Phyisology Of Labor And Delivery Flashcards
Normal pregnancy timeframe
Approximately 39-40 weeks = fully term
- since the last menstraul period
Is divided into three trimesters (13 weeks each)
1st trimester
- characterized by hCG produced by the trophoblast cells at roughly 8 days after fertilization. Maximum levels are at week 9.
2nd and 3rd trimesters
- are marked by production fo steroid hormones
Early events of pregnancy (first 10 days)
Ovulation occurs during LH spike
Fertilization =1 day after ovulation and usually in Fallopian tubes
Blastocyst into uterine cavity by day 4
- after generating morula -> blastocyst which occurs in Fallopian tube
Implantation into uterine cavity by day 5
Formation of trophoblast and attachment by day 6
Onset of HCG production from trophoblast cells By day 8
HCG rescue of the corpus luteum by day 10
Capacitation of sperm
Sperm must undergo this process in the female reproductive tract before they are able to fertilize the egg
Steps
1) removal of cholesterol from he sperm membrane
2) removal of proteins and carbohydrates form the sperm membrane
3) change in sperm membrane potential that allows calcium to enter the sperm and therefore facilitate acrosome reactions
4) phosphorylation of numerous proteins
incapacitated sperm need to bind to epithelial cells of the oviductal isthmus in order to slow capacitation and also induce capacitation to extend the sperm life span
The 6 steps of fertilization
1) sperm cell weaves past follicular cells to sperm receptors in zona pellucida
2) intracellular calcium rises in sperm initiating the acrosome reaction
3) proteolytic enzymes released form the acrosome digest the zona pellucida
4) sperm penetrates the oil Emma, which stimulates a rise in intracellular calcium in the egg and intimates a cortical reaction and development of the first polar body
5) rise in intracellular calcium initiates the completion of the second meiotic division and generates the second polar body
6) sperm enlarges to become male pronucleus which fuses with the female pronucleus
Hyper activation of the sperm in oviduct
Involves the change in flagella motion from a wavelike to whiplike motion and is caused by calcium entry through sperm-specific calcium channels
Called “CatSper” channels
- these channels are activated by progesterone
What is the “receptive period” of the uterine endometrium
Period in the uterine cycle that results in decreases of anti adhesion protein expression and increased adhesion protein expression
- expression = integrins, Cadherins
- decrease = mucins
Occurs during day 20-24 of the menstural cycle assuming ovulation occurred at day 14
Progesterone effects after implantation
Stimulates secretion from uterine glands to provide nutrients to the embryo
Inhibits myometrial contraction and prevents the release of paracrine factors that lead to menstruation
Increases window of receptivity in the uterine endometrium (receptive phase occurs)
How do hormones change during pregnancy as it pertains to maternal-placental-fetal unit
Maternal levels of progesterone and all estrogens increase (higher than those achieved during normal menstrual cycle) during pregnancy
Placenta increases progesterone via syncytiotrophoblast production of bHCG
- **this is INDEPENDENT of fetal viability however
- *Estriol levels increasing from fetus and placenta are DEPENDENT of the fetal viability**
- these levels start to rapidly increase at gestation age 8 (they will not increase if the fetus isnt viable)
**estrgoen by itself is NOT needed for a normal pregnancy
What is the luteal placental shift
Occurs by 8th week of gestation in which the placenta takes over from the corpus luteum to maintain estrogens and progesterone levels during pregnancy
the corpus luteum is needed to prevent menstration, but it by itself is not strong enough to maintain the high levels of progesterone needed in late pregnancy
Progressive changes in labor and delivery
Phase 1: quiescence
- prelude to parturition
- shows contractile unresponsive and cervical softening
- first phase after conception and occurs until right until parturition
Phase 2: activation
- uterine prepares for labor and the cervix ripens
- occurs after parturition and before onset of labor
Phase 3: stimulation
- uterine contraction
- cervix dilates and the fetus and placenta is expelled
- occurs all through labor all three stages
Phase 4: involution
- uterine involution occurs with cervical repair and breast feeding
- fertility is restored at the end
Uterine quiescence
First stage of partition
Focuses on progesterone effects of inhibiting uterine contractility and slow recruitment cascades that promote estrogen
The fetus job at this stage is to produce DHEAS in response to CRH -> ACTH from fetus hypothalamus and pituitary gland which is used to produce estriol in the placenta
- this is a slow phase that is regulated by placental/maternal cortisol levels (cant increase too fast)
Fetus adrenal glands also produce cortisol slowly which works to increase oxytocin, CRH and PGE2 in the placenta (required for inducing birth)
Onset of labor phase of parturition
Focuses on with drawling progesterone effects of inhibiting uterine contractility and the recruitment of cascades that promote estrogen levels at a much fast rate
- high levels of estrogen products leads to upregulation of contraction-associated proteins (CAPs)
the reciprocal decrease of progesterone receptors and increase in estrogen receptors is crucial to induction of labor
CAPs function to:
- upregulate oxytocin receptors on uterus
- upregulate PGE2 receptors on uterus
- increase Gap junctions on uterus
- *all work to increase contractility of the uterus to expel the fetus**
The 3 major factors for forceful and rhythmic contractions needed to produce labor are
1) increased levels of PGEs
2) increased myometerial cell interactivity via gap junctions
3) increased myometrial responsiveness to PGEs and Oxytocin
Stage 3 involution of partition
Mainly high levels of oxytocin are responsible for the continuous sustained and forceful myometrial contraction that is required to constrict spiral arteries and facilitate postpartum hemostasis after placental leaves
- **this is required to help prevent postpartum hemorrhage
What is mifepristone?
A selective progesterone receptor antagonist that blocks progesterone and allows for increased myometrial contractility and excitability
- induces labor at any stage of pregnancy (can induce abortion if too early)
Prostaglandin and oxytocin effects in partition
Roles are to increase uterine contractility
When uterine contractions occur, the cervix dilates which causes afferent nerve signals from the cervix to increase oxytocin secretion (inducing a positive feedback loop)
Oxytocin both acts as an agonist and also promotes production of PGEs which a re used to enhance (positive feedback) on oxytocin contractions on uterus
- PGE doesn’t directly induce contractions, but rather increases oxytocin’s ability to induce contraction
