lecture 27 - the gut 1: saliva and stomach

Question 1

processing of food

Answer 1

• motility
• secretion
• digestion
• absorption
• excretion

Question 2

motility

Answer 2

mechanical breakdown

controlled movement along gut

Question 3

secretion

Answer 3

addition of enzymes and electrolytes

Question 4

digestion

Answer 4

chemical breakdown

Question 5

absorption

Answer 5

transport proteins

Question 6

excretion

Answer 6

secretion of metabolic waste production and xenobiotics

elimination of faeces

Question 7

structure of the gut tube

Answer 7

• plica
• mucosa
• submucosa
• circular mucosa
• longitudinal mucosa
• submucosal glands
• villi

Question 8

regulation of gut function

Answer 8

• neural
• hormonal
• local

Question 9

neural regulation of gut function

Answer 9

ANS
• vagus nerves

enteric nervous system - in the gut wall

Question 10

hormonal regulation of gut function

Answer 10

endocrine

dispersed enters-endocrine cells

Question 11

local regulation of gut function

Answer 11

paracrine

eg. histamine

Question 12

3 key stages of regulation

Answer 12

cephalic

gastric

intestinal

Question 13

functions of saliva

Answer 13

• lubrication - fluid and mucus
• digestion - amylase & R proteins
• solution
• moistness
• protection - fluid and bicarbonate keeps pH up so amylase will work, lysozyme and immunoglobulins

Question 14

salivary glands

Answer 14

3 pairs of glands account for 90% of saliva

parotid glands
• serous (watery)
• amylase

sublingual & submandibular glands
• mixed secretion

10% from minor glands
• mucous
• mucins

Question 15

total secretion from salivary glands

Answer 15

1.5 litres a day

Question 16

salivary gland structure

Answer 16

acinus leads to duct

secrete K+ and HCO3-

Question 17

salivary fluid secretion

Answer 17

primary fluid from acinar epithelial cells
• isotonic - plasma like

secondary ductal modification
• Na+ & K+ reabsorption
• K+ & HCO3- secretion
• ducts impermeable to water

hypotonic saliva - HCO3- rich

Question 18

control of salivation

Answer 18

in cephalic phase
• sight, smell, taste and thought of food

parasympathetic - cholinergic
• cranial nerves VII and IX
• large volume

sympathetic - noradrenergic
• smaller volume
• rich in enzymes and mucus

Question 19

gastric functions

Answer 19

• reservoir
• mixing food with gastric secretions
• digestion
• controlled gastric tempting - food to duodenum
• protection

Question 20

2 types of digestion

Answer 20

mechanical

chemical

Question 21

structure of stomach

Answer 21

starts at oesophagus and enters body of stomach

contains rugae - surface folding increases area

leaves via Antrum by pyloric valve

Question 22

what do gastric pits do?

Answer 22

increase SA

Question 23

composition of gastric juice

Answer 23

• HCl - parietal cells
• pepsinogen to pepsin - chief cells
• mucus and bicarbonate - mucus neck and surface epithelial cells
• intrinsic factor - parietal cells

Question 24

how much gastric juice a day?

Answer 24

2 litres

Question 25

what are parietal cells stimulate by?

Answer 25

ACh gastrin histamine

Question 26

what happens in parietal cells?

Answer 26

H2O & CO2 converted to H+ and HCO3- by carbonic anhydrase H+ is exchanged for K+ by K+/H+ ATPase into lumen of the stomach Na+/K+ ATPase on basolateral membrane potassium leaky channels allow K+ recycling HCO3- exchanged for Cl- H+ and Cl- combine to make HCl

Question 27

what do proton pump inhibitors (PPIs) do?

Answer 27

they block the K+/H+ ATPase so H+ cannot be pumped into the lumen of the stomach to make it more acidic

Question 28

what happens on the apical membrane of parietal cells?

Answer 28

H+/K+ ATPase - primary proton pump K+ channels - supplies K+ for recycling through proton pump Cl- channels - supplies anion for HCl

Question 29

what happens on the basolateral membrane of parietal cells?

Answer 29

Na+/K+ ATPase Cl-/HCO3- exchange

Question 30

what do chief cells do?

Answer 30

secrete pepsin and gastric lipase digest proteins and fats stimulated by: • ACh • acid • secretin

Question 31

what is pepsin inactivated and denatured?

Answer 31

inactivated > pH 3.5 denatured > pH 7.2

Question 32

what do mucous neck cells and surface cells do?

Answer 32

secrete mucus and HCO3- mucus provides physical barrier between lumen and epithelium HCO3- buffers gastric acid to prevent damage of epithelium

Question 33

how does the stomach stop auto digestion?

Answer 33

gastric mucosal protection mucus-HCO3- barrier

Question 34

control of parietal cell function

Answer 34

``` direct and indirect chemical regulators • histamine from ECL cells • somatostatin from D cells • gastrin from G cells • Ach from vagus and enteric neurones ```

Question 35

what do ECL cells do?

Answer 35

in body only secrete histamine stimulate gastric acid secretion

Question 36

what do D cells do?

Answer 36

in body and antrum secrete somatostatin inhibition of gastric acid

Question 37

what do G cells do?

Answer 37

in antrum only secrete gastrin stimulate gastric acid secretion

Question 38

how does histamine act?

Answer 38

binds to H2 receptors on parietal cells in the body increases cAMP leads to HCl secretion

Question 39

what is cimetidine?

Answer 39

a H2 antagonist

Question 40

what are G cells activated by?

Answer 40

ACh peptides amino acids