Flashcards in Lect 3: Pregnancy, Parturition & Lactation Deck (26)
sperm binds zona pellucida; acrosomal reaction stimulated when sperm binds to one of the glycoproteins of the zona pellucida; calcium dependent process leads to fusion of the acrosome with the sperm plasma membrane (exocytosis). Hydrolytic enzymes released from acrosome penetrate the zp and the sperm oscillates to penetrate the oocyte. Cell membranes (of sperm and oocyte) fuse and the cytoplasmic portion of sperm head and tail enter the oocyte. Not the cell membrane
The oocyte undergoes the cortical reaction
triggered by rise in Ca/IP3-dependent process which prevents other sperm from fertilizing the oocyte. The oocyte completes the 2nd meiotic division and a 2nd polar body is expelled. The head of the sperm condenses to become the male pronucelus. Male and female pronuclei fuse to form a zygote. Zygote contains 46 chromosomes from two pairs of 23 chromosomes. CORTICAL REACTION prevents polyspermy.
Both acrosomal and cortical are calcium- dependent
During the female menstrual cycle changes take place in the ovaries and uterus, under the control of the hypothalamus and the ant. pit. During the follicular phase, several primary follicles undergo further development in responses to FSH ad synthesize androgens, which are converted to estradiol under the influence of LH.
Ultimately, one follicle fully matures and the others regress. The uterine endometrium proliferates in response to estradiol. Near midcycle, estradiol rises to a level that initiates positive feedback and thus a surge in LH and FSH release which results in ovulation. During the ensuing luteal phase, the mature follicle becomes the corpus luteum (Gr and Theca cells) which secretes progesterone and estradiol. The uterus undergoes further proliferative and secretory changes 6-7 days. The follicular phase is the late follicular phase and high levels of beta estradiol at this time primes the uterus by increasing the number of progesterone receptors to convert proliferate to secretory uterus…lots of glandular: mucus, juicy uterus. Not acceptable for implantation. This happens over 6-7 days. It becomes more secretory in response to progesterone. Unless pregnancy occurs, endometrial sloughing and menstruation, marking the beginning of a new cycle. Image shows 14-day fixed phase, luteal phase.
At the beginning of fertilization
your placenta is not well developed and cannot sustain blastocyst. Need corpus luteum first 8 weeks. LH luteinizes cells to produces estrogens, progesterone (high). Something has to come in keep the LH/corpus luteum around until the blastocyst can be supported by the placenta. hCG Is that something
Time course of Fertilization and Implantation
o Fertilization occurs in the fallopian tubes (typically)-takes 3-5 days for the blastocyst to make its way to the uterus and another 1-2 days for it to implant into the uterus. The synctiotrophoblasts of the blastocyst makes hCG (early on)…basis of home pregnancy test.
hCG stays high for sustainance of In addition to the flagella beating to cause motility of the sperm, uterine and cervical contractions facilitate sperm transport. At this early stage of pregnancy, the corpus luteum continues to produce steroids to maintain pregnancy as the placenta develops from trophoblasts and adjacent cells
o Is produced in the synctiotrophoblasts of the blastocyst. Looks and acts like LH
o Sustains the corpus luteum in the face of declining levels of maternal LH. This keeps up and increases sex steroid production. Highest during the 8th to the 13 weeks of pregnancy/ reason for morning sickness.
o Immunosuppressant, promotes growth and placental development.
o (In males hCG stimulates the testes of the male fetus to produce testosterone, leading to male organ development. Measured in urine after blastocyst implants)
o Image: hCG is good fr the first trimester but is limited in capacity to make steroids. Need the placenta. Need P-M-F unit. While hCG is high the corpus luteum is making steroids, they are not that high. Midway all the estrogens and progesterone are taking over.
The fetus derives nutrition from
the endometrial decidua (1st trimester) until the food can diffuse thru the placenta.
o Synthesizes 1.steroid hormone, 2. hCG and 3. somatomamotropins are related to growth hormomes promoting fuel economy and mammary gland development in mom
What happens to maternal levels of progesterone and estrogens
Maternal levels progesterone and estrogens rise and remain elevated during pregnancy. Progesterone spikes near -4 & -8 weeks
What's significant about estriol?
