Fetal Growth and Development
Content
Fetal growth and development
• Fertilization – Following ejaculation into the vagina, sperm live approximately 48 to 72 hours – Refers to the union of an ovum (egg) and a spermatozoan (sperm) which results in a zygote – Occurs in the ampulla (outer one-third) of the fallopian tube following ovulation Pre-embryonic stage – This stage encompasses the first 14 days after conception – When the zygote implants in the decidua approxiamtely 8 to 10 days after fertilization, the structure is referred to as an EMBRYO – After implantation, the embryo undergoes rapid growth and differentiation
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Three primary germ layers of embryo
1. ECTODERM – The tissues and organs that develop from the ectoderm include the CNS, PNS, sensory epithelium of the ear, nose, eye, sinus, mouth and anal canal; skin (epidermis), hair, nails, sebaceous glands, sweat glands, hair follicles; and mammary glands, pituitary gland, enamel of the teeth and oral glands 2. MESODERM – The tissues and organ develop from the mesoderm include bone, cartilage, skeleton; connective tissue, smooth and striated muscles; cardiovascular and lymphatic systems, blood and lymph cells; kidneys and reproductive organs; serous membrane lining of the pericardial, pleural and peritoneal cavities; spleen 3. ENDODERM – The tissues and organs that develop from the endoderm include respiratory tract epithelium, epithelial lining of the GIT (pharynx, tonsils, thyroid, parathyroid, thymus), epithelial lining of urinary bladder and urethra, liver and pancreas DECIDUA – The endometrium (the lining of the inside of the uterus) become the decidua following conception and implantation – The portion directly from the blastocyst, where the chorionic villi intersect with the maternal blood vessels, is the decidua basalis – The portion covering the blastocyst is called the decidua capsularis and the portion lining the rest of the uterus is the decidua vera which will protect and nourish the developing embryo
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PLACENTA – Begins to function by the 4th week of gestation; by the 14th week it is complete and independently functioning organ – It transmits nutrients and oxygen to the fetus and removes wastes and carbon dioxide by diffusion – Considered to be the endocrine organ of the placenta which produces the following hormones: • Estrogen (primary estriol) • Progesterone • Human chorionic gonadotropin (HCG) • Human placental lactogen • Estrogen (primary estriol) – It stimulates the growth of uterine muscle (myometium) and glandular epithelium (endometrium) and induces the synthesis of receptors for progesterone
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Progesterone – Promotes thickening and increased viscosity of cervical mucus (the mucous plug) to protect the fetus against invading the bacteria – Decreases motility of oviducts and uterus – It stimulates growth of glandular breast tissue (acini cells) in preparation for lactation – Maintains uterine lining for implantation and relaxes uterine smooth muscle HCG – Is secreted by trophoblast cells of the blastocyst (early product of conception) and the placenta (after the second gestational month). It is partly responsible for maintaining the corpus luteum – Is detected in the urine and plasma (by day 8 ) and the first indicator of a positive pregnancy – Levels may be monitored later in the pregnancy to determine fetal well being Human placental lactogen – Levels increase after 20 weeks of gestation – It is a growthlike substance that stimuates maternal metabolism – It facilitates glucose transport across the placenta – It also stimulates breast development to prepare for lactation
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MULTIPLE PREGNANCIES
• DIZYGOTIC (fraternal) multiple pregnancy – Involves two or more ova fertilized by separate sperm – Fetuses have separate placentas, amnions, and chorions and may be the same or different sex MONOZYGOTIC (identical) multiple pregnancy – Developes from a single fertilized ovum – Fetuses share a common placenta and chorion bt have separate amnions, they are the same sex and same genotype
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Factors influencing embryonic and fetal development
• Environment – Poverty – Malnutrition – Maternal alcohol, nicotine or illicit drug use – Maternal prescription drug use ( anticoagulants, aspirin, anticonvulsants, antibiotics) Anatomic problems – Maternal problems include ectopic pregnancy, uterine abnormality, retroversion of the uterus and incompetent cervical os – Fetal problems include chromosomal defects and poor implantation Maternal complications – Infection, Rh incompatibility, cyanotic heart disease, renal diseases, hypertension and urinary tract infection Fetal complications – Premature rupture of membranes, preterm labor and postmaturity Physiologic problems – Folate deficiency, endocrine deficiency and defective sperm
