REPRO 16) Human Placenta

Placenta progesterone

Placenta cannot produce steroids on its own. Depend on maternal cholesterol as it's substrate for progesterone - Progesterone is secreted 6-7 week of gestation Progesterone function: 1) Blockade of myometrial prostaglandins production, hence less uterine contractibility 2) Stimulation of Endometrial gland secretion 3) Inhibition of ovulation through negative feedback on Hypothalamus 4) acts as immunosuppressant and inhibit Tcell mediated tissue rejection

Factors affecting rate of diffusion

- maternal/ fetal blood capillaries arrangement - blood flow rates on either sides - fetal villous exchange area - concentration gradient - distance of diffusion (membrane thickness)

Foetal Placenta

Umbilical cord - 2 arteries and a vein entwined and surrounded by mucopolysaccharide substance (Wharton's jelly) Amnion - made up of tresodeum and ectoderm - thin, tough membrane covering the embryo and filled with amniotic fluid - Fused with chorion at the end of 2 month of gestation Function: - protect embryo - medium for nutrients The chorion - outer membrane that surrounds the amnion. It is considered as the support platform of the fetus and the amnion Two layers form the chorion: 1) trophoblast as the outer layer The trophoblast are in contact with the maternal decidua 2) mesoderm as the inner layer The mesoderm is the one in contact with the amnion. The trophoblast provides the nutrients for the fetus during its confinement The chorion provides additional protection for the embryo, but it also promotes the exchange of nutrients and other necessary fluids between the mother and the embryo. Additionally, the chorion has a special feature called chorion villi. The villi sprout from the chorion in order to reach more maternal blood, the main fluid that carries nutrients from the mother's food to the embryo.

Placental lactogen (hPL)

aka human chorionic somatomammotrophin secreted by early trophoblast but only detectable in maternal serum at 4-5 weeks similar structure to GH and Prolactin can alter maternal glucose metabolism and lipolysis causes hyperinsulinemia in response to glucose loads diverts glucose to fetus

Placenta transport

function: acts as surrogate fetal lung, gut and kidney Nutrients pass by: simple diffusion facilitated diffusion active transport

maintenance of pregnancy

human placental human chorionic Gonadotropin - a glycosylated protein - only intact hCG (not free) can bind and stimulate LH receptors - produced by trophoblast on day 8-9 after ovulation and peaks at 10 week of gestation hCG functions: 1) acts on corpus luteum prevent luteolysis and stimulate progesterone 2) acts on placenta go enchance conversion of maternal LDL cholesterol to pregnolone and progesterone 3) regulate development of fetal adrenals and gonad during first trisemester 4) suppress maternal immune rejection of fetus

placental estrogen

secreted at 10 week cause growth of myometrial smooth muscle cells to accommodate fetus placenta lacks 17α hydroxylase, (estrogen precursor) DHEA-sulfate comes from fetal adrenal gland is converted by placental sulfatase to free DHEA increasing circulation of estrogen throughout pregnancy is reflection of fetal adrenal size oestriol - main metabolic product of DHEA reflects integrity of fetal circulation and metabolism as well as adequency of the placenta low maternal oestriol is associated with - placental sulfatase deficiency - fetal anencephaly

Human Placenta Structure

- Discoid organ - Haemochorial type (fetal vessels bathed directly in a circulating maternal blood)

Gestational Trophoblastic Diseases

- Hydatidiform mole complete (paternal chromosomes only diploid) fetal parts absent partial (maternal and paternal chromosomes forming triploid) fetal parts present - Invasive mole abnormal Uterine Bleeding usually in early pregnancy and accompanied by passage of thin watery fluid rapid uterine enlargement hCG levels greatly exceed normal can penetrate and even perforate uterine wall - Malignant Choriocarcinoma from Trophoblastic cells clinical features: irregular spotting foul smelling hCG above hydatidiform mole

Decidual basallis

-The endometrial tissue at the implantation site, -the maternal contribution of the placenta - non glandular, non vascular cells of the Endometrial connective tissue - are produced by steroid hormone dependent division and differentiation of material uterine stromal cells