Placenta - Connecting Fetus and Uterine Wall
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Placenta : Connecting Fetus and Uterine Wall

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 15 Apr 2014 - 15:14.

Placenta is the connecting link between the fetus and the uterine wall, present only in pregnant women.

Occurrence of Pregnancy happens only when fertilization takes place. Fertilization occurs only when a lone sperm from the male enters a female egg released by one of the ovaries in a female. The female egg is released only during the ovulation phase of a menstrual cycle, starting from her first periods in her life called menarche till cessation of periods called menopause. This period from menarche till menopause (roughly from 15th to 45th year of her age) is generally known as the fertile age of every woman.

It therefore becomes necessary to understand the basics of fertilization in order to have a better knowledge about the placenta.

The ovulatory phase of a menstrual cycle normally starts from the 14th day from the first day of the menstrual cycle. However, the ovulatory phase may start 3 days before the 14th day and continue for 3 more days after the 14th day. In other words subtracting 3 days and adding 3 days to the 14th day gives us a rough range of the ovulatory phase during which a female egg can be released from either of the ovaries.

It therefore follows pregnancy, most likely to occur if there is sexual intercourse during this phase (known as unsafe period for those observing contraceptive methods) when chances are that a sperm can penetrate an egg when fertilization takes place leading to pregnancy. If fertilization doesn’t take place the egg gets degenerated and comes out as the menstrual flow in the beginning of the next menstrual cycle.

In order to understand fully what we mean by a placenta and how it gets implanted and what functions it serves in a pregnant mother, let us presume that a sperm has penetrated a female egg and has resulted in fertilization.

Ovulation: During ovulation period the cervical canal (the lower portion of the uterus) secretes lots of mucus to facilitate easy passage of the sperm released during a sexual act. One sperm is sufficient to penetrate a female egg, which travels from the ovary towards the body of the uterus. Normally fertilization occurs in the fallopian tube. When once the egg is fertilized it develops into a zygote.

It takes about 4 to 5 days for the zygote to travel all the way to the cavity of the uterus. Once it reaches the uterus, the zygote divides repeatedly to become a blastocyst, which is a hollow mass of cells.

Attachment of the blastocyst to the wall of the uterus is called implantation, which usually takes place near the top of the uterus either in the front or back wall. The wall of the blastocyst has two types of thickness. The inner cells of the very thick wall of the blastocyst develop into the embryo and the outer cells burrow into the wall of the uterus to form the Placenta. Once implanted the placenta continues from conception till delivery including its own delivery after the fetus is expelled out. What follows, deals with the functions and conditions affecting the placenta.

The Placenta produces hormones to help maintain the entire duration of pregnancy and allows the exchange of oxygen, nutrients and waste materials between the mother and the fetus. The implantation of placenta begins 4 to 5 days after fertilization and is complete by 9 or 10 days.

The wall of the blastocyst becomes the outer layer of membranes surrounding the embryo and is called the chorion. By about 10th to 12th day the inner layer of membranes becomes the amniotic sac. The amniotic sac gets filled with a clear liquid called amniotic fluid, which helps to envelope the developing embryo, which floats within.

Tiny projections called villi from the developing placenta extend to the wall of the uterus, which branch and re-branch to form a tree like structure, which greatly enhance the area of contact between the mother and the placenta. This larger area of contact helps allowing more nutrients to pass from the mother to the fetus and waste materials to pass from the fetus to the mother. The placenta is fully formed by 18 to 20 weeks and continues to grow throughout pregnancy to weigh roughly half a kilogram when it is delivered after the fetus is expelled.

Majority of women with a normal full-term pregnancy have a healthy placenta and in most such pregnancies the placenta is delivered intact without encountering any problems. However, in some women the placenta faces lots of problems the most common one being, bleeding.

Placenta conditions: In women with twin pregnancy, there may be a common placenta for both the fetuses or two individual placentas one for each fetus depending on whether separate sperm fertilizes two separate eggs or one fertilized egg splits into two embryos.  In such cases delivery of the placenta differs after the two fetuses are born.

Though rare, the placenta in some pregnancies separates either partially or fully before the child is delivered in a condition called placenta abruption. This detachment may be concealed when blood collects within the wall of uterus and the separated layer of the placenta. In the open type of detachment, bleeding is visible. In either case it is dangerous to the mother because of severe anemia and to the fetus because of lack of oxygen supply through the placenta and the umbilical cord.

The pregnant woman in such cases will have anti-partum hemorrhage (bleeding before delivery) when absolute rest in bed becomes the yardstick to avoid premature delivery. However, in some cases where the bleeding is profuse and rest doesn’t stop bleeding, an emergency caesarian operation becomes necessary to save the mother, the child or both, though it would mean a pre-term baby.

A condition called placenta previa is seen in some pregnancies where the placenta blocks the outlet of the birth canal partially or totally endangering the birth of the fetus if immediate steps are not taken. In this condition there will be controllable or profuse bleeding depending on whether the block is partial or complete, necessitating immediate delivery of the fetus through caesarian operation to save the mother, baby or both.

In yet some other cases, though the fetus is delivered normally the placenta may get deeply attached to the uterus called retained placenta and either separates partially or totally leading to postpartum (after delivery) hemorrhage. Such situations are fraught with danger and need careful handling including surgical approach.

Though seen in 1 in 20,000 pregnancies, a pregnant lady may have choriocarcinoma either soon after delivery, or months or years later which if not diagnosed and attended to, may lead to metastasis affecting other organs like liver. It first starts as a molar pregnancy like in hydatiform mole in the placenta, which later may become malignant. Early diagnosis is achieved through detection of high levels of Human Chorionic Gonodotropin (HCG) a hormone present during pregnancy.

From this brief description on human placenta it becomes clear how important it is for a pregnant lady to have regular antenatal checkups once every month so that any deviation from normal course can be easily detected and corrected, if required through a sacrifice of the fetus like in cases of toxemias of pregnancy endangering the life of the mother.



*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.