External Structure and Parts
Anatomically, the uterus is divided into several consecutive parts:
- Fundus (fundus uteri) — the upper convex portion of the organ.
- Body (corpus uteri) — the main triangular part that gradually narrows inferiorly.
- Isthmus (isthmus uteri) — the narrow zone of transition between the body and the inferior part.
- Cervix (cervix uteri) — the lower cylindrical part.
The body of the uterus has two surfaces. The anterior surface is called the vesical surface (facies vesicalis) because it faces the urinary bladder. The posterior surface is the intestinal surface (facies intestinalis), which lies against the rectum. Laterally, these surfaces converge to form the right and left margins of the uterus (margines uteri). At the superior angles, where the uterine tubes enter the uterus, the uterine horns (cornua uteri) are identified.
Uterine Cavity and Wall
The uterine cavity (cavitas uteri) has a triangular shape on a coronal section. The ostia of the uterine tubes open into its superior angles, while inferiorly the cavity narrows and transitions into the internal os of the uterus, leading to the cervical canal.
The wall of the organ consists of three distinct layers:
- Endometrium (endometrium) — the inner mucous membrane.
- Myometrium (myometrium) — the thick middle muscular layer.
- Perimetrium (perimetrium) — the outer serous layer, which is a reflection of the peritoneum.
Anatomy of the Cervix
The cervix (cervix uteri) is approximately 3–4 cm long and topographically divided into two parts: the upper supravaginal part (portio supravaginalis) and the lower vaginal part (portio vaginalis).
The cervical canal (canalis cervicis uteri) runs through the interior of the cervix. The mucosa of this canal forms characteristic palmate folds (plicae palmatae).
The canal opens into the vagina via the external os (ostium uteri). The shape of this opening depends on obstetric history:
- In nulliparous women, it is circular.
- In pararous (parous) women, the opening takes the form of a transverse slit.
Ligaments and Fixation
The normal position of the uterus in the pelvis is described by the terms anteversion (tipping forward) and anteflexion (bending forward). The organ is securely fixed within the lesser pelvis by a well-developed ligamentous apparatus.
Key ligaments include:
- Broad ligament of the uterus (lig. latum uteri).
- Round ligament of the uterus (lig. teres uteri).
- Ovarian ligament (lig. ovarii proprium).
- Suspensory ligament of the ovary (lig. suspensorium ovarii).
In addition to the ligaments, the parametrium (parametrium), or parametrial connective tissue, plays an important role. Blood vessels and nerve plexuses supplying the organ course through this fatty tissue.
Blood Supply and Innervation
Arterial blood supply is provided by two paired vessels:
- Uterine artery (a. uterina).
- Ovarian artery (a. ovarica).
Venous drainage originates from the uterine venous plexus (plexus venosus uterinus). Blood then drains via the uterine veins (vv. uterinae) and ovarian veins (vv. ovaricae) into the internal iliac vein system (v. iliaca interna).
Innervation of the organ is mediated by autonomic nerve plexuses: the inferior hypogastric plexus (plexus hypogastricus inferior) and the uterovaginal plexus (plexus uterovaginalis).