Issuu on Google+

1999 Obstetrics & Gynaecology By Duy Thai PHYSIOLOGY OF PREGNANCY AND PARTURITION Cross section through normal placenta Umbilical cord containing 2 arteries, 1 vein Chorionic villi with foetal vessels Inter villous space filled with maternal blood Placental septum Anchoring villus Decidua Myometrium Spiral arteries supplying maternal blood rich in O2 and nutrients • • • Decidual vein to drain foetal CO2 and wastes into maternal circulation The cells making up the anchoring villus are called intermediate trophoblast cells. These are special in that they behave much like a cancer cell and invade the spiral arteries, forming a layer on the endothelium By doing this, the spiral arteries are no longer influenced by maternal factors (e.g. sympathetic constriction) and hence provide a steady, uninterrupted flow of maternal blood into the placenta It is postulated that failure to invade these spiral arteries by the intermediate trophoblast cells may be a factor in IUGR (due to inadequate supply of maternal blood) Functions of the placenta 1. Metabolic exchange • Nutrients and oxygen from the maternal blood enters the foetal veins in the villi • Foetal CO2 and wastes exit the foetal circulation via the arteries in the villi and are handled by the maternal circulation 2. Acts as an endocrine organ, mainly producing the placental hormones: • HCG • Oestrogen • Progesterone • HPL (human placental lactogen, aka human chorionic somatomammatropin) 3. Prevents rejection of the foetus The placental hormones 1. Human chorionic gonadotropin A. The normal menstrual cycle: • After ovulation, there is formation of the corpus luteum • The corpus luteum produces progesterone • LH secretion from the anterior pituitary is inhibited by progesterone via negative feedback • The loss of pituitary LH causes the corpus luteum to involute, resulting in reduction of progesterone • This progesterone withdrawal causes sloughing of the endometrium Page 1 of 4


Related publications