Uterus

Uterus (also known as womb) is the pear-shaped, hollow muscular organ located in the female pelvis, in which the fertilized ovum implants and develops. In a young nulliparous female, the uterus measures about 3 inches long, 2 inches wide and 1 inch thick.

External structure:

The uterus is divided into three parts:

  • Fundus: It is the part of uterus that lies above the entrance of the uterine tubes.
  • Body: It is the part of the uterus that lies below the entrance of the uterine tubes.
  • Cervix: It is the narrow part of the uterus that pierces the anterior wall of the vagina.

The cavity of the body of uterus is triangular in frontal plane; however, it is merely a cleft in sagittal plane. The cavity of the cervix is called cervical canal. It is connected to the cavity of the body through the internal os and to the vagina through the external os.

Internal structure:

The uterus is composed of three distinct layers: endometrium, myometrium and parametrium.

  • Endometrium: It is the mucous membrane lining of the uterus, which is continuous above with the mucous membrane lining the uterine tubes and below with the mucous membrane lining the cervix. In the uterus, the mucous membrane is applied directly to the myometrium and there is no submucosa.
  • Myometrium: It is the thick muscular wall of uterus, which is made of smooth muscle fibers supported by connective tissue.
  • Parametrium: It is the visceral pelvic fascia that surrounds the supravaginal part of the cervix. It is here that the uterine artery crosses the ureter on each side of the cervix.

Peritoneal covering of uterus:

The uterus is covered with the peritoneum except its anterior aspect below the internal os. Here the peritoneum passes forward onto the bladder and as a result the uterus is devoid of peritoneum at this place. Laterally, there is also a little space devoid of peritoneum, lying between the attachments of the layers of the broad ligament.

Important relations:

Anterior:

  • Uterovesical pouch
  • Superior surface of the bladder

Posterior:

  • Rectouterine pouch (with coils of ileum or sigmoid colon within it)

Lateral:

  • Broad ligament of uterus
  • Uterine artery and vein

Common Positions of uterus inside female pelvis:

In most women, the uterus is anteverted and anteflexed. Anteversion refers to the position of the uterus in which its long axis is bent forward on the long axis of the vagina. Anteflexion refers to the position in which the long axis of the body of the uterus is bent forward on the long axis of the vagina at the internal os. Therefore, with body in erect position and the bladder empty, the uterus lies almost in the horizontal plane.

In some women, the uterus may be retroverted and/or retroflexed. Retroversion refers to the position in which the fundus and the body of uterus are bent backward on the vagina, so that they lie in the rectouterine pouch. Retroflexion refers to the position in which the body of the uterus is bent backward on the cervix at the internal os.

Blood supply:

  • The arterial supply is provided mainly by the uterine artery, which is a branch of the internal iliac artery. It gives off a small descending branch that supplies the cervix and the vagina.
  • The venous blood drains by way of the uterine vein which is a tributary of the internal iliac vein.

Lymph drainage:

The lymphatics from the fundus and upper part of body of the uterus accompany the ovarian artery and drain into the paraaortic nodes at the level of the first lumbar vertebra. The vessels from the lower part of body and the cervix drain into the internal and external iliac lymph nodes.

Nerve supply:

Inferior hypogastric plexus supplies both the sympathetic and parasympathetic fibers to the uterus.

Support:

The primary support for the uterus is the tone of the levatores ani muscles. In addition the condensations of the pelvic fascia, which form three important ligaments, also add to the support. These ligaments are sacrocervical ligament, pubocervical ligament, and transverse cervical ligament.

Function of uterus:

Uterus is the site for reception, retention and nutrition of the fertilized ovum. During the entire period of gestation, the fetus is developed within the uterus.

Role in parturition:

Parturition, also known as labor, is the series of processes by which the baby, the fetal membranes and the placenta are expelled from the genital tract of the mother. Normally it occurs at the end of the 9th month of pregnancy. During parturition, the contractility of uterus develops fully, in response to estrogen. Once the cervix is stretched by the head of the baby, a nervous reflex mechanism is initiated that increases the force of contractions of the uterine body.

