Lecture 41: Reproductive System: Pregnancy

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Gestation Period

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-Comprises 3 trimesters
-In first trimester individual starts out as a zygote, then morula, blastocyst
-after implantation, is called an embryo
-embryonic phase of development lasts from fertilization until the 8th week of gestation, when it becomes a fetus
-by day 35 the heart is beating, and eye and limb buds are present

Placenta and Umbilical Cord

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-Placenta forms during 3rd month
-Develops from embryonic chorion and maternal uterine tissue
-Site of nutrient, gas and waste exchange
-Secretes hormones that maintain pregnancy
-Barrier to microorganisms, except some viruses
-AIDS, measles, chickenpox, poliomyelitis, encephalitis
-not a barrier to drugs such as alcohol
-The umbilical cord, containing two umbilical arteries and one umbilical vein connects the embryo and the placenta
-At birth, the placenta detaches from the uterus (afterbirth)

Hormone Blood Levels

-Human chorionic gonadotropin (hCG) produced by the chorion is less important after 4 months, because the corpus luteum no longer must be stimulated
-The placenta takes over the steroid hormone secretions of the corpus lutem

hCG

---:
Rescues the corpus luteum from degeneration until the 3rd or 4th month of pregnancy

Progesterone Estrogens

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1. maintain endometrium of uterus during pregnancy
2. help prepare mammary glands for lactation
3. prepare mother's body for birth of baby

Relaxin

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1. increases flexibility of pubic symphysis
2. helps dilate uterine cervix during labor

hCS

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1. Helps prepare mammary glands for lactation
2. Enhances growth by increasing protein synthesis
3. Decreases glucose use and increases fatty acid use for ATP production

Corticotropin releasing hormone

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1. Establishes the timing of birth
2. Increases secretion of cortisol

Primary Germ Layers

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In between the yolk sac and the amniotic cavity is the embryonic disc, which gives rise to the primary germ layers:
-Endoderm
-Mesoderm
-Ectoderm
-Arises from the layering of cells that occurs during gastrulation day 15
Organogenesis is the formation of the organs starts 4th week

Ectoderm

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All nervous tissue
Epidermis of skin

Mesoderm

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Cartilage, bone and connective tissue
Skeletal, cardiac and smooth muscle tissue
Blood and lymphatic vessels
Epithelium of gonads

Endoderm

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Epithelium of digestive tract
Epithelium of respiratory system
Epithelium of thyroid, liver and pancreas
Epithelium of bladder

Menstrual Phase

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-Menstruation lasts for 5 days
-First day is considered beginning of 28 day cycle
-In Ovary
-a cohort of follicles 20 that began to develop 6 days before beginning to secrete estrogen
-Fluid is the filling the antrum from granulosa cells
In uterus:
-declining levels of progesterone causes spiral arteries to constrict and glandular tissue degenerates
-stratum functionalis layer is sloughed off along with 50-150 ml of blood

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