GI 4

Question 1

Primary process of acid secretion from parietal

Answer 1

1. Free H+ actively transported across apical membrane
2. Water dissociates to H+ and OH- freeing more H+ to be actively transported out
3. OH- combines with CO2 via CA to generate HCO3
4. HCO3 exchanged with Cl at basolateral
5. Cl diffuses across apical through open channels

Question 2

What can the primary mechanism of acid secretion create

Answer 2

A lot of HCO3 in interstitial which can cause significant shift in pH of blood leading stomach
- short lived because pancreas

Question 3

What is secondary mechanism of acid secretion

Answer 3

CO2 joins H20 to become H2CO3 which dissociates to H+ which is regularly transported across apical and HCO3 transported across basolateral

Question 4

What happens with endocytosis of apical membrane of parietal cell

Answer 4

Channels internalized and cells not very active, cannot secrete a lot of H+

Question 5

What is the stimuli for acid secretion

Answer 5

Insertion of apical H+/K+ ATPase, Cl- and K+ transported stored in vesicles
Stimuli causes exocytosis and insertion of transporters which turns on acid secretion

Question 6

What is the negative regulator of acid secretion

Answer 6

Somatostatin

Question 7

What is excessive acid treated with

Answer 7

H2 receptor antagonists or proton pump inhibitors (H-K ATPase)

Question 8

What can inhibit acid secretion

Answer 8

Somatostatin
Intestinal hormones
Meds

Question 9

What is the short reflex of gastric acid secretion

Answer 9

• once food enters stomach (further reinforced)
• luminal distension, AAs and peptides increase gastrin secretion which stimulate parietal cells

Question 10

What is long reflex of gastric acid secretion

Answer 10

Cephalic phase (sight, though,etc)
Brain cause increase ENS activity
Stimulates G cells, ECL cells, parietal cells
Increases HCl

Question 11

What can increased HCl stimulate

Answer 11

D cells to increase somatostatin secretion to affect acid secretion

Question 12

Gastric digestive enzyme secretion process

Answer 12

Chief cells release pepsinogen and gastric lipase
Pepsinogen cleaved to pepsin by HCl
Pepsin breaks down protein to peptides

Question 13

What is gastric digestive enzymes stimulated by (secretion by chief cells)

Answer 13

Acid secretion via short reflex

Question 14

What does ECL release of histamine activate

Answer 14

H2 receptors on parietal cells to stimulate HCl secretion

Question 15

What does parietal cells release of intrinsic factor form

Answer 15

Complex with vit B12 so it can be absorbed

Question 16

What does D cells activation of somatostatin cause

Answer 16

Negative feedback for acid secretion (G cells, parietal cells, and ECL)
Inhibits pepsinogen release (inhibit chief cells)

Question 17

Food or cephalic reflexes initiate gastric secretion of what

Answer 17

Gastrin, histamine, and acid

Question 18

Gastrin stimulates what

Answer 18

Acid secretion by direct action on parietal cells

Question 19

What is indirect sitmulus of parietal cells

Answer 19

Histamine

Question 20

Acid stimulate what

Answer 20

Short reflex secretion of pepsinogen

Question 21

Mucus and HCO3 secreted from

Answer 21

Mucous cells (to prevent breakdown of epithelial cells)

Question 22

What is mucus secretion stimulated by

Answer 22

Parasympathetic input and irritation

Question 23

What is HCO3 secretion stimulated by

Answer 23

Parasympathetic input and H+

Question 24

What are the 2 mucous cell types

Answer 24

Mucous surface cell
Mucous neck cell

Question 25

What is the physical barrier

Answer 25

Mucus layer

Question 26

What is the chemical barrier that neutralizes acid

Answer 26

Bicarbonate

Question 27

What is a peptic ulcer

Answer 27

Sore or break in lining of stomach or duodenum (acid + digestive enzymes break down)

Question 28

What is peptic ulcers caused by

Answer 28

Excessive acid production (gastrin secreting tumors) Nonsteroidal anti-inflammatory drugs (chronic use, aspirin, ibuprofen) H. Pylori

Question 29

What was believed to cause ulcer

Answer 29

Stress, spicy foods, over production of acid

Question 30

What was finally hypothesized to cause ulcers

Answer 30

Bacteria

Question 31

How does H.pylori cross mucus layer

Answer 31

Urease inside breaks down urea into NH3 and CO2 Creates buffer zone around themselves Buffer attracted to HCO3 and mucus layer Mucus layer breaks down and exposes epithelia

Question 32

How much food, fluid, secretions enter small intestine

Answer 32

5.5 L and additional 3.5 L added from hepatic, pancreatic, and intestinal

Question 33

Why is motility in small intestine regulated

Answer 33

To ensure proper digestion and absorption

Question 34

What type of contraction mix chyme in small intestine

Answer 34

Combination of segmental and peristaltic

Question 35

What does contractions in sm int cause

Answer 35

Mix chyme with enzymes Expose nutrients to mucosal epithelium for absorption

Question 36

Where is most absorption in sm int

Answer 36

7.5L in duodenum and jejenum (most in jejenu)

Question 37

What promotes and inhibits motility in sm int

Answer 37

Parasympathetic innervation, gastrin, and cholecystokinin promotes Sympathetic innervation inhibits

Question 38

What increase surface area in sm int

Answer 38

Plicae (large folds), villi, microvilli

Question 39

What do villi do

Answer 39

Increase surface area available for absorption and secrete mucus (goblet cells)

Question 40

What do crypts do

Answer 40

Contain hormone and fluid secretory cells and stem cells

Question 41

Where are most nutrients in sm int absorbed into

Answer 41

Capillaries in villi

Question 42

What do lateals of lymph vessels transport

Answer 42

Most fats to lymph

Question 43

What are brush border enzymes

Answer 43

Enzymes stay attached to microvilli

Question 44

Where does venous blood go from GI tract

Answer 44

Hepatic portal system Liver acts as biological filter

Question 45

What does the liver acting as biological filter do

Answer 45

Contains variety of enzymes that metabolize drugs and xenobiotics and clear them from the blood stream before it proceeds to systemic circulation

Question 46

Why do drugs given orally have higher dose then IV

Answer 46

Absorbed in GI then metabolized in liver then travels through systemic

Question 47

How much secretions enter lumen of sm int

Answer 47

3.5 L

Question 48

What 5 types of secretions enter sm it

Answer 48

Digestive enzymes (brush border and pancreas) Bile Bicarbonate (pancreas) Mucus (goblet cells) Isotonic saline (crypt cells)

Question 49

What do mucus and isotonic saline do

Answer 49

Lubricate contents of gut

Question 50

How is isotonic saline produced

Answer 50

1. Na, K+, and CL- enter by cotransport 2. Cl enters lumen through CFTR 3. Na+ is reabsorbed 4. Negative CL in lumen attracts Na by paracellular pathway 5. Water follows