Lecture 45: Structure & Innervation of GI Tract

Question 1

What is the role of salivary glands as support structures in the GIT?

Answer 1

lubrication, buffering, digestion of carbs and fat

Question 2

What is the role of the pancreas as a support structure in the GIT?

Answer 2

buffering, digestion

Question 3

What is the role of the liver as a support structure of the GIT?

Answer 3

“first pass metabolism”
Liver recieves all nutrients absorbed by the gut, goes to the portal vein first before going back to the heart
Important in fat and carb metabolism, makes bile

Question 4

What is the role of the gallbladder?

Answer 4

stores bile

Question 5

There are two surfaces of the GIT wall. What are they?

Answer 5

Mucosal (luminal or apical): faces the lumen
Serosal (basolateral): faces the blood

Question 6

What are the three layers of the GIT wall?

Answer 6

Mucosal layer (lumen)
Submucosal layer
Two layers of smooth muscle

Question 7

What is the function of the mucosal layer of the GIT wall?

Answer 7

Has three types of tissue:
Epithelial cells- absorptive and secretory functions, sloughed off and replaced very often
Lamina propria- connective tissue, some blood and lymph vessels
Muscularis mucosae- smooth muscle cells, important for changing shape and surface area of the epithelial layer

Question 8

True or False: the enteric nervous system can operate independent of the brain and spinal cord.

Answer 8

True
The enteric NS can function even if the vagus nerve is severed

Question 9

How can the enteric nervous system control functions of the GIT in absence of the extrinsic system?

Answer 9

Short reflex arcs- enteric acts as a fast internal response to digestive stimuli PSNS + SNS can modulate activity in enteric

Question 10

What are neuromodulators? How are they different from neurotransmitters?

Answer 10

• usually secreted along with neurotransmitters
• can act to increase or decrease the amount of neurotransmitter released
• can act to modify the response of the post-synaptic cell

Question 11

The parasympathetic innervation of the GIT is supplied by which two nerves?

Answer 11

Vagus nerve (CN X) and pelvic nerve

Question 12

What specific structures does the vagus nerve innervate in the GIT?

Answer 12

Innervates upper GIT
striated muscle in upper third of esophagus, wall of stomach, small intestine and ascending colon

Question 13

What specific structures in the GIT does the pelvic nerve innervate?

Answer 13

Innervates lower GIT
Striated muscle of external anal canal, walls of transverse, descending and sigmoid colon

Question 14

Postganglionic neurons of peripheral nervous system are classified as what?

Answer 14

Cholinergic or peptidergic

Question 15

What neurotransmitters do cholinergic neurons release? What about peptidergic?

Answer 15

Cholinergic- Acetylcholine
Peptidergic- substance P, vasoactive inhibitory peptide (VIP), etc.

Question 16

What are vasovagal reflexes?

Answer 16

Reflexes in which both afferent and efferent limbs are contained in the vagus nerve

Question 17

Afferent fibers in the vagus nerve deliver sensory information from _________ to _________.

Answer 17

periphery (receptors in wall of GIT)
CNS

Question 18

Efferent fibers in vagus nerve deliver motor information from ________ to ________ ________.

Answer 18

CNS
Target tissues (smooth muscle, secretory, endocrine cells)

Question 19

The vagus nerve is ___% afferent fibers and ___% efferent fibers.

Answer 19

75%
25%

Question 20

Sympathetic nervous system has ______ preganglionic fibers that synapse in ganglia where?

Answer 20

Short
outside of the GIT

Question 21

List the four sympathetic ganglia that serve the GIT

Answer 21

Celiac
Cranial mesenteric
Caudal mesenteric
Hypogastric
The celiac+ cranial mesenteric ganglion together are known as the celiacomesenterical ganglia