Physiology Upper GI

Question 1

How is saliva formed?

Answer 1

1. Formed in acinus
2. Modified as it flows down ducts (Cl- exchanged for HCO3-, Na+ exchanged for K+)

Ducts IMPERMEABLE to H2O
PS activity increases secretion rate

Question 2

What affect does the stimulation of saliva do to its composition?

Answer 2

High secretion rate = less time to remove Na & Cl so their conc increases

Question 3

What happens in the oral phase of swallowing?

Answer 3

Voluntary

Tongue stimulates mechanoreceptors in hard palate

Question 4

What happens in the pharyngeal phase of swallowing?

Answer 4

Involuntary

Larynx rises, epiglottis closes entrance to trachea = deglutition apnea = temporary inhibition respiratory ventilation

Question 5

What happens in the oesophageal phase of swallowing?

Answer 5

Receptive relaxation ahead of bolus
Vagovagal reflex
Upper 1/3 = striated = brainstem control
Lower 2/3 = smooth muscle = ENS control

Question 6

What do G cells release?

Answer 6

Gastrin

Question 7

What do D cells release?

Answer 7

Somatostatin

Question 8

What so H cells release?

Answer 8

Histamine

Question 9

What do cheif cells release?

Answer 9

Pepsinogen

Question 10

What do parietal cells release?

Answer 10

HCL

Question 11

What is the effect of excessive alcohol on mucus production?

Answer 11

= Excess mucus production = ulceration as protective effect of HCO3- limited

Question 12

What happens when parietal cells are at rest?

Answer 12

Proton pumps in tubulovesicles of cells - locked away -> Quiescent

Question 13

What happens when parietal cells are stimulated?

Answer 13

Proton pumps activates as tubulovesicles fuse with apical membrane -> enlarging cannaliculus
H/K/ATPase in vesicle membranes

Question 14

How is HCL secreted?

Answer 14

Ionisation of water = H+
H/K/ATPase pump in apical membrane
HCO3- exchanged with Cl- in basolateral membrane

Question 15

What happens in the cephalic phase of digestion?

Answer 15

• stimulated by sight, smell, taste
• secretion of ACh
• G cells secrete gastrin = parietal cells release HCL, Cheif cells release pepsinogen

Question 16

What happens in the gastric phase of digestion?

Answer 16

• due to stomach distention
• vagovagal reflex = ACh secretion
• low pH INHIBITS gastric secretion (somatostatin released from D cells)

Question 17

What happens in the intestinal phase of digestion?

Answer 17

• stimulated by protein digestion
• duodenal release of gastrin (= response to increased protein digestion) -> STIMULATORY
• duodenal release of secretin (= response to increased acid) + CCK + GIP (= response to increased fat digestion) -> INHIBITORY

Question 18

What effect does histamine have on parietal cells?

Answer 18

Potentiates effect of gastrin = HCL secretion

Question 19

What effect does somatostatin have on parietal cells?

Answer 19

Switches off HCL secretion

Question 20

What effect does prostaglandin have on parietal cells?

Answer 20

Helps keep HCL secretion switched off

Question 21

What effect do fats have on gastric emptying?

Answer 21

Inhibitory

Question 22

What neural feedback control switches off acid secretion?

Answer 22

Withdrawal of vagal activity and increase in splanchnic nerve activity (sympathetic)

Question 23

What effect do enterogastrones have on gastrin secretion?

Answer 23

Inhibitory

Released from small intestine

Question 24

How is gastrin secretion inhibited in the gastric phase?

Answer 24

low pH - H+ acts on D cells = increased inhibitory effects of Somatostatin on G cells = reduces gastrin release

Question 25

What enterogastrone enters the intestinal phase in response to FA's?

Answer 25

GIP released by K cells - inhibits gastric secretion | CCK released by I cells (also response to AA's)

Question 26

What enterogastrone enters the intestinal phase in response to H+?

Answer 26

Secretin released by S cells - stimulates D cells to release somatostatin...

Question 27

What is the key difference between pancreatic and saliva secretion?

Answer 27

Ducts in pancreatic acinus = PERMEABLE to H2O

Question 28

Where are Acinar cells and what is their function?

Answer 28

Pancreas Secrete enzymes + Cl- rich sol Stimulated by CCK + ACh

Question 29

Where are Duct cells and what is their function?

Answer 29

Pancreas Secrete HCO3- rich sol Stimulated by secretin

Question 30

How do Duct cells modify acinar secretion?

Answer 30

Using Carbonic hydrase, apical HCO3/Cl exchange + basolateral Na/H exchange

Question 31

What are Duct cell agonists and how do they work?

Answer 31

Secretin & ACh - stimulate HCO3/Cl exchange

Question 32

What happens in the cephalic stage of pancreatic secretion?

Answer 32

Duct cells + Acinar cells activated via PS vagal efferent nerves

Question 33

What happens in the gastric stage of pancreatic secretion?

Answer 33

- Acinar stimulated via gastrin | - Acinar + Duct stimulates via vagovagal reflex

Question 34

What happens in the intestinal stage of pancreatic secretion?

Answer 34

- Acinar (CCK) release enzyme rich | - Duct (secretin) release bicarb rich

Question 35

What effects does CCK have on the gallblader and sphincter of oddi?

Answer 35

Contracts GB and relaxes sphincter

Question 36

What are the 2 mechanisms of bile secretion?

Answer 36

BAD-bile acid dependent 1 - depends on rate of bile return | BAI-bile acid independent 2 - depends on secretion of electrolytes + water

Question 37

What effects do choleretics and cholagogues have on bile secretion?

Answer 37

Increase rate of bile secretion