Anatomy and Physiology of the Uterus

girl-by-lake_0All of us came from it, but not a lot knows what the uterus really is and how it functions. Here we take a look at what this organ actually does.

OVERVIEW OF THE UTERUS AND ITS MAIN FUNCTION

The uterus is a female muscular and hollow organ which houses the fertilized egg (zygote), nourishes it and allows it to develop until it forms into a fully grown fetus ready for delivery. A woman’s uterus is located in the pelvic cavity just in between the bowel and the urinary bladder. It is one of the major reproductive organs of the females. It varies from person to person as to appearance and endometrial linings. The uterus communicates with its uterine tubes on its upper part, one on each side. The bottom part of the uterus opens to the vagina.

Once eggs (ova) are released from the ovaries, they pass through the uterine tube ending their way to the uterine cavity. If an egg gets fertilized by a sperm, it forms into a zygote which would then be imbedded to the uterine wall itself and remains there until it is ripe for delivery. The uterus acts as the source of nourishment for the zygote. It undergoes various changes and muscular development as it conforms to the changes the zygote goes through as it develops into a fetus. However, if the egg is not fertilized, the inner walls of the uterus shed off which results to menstruation in women.

Human uterus measure about 7.5 cm in length, 5 cm in breadth and 2.5 cm in thickness. It weighs anywhere between 30 to 40 grams varying on each person. Midway between the uterine apex and base is a narrow portion called the isthmus (outside). Inside, its corresponding portion is called the internal orifice – a portion that narrows towards the opening of the uterus. Just above the isthmus is the body, and below it is the cervix. We call the part of the uterine body that passes through the points of entrance of the uterine tube as the fundus.

PARTS OF THE UTERUS

Body

The body actually narrows from the fundus to the isthmus. It is composed of the following:

  • Anterior Surface – this is the portion that lies in apposition with the bladder. It is a flattened surface that is covered with peritoneum.
  • Posterior Surface – this is the portion the converse transversely continuing down to the vagina. Just like the anterior surface, it is also covered with peritoneum.
  • Fundus – is that part that curves in all directions and is completely covered with peritoneum (both is vesical and intestinal surfaces). The sigmoid colon and rectum rest on its coils.

Cervix

The lower narrow portion of the uterus is called the cervix. It is coned shape with shortened apex that is positioned downward and then backward. The structure of the cervix is wider in its middle portion compared to its upper and lower portions. The cervix opens into the anterior part of the vagina:

  • Supravaginal portion – the supravaginal cervix is covered with peritoneum and this extends to the rectum forming what is known as the rectouterine excavation.
  • Vaginal portion – this extends into the anterior part of the vagina just between its fornices. On its lower portion is an opening called as the external orifice of the uterus – it is where the cervix connects with the vagina.

Interior of the Uterus

Unlike how big the organ actually is, the size of its interior is actually small (6.25 cm – measured from the fundus to the external orifice) and is divided into two parts:

  • Body Cavity – it is triangular in shape with its base formed by the interior part of the fundus and its apex by the interior opening of the uterus through which the cavity of the body connects with the cervical canal.
  • Cervical Canal – as mentioned, the cervix comes with wider middle portion compared to its other parts. Above it through the internal orifice is the lower portion of the body cavity while below it through the external orifice is the opening to the vagina.

Ligaments

There are eight ligaments composing the uterus:

  • 1 Anterior Ligament – from the front of the uterus, the anterior ligament extends to the bladder at the point in between its cervix and its body.
  • 1 Posterior Ligament – this extends from the back of the posterior fornix of the vagina to the front of the rectum.
  • Two Lateral Ligaments – these two ligaments pass from the uterine sides towards the lateral walls of the pelvis.
  • Two Uterosacral Ligaments
  • Two Round Ligaments – these are situated between the lateral ligament layers just below the uterine tubes.

THE UTERUS AT DIFFERENT STAGE OF LIFE

The uterus is one of the organs of the body which keeps changing in form and size depending on what period of life you are in.

  • Fetal Stage. As a baby, the uterus is inside the abdominal cavity and it projects to the superior opening of the pelvis. During this stage, the cervix is still larger than the body of the uterus.
  • Pubertal Stage. As you move on into puberty, the uterus enlarges to about 17 grams. Now it descends into the pelvis just below its position during the fetal stage. When your urinary bladder is empty, the uterus is directed forward. But when your bladder is distended, the fundus of the uterus will be directed backwards.
  • Menstrual Stage. The entire organ is enlarged during menstruation. It becomes more vascular and its surfaces rounder. The inner lining become softer and thicker as it sheds off completely until it stops. Once menstruation stops, a new layer of mucous membrane undergoes the proliferation phase to replace those that were shed off.
  • Pregnant Stage. When you are pregnant, the uterus enlarges to accommodate the growth of the fetus. It does this by creating new muscle fibers. It is during this stage that the uterus is at its largest size.
  • Post-delivery Stage. The uterus then gradually goes back to its normal size but nothing similar to its virgin state. It now comes with a large cavity and muscular layers which are more defined.
  • Late Adult Stage. When you reach old age, every organ of your body atrophies including the uterus.

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