersed with the pigment producing cells, melanocytes. Cell division in the hair matrix is responsible for the cells that will form the ma%or structures of the hair fiber and the inner root sheath. $he hair matrix epithelium is one of the fastest growing cell populations in the human body, which is why some forms of chemotherapy that kill dividing cells or radiotherapy may lead to temporary hair loss. $he papilla is usually ovoid or pear shaped with the matrix wrapped

completely around it except for a short stalk-like connection to the surrounding connective tissue that provides access for the capillary. Root sheath $he root sheath is composed of an external root sheath Henle8s layer!, a middle layer Huxley8s layer!, and an internal cuticle that is continuous with the outermost layer of the hair fiber. Hair fiber $he hair fiber is composed of a cuticle that is continuous with the root sheath, an intermediate cortex, and an inner medulla. Other structures 9ther structures associated with the hair follicle include arrector pili muscles, sebaceous glands and apocrine sweat glands. Hair follicle receptors sense the position of the hairs.

Morphogenesis
In utero, the epithelium and underlying mesenchyma interact to form hair follicles. Hair-follicle cycling Hair grows in cycles of various phases+ anagen is the growth phase& catagen is the involuting or regressing phase& and telogen, the resting or :uiescent phase. *ach phase has several morphologically and histologically distinguishable sub-phases. 7rior to the start of cycling is a phase of follicular morphogenesis formation of the follicle!. $here is also a shedding phase, or exogen, that is independent of anagen and telogen in which one of several hairs that might arise from a single follicle exits. ;ormally up to )'< of the hair follicles are in anagen phase while, /'=/0< are in telogen and /=>< in catagen. $he cycle8s length varies on different parts of the body. 4or eyebrows, the cycle is completed in around 0 months, while it takes the scalp 2=0 years to finish& this is the reason eyebrow hairs have a much shorter length limit compared to hairs on

the head. ?rowth cycles are controlled by a chemical signal like epidermal growth factor. Anagen phase ,nagen is the active growth phase of hair follicles.$he cells in the root of the hair are dividing rapidly, adding to the hair shaft. 6uring this phase the hair grows about / cm every >@ days. 5calp hair stays in this active phase of growth for >-A years. $he amount of time the hair follicle stays in the anagen phase is genetically determined. ,t the end of the anagen phase an unknown signal causes the follicle to go into the catagen phase. Catagen phase $he catagen phase is a short transition stage that occurs at the end of the anagen phase. It signals the end of the active growth of a hair. $his phase lasts for about >=2 weeks while a club hair is formed. Telogen phase $he telogen phase is the resting phase of the hair follicle. $he club hair is the final product of a hair follicle in the telogen stage, and is a dead, fully keratinized hair. 4ifty to one-hundred club hairs are shed daily from a normal scalp. Hair growth cycle times B 5calp+ $he time these phases last varies from person to person. 6ifferent hair colour and follicle shape affects the timings of these phases. o o o anagen phase, >=2 years occasionally much longer! catagen phase, >=2 weeks telogen phase, around 2 months

B *yebrows etc+ o o o anagen phase, 0=A months catagen phase, 2=0 weeks telogen phase, about ) months

www.theharleystreethairclinic.com Hair Shaft $he part of the hair seen above the skin is called the hair shaft. $he hair shaft is made up of dead cells that have turned into keratin and binding material, together with small amounts of water. $his structure explains why we do not feel any pain while our hair is being cut. $he hair shaft is formed by three layers. $he innermost layer of the hair shaft is named the medulla. It is seen only in large and thick hairs. $he middle layer of the hair shaft is called the cortex, made of keratin fibers. $he strength, color and texture of a hair fiber are provided by the cortex layer of the hair shaft. $he outermost layer of the hair shaft is the cuticle. $his thin and colorless layer made up of between six to ten overlapping layers of long cell remnants, serves as a protection to the cortex.

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