CHAPTER 2 MATERNAL PHYSIOLOGY OF PREG-NANCY

SECTION 1: FERTILIZATION, THE DEVELOPMENT OF THE FERTILIZED OVEM, TRANSPORTATION AND IMPLANTATION

1. Fertilization

When the ejaculation happens in vagina, sperm will enter the uterine cavity the cervical canal, traverse the tube via the tubal lumen. The surface glycoprotein in the sperm acrosome is degraded by amylase α and β which exist in genital tract secretions. This process will result in the structural changes of acrosome thus reducing membrane stability. The sum of these processes is called capacitation.

The ovum, immediately following ovulation is picked up by the tubal fimbriae which partly envelope the ovary. This stays briefly in the ampulla within the isthmus waiting for fertilization.

When the sperm meets with the mature ovum, dissolution of the corona radiata and zona pellucida is followed by the release of acrosomal enzyme. The outer membrane of the sperm and the ovum envelope contact and fuse. The sperm drills into the ovum. Then the second meiotic division of the oocyte will immediately complete to form the female pronucleus. Female pronucleus and male pronucleus merge together that to form a diploid zygote, which is the new life.

2. Implantation

The zygote divides by cleavage from two cells to four cells to 16 cells. This 16 celled ball is called as the morula. The solid morula tansforms into the blastocyst which contains a cavity. By Day 4 or Day 5 the cells differentiate into an inner cell mass, the embryoblast and cells arranged in the periphery, the trophoblast. Implantation is the process by which this blastocyst gets embedded into the prepared endometrium. During this time the zona pellucida gradually disappears.

The necessary conditions for implantation:

1. Zona pellucida gradually disappears.

2. The cells of the trophoblast differentiate into outer trophoblast and inner cytotrophoblasts.

3. The coordinating development of morula and endometrium.

4. Sufficient progesterone in pregnant woman's body, a uterine sensitive period to allow the trophoblast to implant.

After implantation, the endometrium immediateiy undergoes decidual reaction. Depending upon location of blastocyst and deciduas: the decidua is divided into three parts-Decidua basalis, deciduas capsularis or decidua parietalis depending on its location relative to the site of implantation.

（冯祥 潘苗苗）