Uterus

The uterus is a central organ of the female reproductive system responsible for menstruation, implantation, and fetal development. Its structure and function are closely regulated by hormonal and vascular factors. Understanding uterine anatomy and physiology is essential for diagnosing and managing reproductive and gynecological disorders.

Anatomy of the Uterus

Gross Anatomy

The uterus is a hollow, muscular organ situated in the female pelvis between the bladder and rectum. Its size, shape, and orientation can vary with age, parity, and hormonal status.

• Size and Shape: Typically 7-8 cm in length, 4-5 cm in width, and 2-3 cm in thickness; pear-shaped in nulliparous women.
• Regions: Fundus, body, isthmus, and cervix.
• Uterine Wall Layers: Endometrium (inner mucosal layer), myometrium (thick muscular layer), perimetrium (outer serosal layer).

Microscopic Anatomy

The uterine wall has specialized structures at the microscopic level that support its reproductive functions.

• Endometrial Histology: Consists of functional and basal layers; undergoes cyclic changes during the menstrual cycle.
• Myometrial Structure: Smooth muscle fibers arranged in interlacing bundles, allowing uterine contraction during menstruation and labor.
• Blood Supply and Lymphatics: Arterial supply from the uterine and ovarian arteries; venous drainage through the uterine veins; lymphatic drainage to the pelvic and para-aortic nodes.

Embryology and Development

The uterus develops from the paired Müllerian ducts during embryogenesis, undergoing differentiation and fusion to form a single uterine cavity.

• Müllerian Duct Development: Ducts elongate, fuse in the midline, and canalize to form the uterus, cervix, and upper vagina.
• Uterine Differentiation: Hormonal signaling guides myometrial and endometrial development, establishing the capacity for menstruation and pregnancy.
• Common Congenital Anomalies: Septate uterus, bicornuate uterus, unicornuate uterus, and didelphys uterus; these can impact fertility, pregnancy outcomes, and menstrual patterns.

Physiology of the Uterus

Menstrual Cycle

The uterus undergoes cyclical changes under hormonal regulation to prepare for potential implantation and pregnancy.

• Proliferative Phase: Endometrial regeneration occurs under estrogen stimulation following menstruation.
• Secretory Phase: Progesterone from the corpus luteum promotes endometrial maturation, glandular secretion, and preparation for implantation.
• Menstrual Phase: If implantation does not occur, withdrawal of progesterone and estrogen leads to shedding of the functional endometrium.

Reproductive Function

The uterus plays a central role in conception, gestation, and childbirth.

• Implantation: The endometrium provides a receptive environment for embryo attachment and placental development.
• Fetal Development: The uterus accommodates fetal growth, supports nutrient and waste exchange via the placenta, and protects the fetus.
• Uterine Contractility: Coordinated myometrial contractions facilitate sperm transport, menstrual shedding, and labor during childbirth.

Innervation and Blood Supply

The uterine function is maintained by a complex network of blood vessels and nerves that support hormonal, sensory, and contractile activity.

• Arterial Supply: Primarily from the uterine arteries, branches of the internal iliac arteries; anastomoses with ovarian arteries provide collateral circulation.
• Venous Drainage: Uterine veins drain into the internal iliac veins; the rich venous plexus facilitates blood flow during pregnancy and menstruation.
• Lymphatic Drainage: Pelvic, obturator, and para-aortic lymph nodes drain the uterus, important in the spread of malignancies.
• Autonomic and Sensory Innervation: Sympathetic and parasympathetic fibers regulate contractility and blood flow; sensory nerves mediate pain and uterine sensation.

Pathophysiology and Common Disorders

Congenital and Structural Disorders

• Müllerian duct anomalies such as septate or bicornuate uterus
• Uterine fibroids (leiomyomas)
• Endometrial polyps

Endometrial and Hormonal Disorders

• Endometriosis
• Adenomyosis
• Dysfunctional uterine bleeding

Neoplastic Disorders

• Endometrial hyperplasia
• Endometrial carcinoma
• Uterine sarcomas

Diagnostic Evaluation

Accurate diagnosis of uterine conditions requires a combination of clinical assessment, imaging, and laboratory investigations to guide appropriate management.

• Pelvic Examination: Assessment of uterine size, shape, mobility, and tenderness.
• Imaging Studies:
  • Ultrasound: First-line modality for evaluating uterine structure, fibroids, and endometrial thickness.
  • MRI: Useful for detailed soft tissue characterization, congenital anomalies, and tumor evaluation.
• Endometrial Biopsy and Hysteroscopy: Assessment of endometrial pathology, including hyperplasia, polyps, and malignancy.
• Laparoscopy: Evaluation of uterine and pelvic pathology such as endometriosis or adhesions.

Treatment and Management

Medical Management

Medical therapies are often the first-line approach for managing uterine disorders, particularly those related to hormonal or inflammatory causes.

• Hormonal Therapies: Contraceptives, progestins, gonadotropin-releasing hormone agonists to regulate menstrual cycles, reduce bleeding, and manage fibroids or endometriosis.
• Non-Hormonal Medications: Nonsteroidal anti-inflammatory drugs for pain relief, iron supplementation for anemia, and other symptom-targeted treatments.

Surgical Management

Surgical intervention is indicated for structural abnormalities, refractory symptoms, or malignancies.

• Myomectomy: Removal of fibroids while preserving the uterus, often for fertility preservation.
• Hysterectomy: Definitive treatment for severe bleeding, pain, or malignancy.
• Endometrial Ablation: Minimally invasive procedure to reduce excessive menstrual bleeding.
• Hysteroscopic Procedures: Resection of polyps, submucosal fibroids, and correction of congenital anomalies.

Clinical Considerations in Pregnancy

The uterus undergoes significant adaptations during pregnancy to support fetal growth and ensure a safe delivery process.

• Uterine Adaptations: Increase in size, vascularity, and elasticity to accommodate the growing fetus.
• Placental Implantation: Proper implantation in the endometrium is essential for fetal nutrition; abnormalities such as placenta previa can complicate pregnancy.
• Labor and Postpartum Involution: Coordinated myometrial contractions facilitate delivery, followed by gradual reduction of uterine size and return to pre-pregnancy state.

References

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