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    Related Topics

    From Reproductive System

    Male - Prepuce (Foreskin)
    Covers and protects the glans penis.
    Female - Uterine (Fallopian) Tubes
    Transport ova from ovaries to uterus.
    Male - Spermatic Cord
    Contains vas deferens, blood vessels, and nerves.
    Female - Labia Majora
    Outer folds of skin surrounding vaginal opening.
    Male - Ejaculatory Duct
    Passage for semen into the urethra.
    Female - Infundibulum
    Funnel-shaped end of uterine tube near ovary.
    Male - Tunica Albuginea
    Fibrous covering of the testes.
    Male - Prostate Gland
    Secretes fluid that enhances sperm motility.
    Male - Bulbourethral Glands
    Secrete mucus for lubrication.
    Male - Rete Testis
    Network of tubules within the testis.
    Male - Corpus Spongiosum
    Erectile tissue surrounding urethra.
    Female - Vestibule of Vagina
    Space between labia minora containing openings.
    Female - Ampulla of Uterine Tube
    Site of fertilization.
    Male - Penis
    External organ for urination and copulation.
    Female - Cervix
    Lower narrow portion opening into vagina.
    Female - Clitoris
    Erectile organ involved in female sexual response.
    Female - Mons Pubis
    Fat pad over the pubic symphysis.
    Female - Body of Uterus
    Main central region.
    Female - Endometrium
    Inner mucosal lining of the uterus.
    Female - Vaginal Orifice
    External opening of the vagina.
    Female - Round Ligament of Uterus
    Maintains anteversion of uterus.
    Female - Labia Minora
    Inner folds of skin surrounding vestibule.
    Male - Scrotum
    External sac that holds and protects the testes.
    Male - Glans Penis
    Expanded tip of the penis.
    Female - Broad Ligament
    Supports uterus, fallopian tubes, and ovaries.

    Female - Myometrium

    Reviewed by our medical team

    Thick muscular layer of the uterus.

    1. Overview

    The myometrium is the thick, muscular middle layer of the uterus, composed primarily of smooth muscle fibers. It plays a central role in menstruation, pregnancy, and childbirth by facilitating uterine contractions. The myometrium provides structural integrity to the uterus and is hormonally responsive, adapting its size and activity depending on reproductive demands. Its coordinated contractility is essential for expelling menstrual blood, delivering the fetus, and returning the uterus to its pre-pregnant state.

    2. Location

    The myometrium is located between the inner endometrial lining and the outer serous perimetrium of the uterus. It spans the entire uterine wall, including the fundus (top), body (central portion), and cervix (lower segment). As the middle layer of the uterine wall, it surrounds and supports the endometrium and forms the bulk of the uterine mass.

    3. Structure

    The myometrium is made up of densely interwoven bundles of smooth muscle fibers supported by connective tissue, blood vessels, and nerves. It can be divided into three histological layers:

    • Outer longitudinal layer: Muscle fibers run longitudinally, especially prominent in the fundus and play a major role in forceful contractions during labor.

    • Middle circular (or crisscross) layer: Thickest layer, rich in spiral-shaped muscle fibers and blood vessels (often called the “stratum vasculare”). Important for compressing uterine blood vessels during childbirth to prevent hemorrhage.

    • Inner longitudinal and circular layer: Intermixed fibers near the endometrium that help maintain uterine tone and support endometrial shedding.

    The myometrium contains estrogen and progesterone receptors, making it highly responsive to hormonal changes across the menstrual cycle and pregnancy.

    4. Function

    The myometrium has several essential functions:

    • Contraction during menstruation: Helps expel the sloughed endometrial lining through rhythmic contractions.

    • Support for implantation and pregnancy: Provides the structural framework and elasticity to support a growing fetus.

    • Labor and delivery: Contracts powerfully and rhythmically to aid in childbirth, especially in the fundal region.

    • Hemostasis post-delivery: The middle layer compresses uterine vessels to prevent postpartum hemorrhage.

    5. Physiological Role(s)

    The myometrium adapts dynamically to different reproductive phases:

    • Menstrual cycle: Under hormonal control, the myometrium exhibits mild, often unnoticed contractions during the cycle, with increased activity during menstruation to assist in endometrial shedding.

    • Pregnancy: The myometrium undergoes hypertrophy (increase in cell size) and hyperplasia (increase in cell number) to accommodate the enlarging uterus. It remains quiescent under progesterone dominance until labor begins.

    • Labor: At term, oxytocin and prostaglandins stimulate powerful myometrial contractions to initiate and maintain labor.

    • Postpartum involution: The myometrium contracts after delivery to reduce the uterus back to its pre-pregnancy size and limit bleeding.

    These functions are tightly regulated by hormonal and neuroendocrine feedback loops involving the hypothalamic-pituitary-ovarian axis.

    6. Clinical Significance

    The myometrium is involved in various physiological and pathological conditions:

    • Uterine fibroids (leiomyomas): Benign tumors of the myometrium that can cause heavy bleeding, pelvic pain, and infertility. Their growth is estrogen-dependent.

    • Adenomyosis: A condition in which endometrial tissue invades the myometrium, leading to uterine enlargement, dysmenorrhea, and menorrhagia.

    • Preterm labor: Premature myometrial contractions may result in early delivery and are managed with tocolytic agents to relax the uterus.

    • Uterine rupture: A rare but life-threatening event, especially in women with prior cesarean sections or uterine surgery, where the myometrium tears during labor.

    • Myometrial atony: Failure of the myometrium to contract effectively after delivery, leading to postpartum hemorrhage. This is a leading cause of maternal mortality worldwide.

    • Hormonal therapies: Medications like oxytocin (to stimulate contractions) and progesterone (to inhibit them) are used in obstetric and gynecological management to influence myometrial function.

    Ultrasound and MRI imaging are commonly used to evaluate myometrial thickness, integrity, and pathologies. Understanding the structure and behavior of the myometrium is critical in obstetrics, gynecology, and reproductive medicine.

    Did you know? A sperm cell has a lifespan of around 3 to 5 days inside the female reproductive tract.