The Female Reproductive System and Endometriosis

by Robert Tallitsch, PhD | December 14, 2023

Video explaining the Female Reproductive System and Endometriosis with a patient example!

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(A note on sex and gender: Sex and gender exist on a spectrum. This Brain Builder article uses the terms “female” and “male,” or both, to refer to the sex assigned to the individual at birth.)

Endometriosis is a common and painful disorder that results when tissue similar to the lining of the uterus, termed the endometrium, develops outside of the uterus. This tissue typically develops within the pelvis or the lower regions of the abdomen. Endometriosis may cause severe pain and fertility problems within the individual. This Brain Builder will briefly discuss the organs of the female reproductive system and the gross and microanatomy of the uterus. We will then discuss the causes, symptoms, diagnosis, and treatment of endometriosis.

Organs and Functions of the Female Reproductive System

The female reproductive system is composed of the external genitalia and the internal pelvic structures. The external genitalia are the

Labia majora
Labia minora
Clitoris

The internal pelvic structures are the

Ovaries
Uterine (Fallopian) tubes
Uterus
Vagina

The functions of the female reproductive system are:

Production of gametes called ova
Provide a site for fertilization
Support the implantation of the fertilized gamete
Provide nourishment to support the developing fetus
Delivery of a human fetus
Production and release of female sex hormones
Nourishment of the baby following delivery

Gross Anatomy and Microanatomy of the Uterus

Gross Anatomy

The uterus, which is a hollow, pear-shaped organ, is divided into the body, fundus, and cervix. The superior 2/3 of the uterus forms the body of the uterus. The fundus is that portion of the body of the uterus that is superior to the entrance of the uterine tubes into the uterus. The narrow, inferior 1/3 of the uterus is the cervix. The cervix passes through the superior margin of the vagina and occupies the superior most, anterior wall of the vagina.

Microanatomy of the Uterus

The wall of the uterus is composed of three layers.

The outer layer of the uterus, termed the perimetrium (also termed the serosa), is composed of a thin layer of connective tissue.

The myometrium is the middle layer, and it is composed of three layers of smooth muscle.

The outermost layer, termed the supravascular layer, is composed of both circularly and longitudinally arranged smooth muscle.
The middle, or vascular layer, is composed of circularly arranged smooth muscle.
The innermost layer is termed the submucosal layer. It is composed of longitudinally arranged smooth muscle.

The innermost layer of the uterus is termed the endometrium. The endometrium is composed of a superficial layer of simple columnar epithelium. The endometrium also possesses numerous branched and coiled tubular glands surrounded by a rich, cellular connective tissue. The endometrium undergoes histological changes during the menstrual cycle in preparation for implantation of a fertilized ovum, or egg. If a fertilized ovum does not implant, then the superficial portion of the endometrium is sloughed off during the menstrual cycle.

Endometriosis

Endometriosis occurs when tissue similar to the endometrium of the uterus develops elsewhere in the body, typically growing on other organs within the abdomen or pelvis. These cells are sensitive to the female hormones, and often become inflamed during the menstrual cycle. The formation of painful cysts is also common.

Who is Most Likely to Develop Endometriosis, and What Is the Possible Cause of Endometriosis?

Women who develop endometriosis typically have:

Started their menstrual periods at a young age.
Never have had children.
Have menstrual periods that are shorter in duration and/or have heavy menstrual flow lasting more than seven days.
Have a mother or sister that have had endometriosis.

Although no definitive cause of endometriosis has been determined to date, the most probable theory is retrograde menstruation. In retrograde menstruation some, or most of the menstrual tissue flows backwards from the uterus into the uterine tubes, with some of the sloughed-off endometrial tissue flowing into the abdominal or pelvic cavity.

Symptoms

Although the symptoms of endometriosis vary from patient to patient, pain and excessive bleeding during menstrual periods are the most common symptoms. Additional symptoms may include some or all of the following:

Pelvic cramping may begin several days before a menstrual period and may also extend several days into the menstrual period.
Lower back pain, abdominal pain, pain during intercourse, and/or pain during urination or bowel movements.
Fatigue
Constipation
Bloating or nausea, especially during menstrual periods

Diagnosis

When a patient presents with one or more of the above symptoms, a Gynecologist will conduct one or more of the following tests in an attempt to diagnose (or rule out a diagnosis of) endometriosis:

Pelvic examination
Ultrasound
MRI of the pelvis and/or abdomen
Laparoscopic examination of the pelvis or abdomen to confirm endometriosis that is suspected as a result of ultrasound or MRI findings.

Treatment

Whatever treatment is prescribed by the physician, its main goals are to alleviate pain, reduce pelvic masses, and, if it is a goal of the patient, improve fertility.

Prescriptions may be ordered to reduce or eliminate the pain. Hormone treatments may also be used to reduce or stop the spread of endometriosis to other parts of the abdomen or pelvis. In severe cases surgery may be recommended to either remove the endometrial tissue or to remove the uterine tubes, ovaries, and uterus.

There is no cure for endometriosis. A patient’s choice of treatment depends on the age of the patient, desire to have children, and the patient’s ability to tolerate symptoms of varying intensity. Surgical treatment to remove the uterine tubes, ovaries, and uterus oftentimes is the only permanent way to eliminate the pain of endometriosis in a premenopausal female.

Key Terms

Endometriosis - A common and painful disorder that results when tissue similar to the lining of the uterus, termed the endometrium, develops outside of the uterus.

Cervix - The inferior 1/3 of the uterus. The cervix passes through the superior margin of the vagina and occupies the superior most, anterior wall of the vagina.

Endometrium - The innermost layer of the uterus.

Fundus of the uterus - The portion of the body of the uterus that extends superior to the junction between the uterine tubes and the uterus.

Vascular layer of smooth muscle - The middle of the three layers of the smooth muscle of the uterus.

Female - A term used in this Brain Builder to describe the sex assigned to an individual at birth.

Perimetrium - The term used to describe the outermost layer of the uterus.

Retrograde menstruation - A leading theory as to the cause of endometriosis. In retrograde menstruation some, or most of the menstrual tissue flows backwards from the uterus into the uterine tubes, with some of the sloughed-off endometrial tissue flowing into the abdominal or pelvic cavity.

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