Uterus during pregnancy
Uterus during pregnancy
The uterus is an important female reproductive organ, shaped like a pear. The uterus is located in the pelvis, held in its spot by a wide uterine ligament. The uterus can be divided into two parts, the body and the cervix. The cervix is the communication between the uterus and the vagina. The uterine walls are formed by three layers, the mucous layer, the musculature and a fibrous surface layer. The uterine mucous layer undergoes changes every month due to the influence of female sex hormones. It prepares for receiving a fertilized egg. This cycle is known as the menstrual cycle. The largest part of the uterus is formed by muscle tissue made out of smooth muscle fibers, meaning they cannot be controlled by will, and changes during pregnancy. The third part is the surface fibrous layer, through which run the veins and nerves and to which the uterine ligament is anchored. The fertilization of an egg by a sperm, which is the male sex cell, happens in the fallopian tubes. The fertilized egg then travels through the tube towards the uterus, while undergoing cell division. The sixth day it nidates in the uterus's mucous layer, at this point the egg is comprised of about 100 cells. The main purpose of the uterus is providing nutrition for the developing fetus and its eventual expulsion into the birthing canal.
Uterine changes during pregnancy
Pregnancy lasts for 9 calendar months, which corresponds to 10 lunar months. In gynecology the length of pregnancy is given in weeks. The first day of pregnancy is considered to be the first day of the last menstruation. The uterus undergoes a series of changes during pregnancy. It's pear-like shape changes to a spherical or an oval one and its size changes significantly as well. It's original volume of 2-3 ml changes to 4500 to 5000 ml. Its weight changes dramatically as well, from 50–60 g to 900–1000 g. These increases are based on the increase of uterine musculature, which can increase its volume several times. Aside from this, new muscle fibers are grown too. By the third month the uterus is located behind the pubic bone in the pelvis, at the end of the thrid month it passes the pubic bone and reaches partly into the abdominal cavity, due to the increasing size of the fetus. At the end of the ninth month it reaches up to the rib arches. Based on hormonal control the uterus's musculature contracts during birth, expelling the fetus into the birth canal.
During pregnancy a part of the uterus aside from the body and the cervix is created, known as the lower uterine segment. It divides the body and the cervix since the end of the 4th month of pregnancy. First the lower uterine segment is in the form of a narrow strip, which gradually widens up to the width of 8-10 cm. It's mainly composed by connective tissue and develops from the lower segment of the uterine body. It differs from the uterus by not contracting during childbirth, but is expanded by the descending fetus. Cervix undergoes little changes during pregnancy. It is a seal of the uterine cavity and maintains its shape up until birth.
Another organ developing during pregnancy is the placenta. Placenta is the connection between the mother and the fetus. The umbilical cord, which connects the fetus to the placenta is a way through which the fetus receives nutrition. It brings oxygen and nutrients to the fetus and removes metabolic waste. Placenta also produces hormones, which are released into the mother's bloodstream and set her organism for proper growth and development of the fetus. Placenta is fully formed by the end of the 12. week of pregnancy. It is usually located in the upper part of the uterus or on its back wall. After birth it is expelled from the mother's body by contractions of the uterine walls.
Further necessary part of an uterus during pregnancy is the amniotic fluid. Amniotic fluid is a clear liquid, which surrounds the developing fetus in the uterus. It's main purpose is protecting the fetus from impacts and pressure on the mother’s stomach. It also allows movement, which can be felt by the mother. The amount of amniotic fluid increases during pregnancy up to one liter. Afterward, it decreases with coming childbirth, decreasing the fetus's ability to move as well. During birth the amniotic fluid flows out of the mother's body.
In some cases, especially if the mother is of higher age, taking a sample of the amniotic fluid is recommended. From the small sample of amniotic fluid it is possible to discover certain genetic defects, whose risk increases with the mother's age.