Patient Education - Health Library Uterus

The uterus is a hollow muscular organ located in the female pelvis between the bladder and 
rectum. The ovaries produce the eggs that travel through the fallopian tubes. Once the egg has left the ovary it can be fertilized and implant itself in the lining of the uterus. The main function of the uterus is to nourish the developing fetus prior to birth.

The uterus is a pear-shaped organ capable of undergoing major changes during a woman’s reproductive life. From puberty to the menopause, the inner lining of the uterus (the endometrium) provides a suitable environment for embryo implantation and development during pregnancy. The endometrial lining thickens during the proliferative phase (first half) of the menstrual cycle. It forms secretory glands after ovulation as it is stimulated by hormones released from the ovaries.

If the egg is not fertilized, or implantation does not occur, the endometrium is shed and excreted from the body via the vagina during menstruation and is slowly replaced in the course of the next menstrual cycle. The uterus also undergoes powerful, rhythmic contractions during labor, resulting in the delivery of the foetus at birth.

The uterus is composed of two main parts:
  • The bulging upper section called the body, or corpus.
  • The narrow lower section called the neck, or cervix.

The upper portion of the uterine body is called the fundus. The fallopian tubes open into the opposite corners of the fundus and the cervix opens into the vagina. The cervix is a cylinder-like structure that leads from the upper end of the vagina into the interior of the uterus. It is about 2.5 cm long and has a fine canal running through it with openings at each end called the internal and external os, respectively. The inner walls of the cervix contain small sacs called crypts that secrete alkaline mucus, which protects sperm from the acidity of the vaginal secretions. The crypts also act as reservoirs for sperm.

The walls of the uterus contain three layers:

  • The inner lining, called the endometrium.
  • The middle muscular layer, called the myometrium.
  • The outer serosal layer, called the peritoneum.

The serosa secretes a watery (serous) fluid that prevents friction between the uterus and surrounding organs. A cross-sectional view of the uterine structures is shown below.

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