Guyton Physiology

Question 1

What are the layers of the intestinal wall?

Answer 1

serosa
muscularis
submucosa
mucosa

Question 2

What are the two types of electrical waves in the intestinal smooth muscles?

Answer 2

slow wave
spike potentials

Question 3

What is the function of the interstitial cells of Cajal

Answer 3

produce the slow waves - electrical pacemakers

Question 4

What is the threshold potential of intestinal smooth muscle cells?

Answer 4

• 40

Question 5

List 3 factors that make the intestinal smooth muscle membranes more excitable

Answer 5

stretch
ACh
several GI hormones (from food e.g.,)

Question 6

What protein mediates the intestinal muscle activation caused by IC Ca++ entry

Answer 6

calmodulin

Question 7

What are the two plexuses of the enteric nervous system? What are their main functions?

Answer 7

submucosal plexus - Auerbach’s
myenteric plexus - Meissner’s plexus

Question 8

What is the function of the inhibitory effects of the myenteric plexus?

Answer 8

inhibit sphincter muscles

Question 9

What are the divisions of the intestinal parasympathetic enteric nervous system?

Answer 9

cranial and sacral divisions

Question 10

Explain the gastrocolic reflex

Answer 10

food enters the stomach –> stretch –> prevertebral sympathetic ganglia –> colon –> evacuation

Question 10

Explain the enterogastric reflex

Answer 10

duodenum stretched, filled with acid/food –> prevertebral sympathetic ganglia –> stomach emptying inhibited

Question 10

Explain the colonoileal reflex

Answer 10

colon filled –> prevertebral sympathetic ganglia –> inhibit ileal emptying

Question 11

What are the three types of gastrointestinal reflexed (in terms of how high they travel up and back down the nervous system)

Answer 11

• reflexes that travel just within the enteric nervous system within the gut wall
• reflexes that travel from the enteric system to the prevertebral ganglia and back to the GI tract
• reflexes that travel from the GI tract to the spinal cord or brain stem –> back to the GI tract (e.g., defecation reflex)

Question 12

For gastrin: Where is it produced, what is its stimulus, and what is its effect?

Answer 12

G-cells
leads to gastric acid secretions
stimulated by meal ingestion (stomach distention, protein products)

Question 13

For cholecystokinin (CKK): Where is it produced, what is its stimulus, and what is its effect?

Answer 13

produced by I-cells (duodenum, jejunum)
stimulus: food entering the duodenum, fat and fatty acids
effect: gall bladder emptying, inhibits stomach contractions

Question 14

For secretin: Where is it produced, what is its stimulus, and what is its effect?

Answer 14

produced in S-cells
stimulus: gastric acid entering the duodenum
effect: induces pancreatic bicarbonate secretion

Question 15

For glucose-dependent insulinotropic peptide: Where is it produced, what is its stimulus, and what is its effect?

Answer 15

produced by the mucosa of the upper SI
stimulus: fatty acids in the duodenum
effect: slows gastric emptying

Question 16

For motilin: Where is it produced, what is its stimulus, and what is its effect?

Answer 16

produced by the stomach and upper duodenum
stimulus: fasting
effect: interdigestive myoelectric complexes

Question 17

What are the two functional movements of the GI tract?

Answer 17

• propulsive
• mixing

Question 18

What is the main stimulus for peristalsis

Answer 18

stretching/distention

Question 19

How far does each peristaltic contraction usually travel?

Answer 19

5-10 cm

Question 20

List all organs included in the splanchnic circulation

Answer 20

GI tract, pancreas, spleen, liver

Question 21

List mechanisms by which GI gut flow increases after a meal

Answer 21

• vasodilatory substances released after meal (cholecystokinin, vasoactive intestinal peptide, gastrin, secretin)
• kinins (e.g., bradykinin)
• decreased O2 from increased metabolism triggering increased blood flow
• adenosine

Question 22

Why are the intestinal villi especially at risk for ischemic death from decreased local blood flow or circulatory shock?

Answer 22

Counter arterial and venous blood flow exchanges O2, I.e., arteriole give O2 to venules, so most O2 doesn’t even reach the tip of the villi
already lower O2 environment –> if circulation drops further –> ischemic injuries

Question 23

How does the musculature of the esophagus differ between dogs and cats?

Answer 23

dog: all striated cat: 2/3 striated, bottom 1/3 smooth

Question 24

What are the triggers that slow stomach emptying

Answer 24

* stretch of duodenum * fat, protein products and gastric acid in the duodenum * osmolality of the chyme * irritants in the duodenum

Question 25

Name 3 hormones, slowing gastric emptying

Answer 25

* cholecystokinin * secretin * gastric inhibitory peptide (=glucose-dependent insulinotropic polypeptide)

Question 26

How fast do peristaltic waves travel through the intestines, and how far do they typically reach?

Answer 26

0.5-2cm/second 3-5 cm, cannot travel further than 10cm

Question 27

Describe the difference between the gastroenteric and the enterogastric reflexes

Answer 27

gastroenteric --> full stomach triggers duodenal peristaltic activity enterogastric --> overfilled duodenum inhibits further gastric emptying

Question 28

Describe the gastroileal reflex

Answer 28

ileocecal valve usually blocks chyme from moving forward - opening of the valve is triggered by an additional meal

Question 29

Describe how small intestinal diarrhea develops

Answer 29

excessive SI peristaltic movements caused by irritation from infection or chemicals ("peristaltic rush")

Question 30

What are the 2 reflexes initiating mass reflexes of the colon

Answer 30

* intrinsic reflex - opens the internal anal sphincter when feces reaches the rectum * parasympathetic defecation reflex - more powerfully opens the internal anal sphincter note: external anal sphincter must be opened voluntarily

Question 31

Explain how peritonitis, kidney, or urinary bladder disease may cause ileus

Answer 31

inflammation of the peritoneum --> peritoneointestinal reflex --> intestinal paralyzsis renointestinal and viscerointestinal reflexes also cause inhibition

Question 32

How does the saliva's electrolyte/ionic composition differ from plasma?

Answer 32

high K, high bicarbonate, low Na and Cl

Question 33

Describe the secretory cells of the oxyntic gland and what they secrete

Answer 33

peptic cells/chief cells - pepsinogen parietal cells/oxyntic cells- HCl + intrinsic factor enterochromaffin-like cells - histamine

Question 34

What is the pH of concentrated hydrochloric acid?

Answer 34

0.8

Question 35

Describe how parietal cells secrete hydrochloric acid

Answer 35

CO2 and H2O via carbonic anhydrase become H+ and HCO3- H+ is transported out of the cell with countercurrent with K+ (KHATPase pump) HCO3- exits on basolateral membrane in exchange for Cl- --> Cl- then enters lumen through Cl- channel --> HCl formed

Question 36

What is intrinsic factor?

Answer 36

essential factor for vitamin B12 absorption secreted also by parietal cells

Question 37

How is pepsinogen activated?

Answer 37

in the presence of HCl

Question 38

What do the pyloric glands produce?

Answer 38

mucous gastrin (G cells)

Question 39

How does gastrin affect gastric acid secretion?

Answer 39

gastrin stimulates acid secretion gastrin stimulates histamine release by the enterochromaffin-like cells in the oxyntic glands --> histamine is an important trigger for parietal cells' HCl production

Question 40

What inhibits gastric secretions?

Answer 40

* distention of the SI * acid in the SI * food products (protein, fat) in SI * hyper or hypoosmolar chyme in SI --> releases secretin --> opposes acid secretion