Question

• Understand the functions of the placenta

Answer 1

Placenta is an organ that develops within the pregnant uterus which connects the uterine cavity to the foetus inside it through umbilical cord. Human placenta is discoid in shape and deciduate (since some maternal tissue is shed during child birth). At birth of the baby, human placenta is about 500 grams in weight and ratio of weight of placenta to that of baby is around 1:6. Placenta develops from two sources :- fetal component is chorion frondosum (principal component) and maternal component is ddcidua basalis.

Function of placenta :-

- the intervillus blood present in the placenta supplies oxygen and nutrition to the fetus as well as removes carbon dioxide and other waste products from fetal circulation.

- Placenta allows the passage of IgG Immunoglobulin from the maternal circulation into the fetal circulation which helps in providing passive immunity to the fetus

- Placenta produce hormones like human chorionic gonadotropin (hCG), human placental lactogen, estrogen, progesterone.

Human chorionic gonadotropin (hCG) is produced by syncytiotrophoblast of placenta. It maintains corpus luteum (thus the level of progesterone as corpus luteum secretes progesterone) during the first trimester of pregnancy and prevents abortion which would otherwise occur in absence of progesterone. hCH also has role in immunosuppressant activity and thus prevents the rejection of fetus.

Human placental lactogen prepares the mammary glands for lactation. It also promotes maternal lipolysis which increases the level of free fatty acids in maternal blood which is used as a source of energy.

Estrogen promotes the growth of uterus along with progesterone. Estrogen also helps in growth of mammary glands for lactation.

- Placenta also forms placental barrier along with syncytiotrophoblast, cytiotrophoblast and endothelium of fetal capillary wall with its basement membrane. Although it is not a very effective barrier, it still acts as a semipermeable membrane and allows the passage of selected molecules from maternal to fetal circulation and thus helps in protecting the fetus.