KuraCloud 3 - Stomach

Question 1

What are the 3 key functions of the stomach?

Answer 1

• digestion of macronutrients
• storage reservoir for food
• immunological protection (stomach acid)

Question 2

What kind of epithelia lines the stomach mucosa?

Answer 2

columnar epithelium

Question 3

Anteriorly, the stomach can be split into how many sections?

Name them

Answer 3

5

• cardiacum
• fundus
• body
• pyloric antrum
• pyloric canal

Question 4

From which section is gastric acid secreted?

Answer 4

from the fundus

Question 5

What is the only feature of the wall of the stomach that differentiates it from it other parts of the digestive tract?

Answer 5

(the wall of the stomach is structurally similar to other parts of the digestive tract, with the exception that) the stomach has an extra oblique layer of smooth muscle inside the circular layer, which aids in performance of complex grinding motions (mechanical digestion).

Question 6

What are rugae?

What is the function of them?

Answer 6

when the stomach is empty (and contracted), its mucosa and submucosa are thrown into folds called rugae

(the stomach only has a minor role in absorption, so) the presence of rugae (instead of villi) allows the stomach to undertake its reservoir function.

Question 7

What happens to the rugae when food in consumed?

Answer 7

as the volume of the stomach increases, the rugae are stretched and become flat

Question 8

What is the role of the lower oesophageal sphincter?

Answer 8

• to allow movement of food and fluids into the stomach

- to ensure that the acidic contents of the stomach remain separate from the vulnerable oesophageal tissue

Question 9

What is the z-line?

Answer 9

a visible threshold between epithelia of the oesophagus (stratified squamous) and the stomach (simple columnar)

• the oesophageal epithelium is light pink in colour, and functional as a wear and tear lining
• the stomach lining is a bright red and more resistant to low pH

Question 10

What is the role of the mucous gel lining of the stomach?

Answer 10

it provides considerable protection against the corrosive acid

Question 11

What are gastric pits?

What is secreted from the pits?

Answer 11

the columnar epithelium of the stomach mucosa invaginate to form gastric pits
(the stomach is lined with millions of gastric pits, which lead to multiple gastric glands, which house the functional secretory cells of the stomach)

The cells secrete gastric juices, mucous, paracrine signalling molecules and hormones

Question 12

What is the function of the mucus lining the stomach?

Answer 12

(helps to protect the stomach lining)

• it keeps the pH next to the lining close to 7, although the environment in the stomach is strongly acidic
• it also helps to protect the stomach lining from active lipase and proteases

Question 13

What are the parental cells of the stomach?

Answer 13

• the acid-secreting cells of the stomach
  HCl:
  1) kill ingested pathogens
  2) activate protease zymogens
  3) alter protein structure to help digestion
• rich in mitochondria (to provide energy for membrane transport)
• they also secrete intrinsic factor, a glycoprotein essential for the absorption of vitamin B12

Question 14

Give a general overview of the process of activation of the parietal cells of the stomach

Answer 14

• they exist in a quiescent (sleeping) state until activated
• then, the high number of tubovesicles in the cytoplasm fuse with the small invaginations on the apical surface
• this makes a complicated canalicular surface, with a large surface area for acid secretion.

Question 15

What do chief cells produce?

What effect does this have?

Answer 15

These cells produce a protease zymogen (pepsinogen) and a lipase (gastric lipase).
- pepsinogen is activated to pepsin in the presence of HCl (secreted as a precursor to stop auto-digestion)
pepsin breaks dietary proteins into smaller peptide chains
- gastric lipases digest fats

Question 16

G cells

Answer 16

• enteroendocrine cells found at the bottom of the gastric pits
• release the hormone gastrin into the bloodstream in response to vagus nerve stimulation, the presence of peptides in the stomach, and stomach distension.

Gastrin travels through the blood to receptor cells in the stomach where it stimulates gastric secretion and motility. Stimulation of smooth muscles by gastrin leads to stronger contractions of the stomach and the opening of the pyloric sphincter to move food into the duodenum.

Gastrin also binds to receptors on cells in the pancreas and gallbladder where it increases the secretion of pancreatic juice and bile.