Gastric secretions

Question 1

Which cells do the stomach release gastric secretions from

Answer 1

Gastric mucosa

Question 2

Where are the oxyntic mucosa found

Answer 2

In the fundus and body

Question 3

Where are the pyloric gland area found

Answer 3

In the antrum

Question 4

where are mucosal gland cells found

Answer 4

IN gastric pits

Question 5

What cells in the stomach produce HCL

Answer 5

Parietal cells

Question 6

What else do parietal cells produce

Answer 6

Intrinsic factors which are involved in vitamin B12 production

Question 7

What cells in the stomach are responsible for producing pepsinogen

Answer 7

Chief cells

Question 8

What cells are responsible for secreting mucous

Answer 8

Surface epithelial and mucous neck cells

Question 9

How is HCL produced by parietal cells

Answer 9

1) carbonic anhydrase catalyses Co2 with water to produce carbonic acid
2) This then dissociates into bicarbonate and H+
3) H+ leave parietal cell via proton pump into gastric lumen in exchange for K+ coming into parietal cell
4) Bicarbonaye ions transporter moves it out of cell into blood and chloride moves into parietal cell
5) Chloride then moves out of cell into lumen via a cotransporter while the K+ moves in from lumen

Question 10

How does HCl aid digestion

Answer 10

activating the enzyme pepsin and providing an acid medium for optimal pepsin activity

Aids the breakdown of connective tissue and muscle fibres

Question 11

What produces pepsinogen

Answer 11

Chief cells

Question 12

How is pepsinogen activated

Answer 12

The acidic environment caused by HCL turns pepsinogen into pepsin which breaks down protein and produces smaller and smaller peptide fragments

Pepsin can also break down pepsinogen to form more pepsin

Question 13

When is the cephalic phase stimulated by and what is it

Answer 13

Gastric secretion stimulated prior to the arrival of food in the stomach

-stimulated by the thought or expectation of food and the sight, taste, chewing or swallowing of food and the sight, taste, chewing or swallowing of food

Question 14

What nerve is the action of the cephalic phase dependant on

Answer 14

Vagus nerve

Question 15

How does enterochromatin cells contribute to the release of HCl

Answer 15

Enterochromatin cells receive ACh on its muscarinic receptors which releases histamine
-Histamine acts on H2 receptors on parietal cells which then release HCL

Question 16

How do Antral G- cells contribute to the release of HCl

Answer 16

Innervated by parasympathetic nn system. When activated it releases gastrin releasing polypeptide which causes release of gastrin from Antra G cells

-It passes into capillary cells and binds to CCK-2 receptors on enterochromatin like cells which releases more histamine which binds to H2 on parietal cell which releases more HCL

Question 17

How do D cells affect HCl secretion

Answer 17

Under normal conditions they release somatostatin (SS) which suppresses release f=of gastrin. Activated by parasympathetic nervous system which stops the release of SS from D cells so more gastrin released from antra cell

Question 18

What is the gastric phase and why

Answer 18

When food reaches stomach, gastric secretion is further increased

• Local vago-vagal reflexes in response to mechanical stimulation, due to presence of food in the antrum (doesn’t involve the CNS)
• Stimulation of gastrin release from G-cells by peptide fragments of partially digested proteins

Question 19

How does gastric circulation increase when eating a meal

Answer 19

-Local metabolite production (prostaglandins maintain capillary network) may be release of vasoactive intestinal polypeptide (VIP) from local nerves causing vasodilatation

Question 20

As a meal is gradually passed to small intestine, how are gastric secretions reduced

Answer 20

Removal of peptide fragments (no longer present to stimulate gastrin release)

Removal of food leads to a decrease in pH. At pH less than 2, gastrin release from G cells is inhibited directly and via somatostatin release

Question 21

What role does the duodenum play in inhibiting gastric secretion

Answer 21

Once food passes into small intestine, they stretch.They sample the contents of the duodenum and sense the acidity. They can sense if fat is present. If there is fat or acid present, they release enterogastrone which inhibits the release of gastrin

Question 22

What cephalic factors influence gastric secretion

Answer 22

Fear

Depression