What is the detailed anatomy of the uterus?

From the Guidelines

The uterus is a complex, hollow, pear-shaped muscular organ with a detailed anatomy that includes three main parts: the fundus, corpus, and cervix, and is supported by various ligaments and supplied by uterine and ovarian arteries. The uterine wall consists of three distinct layers: the endometrium, myometrium, and perimetrium, each playing a crucial role in its function 1. The uterine cavity is triangular and connects to the fallopian tubes via openings called ostia at the superior corners. Key features of the uterus include:

• The fundus, which is the dome-shaped upper portion
• The corpus or body, which is the main central section
• The cervix, which is the narrow lower portion that opens into the vagina
• The uterine wall layers: endometrium, myometrium, and perimetrium
• The uterine cavity and its connection to the fallopian tubes
• The cervical canal with its internal and external os
• Blood supply from the uterine and ovarian arteries
• Lymphatic drainage to pelvic lymph nodes
• Innervation by sympathetic and parasympathetic fibers
• Support by ligaments such as the broad, round, cardinal, and uterosacral ligaments. When examining the uterus, particularly through transvaginal ultrasound, it is essential to visualize the organ in both sagittal and coronal planes, sweeping the transducer laterally to capture its entirety, as it may be deviated to one side, and then rotating the transducer to obtain a full assessment, as described in the emergency ultrasound imaging criteria compendium by the American College of Emergency Physicians 1.

From the Research

Uterine Structure

• The human uterus is composed of three layers: endometrium, myometrium, and perimetrium 2
• The myometrium is the middle layer of the uterine wall, consisting of smooth muscle cells organized into three layers: inner, outer, and intermediate layers 3
• The inner and outer layers are mainly composed of smooth muscle cells, while the intermediate layer is richly vascularized 3

Uterine Artery and Blood Supply

• The uterine artery originates from the internal iliac artery and supplies blood to the uterus 4
• The uterine artery has three segments: descending, transverse, and ascending, which vary in length with age and pregnancy 4
• The number of uterine artery branches running towards the body and cervix of the uterus is variable and depends on age and pregnancy 4

Myocytes and Uterine Contractions

• Myocytes are the functional cells of the uterus, responsible for generating contraction forces, passing action potentials, and controlling contractility 5
• The myocytes are a homogeneous cell type, but their function is modified by hormones, stretch, paracrine factors, and the extracellular environment 6
• The myocytes have an intrinsic pacemaker and rhythmicity, which is modified by various factors, including hormones and stretch 6

Uterine Wall and Cervix

• The uterine wall consists of a smooth muscle (myometrium) organized into three layers, with the musculature being thick in the corpus uteri and vanishing at the level of the corpus/cervix junction 3
• The cervix is formed mainly by connective tissue, with a small amount of smooth muscle cells 3
• The uterine wall remodels during the monthly menstrual cycle and more significantly during the complex stages of reproduction 2