Unit 7 - Pregnancy, Parturition, and Lactation

Question 1

what are the 8 steps of fertilization?

Answer 1

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

Question 2

what 3 things does intracellular calcium rise do?

Answer 2

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

Question 3

what is the time course for fertilization?

Answer 3

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

Question 4

what is sperm transport facilitated by?

Answer 4

• contractions of uterus, cervix, and fallopian tubes in response to oxytocin released in female orgasm
• flagella motility
• prostaglandins in male seminal fluid

Question 5

where does the placenta derived?

Answer 5

trophoblasts and adjacent cells

Question 6

what maintains early pregnancy?

Answer 6

corpus luteum (maintained by hCG)

Question 7

what produces hCG and what does it do?

Answer 7

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

Question 8

where does fetus get nutrition in early and later pregnancy?

Answer 8

early: endometrial decidua (developed from progesterone)
late: diffusion through placenta

Question 9

what placental steroid hormones are needed for pregnancy? which is most important?

Answer 9

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)

Question 10

what is the most important placental peptide hormone?

Answer 10

hCG

Question 11

what are human somatomammotropins?

Answer 11

hCS1 and 2

• coordinate fuel economy by contributing to conversion of glucose to FA and ketones
• promote mammary gland development in pregnant mother

Question 12

how are placenta and fetus similar to granulosa and theca cells, respectively?

Answer 12

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)

Question 13

in pregnancy, what happens to:

• blood volume
• MAP
• cardiac output
• alveolar ventilation
• demand for nutrients
• uterus/breast size
• weight gain
• BMR?

Answer 13

• 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

Question 14

what is the mean duration of pregnancy?

Answer 14

38 weeks from time of ovulation (or 40 weeks from first day of last menstrual period)

Question 15

what is parturition believed to be triggered by? what about contractions?

Answer 15

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

Question 16

why is oxytocin released in bursts during labor?

Answer 16

in response to distension of cervix (Ferguson reflex)

-estrogen increases number of oxytocin receptors on myometrial tissue in uterus throughout pregnancy

Question 17

what is relaxin?

Answer 17

made by corpus luteum, placenta, and decidua (endometrium)

-increased production during labor will soften/dilate cervix

Question 18

what are the stages of birth?

Answer 18

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)

Question 19

what kind of hormones act on the breast? important ones? (4 classes)

Answer 19

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)
   - oxytocin
4. galactopoietic - maintains milk production once established
   - PRL

Question 20

how do mammogenic hormones work?

Answer 20

progesterone and estrogen act synergistically with other hormones to cause additional growth of breast lobules, with alveoli budding and secretory characteristics

Question 21

what is the functional secretory unit of the breast? organization?

Answer 21

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

Question 22

what is colostrum? how does it compare to breast milk and cow’s milk?

Answer 22

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

Question 23

what maintains milk production after parturition? what would inhibit milk secretion?

Answer 23

prolactin (lactogenic effect)

-estrogen and progesterone prevent actual secretion of milk, despite being needed for breast development

Question 24

effect of suckling (4)

Answer 24

1. stimulates sensory nerves
2. in arcuate nucleus of hypothalamus, afferent input from nipple inhibits neurons that release dopamine, so increase PRL release
3. in supraoptic and paraventricular nuclei of hypothalamus, afferent input from nipple triggers production and release of oxytocin from posterior pituitary
4. in preoptic area and arcuate nucleus, afferent input from nipple inhibits GnRH release, inhibiting FSH and LH release, and inhibiting ovarian cycle in lactating females (thus acts as birth control)