Lecture 19: Placentation, the Endocrinology of Gestation and Parturition

Placenta

-transient organ of metabolic interchange between the conceptus and the sam

-also a transient endocrine organ

-composed of a fetal component derived from the chorion and a maternal component derived from modifications of the uterine endometrium

-regions of contact between the two allow for metabolic exchange

-classified by the distribution of chorionic villi on their surfaces=results in distinct anatomical appearance

-diffuse=mare and sow

-zonary=dogs and cats

-discoid=rodents and primates

-cotylendonary=ruminants (cow and ewes)

-regulates exchange between the fetus and dam=simple diffusion facilitated diffusion active transport, glucose immunoglobulins steroid hormones thyroid hormone catecholamines vitamins and minerals toxic substances

Teratogenic

-many toxic substances easily cross the placenta=alcohol lead phosphorus mercury opiate drugs barbiturates and antibiotics, some are highly teratogenic

-inducing abnormal development (birth defects)

-LSD, amphetamines, lithium, DES

-a wide range of microorganisms can contaminate the fetus=viruses can cross the placental barrier with ease, transmitted from the dam to the fetus

-human diseases that can be transmitted by the pregnant mother to the fetus=german measles, herpes virus, HIV, and syphilis

Equine Chorionic Gonadotropin

-or pregnant mare serum gonadotropin

-luteotropic=stimulus for maintenance of the primary CL, causes formation of the accessory CL

-accessory CL=forms following ovulation between days 40 and 70 of pregnancy, ovulation stimulated by eCG

Human Chorionic Gonadotropin

-found in humans and other primates

-can be detected in blood and urine of women as early as 8-10 days of gestation

-luteotropic-stimulates transitional CL=luteal receptors bind hCG resulting in sustained P4

Progesterone

-inhibits myomeytrial contractions=”progesterone block”

-placenta takes over P4 production in some species=after 50 days of gestation in the ewes, around the 8th month of gestation in the cow

Estrogen

-peak of estrogen marks the start of the preparturient period

-stimulates secretions and motility in repro tracts

Placental Lactogen

-promotes growth of the fetus (like GH)

-stimulates the mammary gland

Relaxin

-causes the cervix to dilate and softens the ligaments in the pelvic region

Parturition

-the act of giving birth

-fetus triggers the onset of parturition

-the fetal hypothalamo-pituitary-adrenal axis is obligatory for the initiation of parturition

-during the end of gestation, fetal mass approaches the space limitations of the uterus=it is believed that this causes the fetus to become stressed

-in response to stress, the fetal anterior pituitray releases adrenal corticotropin (ATCH)=ATCH stimulates the fetal adrenal gland to produce corticoids, corticoids initiate a cascade of events

-two major events occur=removal of the myometrial “progesterone block” enabling contractions to begin, increased repro tract secretions particularly the cervix

Dystocia

-extension beyond what is considered to be the normal upper end duration of parturition

-difficult birth

Puerperium

-period after parturition when the repro tract returns to its normal non-pregnant condition so that the female may become pregnant again

-damaged reproductive tissue are repaired and ovarian function returns

Uterine Involution

-the process whereby the uterus returns to its normal non-pregnant size and function following parturition