Uterus Anatomy

1. Overview and Position

2. Parts of the Uterus

3. Wall Layers (from lumen outward)

Endometrium (innermost)

• Simple columnar epithelium with ciliated and secretory cells
• Tubular uterine glands that invaginate into the stroma
• Two functional zones:
  • Basalis (basal layer) - not shed during menstruation; source of cyclical regeneration
  • Functionalis (functional layer) - undergoes cyclic changes and is shed during menstruation (consists of the spongy layer deep and compact layer superficially)

Myometrium (middle, thickest layer)

• Inner (subvascular) layer - thin
• Middle layer - thickest; richly vascularized, spongelike; muscle fibers form a 3D meshwork; this is the layer mainly responsible for expelling the fetus during birth
• Outer (supravascular) layer - thin

Perimetrium (serosa, outermost)

4. Cervix

• Mostly fibrous connective tissue (collagen types I and III), with circumferentially oriented smooth muscle cells more abundant in the upper half
• Endocervical canal lined by columnar epithelium with branching, tubular cervical glands secreting alkaline mucus
• Vaginal part (ectocervix/portio) covered by stratified non-keratinized squamous epithelium
• The transformation zone (squamocolumnar junction) where columnar epithelium meets squamous epithelium is the most common site for cervical carcinoma
• Color Atlas of Human Anatomy, Vol. 2 (Internal Organs); Creasy & Resnik's Maternal-Fetal Medicine

5. Ligaments and Supports

6. Blood Supply

• Uterine artery - the main supply; a branch of the internal iliac artery. It crosses above the ureter ("water under the bridge") near the lateral fornix of the vagina - a key surgical landmark during hysterectomy
• Ovarian artery - supplements the upper uterus and tubes; arises directly from the aorta
• Venous drainage mirrors the arterial supply via the uterine venous plexus → internal iliac vein

7. Lymphatic Drainage

• Fundus and upper body → para-aortic (lumbar) lymph nodes (following the ovarian vessels)
• Body → internal and external iliac lymph nodes
• Cervix → internal and external iliac lymph nodes, and obturator nodes

8. Nerve Supply

• Sympathetic - T10-L1 (via hypogastric plexus); responsible for vasoconstriction and uterine contractions
• Parasympathetic - S2-S4 (pelvic splanchnic nerves / nervi erigentes)
• Sensory - pain from the body travels via T10-L1; pain from the cervix travels via S2-S4

9. Normal Position

• Anteverted (long axis of uterus angled forward relative to vagina at ~90°)
• Anteflexed (body tilted forward on the cervix)
• Retroversion/retroflexion are common anatomical variants (seen in ~20% of women)

10. Menstrual Cycle and the Endometrium

1. Proliferative phase (days 5-14) - estradiol-driven restoration of the shed layer; glands elongate
2. Secretory phase (days 15-28) - progesterone + estrogen cause glands to coil, secrete glycogen-rich mucus; stromal cells become pseudodecidual
3. Menstrual phase (days 1-4) - progesterone withdrawal → ischemia → shedding of the functionalis

• The ureter crosses under the uterine artery ~1.5 cm lateral to the cervix - the most common site of ureteric injury during hysterectomy (Gray's Anatomy for Students)
• Leiomyomas (fibroids) are benign smooth muscle tumors of the myometrium, the most common pelvic tumor in women
• Adenomyosis = endometrial tissue within the myometrium, causing an enlarged globular uterus, dysmenorrhea, and menorrhagia
• The lower uterine segment (formed from the isthmus) is the preferred site for Cesarean section incision

Uterus Anatomy: Superior, Inferior, Anterior & Posterior Parts Explained

Diagram 1 - Anterior View (Sectioned)

Diagram 2 - Macroscopic Structure (Longitudinal & Anterior Views)

Diagram 3 - Posterior View with Ligaments & Vasculature

Diagram 4 - Sagittal/Lateral Section Showing Uterus in Pelvic Context

Superior Parts

Fundus

• The rounded dome-shaped top of the uterus, projecting above the openings of the uterine (fallopian) tubes
• It is the most superior part of the organ
• During pregnancy it rises progressively into the abdomen; at term it can reach the epigastric region
• The fundus has a convex posterior surface and a slightly flattened anterior surface
• It is covered by peritoneum (perimetrium) on all sides

Uterine Horns (Cornua)

• Where the uterine tubes enter the uterus at its superolateral corners
• The right horn (cornu) and left horn are the entry points for sperm and the sites of tubal implantation in ectopic pregnancy

Middle Parts

Body (Corpus)

• The large middle portion, making up the upper two-thirds of the organ
• Anterior surface is nearly flat (vesical surface - faces the bladder)
• Posterior surface is convex (intestinal surface - faces the rectum and sigmoid colon)
• Both surfaces are covered by peritoneum
• Contains the triangular uterine cavity lined by endometrium

