A Sphincter Is a

Multiple Choice

A sphincter is a

A) thickening of the longitudinal layer of the muscularis that propels materials through the GI tract.
B) thickening of the circular layer of the muscularis that controls movement of materials through the GI tract.
C) fold of the mucosa of the GI tract that increases the total surface area for absorption of nutrients.
D) circle of adventitia that anchors the GI tract to neighboring structures.