Uterus and its Anatomy

Anatomy of the Uterus

The uterus is a female reproductive system organ where the growth of the baby takes place. It is also referred to as the womb. The uterus is structurally hollow and pear-shaped with almost a fist size. The uterus is connected to the fallopian tube assisting in the translocation of eggs from the ovary into the uterus. On the other hand, the uterus’ lower parts form the cervix that connects to the vagina. At the same time, the upper part of the uterus is more expansive and forms the corpus. Subsequently, the uterus is divided into three layers known as endometrium, myometrium, and serosa.1

Also, the uterus comprises four sections: the upper area, which is broadly curved, is known as the Fondus. It is within this region that the fallopian tube connects to the uterus. Another section is the body which is the largest part of the uterus. The body begins directly below the fallopian tube and extends downwards until the cavity and uterine walls narrow.

Also is the isthmus, which is the narrow lower neck region. Finally, is the cervix that also continuous downwards until it opens into the vagina. The uterus size is approximated to be 6 to 8 cm long. In comparison, the thickness of the walls is estimated to be 2 to 3 cm. the width of the organ is approximated to 6cm but usually varies.2

The outer layer of the Uterus (Peritoneum membrane) partially covers the organ. In front, Peritoneum covers the cervix body only. While from behind, it covers the cervix’s parts and body that lies above the vagina and is extended to the posterior vaginal walls, after which it is folded back to the rectum.

Also, from the sides, peritoneal layers extend from the uterus’ margin to each sidewall of the pelvis resulting in two broad ligaments of the uterus. The myometrium, composed of the larger part of the organ’s bulkiness, is firm and has unstriped, densely packed, and smooth muscle fibers. Also present are the blood vessels, nerves, and lymph vessels. The outermost fibers are longitudinally arranged, while the middle layer has no pattern of arrangement, thus, running in all directions in a disorderly manner. The middle layer being the thickest.3

The uterine lining cavity forms the endometrium, which is a moist mucous membrane. Usually, when an egg is released into the fallopian tube, the endometrium of the uterus thickens to receive a fertilized egg. The thickness of the lining varies during the menstrual cycle. The lining thickens during the egg release in preparation for implantation. When the egg is fertilized, it gets attached to the endometrium walls to start development. However, an unfertilized egg leaves the uterus through the vagina while the endometrium lining is shed during the menstrual period.

Furthermore, the sperms and eggs are kept alive by secretions produced by the endometrium. The endometrium fluid contains potassium, water, glucose, iron, chloride, proteins, and sodium. Glucose acts as the reproductive cells’ nutrients while proteins aid in the implantation of the fertilized egg. At the same time, the other constituents avail a conducive environment for the sperm cells and the egg.5

In addition, the uterine wall is composed of three-layered muscle tissue. The muscle fibers move obliquely, longitudinally, and circularly entwined between elastic fibers, collagen fibers, and connective tissues of blood vessels. Thus, forming a solid muscle wall that protrudes and grows thinner as the baby develops within the uterus.

In around six to eight weeks after birth, the expanded uterus renormalizes in size with increased dimensions of around 1 cm larger in all directions than pre-child bearing. The uterine cavity remains larger with a slightly heavier uterus. However, the uterus usually remains small for the children until they attain puberty, when the uterus rapidly grows to its adult shape and size. Subsequently, when the female attains the menopause age, the uterus shrinks, becomes paler and more fibrous.

The uterus usually takes an anteverted position with the vagina forming a right angle with the vagina. The uterus’ position is influenced by the amount of distension within the rectum and urinary bladder. During pregnancy, the uterus enlargement raises the abdominal cavity, resulting in nearer alignment with the vagina. On the other hand, the uterus of those not pregnant gently curves forward, usually referred to as anteflexed.1

Consequently, the uterus’ cavity is remarkably more petite than the organ size. However, during pregnancy, the cavity gets flattened with the rear and front walls touching and triangular. The triangle is inverted, the base being at the top, between the two fallopian tube openings.3

The apex is at the uterus’ isthmus, opening into the cervix. The canal of the cervix is relatively more extensive in the middle and flattened from front to back. Two longitudinal ridges traverse the canal cervix and contain an oblique fold protruding from each ridge-like tree branch. The cervical canal has a length of 2.5 cm and has an external OS, which is an opening into the vagina. External OS is often depressed, relatively circular, and is small in size.

Nonetheless, it becomes more slitlike after birth due to lips that bound both its front and backside. The cervical canal has a lining of mucous membrane that has several glands secreting a clear alkaline mucus. The lining’s upper part goes through cyclical changes similar, though not marked as, those taking place in the uterus’ body. The cervical mucous membrane also contains several small cysts.

The uterus is held and supported in position through the muscular floor, also known as the diaphragm of the pelvis, through folds of the Peritoneum, some fibrous ligaments, and other pelvic organs. Also are supporting ligaments that include two double-layered broad ligaments, each carrying a fallopian tube at the upper free border. The two cardinal ligaments found at each side of the cervix are essential to maintain the uterus’ position. Some of the ligaments that provide further support include4;

Broad ligaments: a double-layered peritoneum that attaches the sides of the uterus to the pelvis. It also works as the Uterus’ mesentery and helps in maintaining it in a position.

Round ligaments: it helps in maintaining the uterus’ anteverted position.

Cardinal Ligament: usually situated at the broad ligament’s base, extending from the cervix to the lateral pelvic walls. Provides support to the uterus and also contains the uterine veins and arteries.

Ovarian Ligament: it connects the uterus and the ovaries.

Uterosacral Ligament: It gives support to the uterus as it projects from the cervix to the sacrum.

On the other hand, the uterus suffers from multiple gynecological disorders, including polyps, cancer, fibroids, adhesions, infections, and malformations. Such disorders on a need basis may require surgical access. As a result, hysterectomy is one of the commonly used surgical procedures in treating the uterus. Superior knowledge of the uterus and regional anatomy is key to avoiding accidental damage to the pelvic region and other structures during the process.

For the blood supply, the uterus receives blood from the ovarian and uterine arteries that project from the anterior branch of the internal iliac artery. The major blood vessels responsible for the supply of blood to the uterus are the uterine arteries. Equally, the uterine arteries take the blood to various parts of the uterus, thus, playing a critical function in keeping a constant blood supply during pregnancy and the menstrual cycle.3

However, the autonomic, parasympathetic, and sympathetic nervous systems supply the nerves to the internal pelvic organs. Subsequently, autonomic T12 plus T11 innervates the uterus, and it obtains the sympathetic nerve supply from the hypogastric plexus, while parasympathetic supply is derived from S2 to S4.2 Nonetheless, the cervix and the uterus are not sensitive to burning or cutting, enabling cauterization of the cervix without anesthesia while carrying out inportant therapeutic procedures. On the contrary, the cervix and uterus are sensitive to dilation and distension; thus, the reason for the pain experienced during normal delivery.4