Costanzo (1)

Question 1

What are the surfaces of the GI wall?

Answer 1

the mucosal surface (consisting of epithelial cells, a lamina propria, and a muscularis mucosae) faces the lumen and the serosal surface faces the blood

Question 2

Describe the muscle layers of the GI wall

Answer 2

The longitudinal muscle layer is thin and contains few nerve fibers, whereas the circular muscle layer is thick and more densely innervated

Note that neurons do not make synapses on the GI smooth muscles, rather they release transmitters from varicosities (swellings) along their axon length

Question 3

Where is Meissner’s Plexus located?

Answer 3

aka the submucosal plexus lies between the submucosa and the circular muscle

Question 4

Where is Myenteric Plexus located?

Answer 4

between the circular and longtiduinal muscle layers

Question 5

Question 6

What is the parasympathetic innervation of the GI?

Answer 6

the vagus nerve (CN X) in the upper Gi tract including the striated muscle of the upper 1/3rd of the esophagus, the wall of the stomach, the small intestine, and ascending colon, and

the pelvic nerve in the lower GI tract including the striated muscle of the external anal canal and the walls of the transverse, descending, and sigmoid colons

Question 7

Question 8

Postganglionic neurons of the parasympathetic nervous system are classified as either cholinergic or peptidergic. What are the transmitters of each in the GI?

Answer 8

Cholinergic- Ach

Peptidergic- Substance P, VIP, others

Question 9

T or F. 75% of Vagus nerve fibers are afferent

Answer 9

T. Delivering sensory info from the periphery to the CNS.

NOTE that both the afferent and efferent transmission of GI impulses/functioning are mediated via the vagus nerve, a phenomenon called a vagovagal reflex

Question 10

What are the main sympathetic ganglia of the GI?

Answer 10

celiac, superior mesenteric, inferior mesenteric, and hypogastric

Question 11

What transmitter do post-ganglionic sympathetic fibers release in the GI?

Answer 11

Nor

Question 12

T or F. The intrinsic or enteric nervous system can direct ALL functions of the GI tract, even in the absence of extrinsic (ANS) innervation

Answer 12

T. Although typically the enteric plexus receives input/gives output to the ANS in the GI wall, as well as mechanoreceptors/chemoreceptors

Question 13

How does Ach (parasympathetic) affect the GI?

Answer 13

• Contraction of smooth muscle in GI wall and relaxation of sphincters
• increased salivary, pancreatic, and gastric secretion

Question 14

How does VIP affect the GI?

Answer 14

Smooth muscle relaxation

increased intestinal and pancreatic secretion

Question 15

How does gastrin-releasing peptide (GRP)/Bombesin affect the GI?

Answer 15

increases gastrin secretion