Choudhury - Secretory Function of GI Tract: Salivary and Gastric

Question 1

List the constituents of saliva

Answer 1

0.5 % proteins, mucus, amylase, lysozyme

Question 2

Functional significance of saliva?

Answer 2

Functions of Saliva:

Taste
Lubrication
Protection
Digestion
Speech
Not essential for life

Question 3

Describe regulatory pathways for saliva production

Answer 3

•Parasymp ns stimulate secretion -Dominant

• increases IP3 (major), increase fluid secretion
  - vasodilation to surrounding blood vessels
  - activation of both acinar & duct cells transporter
  - releases kallikrein
  - greater influence than symp ns

•Symp ns stimulates secretion:

 - increases cAMP (major), increase amylase secretion
 - increases IP3 (minor), increase fluid secretion

Question 4

Describe ion transport pathways that modify saliva composition

Question 5

List conditions where saliva production may be abnormal (long ass list, be familiar for vinettes)

Answer 5

Printed.

Question 6

List common disorders of esophageal function

Question 7

Physiologic role of gastric acid secretion?

Question 8

Acetylcholine, gastrin, and histamine (function on parietal cells)

Answer 8

All stimulate release of HCl (activates pepsin, kills bacteria) and intrinsic factor (complexes with VB12 to permit absorption)

All three agonists (Acetylcholine, gastrin, and histamine) synergistically stimulate and potentiate acid secretion from parietal cell

Question 9

Parietal cell agonists:

Answer 9

All three agonists synergistically stimulate and

potentiate acid secretion from parietal cell

Question 10

Parietal cell receptors:

Answer 10

M3 receptors (ACh receptors)

H₂ receptors (histamine receptors)

CCK_B receptors (gastrin receptors)

Question 11

Secretagogues involved in gastric acid secretion:

Question 12

Describe the cephalic phase of the secretory response

Answer 12

30% of total gastric acid secretion -conditioned reflexes (thought, smell, taste, hypoglycemia

chewing, swallowing, hypoglycemia) send impulses to medulla oblangata which stimulates vagus nerve: -ACh acts on parietal cells to release acid -ACh acts on ECL cells to release histamine -ENS stimulate G cells to release gastrin -Chief cells release pepsinogen -Inhibits D cells, reduce release of somatostatin (somatostatin inhibits gastrin release)

Question 13

Describe the gastric phase of the secretory response

Answer 13

50-60% of total gastric acid secretion -food distends gastric mucosa -vagus & ENS reflexes activated -increase in acid and pepsinogen secretion –peptides (peptones) & a.a stimulate gastrin release

Question 14

Describe the intestinal phase of the secretory response

Answer 14

• peptides in duodenum stimulates gastrin secretion -chyme containing lipids or acid (pH 2) inhibits impulses from medulla oblangata and decrease vagal nerve stimulation, decrease acid secretion -duodenum releases 3 hormones-inhibits acid secretion
• Secretin
  
  • GIP (gastric inhibitory peptide) -

CCK (cholecystokinin)

Question 15

What controls saliva release?

Answer 15

Saliva is under neuronal control

not hormonal

(hormones modify)

Salivary acinar & ductal cells have both Symp and

** Parasymp innervation**

Question 16

Role of bicarbonate (HCO3-) in saliva?

Answer 16

minimizes tooth decay (neutralizes bacterial acid)

neutralizes refluxed gastric acid into lower esophagus (heartburn)

Question 17

Which cells of the salivary glands allow for a hypotonic secretion?

Answer 17

Ductal cells are water impermeable, water is not

absorbed along with the solute, water remains

in lumen and saliva is secreted hypotonic relative

to plasma

Question 18

Salivary secretion - rate and composition

Answer 18

Ionic composition of saliva changes as salivary flow rate changes

Duct cells modifies the composition of saliva

Faster flow rate = less hypotonic (less chance for the ductal cells to take the solutes back up, * except for K+ and HCO3-)

Question 19

Which side of the ductal cells require energy for pumps?

Answer 19

Basolateral membrane contains:

• Na +/K + ATPase and Cl channels

Question 20

What we need to know for neuronal regulation of salivary secretion:

Answer 20

Both Symp and Parasymp stimulates secretion
Parasymp stimulates more than Symp
Symp: major beta receptors: protein secretion, minor alpha receptors fluid secretion
Parasymp: major M3 receptors: fluid secretion

Question 21

Salivary secretion and composition are controlled solely by the autonomic nervous system, in contrast, other parts of the GI tract include local reflexes and hormonal mechanisms as well

Answer 21

Salivary secretion and composition are controlled solely by the autonomic nervous system, in contrast, other parts of the GI tract include local reflexes and hormonal mechanisms as well

Question 22

Gastric secretion - rate and composition

Answer 22

Inverse relationship between luminal concentration of H+ and Na+ as a function of the rate of gastric secretion

Question 23

pH of blood leaving the stomach?