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• Fertilization – Following ejaculation into the vagina, sperm live approximately 48 to 72 hours – Refers to the union of an ovum (egg) and a spermatozoan (sperm) which results in a zygote – Occurs in the ampulla (outer one-third) of the fallopian tube following ovulation Pre-embryonic stage – This stage encompasses the first 14 days after conception – When the zygote implants in the decidua approxiamtely 8 to 10 days after fertilization, the structure is referred to as an EMBRYO – After implantation, the embryo undergoes rapid growth and differentiation
•
Three primary germ layers of embryo
1. ECTODERM – The tissues and organs that develop from the ectoderm include the CNS, PNS, sensory epithelium of the ear, nose, eye, sinus, mouth and anal canal; skin (epidermis), hair, nails, sebaceous glands, sweat glands, hair follicles; and mammary glands, pituitary gland, enamel of the teeth and oral glands 2. MESODERM – The tissues and organ develop from the mesoderm include bone, cartilage, skeleton; connective tissue, smooth and striated muscles; cardiovascular and lymphatic systems, blood and lymph cells; kidneys and reproductive organs; serous membrane lining of the pericardial, pleural and peritoneal cavities; spleen 3. ENDODERM – The tissues and organs that develop from the endoderm include respiratory tract epithelium, epithelial lining of the GIT (pharynx, tonsils, thyroid, parathyroid, thymus), epithelial lining of urinary bladder and urethra, liver and pancreas DECIDUA – The endometrium (the lining of the inside of the uterus) become the decidua following conception and implantation – The portion directly from the blastocyst, where the chorionic villi intersect with the maternal blood vessels, is the decidua basalis – The portion covering the blastocyst is called the decidua capsularis and the portion lining the rest of the uterus is the decidua vera which will protect and nourish the developing embryo
•
PLACENTA – Begins to function by the 4th week of gestation; by the 14th week it is complete and independently functioning organ – It transmits nutrients and oxygen to the fetus and removes wastes and carbon dioxide by diffusion – Considered to be the endocrine organ of the placenta which produces the following hormones: • Estrogen (primary estriol) • Progesterone • Human chorionic gonadotropin (HCG) • Human placental lactogen • Estrogen (primary estriol) – It stimulates the growth of uterine muscle (myometium) and glandular epithelium (endometrium) and induces the synthesis of receptors for progesterone
•
Progesterone – Promotes thickening and increased viscosity of cervical mucus (the mucous plug) to protect the fetus against invading the bacteria – Decreases motility of oviducts and uterus – It stimulates growth of glandular breast tissue (acini cells) in preparation for lactation – Maintains uterine lining for implantation and relaxes uterine smooth muscle HCG – Is secreted by trophoblast cells of the blastocyst (early product of conception) and the placenta (after the second gestational month). It is partly responsible for maintaining the corpus luteum – Is detected in the urine and plasma (by day 8 ) and the first indicator of a positive pregnancy – Levels may be monitored later in the pregnancy to determine fetal well being Human placental lactogen – Levels increase after 20 weeks of gestation – It is a growthlike substance that stimuates maternal metabolism – It facilitates glucose transport across the placenta – It also stimulates breast development to prepare for lactation
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•
MULTIPLE PREGNANCIES
• DIZYGOTIC (fraternal) multiple pregnancy – Involves two or more ova fertilized by separate sperm – Fetuses have separate placentas, amnions, and chorions and may be the same or different sex MONOZYGOTIC (identical) multiple pregnancy – Developes from a single fertilized ovum – Fetuses share a common placenta and chorion bt have separate amnions, they are the same sex and same genotype
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Factors influencing embryonic and fetal development
• Environment – Poverty – Malnutrition – Maternal alcohol, nicotine or illicit drug use – Maternal prescription drug use ( anticoagulants, aspirin, anticonvulsants, antibiotics) Anatomic problems – Maternal problems include ectopic pregnancy, uterine abnormality, retroversion of the uterus and incompetent cervical os – Fetal problems include chromosomal defects and poor implantation Maternal complications – Infection, Rh incompatibility, cyanotic heart disease, renal diseases, hypertension and urinary tract infection Fetal complications – Premature rupture of membranes, preterm labor and postmaturity Physiologic problems – Folate deficiency, endocrine deficiency and defective sperm
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