Gastric Digestion and Disease

Question 1

Functions of the stomach

Answer 1

• food reservoir
• food digestion (antrum mixes/grinds)
• controls passage of food to SI (pylorus regulates size/timing)
• Gastric acid secretion (+ other secretions for protection against acid)

Question 2

What is required to have normal function of gastric emptying

Answer 2

• intact atrum, pylorus and duodenum
• Normal vagal function to co-ord activity
• normal hormonal function

Question 3

How does food move through the stomach?

Answer 3

1- Fundus (storage) relaxes when food is about to enter, (vagus nerve), causing reflex
2- body & antrum contract together allowing food to be moved to the distal stomach
3- Pylorus is contracted (stops spillage)
4- mixing of food in antrum (retropulsion)

Question 4

Abnormal Gastric emptying

Answer 4

Rapid GE: common post-gastric surgery, when antrum/pylorus removed> “dumping Syndrome”
Delayed GE: eg) diabetic gastroparesis due to vagal nerve damage, usually due to ANS neuropathy

Question 5

Role of Gatric Acid

Answer 5

main role is to sterilise food, make the stomach environment hostile to bacteria (par H.pylori)

Question 6

Dumping syndrome is?

Answer 6

nausea vomiting cramping, poop as food moves too fast stomach > duodenum, food not completely digested.
-Hyperosmolar chyme = fluid shift = intestinal distention = pain =diarrhoea

Question 7

Achlorhydria

Answer 7

absent or low gastric acid, often related to pernicious anaemia

Question 8

How is acid secreted in the stomach?

Answer 8

Parietal cells. Located in the body, with proton pumps to secrete HCL. Secrete ~2L/day

Question 9

how does the H/K ATPase pump in the Parietal cells work and what is it for

Answer 9

A proton pump that actively pumps H+ from cells into stomach
H20 + CO2&raquo_space; H+ + HCO3
in exchange K enters cell, HCO3 transported out of cell into bloodstream exchanged with Cl-.
Requires ATP

Question 10

H20 + CO2&raquo_space; H+ + HCO3

is catalysed by what enzyme

Answer 10

carbonic anhydrase

Question 11

Why does HCO3 swap for Cl- and H+ swap for K+

Answer 11

because pH and osmolarity need to stay in equilibrium.

Question 12

How exactly does the parietal cells secrete acid?

Answer 12

Tubovesicles fuse with canaliculus, increased SA and proton pump numbers increase acid secretion into lumen and gut, against a 3 mill fold conc gradient

Question 13

Protective factors of the gastric mucosa?

What happens if these protective factors results in?

Answer 13

Mucus layer
Bicarbonate secretion

Damage to these = ulceration

Question 14

ECL cells are?

Answer 14

Enterochromaffin-like cells
-located body of stomach, secrete histamine (paracrine activity)
Stimulates acid secretion from adjacent parietal cells

Question 15

G cells

Answer 15

antrum of stomach
secrete gastrin
endocrine activity
(enters blood circ. binds to ECL, > histamine release > HCL release)

Question 16

D cells

Answer 16

antrum of stomach
secrete somatostatin
endocrine & paracrine
inhibits acid secretion by acting on adjacent G cells

Question 17

ACh

Answer 17

neurotransmitter, released by vagus and enteric neurons

Stimulates parietal, ECL and gastrin cells

Question 18

Abnormal Gastric Secretion

Answer 18

Increased : ‘Gastrinoma’, cancer with tumours that produce gastrin> ulcers and destruction of gastric mucosa
Decreased:
-‘Pernicious anaemia’ AB against parietal cells and/or IF
-gastric surgey, body or antrum removed
-vagotomy: loss of vagus nerve > less ACh
-drugs

Question 19

What are other gastric secretions

Answer 19

• pepsinogen
• Intrinsic Factor
• Prostaglandins

Question 20

Pepsinogen?

Answer 20

from Chief cells
cleaved to form pepsin
pepsin degrades protein

Question 21

Intrinsic Factor?

Answer 21

Parietal cells

B12 absorbtion

Question 22

Prostaglandins

Answer 22

Lipid molecules to repair mucosa due to acid damage

Question 23

Celiac phase

Answer 23

think/see/smell food
brain stimulates vagus/enteric nerve
ACh release
Parietal, HCL and G cells released

Question 24

Gastric phase

Answer 24

• when food starts to enter the stomach
• physical digestion + AA release (stimulate G cells)
• food causes distention, stimulates enteric nerves > ACh > parietal, ECL and G

Question 25

Intestinal Phase

Answer 25

too much acid in stomach, time to turn off acid secretion

• Excessive HCl > D cells
• somatostatin release
• G cells inhibited (stopping HCl)

also

• Fats + HCl in duodenum release ‘secretin’ & ‘cholecystokinin
• inhibit cid secretion

Question 26

Why is Secretin released. extra job other then inhibiting acid secretion?

Answer 26

due to HCl

-also stimulate pancreas and bile ducts to release HCO3

Question 27

Why is cholecystokinin. Extra job other then inhibiting acid secretion?

Answer 27

due to partially digested fats and proteins.

-also stimulate release of pancreatic enzymes and gallbladder contraction to release bile to digest the fats

Question 28

What does Helicobacter pylori cause?

Answer 28

• Gastritis (non-specific inflammation post infection)
• Peptic Ulcer
• gastric cancer
• Gastric MALToma - lymphoid tissue lymphoma cancer

Question 29

Who does H.pylori infect and where?

Answer 29

Only humans in the antrum of the stomach. Via person-to-person transmission (oral-oral or faecal-oral)
Tends to be childhood infection (1-5 yrs), and is caused by living conditions, ethnic group, country of birth

Question 30

Treatment for H.pylori

Answer 30

‘triple therapy’ as single AB doesn’t work

• omeprazole, clarithromycin and amoxycillin for 14 days
• is resistance, 2nd regime

Question 31

Causes of Peptic Ulcer Disease (stomach or duodenum)

Answer 31

Mainly H.pylori and aspirin and NSAIDs

Question 32

How did they initially treat peptic ulcers

Answer 32

gastrectomy (remove antrum)
Vagotomy (part of vagus nerve)
Pyloroplasty: cut and resuture pylorus

Question 33

Symptoms of peptic ulcers

Answer 33

non-specific epigastric pain
bleeding
perforation
obstruction due to scarring/fibrosis

Question 34

2 main types of Gastric Cancer

Answer 34

1) Intestinal : well differentiated and cells arranged in a tubular/glandular pattern
2) Diffuse: Poorly differentiated cells, lack of glandular formation. Can infiltrate gastric wall

Question 35

How does H.pylori affect gastric cancer

Answer 35

Can produce widespread inflammation of gastric mucosa and destruction of parietal cells > low acid (achlorydria) > bacterial overgrowth > carcinogens