Answer 23

Increased pH of venous blood leaving stomach following a meal is alkaline & referred to as alkaline tide

Question 24

Parietal cell agonists, agaaaaain:

Answer 24

Agonists: ACh, Gastrin and Histamine

all stimulate parietal cell to secrete acid

ACh binds to M3 receptors

Gastrin binds to CCKB receptors

      (gastrin 1500 X potent than

      histamine in releasing HCl)

Histamine binds to H2 receptors

Question 25

Inhibitors of parietal cells:

Answer 25

Inhibitors: Somatostatin and PGs directly binds to parietal cell and inhibits Histamine §Somatostatin binds to SST receptors §PGs binds to PGs receptors Both are linked to G protein (Gai) and oppose action of histamine and Gs

Question 26

Vagotomy details (cutting of vagus nerve):

Answer 26

- inhibits gastric acid secretion - used to treat peptic ulcers - side effects: delay in gastric emptying, diarrhea Selective vagotomy: -cutting vagal nerves supplying parietal cells only

Question 27

Secretin is referred to as what? Why?

Answer 27

Secretin is referred to as nature’s antacid Release by S cells of duodenum Stimulated by lower pH in duodenal lumen and by fatty acids Actions: increase pancreatic HCO3- sectretion (neutralizes H+); trophic effect on exocrine pancreas; increases bile production; decreases gastric acid production

Question 28

What is a selective vagotomy?

Answer 28

cutting vagal nerve fibers supplying parietal cells only

Question 29

Pernicious anemia

Answer 29

Absence of IF --\> decreased Vit B12 (not absorbed) --\> leads to anemia and even neurological symptoms (weakness, numbness) This produces macrocytic anemia (megablastic anemia) as B12 is required for DNA synthesis in RBC progenitor cell in bone marrow. Inflammation destroys parietal cells and chief cells, reducing acid secretion causing hypochloremic metabolic alkalosis Loss of feedback mechanism, gastrin levels rises sharply. Prolong B12 deficiency causes neurological symptoms

Question 30

Another name for Vit B12

Answer 30

Cobalamin

Question 31

Vit B12 deficiency caused by:

Answer 31

Decreased dietary intake (vegan) Decreased absorption - gastric resection (decreased IF) - autoimmune disease (antibody against parietal cells and IF)

Question 32

"1-2 questions on peptic ulcer disease"

Answer 32

damage to the mucosa can cause ulcers

Question 33

ASA and ulcers

Answer 33

•NSAIDS (aspirin) inhibits COX-1 - COX-1 forms PGs - PGs protects gastric mucosa ØAspirin (a weak acid) is easily absorbed in low pH of the stomach ØOnce absorbed it acts by acid stimulating histamine release and disruption of local mucosa ØAspirin suppresses protective mucosal barrier production

Question 34

Zollinger-Ellison syndrome

Answer 34

Tumor that causes excessive secretion of gastrin, which stimulates acid hyper-secretion

Question 35

Other causes of ulcers?

Answer 35

H. Pylori ( \> 80%) * Alcohol * Bile acid Stressful situations - physical - emotional

Question 36

Gastric ulcer disease's "vicious cycle"

Answer 36

* Acid and pepsin break through mucosal barrier * Acid stimulates histamine release * Histamine stimulates parietal cells to release acid * Acid diffuses through broken barrier * Vicious cycle continues

Question 37

Gastric Ulcer Disease

Answer 37

Gastrinoma or Zollinger-Ellison syndrome (increases gastrin secretion)

Question 38

Duodenal ulcer disease

Answer 38

* Occurs in the duodenum * Increase acid secretion in the gastric region * Pepsin remains active for too long * Decrease bicarbonate secretion from pancreas (pancreatitis)

Question 39

KNOW THIS

Answer 39

Gastric ulcers: H+, pepsin; less mucosal protection Peptic ulcers: H+, pepsin; less mucosal protection Duodenal ulcers: H+ and pepsin, 2-3 X more parietal cells than normal

Question 40

Gastric acid determination

Answer 40

* Serum gastrin levels and gastric acid secretion used to evaluate gastric function * Pentagastrin is used to stimulate acid secretion

Question 41

Gastrinoma or Zollinger-Ellison syndrome:

Answer 41

VINETTE: Serum gastrin "will be very highhhh" Pancreatic islet cell adenoma results - gastrin secretion stimulates parietal cells HCl secretion gastric acid secretion both at rest and after meal. Gastric and/or duodenal ulceration due to acid and pepsin activity

Question 42

Bacterium causing peptic ulcer disease?

Answer 42

Helicobacter pylori

Question 43

Things to know about increased H+ in the stomach (causes/tx's)

Answer 43

uHistamine potentiates effects of gastrin & ACh on parietal cells via H2 to release acid Inhibiting H2 will decrease H+ release in the stomach PPIs inhibits proton pump and decreases H+ release, increases gastric pH Long term side effects of PPIs usage are: Pneumonia Clostridium difficle growth in gut Osteoporosis

Question 44

READ SUMMARY

Answer 44

READ SUMMARY