HRR: secretions and motility III

Question 1

What are secretions of the LES and cardia?

Answer 1

Mucus and bicarb

Question 2

What is unique about the cardia of the stomach?

Answer 2

It has the oblique layer of muscle in the ME. It helps the valve function of the LES

Question 3

What are secretions of the fundus and body?

Answer 3

Protons, IF, mucus, bicarb, lipase, pepsinogens

Question 4

What motility functions occur in the fundus and body?

Answer 4

Reservoir, tonic force during emptying

Question 5

What are secretions of the antrum and pylorus?

Answer 5

Mucus and bicarb

Question 6

What motility functions occur in the antrum and pylorus?

Answer 6

Mixing, grindings, regulation of emptying

Question 7

What do surface epithelial cells do?

Answer 7

Secrete bicarb and mucous to protect the epithelium

Question 8

What do mucus neck cells do?

Answer 8

Secrete mucus; higher in cardia and antral regions

Question 9

What do parietal cells do?

Answer 9

Secrete HCL and IF. Higher amount in body and fundus

Question 10

What do chief cells do?

Answer 10

Secrete pepsinogens

Question 11

What do enterochromaffin cells do?

Answer 11

Secrete histamine

Question 12

What do D cells do?

Answer 12

Secrete somatostatin

Question 13

When are stomach acids produced?

Answer 13

Prior to the gastric phase; their production is initiated in the cephalic and oral phases from vagal stimulation

Question 14

What are the stimuli for increased gastric acid secretion during the gastric phase?

Answer 14

Distension of the stomach and partially digested proteins or amino acids sensed by G cells

Question 15

Describe what happens when food enters the stomach and causes distension.

Answer 15

The vagovagal reflex is activated, resulting in ach and GRP release that will lead to activation of parietal cells. Local ENS reflex pathways are also activated, leading to Ach release and further activation of parietal cells

Question 16

Describe how partially digested proteins increase gastric acid secretion.

Answer 16

G cells sense the proteins and secrete gastrin that will act on parietal cells to increase HCL secretion. Enterochromaffin cells will secrete histamine and activate parietal cells

Question 17

Which cells does vagal efferent outflow impact?

Answer 17

Parietal cells, ECL cells, G cells, and chief cells

Question 18

How does the vagus nerve impact the stomach?

Answer 18

Through the enteric nervous system

Question 19

What stimulates parietal cells to make acid?

Answer 19

Gastrin, ach, histamine

Question 20

What receptor in the parietal cell responds to gastrin?

Answer 20

CCK2

Question 21

What receptor in the parietal cell responds to histamine?

Answer 21

H2

Question 22

What molecules are inhibitory for parietal cells?

Answer 22

Somatostatin and prostaglandin

Question 23

Describe what happens to parietal cells upon stimulation to become activated.

Answer 23

They undergo cytoskeletal rearrangement, resulting in fusing of tubulovesicular and canalicular membranes. This increases their surface area. They also add a bunch of HK pumps, K channels, and Cl channels to the canalicular membrane

Question 24

How do parietal cells produce acid?

Answer 24

Water and CO2 enter the cell, where carbonic anhydrase forms carbonic acid. Carbonic acid dissociates into H and bicarb. The proton will be secreted into the lumen by the HK pump, and the bicarb gets exchanged into the blood

Question 25

What is the major pump for protons to move into the gastric lumen?

Answer 25

HK pump

Question 26

What do D cells do?

Answer 26

Sense when the pH falls below 3. When this happens, they secrete somatostatin to inhibit gastrin secretion to decrease parietal cell function and HCL secretion

Question 27

What are some effects of somatostatin?

Answer 27

Splanchnic vasoconstriction, decreases pepsinogen secretion, reduces pancreatic enzyme and bile secretion, and overall reduces GI motility and gastric emptying

Question 28

What happens to gastric pH when we eat a meal?

Answer 28

It actually will initially drop! The food we eat is more neutral than stomach pH.

Question 29

What is a gastrinoma?

Answer 29

A neuroendocrine tumor that produces gastrin autonomously; it does not respond to negative feedback. This overwhelms the stomach and may lead to ulcers, heartburn, and diarrhea

Question 30

What is autoimmune atrophic gastritis?

Answer 30

Antibody and T cell mediated destruction of parietal cells that causes a lack of IF secretion leading to pernicious anemia as well as low HCl secretion that causes iron deficiency and high gastrin

Question 31

What can cause chronic atrophic gastritis?

Answer 31

H pylori

Question 32

What is the main stimulator of chief cells?

Answer 32

Ach

Question 33

What is pepsinogen?

Answer 33

Inactive proenzyme of pepsin secreted by chief cells

Question 34

What is required for pepsinogen activation?

Answer 34

Low pH

Question 35

When does pepsin become inactivated?

Answer 35

In the neutral environment of the duodenum

Question 36

Describe how NSAIDs impact the GI system.

Answer 36

They inhibit prostaglandin production. Normally, prostaglandins reduce gastric acid secretion and stimulate gastric mucus and bicarb secretion. Inhibiting prostaglandins leads to more stomach acid and potential damage to gastric epithelium

Question 37

How does the stomach achieve emptying?

Answer 37

Contraction of proximal and distal stomach and relaxation of pyloric sphincter

Question 38

What is adaptive relaxation?

Answer 38

Relaxation of the stomach in response to food entering

Question 39

Describe the process of adaptive relaxation.

Answer 39

Mechanoreceptors sense distension, leading vagal afferent nerves to signal the vagal ganglion, then vagal efferent nerves stimulating ENS to relax smooth muscle. The ENS itself will also stimulate interneurons followed by motor neurons to stimulate relaxation of smooth muscle

Question 40

Which portion of the stomach has thicker muscle: proximal or distal? Why?

Answer 40

Distal to aid in churning and mixing to create chyme

Question 41

What impacts the rate of gastric emptying?

Answer 41

Food composition, volume, medications, nerve/muscle conditions, and hormones

Question 42

Which macronutrient empties the fastest?

Answer 42

Carbs

Question 43

Describe the process of gastric emptying.

Answer 43

As gastric contents become chyme, antral contraction and transient relaxation of the pyloric sphincter results in some entering the duodenum. The proximal stomach will increase tone and distal stomach contractions become more forceful to propel chyme into the transient openings of pyloric sphincter and into the duodenum. When pylorus is open, distal portion relaxes and chyme just flows

Question 44

What is the enterogastric reflex?

Answer 44

The process by which signals travel to the CNS resulting from duodenum sensing distention/fats, followed by signals back to the GI tract to stop gastric emptying, decrease gastric motility, and decrease gastric acid production

Question 45

What is gastroparesis?

Answer 45

Delayed emptying of the stomach due to damage to the stomach's neural network and interstitial cells of cajal

Question 46

What is the most common cause of gastroparesis?

Answer 46

Diabetes