Gastrointestinal secretions: pancreas, saliva, bile

Question 1

volume of secretions produced daily

Answer 1

7L

Question 2

types of secretion

Answer 2

salivary, gastric, pancreatic and biliary

Question 3

average production of saliva

Answer 3

1.5 L per day

Question 4

three types of salivary gland plus composition of saliva

Answer 4

parotid- watery, serous

submandibular- serous and mucous

sublingual- mucous

Question 5

functions of serous saliva

Answer 5

moistening oral mucosa

dissolving enzymes

lubrication of speech

germicidal protection

teeth protection

Question 6

mucous component function

Answer 6

lubrication

diffusion barrier to nutrients, drugs and toxins

binding bacteria, viruses and parasites

protection against proteases

Question 7

two stages of saliva production + location

Answer 7

primary secretion- within acinus

secondary modification- along intralobular ducts

Question 8

stages of primary secretion

Answer 8

1. basolateral Na/K pump creates inward sodium gradient
2. this results in potassium moving out basally and apically
3. basolateral NK2CC symporter moves ions into the cell from the blood
4. chloride accumulates then diffuses apically through a chloride bicarbonate symporter in the lumen
5. chloride in the lumen makes it negative, pulling sodium paracellularly alongside water

Question 9

stages of secondary modification

Answer 9

1. sodium is absorbed through ENaC and apical sodium hydrogen exchanger (NHE4) - exits into body via sodium potassium pump
2. potassium diffuses into the saliva via potassium hydrogen exchanger
3. chloride reabsorbed by chloride bicarbonate apical exchanger, then exits into blood via basolateral chloride channels

bicarbonate ions initially formed in cell due to carbonic anhydrase

Question 10

water permeability in salivary glands

Answer 10

high in acinus, lower in ducts

Question 11

composition of saliva

Answer 11

high bicarbonate and potassium

hypotonic

Question 12

protein components of saliva

Answer 12

alpha amylase, lingual lipase, mucins, kallikrein, lysozymes

Question 13

main regulation of saliva secretion

Answer 13

autonomic parasympathetic

Question 14

stages of autonomic regulation

Answer 14

1. parasympathetic nerves IX and X release ACh
2. ACh binds to M3 GqPCR on basolateral membrane
3. increases IP3, increases calcium secretion
4. more calcium activates PKC

Question 15

PKC functions

Answer 15

phosphorylates chloride and potassium channels

phosphorylation of cytoskeletal elements which induces export of vesicles containing enzymes

myoepithelial cell contraction, secrete contents

Question 16

stages of sympathetic regulation

Answer 16

1. superior cervical ganglion leads to release of noradrenaline
2. NA binds to alpha receptors , mobilises calcium release by IP3
3. NA binds to beta receptors raising cAMP activating PKA and stimulates vesicle release

Question 17

volume of daily pancreatic secretions

Answer 17

1.5L per day

Question 18

protein components of pancreatic juice

Answer 18

zymogens of proteases

amylases, lipases, nucleases, protease inhibitors

Question 19

pancreatic primary secretion stages

Answer 19

1. sodium potassium pump lowers sodium inner concentration
2. basolateral NK2CC utilises gradient, sodium, potassium and chloride move in
3. potassium becomes recycled via basolateral channels
4. chloride diffuses apically, creating a negative lumen
5. sodium then moves down the electrochemical gradient paracellularly, followed by water

Question 20

secondary modification stages

Answer 20

1. electrogenic basolateral sodium bicarbonate cotransporter into the cell
2. apical bicarbonate chloride exchanger moves bicarbonate ions into the lumen
3. chloride is recycled via the CFTR apical channel

Question 21

glycoprotein secretion in pancreas

Answer 21

acinar cells- formed in large vesicles then released by exocytosis

duct cells- released constantly

Question 22

enterohepatic circulation definition

Answer 22

circulation of biliary acids, bilirubin and drugs from the liver to the bile to the small intestine, absorption by enterocyte to then be transported back to the liver

Question 23

stages of enterohepatic circuit

Answer 23

1. hepatocytes metabolise cholesterol to cholic acid
2. cholic acid conjugated with glycine or taurine molecules to form water soluble bile salts
3. bile salts travel to gall bladder
4. bile salts become ionised in small intestine and are reabsorbed in the ileum into the hepatic portal circulation
5. bile acids are extracted efficiently in the liver sinusoids

Question 24

composition of bile

Answer 24

water, bile salts, bilirubin and fats