Uterus:

Uterus is the pear-shaped, hollow muscular organ located in the female pelvis, in which the fertilized ovum implants and develops. In a young nulliparous female, the uterus measures about 3 inches long, 2 inches wide and 1 inch thick.

External structure:

The uterus is divided into three parts:

Fundus: It is the part of uterus that lies above the entrance of the uterine tubes.

Body: It is the part of the uterus that lies below the entrance of the uterine tubes.

Cervix: It is the narrow part of the uterus that pierces the anterior wall of the vagina.

The cavity of the body of uterus is triangular in frontal plane; however, it is merely a cleft in sagittal plane. The cavity of the cervix is called cervical canal. It is connected to the cavity of the body through the internal os and to the vagina through the external os.

Internal structure:

The uterus is composed of three distinct layers: endometrium, myometrium and parametrium.

Endometrium: It is the mucous membrane lining of the uterus, which is continuous above with the mucous membrane lining the uterine tubes and below with the mucous membrane lining the cervix. In the uterus, the mucous membrane is applied directly to the myometrium and there is no submucosa.

Myometrium: It is the thick muscular wall of uterus, which is made of smooth muscle fibers supported by connective tissue.

Parametrium: It is the visceral pelvic fascia that surrounds the supravaginal part of the cervix. It is here that the uterine artery crosses the ureter on each side of the cervix.

Peritoneal covering of uterus:

The uterus is covered with the peritoneum except its anterior aspect below the internal os. Here the peritoneum passes forward onto the bladder and as a result the uterus is devoid of peritoneum at this place. Laterally, there is also a little space devoid of peritoneum, lying between the attachments of the layers of the broad ligament.

Important relations:

Anterior:

Uterovesical pouch

Superior surface of the bladder

Posterior:

Rectouterine pouch (with coils of ileum or sigmoid colon within it)

Lateral:

Broad ligament of uterus

Uterine artery and vein

Common Positions of uterus inside female pelvis:

In most women, the uterus is anteverted and anteflexed. Anteversion refers to the position of the uterus in which its long axis is bent forward on the long axis of the vagina. Anteflexion refers to the position in which the long axis of the body of the uterus is bent forward on the long axis of the vagina at the internal os. Therefore, with body in erect position and the bladder empty, the uterus lies almost in the horizontal plane.

In some women, the uterus may be retroverted and/or retroflexed. Retroversion refers to the position in which the fundus and the body of uterus are bent backward on the vagina, so that they lie in the rectouterine pouch. Retroflexion refers to the position in which the body of the uterus is bent backward on the cervix at the internal os.

Blood supply:

The arterial supply is provided mainly by the uterine artery, which is a branch of the internal iliac artery. It gives off a small descending branch that supplies the cervix and the vagina.

The venous blood drains by way of the uterine vein which is a tributary of the internal iliac vein.

Lymph drainage:

The lymphatics from the fundus and upper part of body of the uterus accompany the ovarian artery and drain into the paraaortic nodes at the level of the first lumbar vertebra. The vessels from the lower part of body and the cervix drain into the internal and external iliac lymph nodes.

Nerve supply:

Inferior hypogastric plexus supplies both the sympathetic and parasympathetic fibers to the uterus.

Support:

The primary support for the uterus is the tone of the levatores ani muscles. In addition the condensations of the pelvic fascia, which form three important ligaments, also add to the support. These ligaments are sacrocervical ligament, pubocervical ligament, and transverse cervical ligament.

Function of uterus:

Uterus is the site for reception, retention and nutrition of the fertilized ovum. During the entire period of gestation, the fetus is developed within the uterus.

Role in parturition:

Parturition, also known as labor, is the series of processes by which the baby, the fetal membranes and the placenta are expelled from the genital tract of the mother. Normally it occurs at the end of the 9th month of pregnancy. During parturition, the contractility of uterus develops fully, in response to estrogen. Once the cervix is stretched by the head of the baby, a nervous reflex mechanism is initiated that increases the force of contractions of the uterine body.