Wednesday, April 22, 2009



What organs and functions to ensure delivery of a healthy infant?

Placenta has the functions to produce the hormone for control of pregnancy, transfer of food materials and waste products, transfer of blood and oxygen for the survival of fetus, between mother and fetus.
The umbilical cord with umbilical artery and vein which connect the placenta and fetal circulation

Picture: Relationships of stuctures in the uterus at the end the 7th week of pregnancy.On the top of the picture is decidua basalis which is the site of future development of placenta, in the center is the embryo.

Following fertilization, the ovum develops into the embryonic blastocyst. About 3-4 days are required for the blastocyst to reach the uterus. Normally, the blastocyst implants on the 5th or 6th day after entry into the uterus, most commonly in the decidua lining the anterior or posterior wall of the fundus. The site of implantation immediately heals over.

Three decidual areas may be recognized::
Decidua capsularis [reflexa], or that portion of the uterine mucosa immediately overlying the embryo;
Decidua basalis, beneath the embryo;
Decidua parietalis, the remainder of the uterine lining.
The decidua capsularis disappears as the embryo increases in size to fill the uterine cavity. The decidua basalis is the site of future development of the placenta. The vascularized tufts are now referred to as villi. In the decidua basalis under the developing embryo there is stage a great dilatation of the maternal blood vessels, the chorionic villi, grow into them by erosion of the decidua. This penetration of the villi aided by obliteration of small arteries of the decidua causing necrosis and the formation of a large spaces in the decidua which fill with maternal blood. As the villi are soon invaded by mesoderm carrying fetal blood vessels the fetal and maternal circulations are brought very close to one another and in this way the placenta is formed.
The mature placenta is a blue-red, rounded, flattened, meaty organ about 15-20 cm in diameter and 3 cm thick. It weights 400-600 gm.
The umbilical cord extends from the fetal surface of the placenta to the umbilicus of the fetus; the fetal membranes arise from the placenta at its margin. The fetal portion of the placenta is composed of numerous functional units called villi. These are branched terminals of the fetal circulation, and provide for transfer of metabolic products. The villous surface, which is exposed to maternal blood, may be as much as 160 feet square. The fetal capillary system within the villi is almost 30 miles long. Most villi are free within the intervillous spaces, but an occasional anchor villus attaches the placenta to the decidua basalis. The fetal surface of the placenta is covered by amniotic membrane and is smooth and shiny. The umbilical cord vessels course over the fetal surface before entering the placenta.

The umbilical cord is a gray, soft, coiled, easily compressible structure which connects fetus with the placenta. It averages 50 cm in length and 2 cm in diameter and is covered by a thin layer of stratified squamous epithelium which is comparable to fetal skin .Usually, the cord contains 2 arteries which carry deoxygenated blood from the fetus, and one vein, which supplies the fetus with oxygenated blood.

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