Introduction to Gastrointestinal Physiology

Question 1

What are the components of the GI tract in order?

Answer 1

Oral cavity, pharynx, oesophagus, stomach, duodenum, jejunum, ileum, ascending large intestine, transverse large intestine, descending colon, rectum and anal canal. Accessory organs are the teeth, tongue, salivary glands, pancreas, liver and gall bladder.

Question 2

What is the general structure of the GI wall from the inside out?

Answer 2

the mucosa, the submucosa, the submucosal plexus, the muscularis externa (with the myenteric plexus between its two layers) and the serosa.

Question 3

What is the structure of the mucosa?

Answer 3

From the inside out, consists of a layer of epithelial cells, surrounded by the lamina propria (their basement membrane), and the muscularis mucosa, consisting of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle.

Question 4

Describe the structure of the submucosa

Answer 4

made up of loose connective tissue with collagen and elastin fibrils, blood vessels, lymphatics and in some regions submucosal glands.

Question 5

Describe the structure of the muscularis externa

Answer 5

inner layer consists of circular smooth muscle, the outer is longitudinal. the inner is 3-5x thicker than the outer. At intervals along the tract, inner layer is thickened and modified to form a sphincter, controlling rate of movement of GI contents from one part of the gut to another.

Question 6

What is the role of the myenteric plexus?

Answer 6

largely motor in function, regulates the motility of the GI tract. Hirschsprung’s disease, missing ganglion cells in the myenteric plexus cause loss of motility and severe constipation.