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Flashcards in GI: Functions of the stomach Deck (17)
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1
Q

What are the functions of the stomach?

A
  • short term storage (receptive relaxation prevents increased pressure and therefore prevents reflux)
  • disrupts food through vigorous contractions
  • digestion of proteins (acidic conditions activate proteases)
  • disinfects
2
Q

Describe the structure of the stomach?

A

Where the oesophagus enters the stomach is the cardia, with a small cardial notch leading to the fundus (top part)
Then there is the main body leading to the antrum and the pylorus.
There is a lesser and greater curve

3
Q

What type of epithelia is present in the stomach?

A

From the lower oesophagus to the stomach there is an abrupt change of epithelia from stratified squamous to columnar.

4
Q

What are the gastric pits?

A

Lots of little holes in the stomach wall which form the entrance to the gastric glands.
There are mucous, parietal, chief and G cells

5
Q

Why is the stomach larger proximally than distally?

A

Accelerates the contents so liquid chyme ejected into duodenum
Separates the contents so that lumps are left behind

6
Q
What does each cell type secrete?
Parietal cells
G cells
Chief cells 
D cells
Mucous cells
A
Parietal cells - HCL and intrinsic factor
G cells - Gastrin
Chief cells - pesinogen 
D cells - somatostatin 
Mucous cells - mucus
7
Q

What are some stimulants of parietal cells? therefore causing increased HCL production

A

Gastrin, histamine, Ach

8
Q

How is gastrin secretion controlled?

A

G cells are stimulated by peptides in the stomach and vagal stimulatin - Ach and gastrin-releasing peptide (GRP)

G cells are inhibited by a drop in pH (eg when food leaves the stomach) because low pH activates D cells which release somatostatin which inhibits G cells

9
Q

Outline the production of HCL in the stomach

A

Water splits into OH- and H+

  • the OH- combines with CO2 to form HCO3- which is moved into blood stream via HCO3- Cl- antiporter
  • the H+ and Cl- from above are transported into the stomach lumen where they combine to form HCL
10
Q

What are the 3 phases of digestion?

A

Cephalic, gastic and intestinal

11
Q

Outline the cephalic phase of digestion

A

Accounts for 30% of HCl
Comprises smelling, tasting, chewing, swallowing
Parietal cells and G cells stimulated by vagus nerve
(anticipating food also increases gastric motility slightly)

12
Q

Outline the gastric phase of digestion

A

Accounts for 60% of HCl
Distension of the stomach stimulates vagus which then stimulated parietal and G cells
Presence of AA stimulates G cells
Food acts as a buffer in the stomach so removed gastrin inhibition

13
Q

Outline the intestinal phase of digestion

A

Accounts for 10% of HCl
Chyme initially stimulates gastrin secretion then this is soon overtaken by inhibition of G cells (reduced vagal stimulation) due to presence of lipids

14
Q

How does the stomach protect itself from being digested?

A
  • mucus and HCO3- which are released by surface mucus cells and neck cells in the gastric pits.
    They form a thick alkaline layer which adheres to epithelia to keep it at a higher pH
  • high turnover of epithelial cells
  • prostaglandins help maintain mucosal blood flow
15
Q

What can breach stomach defences against acid?

A

Alcohol dissolves the mucus layer
H. pylori causes chronic gastritis
NSAIDs inhibit prostaglandin

16
Q

What medications can reduce acid production?

A

H2 blockers are histamine antagonists - histamine usually stimulates parietal cells via H2 receptors
Proton pump inhibitors eg omeprazole (stops H+ entering stomach so cant join with Cl- to make acid)

17
Q

What is the blood supply to the stomach?

A

The arterial supply is from the celiac trunk and its branches
Right gastric is a branch of the common hepatic which arises from celiac trunk
Left gastric arises from celiac trunk
Right gastro-omental terminal branch of common hepatic
Left gastro-omental branch of splenic artery which arises from celiac trunk

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