Uterus: MRCOG Part 1 questions and key facts

The round ligament is a key structure in female pelvic anatomy. It originates from the uterine horns, which are the upper, outer angles of the uterus where the fallopian tubes enter. From there, it travels through the inguinal canal, a passage in the anterior abdominal wall, and ultimately attaches to the labia majora, the outer folds of the vulva. Embryologically, the round ligament is a remnant of the gubernaculum, a structure that guides the descent of the gonads during foetal development.

While the ovarian ligament is also a remnant of the gubernaculum, it connects the ovary to the uterus, not the labia majora. The broad ligament is a wide sheet of peritoneum that drapes over the uterus, fallopian tubes, and ovaries, providing general support but not a direct connection from the uterine horns to the labia majora. The cardinal and uterosacral ligaments provide crucial support to the uterus and cervix, anchoring them within the pelvis, but they do not extend to the labia majora or pass through the inguinal canal.

During pregnancy, hormonal changes lead to significant alterations in the cervix. One of these changes is the thickening of the cervical mucus secretions.

This thickened mucus forms a mucus plug that occludes the cervical canal. The primary function of this plug is to act as a mechanical barrier to infection. It helps prevent bacteria and other pathogens from ascending from the vagina into the uterine cavity, which is crucial for protecting the developing foetus and maintaining the integrity of the pregnancy.

While cervical mucus does play a role in sperm transport during the fertile window, this is not its function during pregnancy when conception is no longer a goal. The mucus plug does not nourish the developing foetus, as this is primarily the role of the placenta. Options to aid in cervical dilation and prevent uterine contractions are incorrect, as the mucus plug's role is primarily protective against infection. Cervical dilation occurs during labour, while preventing uterine contractions is mainly due to hormonal influences, not the mucus plug itself.

Epithelial classifications are a high-yield MRCOG anatomy topic, because epithelial transitions map onto the origin of many gynaecological and GI malignancies.

The endocervix (the correct answer) is lined by simple columnar, mucus-secreting epithelium thrown into complex folds (plicae palmatae). Its primary functions are to produce cervical mucus, form the mucus plug of pregnancy, and act as a physiological barrier. The squamocolumnar junction (SCJ) — where this endocervical columnar epithelium meets the ectocervical stratified squamous epithelium — migrates with age and hormonal state, defining the transformation zone (the site of most cervical pre-invasive dysplasia and invasive squamous cell carcinoma).

Other columnar-epithelium locations worth remembering (not in the options but relevant for MRCOG):

• Fallopian tube mucosa — simple columnar, both ciliated and secretory; the ciliary beat and peristalsis together transport the ovum/embryo toward the uterus.
• Endometrium — simple columnar, with glands extending into the stroma; responsive to oestrogen and progesterone.
• Stomach and small/large intestine — simple columnar with specialised cells (parietal, chief, enterocytes, goblet).
• Gallbladder — simple columnar with microvilli.
• Upper respiratory tract and trachea — pseudostratified ciliated columnar with goblet cells.

Distractors.

• Distal anal canal — below the pectinate (dentate) line, the anal canal is lined by stratified squamous epithelium (continuous with perianal skin). The epithelial transition at the pectinate line is the embryological boundary between endodermal hindgut and ectodermal proctodeum.
• Lung alveoli — lined by simple squamous epithelium (type I pneumocytes forming the thin gas-exchange surface, with scattered cuboidal type II pneumocytes producing surfactant).
• Vagina — non-keratinised stratified squamous epithelium. Responds to cyclical oestrogen by thickening and accumulating intracellular glycogen (substrate for lactobacilli → acidic vaginal pH).
• Ureter — transitional epithelium (urothelium). Stretchable, waterproof, continuous from renal calyces through bladder and proximal urethra.