1 B: Anatomy of GI wall / Intro to GI regulation

Question 1

Describe the lumen of the GI tract? Where are the contents located?

Answer 1

It is continuos with the external environment

-The contents are located within the lumen are technically OUTSIDE the BODY.

Question 2

Why is the GI tract lumen environment important?

Answer 2

B/c conditions essential to the digestive process can be tolerated in the GI tract lumen but are generally NOT TOLERATED in the BODY PROPER

Question 3

What happens when the contents escape from the GI tract lumen?
Examples?

Answer 3

The can produce symptoms that often indicate GI dysfunction

EX: Peptic ulcer disease (PUD) & Acute pancreatitis

Question 4

What is Peptic ulcer disease (PUD)?

Answer 4

Gastric juice that penetrates the gastric mucosal barrier, which injures the gastric wall with its “acidic & enzymatic contents”

Question 5

What is Acute Pancreatitis ?

What can this cause?

Answer 5

Pancreatic juice that escapes the pancreas and/or duodenum.

-The pancreatic digestive enzymes can cause the widespread destruction of pancreatic tissue & possible hemorrhage.

Question 6

What does the pathogenesis of Acute Pancreatitis involve?

Answer 6

Active secretion of pancreatic juice while the main pancreatic duct is obstructed at tis entrance into the duodenum.

Question 7

What does the build up of obstructed secretion cause?

Answer 7

Greatly increases the pressure within the duct system, causes the ducts to rupture & the pancreatic juice to escape.

Question 8

What occurs in the case of a ruptured appendix?

Answer 8

The colon wall tears open, allowing intestinal bacteria (flora) to escape to the abdominal & pelvic cavities, causing PERITONITIS or even DEATH.

Question 9

What are the 4 layers of the GI tract wall? (inner to outer)

Answer 9

1) Mucosa
2) Submucosa
3) Muscularis Externa
4) Serosa (Visceral peritoneum)

Question 10

How are some smooth muscle regulated (Autonomous Smooth muscle function) ?

Answer 10

Some are “pacemaker” cells that display rhythmic spontaneous variations in membrane potential

Question 11

What is the prominent type of self-induced electrical activity in digestive smooth muscle called?

Answer 11

Slow-wave potential

or alternatively called, Basal electrical rhythm (BER) or pacemaker potential

Question 12

What are the neurons of the submucosal & myenteric plexuses called?

Answer 12

The intrinsic nerve plexuses or enteric nervous system (ENS) “Brain in the GUT” (intrinsic nerves)

Question 13

What are the two kinds of neurons in the ENS ? Explain

Answer 13

1) SENSORY: Posses receptors that respond to specific local stimuli (pain) in the GI tract
2) MOTOR: Innervate smooth muscle cells, exocrine cells & endocrine cells of the GI tract ( to directly affect GI tract motility, secretion of digestive juices & secretion of GI hormones )

Question 14

What does the Motor neurons directly affect?

Answer 14

directly affects GI tract motility, secretion of digestive juices & secretion of GI hormones

Question 15

What are the extrinsic nerves (parasympathetic innervation) ?

Answer 15

Nerves that originate outside the GI tract & innervate the various GI organs

***Nerve fibers from both branches of the autonomic nervous system

Question 16

What innervates the upper GI tract?

Answer 16

The vagus nerves

Question 17

What does the vagus nerves innervate?

Answer 17

1) Esophagus
2) Stomach
3) small intestine
4) ascending colon

Question 18

The vagus nerves are mixed nerves in which 75% of the fibers are __________and 25% are ______________

Answer 18

75%= AFFERENT
25% = EFFERENT

Question 19

The lower GI tract is innervated by ?

Answer 19

The pelvic nerves (Pelvic splanchnic)

Question 20

What does the pelvic nerves innervate?

Answer 20

1) Transverse, descending & sigmoid colons

2) Anal canal

Question 21

Where are the pelvic nerves derived from ?

Answer 21

Spinal nerve pairs S2, S3, and S4

Question 22

What are the majority of parasympathetic post-ganglionic neurons servicing the GI system?

Answer 22

Cholinergic (acetylcholine) ; SOME are peptidergic (VIP, enkephalins, neuropeptide Y, substance P)

Question 23

What are the 3 sympathetic ganglia that serve the GI tract? Where is it located (Extrinsic Nerves) ?

Answer 23

1) Celiac
2) Superior mesenteric
3) Inferior mesenteric

***Thoracolumbar region

Question 24

What are these post-ganglionic fibers made up of?

Answer 24

Adrenergic (norepinephrine)

Question 25

Approximately 50% of the sympathetic nerve fibers are _______ and 50 % are _____________

Answer 25

Afferent and Efferent

Question 26

How does the Autonomic nerves influence GI tract motility and secretion by?

Answer 26

1) Modifying ongoing activity in the enteric nervous system
2) altering the level of GI hormone secretion
3) acting directly on smooth muscle and glands

Question 27

What makes up the Enteric nervous system?

Answer 27

1) Myenteric plexus

2) Submucosa plexus

Question 28

What do mucosa of certain regions of the GI tract contain?

Answer 28

Endocrine cells that secrete hormones

Question 29

How are GI hormones transported?

What do they exert ?

Answer 29

Thru blood to other areas of the GI tract or accessory GI structures

***Exert excitatory/inhibitory influences on smooth muscle & exocrine cells