Pregnancy, Parturition, and Contraception Flashcards
(34 cards)
How much sperm is released into the vagina and how many reach the uterine cavity? How many arrive at the fallopian tube?
250,000,000 released into vagina.
100,000 reach the uterine cavity.
50 or less arrive at distal end of the fallopian tube
After the sperm enter the fallopian tube, what happens and how long do these stages take?
They get delayed in the ampullary-isthmic junction where fertilization occurs (Days 1-2)
Then delayed at utero-tubal junction (2-3 days)
Egg enters uterine cavity as a morula at days 3-4, and the blastocyst implants at day 7.
Difference between CBG and SHBG?
sex hormone binding globulin (SHBG; carries estrogen and testosterone)
cortisol binding globulin (CBG;carries cortisol and progesterone)
Estrogen on CBG and SHBG levels
estrogen is a very potent stimulus for the production of both CBG and SHBG. Because of this, blood levels of CBG and SHBG are highest in pregnant women at term; the time at which circulating estrogens are maximally elevated.
What is the general stepwise mechanism for steroids causing a cellular function, starting at binding?
- Target cell penetration and subsequent binding to a specific cytoplasmic receptor.
- Transfer of the steroid hormonereceptor complex into the nucleus where it binds to specific chromatin receptor sites.
- Activation of the genome results in the transcription of new RNA.
- The newly formed mRNAs direct the translation of specific proteins.
- The action of the steroid hormone is then manifest by the functions of the proteins produced, whether they may be structural or enzymatic (regulatory) proteins
Principal site of steroid inactivation?
Liver
Discuss the biochemical modifications made to steroids to excrete them
The major chemical modifications are reduction, glucuronidation and sulfation.
Double bonds and keto groups are reduced by hydrogenation.
Glucuronic acid or sulfate are then added to the metabolite.
Reduction renders steroid hormones inactive and glucuronidation or sulfation increase the water solubility of the metabolites so they may be readily excreted in the urine.
Where does sperm capacitation occur, and why is it important?
Capacitation occurs in the female reproductive tract and involves the sequential activation of a series of hydrolytic enzymes and the merging of membranes on the sperm head. This series of reactions is collectively referred to as the acrosome reaction.
The result is a sperm which is capable of (i) interacting with receptors on the zona pellucida and (ii) digesting its way through the cell layers and membranes surrounding the egg (cumulus oophorus, corona radiata, zona pellucida and vitelline membrane).
Penetration of the vitelline membrane by the sperm initiates two important reactions:
- the release of cortical granules into the perivitelline space which prevents polyspermy
- triggering the final stages of meiosis in the oocyte. The second polar body is extruded from the egg and a haploid number of maternal chromosomes is achieved.
When does the ovum undero its first mitotic division? (Note MITOTIC, not MEIOTIC)
The ovum undergoes its first mitotic division about 24 hours after penetration.
What are the three distinguishing regions of the blastocyst and what do they lead to?
cytotrophoblast, outer surrounding cells: which will form the syncytiotrophoblast
inner cell mass, which gives rise to the fetus and amniotic ectoderm
hypoblast, which gives rise to the endodermal lining of the yolk sac
Why, specifically, is progesterone absolutely required for implantation?
The endometrium at the site of contact, under the influence of progesterone from the corpus luteum, is transformed into the maternal placenta, the decidua. In the absence of progesterone, implantation cannot occur.
Thus the placenta is formed by the union of what two tissues?
Union of fetal tissue (trophoblast) and maternal tissue (decidua).
What does the trophoblast secrete, and why?
HCG is a glycoprotein hormone (38,000 mw) secreted by the trophoblast.
The major role of HCG is to maintain corpus luteum progesterone secretion, a function essential for the maintenance of pregnancy through the 7th week as calculated from the last menstrual period.
Another essential function of HCG is stimulation of testosterone secretion by the fetal testis.
What is HPL and what is it also called?
Human placental lactogen (HPL) is a protein hormone (22,000 mw) which resembles both prolactin and growth hormone in structure and function.
Because of this HPL is also referred to as chorionic growth hormone and chorionic somatomammotropin.
What does HPL do?
- Mobilize and metabolize maternal fat stores, resulting in insulin resistance peripherally in the mother (can lead to gestational diabetes) and glucose for the fetus by sparing protein
- Promote breast development (mammotropic action)
- Possibly ion movement for salt control
When do we see HPL in serum?
HPL production starts around 6 weeks gestation with greatest production occurring in the last half of pregnancy.
At term, concentrations of HPL in plasma are highest of all the placental protein hormones.
Immediately after implantation, HCG from the trophoblast acts on the corpus luteum to enhance progesterone secretion. What does this result in?
This action of HCG rescues the corpus luteum from the spontaneous regression that would have occurred in the absence of implantation. Progesterone from the “rescued” corpus luteum, in turn, signals the hypothalamus that implantation has occurred and not to initiate another menstrual cycle.
Specifically, how does Progesterone stop another menstrual cycle?
Specifically, progesterone feeds back to prevent the rise in FSH which would normally initiate the next follicular phase. Thus, progesterone from
the maternal ovary is an important neuroendocrine signal for the establishment of pregnancy
How does progesterone “quiet the uterus”
Decreases uterine motility in the face of the extraordinarily high levels of estrogen that circulate during pregnancy.
Progesterone acts on the uterine smooth muscle to inhibit contractility throughout pregnancy.
Progesterone also acts on the uterus and cervix to inhibit the formation of prostaglandins, agents critically involved in the events of parturition.
Where does the progesterone come from during pregnancy?
During the first 6-8 weeks of gestation the corpus luteum is the major source of circulating progesterone. After 8 weeks gestation the placenta becomes the major source of blood-borne progesterone
Estrogen works synergistically with progesterone in the development and growth of the uterus. This action serves to maintain the growth potential of the uterus for accommodating the developing fetus.
What else does estrogen do during this period?
- estrogen acts together with progesterone to promote breast development for lactation
- Acts to soften the elastic tissues of the pelvic ligaments and vagina in preparation for parturition
- Increases the production of steroid hormone carrier proteins by the liver
- Stimulates the production of clotting factors
What makes estrogen during all of this stuff?
Prior to the 6th week of gestation estrogen originates from the mothers ovaries. After the 7th week the fetal-placental unit is the primary source of estrogen in blood
Discuss what causes “Estrogen dominance” in the last few days of pregnancy
In all non-primate animals progesterone secretion declines during the last few days of pregnancy. This loss of progesterone removes the direct quieting influence of progesterone on uterine contractility and permits the unimpeded actions of estrogen. In women, a decline is not seen in the actual levels of progesterone, however, estrogen levels continue to rise at term, whereas, progesterone levels plateau. The result is an estrogen dominance
