3. DSA Intro to GI Physiology

Question 1

The main functions of the gastrointestinal tract is digestion and absorption of nutrients. What are the main properties?

Answer 1

Motility and secretions

Question 2

GI tract sphincters restrict the passage of intestinal content to optimize digestion and absorption. What are all 7 sphincters throughout the GI tract?

Answer 2

Upper esophageal sphincter (UES)
Lower Esophageal sphincter (LES)
Pylorus (end of stomach)
Sphincter of Oddi 
Ileocecal Valve
Internal anal sphincter
External anal sphincter

Question 3

What are the functional layers of the small intestine wall structure? (5)

Answer 3

Mucosal layer
Submucosa
Muscle Layers: Circular/Longitudinal
Serosa

Question 4

What are the two plexuses that make up the enteric nervous system (ENS) or nervous system of the GI tract?

Answer 4

Submucosal plexus

Myenteric plexus

Question 5

What consists of the mucosal layer of the intestinal wall? (3)

Answer 5

Epithelium, lamina propria, muscularis mucosae

Question 6

What consists of the muscularis propria of the intestinal wall? (3)

Answer 6

Myenteric plexus, circular muscle and longitudinal muscle

Question 7

The ENS is known as the second brain or little brain in the gut because it is innervated by the extrinsic autonomic nervous system and can exert functions without CNS input. What are the steps to get a response from the ENS? (4)

Answer 7

Stimuli in wall of gut
Sensory neuron
interneuron
motor neuron = Output Response!

Question 8

the ENS receives information from para/sympathetics, CNS, and sensory information from mechano/chemoreceptors in the mucosa. What does the ENS control? (3)

Answer 8

contraction
secretion
endocrine function

Question 9

The CNS has important roles in regulating GI function. What does it have?

Answer 9

the vago-vagal reflex (gastric receptice relaxation reflex)

Question 10

The vago-vagal reflex modulate ENS responses, as well, the centers that control food intake are in the brain. How does the reflex work?

Answer 10

Vagal afferents sent via nodose ganglion to the NTS (nucleus of th tractus solitarius) and back to the stomach via vagal efferents

Question 11

Parasympathetic innervations modulate the Gi functions via vagus and pelvic nerves. Where are pre/post ganglionic neurons and how do they synapse?

Answer 11

Preganglionic nerve cell bodies in brainstem/sacral spinal cord
Postganglionic neurons lie in wall of organ
Synapse via nicotinic (nAChRs)

Question 12

Sympathetic innervations via nerves running between SC and prevertebral ganglia, and between ganglia and GI. Where are the pre/post ganglionic and how do they synapse?

Answer 12

Preganglionic efferent arise in SC and end in prevertebral ganlia
Postganglionic from prevertebral to myenteric/submucosal plexuses
Synapse: pre: ACh post: NE

Question 13

Overview of parasympathetic innervation…?

Answer 13

CNS ganglion to PNS ganglion on the wall of the organ within plexus releasing ACh to nAchR. Goes to smooth muscle via ACh/mAChR

Question 14

Overview of sympathetic innervation?

Answer 14

CNS ganglion synapse before PNS via ACh/nAChR outside of GI tract. releases norepinephrine as effector to smooth muscle via ADRa or ADRb

Question 15

Cellular communication via paracrine regulation is key in GI regulation via for example somatostatin or histamine. What are the characteristics of paracrine regulation?

Answer 15

paracrine acts locally and signals reach their target cells by diffusion over short distances

Question 16

Somatostatin is secreted by D cells of the GI mucosa when there is a decrease in luminal pH. What are its actions? (2)
Where else is it secreted? (2)

Answer 16

inhibits gastric H+ secretion
Inhibits secretion of other GI hormones

(also secreted by hypothalamus and sigma cells of exocrine in pancreas)

Question 17

Histamine in the stomach is stored and secreted by enterochromaffin-like (ECL) cells in gastric glands. What is histamines target and action?

Answer 17

target is parietal cells to stimulate acid production

Question 18

GI is also regulated via endocrine regulation- the action of hormones. How are the hormones stored and secreted?

Answer 18

Enteroendocrine cells (EECs) contain secretary granules filled with hormones that are released upon stimulation and secreted into circulation to travel via blood (long distances) to target cells

Question 19

Gastrin is secreted from G cells of the stomach due to small peptides, distention of the stomach and vagal stimulation. What are its actions? (2)

Answer 19

Increase gastric H+ secretion

Stimulates growth of gastric mucosa

Question 20

Cholecystokinin (CCK) is secreted from I cells of the duodenum and jejunum due to small peptides/AA and fatty acids. What are its actions? (5)

Answer 20

1. Increase pancreatic enzyme secretion
2. Increase pancreatic HCO3- secretion
3. Stimulates contraction of the gallbladder and relaxation of the sphincter of oddi
4. Stimulates growth of exocrine pancreas and gallbladder
5. Inhibits gastric emptying (paracrine signaling)

Question 21

Secretin is secreted by S cells of the duodenum due to H+ or fatty acids in the duodenum. What are its actions? (4)

Answer 21

Increase pancreatic HCO3 secretion
Increase biliary HCO3 secretion
Decrease gastric H+ secretion
Inhibits trophic effect of gastrin on gastric mucosa (paracrine signaling)

Question 22

Glucose dependent insulinotropic peptide (GIP) is secreted by the duodenum and jejunum in response to fatty acids, AA, and oral glucose. What are its actions? (2)

Answer 22

increase insulin secretion from pancreatic B cells

decrease gastric H+ secretion

Question 23

What would be more effectin in increasing insulin secretion? Oral glucose or IV glucose? Why?

Answer 23

Oral because it stimulates GIP which stimulates insulin secretion and has direct stimulatory effects on B cells… Incretin effect

Question 24

Neural regulation is also a key cellular communication for regulation of GI. Action via NTs, need APs to release the NTs. How do NTs work?

Answer 24

They diffuse across the synapse and bind to their specific receptors in the postsynaptic cell

Question 25

Acetylcholine from cholinergic neurons have what actions? (5)

Answer 25

Contraction of smooth muscle in wall
relaxation of sphincters
increase salivary secretion
increase gastric secretion
increase pancreatic secretion

Question 26

Norepinephrine from adrenergic neurons have what actions? (3)

Answer 26

Relaxation of smooth muscle in wall
Contraction of sphincters
increase in salivary secretion

Question 27

Vasoactive intestinal peptide (VIP) from neurons of the ENS have what actions? (3)

Answer 27

Relaxation of smooth muscle
increase intestinal secretion
increase pancreatic secretion

Question 28

Nitric Oxide (NO) from neurons of the ENS has what action?

Answer 28

Relaxation of smooth muscle

Question 29

Gastrin-releasing peptide (GRP) from vagal neurons of the gastric mucosa has what action?

Answer 29

Increase in gastrin secretion

Question 30

Enkepahlins from neurons of the ENS has what actions? (2)

Answer 30

Contraction of smooth muscle

decrease in intestinal secretion

Question 31

Neurpeptide Y from neurons of the ENS has what actions (2)?

Answer 31

relaxation of smooth muscle

decrease intestinal secretion

Question 32

Substance P which is co-secreted with ACh by neurons of the ENS have what actions?

Answer 32

contraction of smooth muscle

increase in salivary secretion