The gut of a vertebrate is often described as an elongated tube consisting of four layers of different cell types. Which of the following represents the correct order of those layers, from innermost (lumen-facing) to outermost?
A) Submucosa, cartilage, mucosa, endoplasmic reticulum
B) Smooth muscle layers, submucosa, mucosa, cartilage
C) Cartilage, smooth muscle layers, mucosa, circular muscle
D) Mucosa, submucosa, circular muscle, longitudinal muscle
E) Cartilage, mucosa, endoplasmic reticulum, submucosa

Question

Quizplus · Accepted Answer

The correct order of the layers of the vertebrate gut from innermost (lumen-facing) to outermost is mucosa, submucosa, circular muscle, longitudinal muscle. The mucosa layer contains the epithelial cells that absorb nutrients from the lumen of the gut. The submucosa layer contains connective tissue, blood vessels, and nerves. The circular muscle layer is responsible for mixing and grinding food, while the longitudinal muscle layer moves the food along the gut. There is no cartilage or endoplasmic reticulum in the layers of the vertebrate gut.

The Gut of a Vertebrate Is Often Described as an Elongated