Rectal ampulla

The rectal ampulla is the terminal dilated portion of the rectum, immediately proximal to the anal canal. It serves as a temporary storage site for feces before defecation and plays a crucial role in the regulation of bowel evacuation.

Species-Specific Considerations

While the general structure and function of the rectal ampulla are conserved across domestic species, its morphology and prominence vary:

1. Ruminants (e.g., cattle, sheep, goats)

• The rectal ampulla is well-developed and capacious, often forming a visible bulge on rectal palpation.

• It is located dorsal to the reproductive tract and ventral to the sacrum in the pelvic cavity.

• Used routinely as a landmark during rectal examinations.

2. Horses

• The ampulla is less distinctly dilated but still recognizable.

• It is significant in per rectum clinical examinations due to the horse’s large pelvic cavity and spacious rectal lumen.

• Closely related anatomically to structures like the mesorectum, rectogenital pouch, and dorsal bladder wall.

3. Dogs and Cats (Carnivores)

• The rectal ampulla is less pronounced than in large animals.

• The rectum transitions gradually into the anal canal without a marked dilation.

• In these species, the ampulla still serves a reservoir function but is anatomically subtler.

4. Pigs

• Moderate dilation may be present, but the rectum is generally straight and relatively short.

• The ampulla is less clinically emphasized compared to ruminants and equines.

Histological Features

• Lined by simple columnar epithelium with abundant goblet cells for mucus secretion.

• The submucosa contains a rich plexus of nerves (including parasympathetic fibers) crucial for defecation reflexes.

Function

• Acts as a temporary fecal reservoir.

• Initiates defecation reflexes when distended, involving mechanoreceptors in the rectal wall.

• Coordinates with anal sphincters to maintain continence.