Which layer is a bilayer of smooth muscle which consists of a layer running circularly and another running longitudinally?

Which layer is a bilayer of smooth muscle which consists of a layer running circularly and another running longitudinally?

• A. Mucosa
• B. Serosa
• C. Muscularis externa
• D. Submucosa

Answer: (C)

The muscularis externa is the layer responsible for GI motility, made up of two smooth muscle layers arranged in a bilayer: an inner circular layer and an outer longitudinal layer. This arrangement sits between the submucosa and the serosa. The circular layer constricts the lumen, while the longitudinal layer shortens the tube, and the two layers work together to produce peristalsis and segmentation. The myenteric (Auerbach) plexus lies between these two muscle layers to coordinate their contractions. Other tunics—mucosa (epithelium, lamina propria, muscularis mucosae), submucosa (dense connective tissue with vessels and nerves), and serosa (visceral peritoneum)—are not muscular layers.

The muscularis externa is the layer responsible for GI motility, made up of two smooth muscle layers arranged in a bilayer: an inner circular layer and an outer longitudinal layer. This arrangement sits between the submucosa and the serosa. The circular layer constricts the lumen, while the longitudinal layer shortens the tube, and the two layers work together to produce peristalsis and segmentation. The myenteric (Auerbach) plexus lies between these two muscle layers to coordinate their contractions. Other tunics—mucosa (epithelium, lamina propria, muscularis mucosae), submucosa (dense connective tissue with vessels and nerves), and serosa (visceral peritoneum)—are not muscular layers.