Placenta (Structure, types and functions of placenta) | Zoology Optional Notes for UPSC PDF Download

Definition and Characteristics

1. Definition of Placenta:

   • The placenta is a transient organ crucial for nourishing and safeguarding the fetus during pregnancy. It develops alongside the fetus and is expelled during childbirth.
   • It is colloquially known as the "afterbirth" due to its expulsion after delivery.

2. Transient Circulatory Organ:

   • The placenta, unique to mammals, serves as a temporary circulatory organ connecting the fetal and maternal systems during pregnancy.
   • The umbilical cord links the fetus to the placenta, facilitating the transfer of materials.

3. Attachment to Uterus:

   • The placenta is typically attached to various parts of the uterus, including the top, bottom, side, front, or back.
   • An abnormal attachment, such as in placenta previa, can pose serious complications during pregnancy.

Structure of Placenta

1. Finger-like Projections (Chorionic Villi):

   • Chorionic villi, projections from the chorion's outer surface, infiltrate the uterine tissue, forming the placenta.
   • This connective tissue serves as both embryonic and maternal, facilitating material exchange.

2. Role in Nutrient Exchange:

   • The developing embryo receives oxygen and nutrients from the mother through the placenta.
   • Simultaneously, waste products like carbon dioxide and nitrogenous waste are eliminated.

Types of Placenta

1. Based on Embryonic Tissue Involvement:

   • Yolk-Sac Placenta and Chorio-Allantok Placenta are classified based on the embryonic tissue's interaction with the uterine wall.

2. Villi Distribution:

   • Diffused, Cotyledonary, Zonary, and Discoidal Placenta exhibit variations in the distribution and formation of villi.

3. Villi's Relationship with Uterine Wall:

   • Deciduate and Indeciduate (Adeciduate) Placenta differ in the degree of villi attachment to the uterine wall and their persistence after birth.

4. Degree of Tissue Involvement:

   • Epitheliochorial, Haemochorial, Haemoendothelial, and Syndesmochorial Placenta are distinguished by the involvement of fetal and maternal tissues.

Function of the Placenta

1. Life Support Functions:

   • Gas exchange, nutrient acquisition, and waste removal are essential functions ensuring the fetus's well-being.

2. Barrier and Immunological Functions:

   • The placenta acts as a barrier, protecting the fetus from infections and filtering out potential threats.
   • Immunological protection is provided through the transfer of antibodies from the mother to the fetus.

3. Endocrine Function:

   • The placenta secretes hormones (estrogen, progesterone, HCG), maintaining a pregnancy-ready state in the mother.

Purpose of the Placenta

1. Nutrition and Storage:

   • Nutrient transfer from maternal to fetal blood, storage of glycogen and nutrients before liver development.

2. Endocrine Secretion:

   • The placenta functions as an endocrine gland, secreting hormones vital for pregnancy.

3. Protein Digestion and Excretion:

   • Trophoblasts in the placenta break down proteins for fetal circulation, and it aids in excreting nitrogenous wastes.

4. Respiration and Barrier Function:

   • Oxygen and carbon dioxide exchange between fetal and maternal blood, and the placenta acts as a barrier against harmful substances.

Understanding the multifaceted roles and structures of the placenta is crucial for comprehending its significance in fetal development and maternal-fetal interactions.