Uterus

The uterus undergoes cyclic changes during the menstrual cycle divided in proliferative, secretory and menstrual phases. This specimen is from the early secretory phase.

Note: The gap between the epithelium and the lamina propria is a shrinkage artifact.

The uterine wall is composed of three layers:

• Endometrium - specialized mucosa that undergoes marked changes during the menstrual cycle.
• Functional Layer (or Pars Functionalis) - upper two thirds of the mucosa that contains the glands.
• Simple Columnar Epithelium - ciliated columnar and non-ciliated secretory cells.
• Endometrial Stroma - the underlying lamina propria is highly cellular (stellate cells, macrophages and lymphocytes).
• Uterine Glands - simple tubular glands lined with mostly non-ciliated secretory cells that begin secreting under the influence of progesterone.
• The glands become coiled with slightly dilated lumens.
• Glycogen accumulates in the base of the columnar cells. (It appears empty because glycogen is extracted during sample preparation.).
• Secrete nutrients to support development of the embryo if implantation occurs.
• Basal Layer (or Pars Basalis) - lower third of the mucosa that is retained during menstruation and regenerates the functional layer.

• Myometrium - composed of three indistinct layers of smooth muscle.
• Inner and Outer Layers - mostly longitudinal bundles of smooth muscle.
• Middle Layer (or Stratum Vasculare) - thickest layer of mostly circular or spiral bundles of smooth muscle with numerous blood vessels.
• Perimetrium - covered by an outer serous layer or visceral peritoneum. (Not found in this specimen.)

The endometrium contains a unique system of blood vessels that undergo marked changes during the menstrual cycle.

• Arcuate Arteries - 6 to 10 branches of the uterine artery that encircle the uterus in the myometrium.
• Radial Arteries (#1 and #2) - branches of arcuate arteries that ascend into the endometrium and give rise to:
• Straight Arteries - supply the basal layer.
• Spiral (or Coiled) Arteries (#1 and #2) - pass through the basal layer and supply the functional layer.
• Terminal Capillaries - dilated (or ectatic) capillaries that arise from spiral arteries.

Because the two layers of the endometrium have separate blood supplies, the basal layer is unaffected by the loss of blood to the functional layer during menstruation.