Flashcards in Unit 7 - Pregnancy, Parturition, and Lactation Deck (24)
what are the 8 steps of fertilization?
1. sperm binds to ZP (made of 3 glycoPRO that make mucus-like lattice)
2. increase in [Ca++]i in sperm triggers exocytosis of acrosome (acrosomal reaction) triggered by sperm binding to one of glycoPRO
3. acrosomal enzymes penetrate ZP; sperm oscillates to help
4. cell membranes fuse, and cytoplasmic part of head/tail enter oocyte
5. rise in [Ca++]i of oocyte triggers cortical reaction to harden ZP and prevent polyspermy
6. rise in [Ca++]i of oocyte completes 2nd meiotic division (to make female pronucleus), and 2nd polar body expelled
7. sperm head enlarges to become male pronucleus
8. pronuclei fuse to form zygote
what 3 things does intracellular calcium rise do?
1. exocytosis of acrosome in sperm (acrosomal reaction)
2. hardening of ZP in oocyte (cortical RXN)
3. 2nd meiotic division and formation of 2nd polar body
what is the time course for fertilization?
several days; fertilization must occur within 24 hrs of ovulation
-usually in fallopian tube, and 3-5 days pass as blastocyst makes way to uterus (around day 4-5)
-by day 5-7, has implanted
what is sperm transport facilitated by?
-contractions of uterus, cervix, and fallopian tubes in response to oxytocin released in female orgasm
-prostaglandins in male seminal fluid
where does the placenta derived?
trophoblasts and adjacent cells
what maintains early pregnancy?
corpus luteum (maintained by hCG)
what produces hCG and what does it do?
made by syncytiotrophoblasts in blastocyst shortly after it implants
-closely related to LH; sustains CL in face of declining levels of maternal LH, so that sex steroids are produced
-immunosuppressive agent with growth-promoting activity to promote placental development
-stimulates testes of male fetus to make testosterone for male sex organ development
where does fetus get nutrition in early and later pregnancy?
early: endometrial decidua (developed from progesterone)
late: diffusion through placenta
what placental steroid hormones are needed for pregnancy? which is most important?
progesterone, estrone, estradiol, and estriol
-all need high levels to maintain pregnancy
-E3 is most important
-at 8 weeks gestation, coordinated activity of maternal-placental-fetal unit maintains high level (reflected by rapid rise in E1)
what is the most important placental peptide hormone?
what are human somatomammotropins?
hCS1 and 2
-coordinate fuel economy by contributing to conversion of glucose to FA and ketones
-promote mammary gland development in pregnant mother
how are placenta and fetus similar to granulosa and theca cells, respectively?
placenta lacks 17-alpha-hydroxylase, 17,20 desmolase, and 16-alpha-hydroxylase (make precursors of E1-3)
-cannot get cholesterol to start synthesis either
fetus lacks 3-beta-hydroxysteroid dehydrogenase and aromatase (cannot directly make estrogen)
in pregnancy, what happens to:
-demand for nutrients
-increased blood volume (increased plasma volume and erythrocytes meet demands of enlarged uterus and hypertrophied vascular system)
-MAP decreases midpregnancy (usually remains at or lower than normal, sometimes rises in 3rd trimester)
-increased CO (35-40%) b/c increased stroke volume (NOT HR) in 1st trimester
--to kidney and uterus, with some increase to heart, skin, breast
-increased alveolar ventilation b/c increased TV (~40%); early changes due to steroid effects
--causes decreased maternal arterial pCO2
-increased demand for dietary PRO, Fe, and folic acid (dietary production of blood cells)
-uterus increases from 50 g to 1.1 kg, and breasts double
-average gain 25-35 pounds (fetus is 8 pounds)
-BMR increases 15%, especially in latter half
what is the mean duration of pregnancy?
38 weeks from time of ovulation (or 40 weeks from first day of last menstrual period)
what is parturition believed to be triggered by? what about contractions?
birth: increase in fetal production of cortisol near term, which increases the ratio of E:P, thus sensitivity of uterus to contractile stimuli
labor: prostaglandins sustained by oxytocin and other prostaglandins (but oxytocin does NOT trigger labor)
-PGE2 and PGF2a act by paracrine mech to stimulate uterine smooth muscle cells, promote formation of gap junctions between USMC (increase oxytocin response), and soften (effacement of) cervix; in other words
-maintained via positive feedback
why is oxytocin released in bursts during labor?
in response to distension of cervix (Ferguson reflex)
-estrogen increases number of oxytocin receptors on myometrial tissue in uterus throughout pregnancy
what is relaxin?
made by corpus luteum, placenta, and decidua (endometrium)
-increased production during labor will soften/dilate cervix
what are the stages of birth?
0 - uterine tranquility and refractoriness to contraction
1 - uterine awakening; initiation of parturition, extending to complete cervical dilation (increase in number of gap junctions between myometrial cells, and increase in number of OT receptors)
2 - active labor; from complete cervical dilation to delivery of newborn
3 - from delivery of fetus to expulsion of placenta and "final uterine contraction" (important to prevent hemorrhage, and may be stimulated by lactation)
what kind of hormones act on the breast? important ones? (4 classes)
1. mammogenic - promote cell proliferation (to increase breast size)
-estrogen and progesterone (many other permissive)
2. lactogenic - promote initiation of milk production by alveolar cells
-PRL (other permissive)
3. galactokinetic - promotes milk ejection (contraction of myoepithelial cells)
4. galactopoietic - maintains milk production once established
how do mammogenic hormones work?
progesterone and estrogen act synergistically with other hormones to cause additional growth of breast lobules, with alveoli budding and secretory characteristics
what is the functional secretory unit of the breast? organization?
alveolus is unit
-organized into lobules, which drain into ductules
-15-20 ductules drain into a duct leading to the outside
-contractile myoepithelial cells around each alveolus and adipose cell, and promote milk let down in response to oxytocin
-secretory epithelial cells make up alveolus and secrete milk in response to PRL and cortisol
what is colostrum? how does it compare to breast milk and cow's milk?
colostrum is "first milk" providing concentrated, low-volume form of nutrition for neonate's immature GIT in first few days of life
-little fat, low calories, but high PRO (comparable to cow's)
-as with human milk, contains protective Ab
cow's milk has higher electrolyte concentration, more PRO than human milk (due to casein), and cannot be tolerated by newborn
what maintains milk production after parturition? what would inhibit milk secretion?
prolactin (lactogenic effect)
-estrogen and progesterone prevent actual secretion of milk, despite being needed for breast development