Session 5

Question 1

Describe the macro and microscopic structure of the gastric mucosa LO

1. What epithelium is present in the GI tract?
2. What folds are present in the stomach?
3. What are the holes in the stomach?
4. What cells make up the pits? Function?

Answer 1

1. Stratified squamous epithelium -> simple columnar (oesophagus & stomach)
2. Rugae (Mucosa & submucosa)
3. Gastric pits
4. Mucous cell -> mucous (surface and neck) -> cardia
   * *Parietal cell** -> HCL & Intrinsic factor (pH) -> fundus/body
   * *G cell** -> Gastrin (gastrin) -> pylorus/antrum
   * *ECL** -> histamine (histamine)
   * *Chief cell** -> pepsinogen (chief enzyme) -> fundus/body
   * *D cell** -> somatostatin -> pylorus

Question 2

What are the phases of digestion & highlight the key points of each phase

Answer 2

Cephalic (30% of HCL)

Parasympathetic (• Smelling, tasting, chewing, swallowing • Direct stimulation of parietal cell by vagus nerve • Stimulation of G cells by vagus (GRP released))

Anticipating food

Increases gastric motility (slightly)

Gastric: (60% of HCL)

• Distension of stomach stimulates vagus nerve (stim Parietal & G cells)
• aa (stim G cells)

Food acts as a buffer in stomach

• reduce acidity of the stomach lumen
• Removes inhibition on Gastrin production

Enteric NS and Gastrin

Intestinal (10%)

– Chyme initially stimulates Gastrin secretion – Partially digested proteins detected in duodenum
– Short phase
– Soon overtaken by inhibition of G cells
– Presence of lipids activate enterogastric reflex » Reduces vagal stimulation
– Chyme stimulates CCK and secretin (help suppress secretion)

Question 3

Draw a diagram to show how gastrin, histamine and ACh result in parietal cells producing HCL

Answer 3

Question 4

Explain the control of gastric acid secretion LO

1. Where are g cells located?
2. Draw a diagram to show how G cells are stimulated

Outline the ways in which gastric acid secretion may be reduced by drugs LO

3. Inhibition of HCL production basically means an inhibition of?
4. How is gastric secretion naturally reduced?

Answer 4

1. G cells located in Antrum
2. Image
3. G cells
4. – When food leaves stomach pH drops
   • Food is a buffer
   – Low pH activates D cells
   • D cells release somatostatin
   • Somatostatin inhibits G cells (and ECL cells)
   – Stomach distension reduces
   • Reduced vagal activity

Question 5

Draw a diagram to show how HCL secretion is inhibited naturally (HCL production should stop when there is no food in the stomach

Answer 5

Question 6

Explain why the pH of blood increases when eating (draw a diagram to explain you answer)

Answer 6

Question 7

1. Stomach designed to digest biological material, therefore it can digest itself. Needs to protect itself how?

Answer 7

– Mucus
– HCO3- release

Released by: surface mucus cells
Located: Neck cells in gastric glands
– Forms thick alkaline viscous layer that adheres to epithelium
– Epithelial surface kept at higher pH