PLACENTA
Placenta may be defined as a temporary structure formed by the association or fusion between the extra-embryonic membranes of the foetus and the endometrium of mother for the pur¬pose of physiological exchange of materials.
Choriovitelline Placenta (Yolk-sac Pla¬centa):
In some mammals, particularly in most marsupials (Didelphys, Macropus), the allan¬tois remains relatively small and never makes contact with the chorion.
Chorioallantoic Placenta:
In most eutherian mammals and in some marsupials (Parameles, Dasyurus), the yolk sac remains rudimentary, while the allantois becomes well developed, fuses with the chorion and provides the chorionic circulation. This type of foetal placenta is called chorioallantoic.
Functions of Placenta:
1. Nutrition:
Food materials pass from the mother’s blood into the foetal blood through the placenta. Monosaccharide’s, lipids, amino acids, vita- mines and hormones pass by diffusion or active transport.
Digestion:
The trophoblast ol the placenta digest protein before passing them into foetal blood.
Respiration:
Gaseous exchange takes place by diffusion across the foetal membrane. Through the placenta oxygen passes from the maternal blood to the foetal blood, and carbon dioxide passes from foetal blood to maternal blood.
Excretion:
Waste products like urea, uric acid and creatinine are pass from foetal blood into maternal blood through placenta and are filtered out by the kidneys of the mother.
Storage:
Glycogen, fats and some inorganic salts are stored in the placenta to be utilized when diet of the foetus is inadequate. For the foetus before liver is formed.
Enzymatic Function:
Barrier:
Placenta functions as an efficient barrier (defensive wall) and allows useful: aerials to pass into the Social blood.
Endocrine function:
Placenta acts temporarily as an endocrine organ. It secretes many hormones such as estradiol, proges¬terone, chorionic gonadotropin in most mammals and also placental lactogen in human female, the placenta is a significant source of relaxin, that relaxes the pelvic liga¬ments to facilitate child birth.
Placenta produces various enzymes such as diamine oxidase, oxytocinase and phospholipase-A2, which protects the foetus.
Dr. K. Rama Rao
Govt. Degree College
TEKKALI; Srikakulam Dt. A. P
Phone: 9010705687
