Human Anatomy: Physiology Of Pregnancy

Physiology of pregnancy is mainly concerned with maternal adaptation to provide ideal atmosphere for fertilization, nutrition to growing foetus, and safe child-birth. It can be discussed under the following headings -

• Fertilization and implantation
• Formation of placenta and its functions
• Physiological changes during pregnancy
• Applied aspects

Fertilization and Implantation

-Fertilization-

It refers to fusion of male and female gametes (i.e., spermatozoa and ovum). It takes place in the middle segment (ampulla) of the fallopian tube. It involves following events -

1. The Transport of Gametes - Before fertilization, the ovum and sperms reach ampulla for fertilization.

1. Sperm Capacitation - It refers to the process that makes a sperm to fertilize an ovum. Capacitation occurs due to removal of certain factors, which normally remain quiescent in male genital tract.

1. Fusion of Gametes - Fusion occurs by penetration of sperm through ovum coverings due to acrosomal reaction which involves release of acrosin (protease enzyme) from anterior membrane of acrosome of sperm. Only one sperm can enter into the oocyte, and further entry of sperms is prevented by the activation of ovum.

-Implantation-

Implantation of fertilized ovum involves following steps -

1. Formation of Blastocyst - The fertilized ovum starts dividing immediately and is called morula (16-cell stage) and blastocyst (100-cell stage).

1. Transportation of Blastocyst (In Urine Cavity) - In next 3-4 days, blastocyst is transported into the cavity of uterus.

1. Implantation of Blastocyst (In Endometrium) - The blastocyst then erodes and burrows into the endometrium (Implantation). It goes deeper and deeper into uterus mucosa till whole of it lies within the endometrium.

1. Decidual reaction - After implantation, endometrium is called decidua. Stroma cells enlarge, become vacuolated and filled with glycogen and lipids, called decidual cells. They are source of nutrition. This change of stroma cells is called decidual reaction.

Fig: Decidual Reaction