Female - Uterus

1. Overview

The uterus is a hollow, muscular, pear-shaped organ in the female reproductive system that plays a central role in menstruation, implantation, pregnancy, and childbirth. It serves as the site for fetal development and provides structural support for the reproductive tract. The uterus undergoes dynamic changes throughout a woman’s life and is highly responsive to hormonal signals from the ovaries.

2. Location

The uterus is located in the midline of the female pelvis, between the urinary bladder anteriorly and the rectum posteriorly. It is positioned superior to the vagina and connected laterally to the uterine (fallopian) tubes and ovaries. In most women, the uterus is anteverted and anteflexed, meaning it tilts forward over the bladder. Its exact orientation can vary depending on anatomical and physiological factors such as pregnancy, bladder fullness, and pelvic tone.

3. Structure

The uterus is about 7–9 cm long, 4–5 cm wide, and 2–3 cm thick in non-pregnant adult females. It consists of three main regions:

• Fundus: The dome-shaped upper portion, located above the openings of the fallopian tubes.

• Body (Corpus): The central portion, which houses the uterine cavity and is the primary site for implantation and pregnancy.

• Cervix: The lower, narrow segment that opens into the vagina and serves as the gateway between the uterus and external environment.

Histologically, the wall of the uterus consists of three layers:

• Endometrium: The innermost mucosal layer, which undergoes cyclic changes and is shed during menstruation. It is also the implantation site for a fertilized egg.

• Myometrium: The thick middle layer of smooth muscle responsible for uterine contractions during menstruation and labor.

• Perimetrium: The outermost serous layer (visceral peritoneum) that covers the fundus and body of the uterus.

4. Function

The uterus has several critical functions:

• Menstruation: Supports cyclic shedding of the endometrial lining if fertilization does not occur.

• Fertilization and implantation: Provides a site for the fertilized egg to implant and initiate pregnancy.

• Pregnancy support: Nourishes and houses the growing fetus through placental connections.

• Labor and delivery: Contracts rhythmically to expel the fetus during childbirth.

• Hormone interaction: Responds to estrogen and progesterone to regulate menstrual cycle and endometrial development.

5. Physiological Role(s)

The uterus plays a dynamic role in reproductive physiology:

• Menstrual cycle regulation: The endometrium thickens under the influence of estrogen (proliferative phase) and becomes secretory under progesterone. If no pregnancy occurs, the hormonal decline leads to endometrial shedding (menstruation).

• Pregnancy adaptation: During pregnancy, the uterus enlarges dramatically due to myometrial hypertrophy and hyperplasia, accommodating the growing fetus and placenta.

• Immune modulation: The uterus creates an immune-tolerant environment to protect the embryo from maternal immune attack.

• Postpartum involution: After childbirth, the uterus contracts and returns to its non-pregnant size and tone over several weeks, a process aided by oxytocin.

Throughout a woman’s life, the uterus undergoes multiple changes influenced by puberty, menstrual cycles, pregnancy, and menopause.

6. Clinical Significance

The uterus is commonly involved in a wide range of gynecologic and obstetric conditions:

• Uterine fibroids (leiomyomas): Benign tumors of the myometrium that can cause heavy menstrual bleeding, pelvic pain, and infertility.

• Adenomyosis: Invasion of endometrial tissue into the myometrium, leading to painful and heavy periods.

• Endometrial hyperplasia and cancer: Abnormal proliferation of the endometrial lining, especially postmenopausally, can lead to malignancy.

• Uterine prolapse: Descent of the uterus into the vaginal canal due to weakened pelvic support structures, often seen in multiparous or older women.

• Infertility: Congenital or acquired abnormalities (e.g., septate uterus, Asherman’s syndrome) may impair implantation and successful pregnancy.

• Abnormal uterine bleeding: Can result from hormonal imbalances, fibroids, polyps, or malignancy and often requires diagnostic evaluation (e.g., ultrasound, biopsy).

• Hysterectomy: Surgical removal of the uterus performed for various indications, including fibroids, cancer, chronic pain, or bleeding disorders.

Imaging modalities such as transvaginal ultrasound, hysteroscopy, and MRI are used to assess uterine health. Maintaining uterine integrity is crucial for fertility, menstrual regulation, and overall reproductive health.