The uterus is a hollow muscular organ of the female reproductive system. It measures 7.5cm x 5cm and its upper portion is approximately 2.5cm thick. The uterus weighs around 30 to 40 gm. It is located between the bladder and rectum. The main function of the uterus is to carry the foetus and to provide nourishment to the developing baby prior to birth. While the word ‘uterus’ is frequently used in medical terminology it is more popularly known as the womb.
The uterus or womb can be anatomically divided into mainly two parts
Corpus – Corpus can be defined as the body of the uterus. It lies below the orifices of the uterine tubes and above the isthmus. Fundus, which lies at the base of the cavum uteri, forms the top most part of the corpus. Fundus rises upwards as the womb grows during pregnancy. The height of the fundus is routinely measured during pregnancy to determine the growth rate of the foetus. The corpus uteri is triangular in shape and is widest at the fundus. It tapers as it reaches the isthmus.
Cervix – Cervix is the narrow end of the uterus, and it connects the uterus with the vagina. The cervix is like a canal that lies between the internal orifice and the external orifice. It slightly tapers at both the ends and is widest in the middle. The cervical opening known as OS allows the menstrual flow during periods. During pregnancy it closes to contain the foetus inside the womb. It projects through the anterior walls of the vagina, and is hence divided into a supra vaginal portion and a lower vaginal portion.
Between these two prominent parts of the womb lies the isthmus (identified by a slight constriction). The internal orifice of the womb is a narrowing cavity that lies just below the corpus corresponding to the isthmus.
The uterus consists of three tissue layers called:
Endometrium – This is the innermost and most active layer of the uterine lining. Following menarche, during each menstrual cycle, the uterus prepares itself to receive a fertilised oocyte through proliferation and differentiation. If the egg is not fertilised and implanted in the wall, the endometrium breaks down, resulting in menstruation.
Myometrium – This muscular layer is primarily composed of the smooth muscle cells. It lies between the endometrium and perimetrium and makes up most of the uterine volume.
Perimetrium – This is the outermost layer of the uterus and is also called serosa. It is a thin layer of epithelial cells that envelops the womb.
Female reproductive system and the functions of uterus
The uterus plays a vital role in several important reproductive functions like menses, implantation, gestation, labour, and delivery. The egg that is released from the ovary travels through the fallopian tube, where it is likely to get fertilized by a sperm. The endometrial layer thickens so that the fertilized egg, when it enter the uterus, gets implanted in it. However, if this does not happen, the endometrial layer dissolves and is passed through the vagina in the form of menstrual bleeding. Thus, it is the womb that is responsible for menstrual cycles in females. The onset of menses is considered to be a sign of puberty in girls.
The uterus is an organ that responds to hormones and directs blood flow to the vagina. It undergoes contractions during intercourse thus helping the male sperms to reach the fallopian tube. Apart from causing regular menses in females the uterus also plays an important role in reproduction. If an egg gets fertilized in the fallopian tube, it travels to the womb and implants itself on the endometrial lining. The womb further provides nourishment, and the fertilized egg develops into a foetus and grows during the gestational period. It is a very elastic organ, and as the foetus develops it stretches to accommodate the baby, a litre of amniotic fluids, and placenta. Apart from accommodating and nourishing the growing embryo it also provides a structural support to the bowels and the bladder.
The uterine contractions also facilitate childbirth. The cervix that is a part of the womb is thick and closed during pregnancy. However as the time of childbirth approaches the womb undergoes contractions, thus pulling the cervix upwards. These contractions cause the cervix to fully dilate and as it opens up to about 10 cm the baby’s head enters the cervix. Further pressure during labour helps the baby move downward, resulting in child birth.