Estriol reflects adequate development of the placenta around 8 weeks.
Mom and fetus cooperate to produce pregnancy hormones:
o After about 8 weeks of gestation, the coorodinated activity of maternal-placental-fetal unit maintains high levels of estrogens & progesterone
o The placenta needs both mother and fetus to produce steroid hormones, unlike the self-sufficient corpus luteum. It lacks three enzymes: 17-alpha-hydroxylase, 17,20-desmolase and 16-alpha-hydroxylase enzymes.
o The fetus lacks 3-beta-hydroxysteroid dehydrogenase and aromatase activity. It doesn’t make steroids
o The mama supplies cholesterol in the form of LDL, which the placenta uses to make progesterone for export to the mother to maintain pregnancy.
o The fetal adrenal gland and liver supply the three enzymes (estrogens) lacking in the placenta.
o The fetus lacks the enzymes that catalyze the final steps in estrogen synthesis. If the fetus alone were to generate estrogens, it would be exposed to dangerous levels of hormones needed by mom.
How does mom's body respond to preganncy?
o Increased blood volume-hypertrophied uterus has more demands
o MAP decreases or is normal maybe due to vasodilation
o Increased cardiac output usually first trimester, due to SV
o Increased alveolar ventilation
o Increased demand for dietary protein, iron, folic acid
o Increased uterus and breasts
o Weight gain 25-35 lbs
o BMR increases especially in the latter half of pregnancy
o Adaptive change in cardiovascular and respiratory systems, fluid volume, metabolism and nutrition
o Uterus is quiescent throughout the pregnancy due to progesterone and relaxin.
o Last month of pregnancy has irregular braxton hicks contractions until the regular labor contractions occur
o Parturition may be triggered by an increase in fetal cortisol which increases the estrogen/progesterone ratio and thus the uterus’s contractile stimuli
o Prostaglandins initiate contractions of the uterine smooth muscle. These are sustained by oxytocin and more prostaglandins
Parturition and prostaglandins
The uterus, fetal membranes and placenta produce prostaglandins which act by paracrine mech to stimulate uterine smooth muscle cells, promote formation of gap junctions betw smooth muscles WHICH POTENTIATES their response to oxytocin to cause softening/thinning/dilation or effacement of the cervix. Oxy doesn’t initiate contractions. Ratio of estrogen/progesterone might
o During pregnancy, estrogen increases the number of oxytocin receptors on myometrial tissue in the uterus. Maternal oxytocin is released in bursts with increasing frequency during labor. This occurs in response to distension of the cervix
Positive feedback loops
sustain production of prostaglandins and oxytocin as labor progresses
is produced by the corpus luteum placenta and decidua. Increased production during labor may help to soften/dilate the cervix.
Involution of the uterus
Involution of the uterus occurs after delivery in response to the changed endocrine milieu
Baby’s head stretches cervix→cervical stretch excites fundic contraction→ fundic contraction pushes baby down & stretches cervix more→cycle repeats. During “uterine awakening” or initiation of parturition there is an increase in the # of gap junctions b/w myometrial cells. During “active labor” complete cervical dilation to deliver the newborn
o Oxytocin promotes milk let-down & uterine contractility
o Prolactin promotes milk synthesis after birth
o Both hormones released in response to suckling
Breasts respond to hormones even after pregnancy.
promote cell proliferation. Progesterone acts synergistically with estrogen to cause additional growth of breast lobules, with alveoli budding and secretory characteristics
promote milk production; Prolactin
promotes milk let-down; Oxytocin
maintains milk production Prolactin and *cortisol
The functional secretory unit of the breast. It is organized into lobules, which drain into a ductile.15-20 ducts drain into a duct that leads to the outside. There are myoepithelial cells surrounding each alveolus which promotes milk let down in response to oxytocin. Secretory epithelial cells comprise the alveolus and secrete milk in response to prolactin and cortisol
provides concentrated low-volume form of nutrition for the neonate’s immature GI tract during the first few days of life.
o It does not contain much fat as compared to human milk. Has lots of antibodies
*Estrogen and progesterone prevent actual secretion of milk.
The sudden loss of these steroids after deliver allows prolactin to exert its lactogenic effect. Upon suckling, prolactin levels spike