Isthmus

• A narrow constriction ~1 cm long between the body and the cervix
• Identifiable externally as a shallow groove
• In pregnancy, it expands dramatically to form the lower uterine segment - the preferred incision site for Cesarean section
• Internally marked by the histological internal os

Inferior Parts

Cervix

• The cylindrical lower one-third of the uterus, directed posteriorly and inferiorly
• ~2.5 cm long; mostly fibrous connective tissue with less smooth muscle than the body
• Divided into:
  • Supravaginal part - above the vagina; the uterosacral and cardinal ligaments attach here
  • Vaginal part (portio vaginalis) - protrudes into the vaginal vault and is visible on speculum exam
• The external os opens at the tip of the portio into the vagina
  • Round/circular in nulliparous women
  • Slit-like / transverse after vaginal delivery
• The cervical canal runs between the internal os (above) and external os (below); it has characteristic palmate (arbor vitae) folds
• Lined by columnar epithelium; the transformation zone (junction with the squamous epithelium of the vaginal portio) is the most common site for cervical carcinoma

Anterior Relations

Vesicouterine pouch - a shallow peritoneal recess between the bladder and the anterior surface of the uterus. It becomes very shallow (or obliterated) when the bladder is full.

• Anteriorly: Urinary bladder
• At the cervix: The ureter passes ~1.5 cm lateral to the cervix, crossing beneath the uterine artery ("water under the bridge") - key surgical landmark in hysterectomy

Posterior Relations

Rectouterine pouch (Pouch of Douglas) - the deepest point of the female peritoneal cavity; bounded laterally by the uterosacral folds containing the uterosacral ligaments and inferior hypogastric nerve plexus.

• Posteriorly: Rectum and sigmoid colon (separated by the pouch of Douglas)
• The posterior surface of the uterus and broad ligament can be felt through the rectum on rectal examination

Summary Table

Position

• Anteverted - the whole uterus is tilted forward relative to the vaginal axis (~90° angle)
• Anteflexed - the body is flexed forward on the cervix

The Broad Ligament of the Uterus - A Beginner's Guide

Start with a Simple Picture

What Exactly Is It?

• The front layer = anterior leaf
• The back layer = posterior leaf

The Diagram

The Three Zones - Think of a Flying Bird 🐦

1. Mesosalpinx (Top zone - the "wing tip")

• "Meso" = middle / connecting | "salpinx" = tube
• This is the topmost free edge of the broad ligament
• It wraps around and suspends the fallopian (uterine) tube up in the air
• Think of it as the pocket that holds the fallopian tube, keeping it floating above everything else

2. Mesovarium (Middle zone - the "bump on the wing")

• "Ovarium" = ovary
• A small, backward-pointing fold of the broad ligament that attaches to the ovary
• The ovary hangs from this like a pendant from a necklace
• Note: the ovary itself is NOT inside the broad ligament - it is attached to its back surface and sits just behind it

3. Mesometrium (Bottom zone - the "main body of the wing")

• "Metrium" = uterus
• The largest, biggest part of the broad ligament
• It stretches from the body of the uterus sideways to the pelvic wall
• Contains the most important structures (see below)
• Gray's Anatomy for Students; Campbell-Walsh Urology

What Does the Broad Ligament Carry Inside It?

What Does the Broad Ligament Actually DO?

1. It creates two separate spaces in the pelvis

• Vesicouterine pouch (front space) - between bladder and uterus
• Rectouterine pouch / Pouch of Douglas (back space) - between uterus and rectum

2. It keeps the uterus in place (a little)

3. It carries the "lifelines" to the uterus and ovary

A Quick Analogy to Tie It All Together

Imagine the uterus is a person standing in the middle of a room. The broad ligament is like their coat - it hangs from their shoulders (fallopian tubes at the top), drapes over their sides (mesometrium), and the coat pockets hold their valuables (blood vessels, ureter, nerves). On each side of the room there's a wall (the pelvic sidewall), and the coat stretches all the way to both walls, keeping the person centered.

Clinical Relevance (Why Doctors Care)

• Hysterectomy (uterus removal): Surgeons must carefully open the broad ligament, identify the ureter running inside it, then clip the uterine artery - all without accidentally cutting the ureter
• Broad ligament hematoma: After trauma or difficult delivery, blood can collect inside the two layers of the broad ligament, forming a dangerous expanding mass
• Broad ligament fibroid: A uterine fibroid can grow sideways into the broad ligament, making surgery very difficult because of the vessels and ureter inside
• Endometriosis: Endometrial tissue commonly implants on the posterior leaf of the broad ligament

Summary in One Sentence