Salivation and Gastric Function

Question 1

how are GI hormones delivered?

Answer 1

they are secreted into capillaries, go through the liver and return in the systemic blood

Question 2

what is paracrine signaling and what are the three main factors?

Answer 2

chemicals that act in the same tissue that secretes them
serotonin (excites ENS), somatostatin (inhibits pancreatic and gastric secretion and motility) and histamine (stimulates HCl secretion with H2 receptors)

Question 3

what are neurocrine signals?

Answer 3

signaling molecules synthesized in ENS neurons and released with action potential (neurotransmitters)

Question 4

where is gastrin secreted and what does it do?

Answer 4

secreted by antral mucosa (G cells)- distension and vagus

increases parietal cell action and mucosal growth

Question 5

what is CCK secreted by and what does it do?

Answer 5

in duodenum and jejunal I cells- fats and protein

gall bladder contraction, increases pancreatic enzyme and bicarbonate secretion and inhibits gastric emptying

Question 6

where is secretin secreted and what does it do?

Answer 6

duodenum (S cells)- acidic chyme

increases bicarb and fluid secretion, decreases gastric acid secretion (decreases gastrin), inhibits gastric empty

Question 7

where is motilin secreted and what does it do?

Answer 7

small intestine mucosa (M cells) during fasting

promotes clearance of indigestible materials

Question 8

where is glucose dependent insulinopic peptide (GIP) secreted and what does it do?

Answer 8

small intestine mucosa (K cells)- fat and carbohydrates

stimulates insulin secretion and inhibits HCl secretion

Question 9

digestion of what materials is initiated in the mouth?

Answer 9

carbohydrates and lippids

Question 10

what type of digestion occurs in the stomach?

Answer 10

protein and lipid (salivary amylase denatured by acid)

Question 11

where are enzymes in the small intestine located?

Answer 11

secreted into the lumen or anchored to the brush border

Question 12

what is the function of saliva?

Answer 12

to lubricate (mucus)
protect (clear bacteria off teeth and substances that reduce bacterial growth)
digest (salivary amylase and lingual lipase)

Question 13

what is secreted by acinar cells?

Answer 13

alpha amylase and watery substance

Question 14

what is sjogren syndrome?

Answer 14

autoimmune disease that destroys salivary and lacrimal glands

Question 15

what is xerostomia?

Answer 15

dry mouth

Question 16

describe the secretions from salivary glands

Answer 16

basal flow rates: high in K and low in Na and Cl (reabsorbed)
high flow rates: saliva more like plasma with higher bicarb

Question 17

what is the only agent that affects salivation?

Answer 17

aldosterone- stimulates Na reabsorption and K secretion

Question 18

where is lingual lipase added to the saliva?

Answer 18

in the mouth

Question 19

what controls salivary secretion

Answer 19

ANS (unaffected by GI hormones)
PNS increases and sustains secretion
SNS more transient stimulation

Question 20

what types of mouthfeel stimulate salivation

Answer 20

smooth tactile stimuli- not rough

Question 21

responses to what GI upset causes salivation?

Answer 21

stomach and small intestine with irritation or nausea

Question 22

what does the activation of salivary glands cause?

Answer 22

release of kallikrein- results in bradykinin production

vasodilation of capillary increases filtration

Question 23

where are oxyntic glands located and what cell types do they contain?

Answer 23

in body and fundus

mucous neck cells (mucous), chief cells (pepsinogen and gastric lipase) and parietal cells (IF and HCl)

Question 24

what occurs when parietal cells are destroled?

Answer 24

achlorhydria and perinicious anemia

Question 25

what do pyloric glands do? where are they located?

Answer 25

secrete mucus for protenction, gastrin and somatostatin | ;pcated om tje amtri,

Question 26

what do cardiac glands secrete and where are they?

Answer 26

mucus- near LES

Question 27

what stimulates oxyntic glands?

Answer 27

vagus and ENs

Question 28

what type of enzyme is pepsin and how is it made

Answer 28

endopeptidase | activated from pepsinogen by HCl (pH 3-5) by removing N terminal

Question 29

what does mucus do in the stomach?

Answer 29

prevents H+ and pepsin access to mucosa | traps bicarb to be a buffer to H+ and inactivate pepsin

Question 30

what occurs if H+ reaches the gastric mucosa

Answer 30

degranulation of mast cells increasing blood flow and mucous and bicarb production

Question 31

what is erosive gastritis and what is it caused by

Answer 31

decreases secretion of mucus and bicarbonate | chronic NSAID use that inhibits prostaglandin synthesis in stomach

Question 32

what is the main driving force for HCl secretion by parietal cell?

Answer 32

H+ K+ ATP ase in the luminal membrane Cl follows by diffusion through channels (targeted by proton pump inhibitors)

Question 33

where do the H+ ions come from in parietal cells?

Answer 33

CO2 enters the cell and becomes an acid- dissociates into H+ and bicarb H+ transported into lumen and HCO3- transported into blood with Cl exchanger

Question 34

where is the vomiting center? what does it cause?

Answer 34

in the medulla | causes salivation, reverse peristalsis, relaxation of UES and expulsion of contents through the mouth

Question 35

name 4 stimuli that initiate vomiting

Answer 35

irritants in stomach or SI systemic irritant sensed by 4th ventricle chemoreceptor head injury abnormal stimulation of vestibular organs

Question 36

what does prolonged vomiting cause?

Answer 36

dehydration, lakalosis, hypokalemia

Question 37

what are 6 stimulators of acid secretion?

Answer 37

vagus (direct and indirect), gastrin (acts on cell and triggers histamine), histamine, insulin, caffeine (increases proton pump) and stress

Question 38

what are inhibitors of acid secretion?

Answer 38

somatostatin (acts on G cells and parietal cells), GIP (acts on parietal cells) and secretin (acts on G cells)

Question 39

describe the action of ACh and gastrin on parietal cells.

Answer 39

activate G coupled receptors (separate)> activate phospholipase C> activates protein kinase C> increases intracellular Ca

Question 40

describe the action of histamine on parietal cells

Answer 40

binds to H2 receptor (g coupled) >activation of adenlyly cyclase> cAMP increase> PKA activation

Question 41

describe the action of somatostatin and prostaglandins on parietal cells

Answer 41

separate g linked receptors that oppose the action of histamine (decrease cAMP

Question 42

what do H2 receptor antagonists do?

Answer 42

OTC antacid agents, decrease HCl production

Question 43

what do proton pump inhibitors do?

Answer 43

block final common pathway of all secretagogues (more effective than histamine antagonists)

Question 44

describe the cephalic phase

Answer 44

smelling and tasting vagus directly stimulates parietal cells indirect stimulation by gastrin productions (gastrin releasing peptide)

Question 45

describe the gastric phase

Answer 45

distension of the stomach and presence of amino acids direct and indirect vagal parietal stimulation distension of antrum and AA> gastrin releasing reflex

Question 46

describe the intestinal phase

Answer 46

mediated by amino acids | only 10% of gastric acid secretion

Question 47

when is HCl secretion inhibited? what is the major mediator of this?

Answer 47

when it is no longer needed to activate pepsinogen | somatostatin through direct and indirect effects

Question 48

what does vagal stimulation of D cells do?

Answer 48

inhibits the release of somatostatin

Question 49

what are the negative and positive feedback mechanisms of HCl release?

Answer 49

luminal H+ causes release of somatostatin | protein digestion products stimulate gastrin secretion