Gastrointestinal Tract II

Question 1

functions of the stomach

Answer 1

• temporary storage
• digestion: starts chemical breakdown of protein digestion
• absorption
• converts bolus of food into chime
• gatekeeper to the small intestine

Question 2

Rugae

Answer 2

• empty stomach: muocsa forms many folds

- 50mL vol

Question 3

Digestion

Answer 3

Mechanical: churning
Chemical: pepsin partially digests proteins into shorter peptide chains
- gastic lipase and lingual lipas begin fat digestion
Absorption: the small intestine is the main organ of absorption but some things are absorbed by the stomach: water and alcohol, some medication

Question 4

Regulation of gastric emptying

Answer 4

• duodenum can prevent overfilling by controlloing how much chime enters, duodenul receptors respond to stretch and chemical signals
• enterogastric relfex and enterogastrones inhibit gastric secretion and duodenul filling
• stomach empties in around 4 hours, but increase in fatty chime entering duodenum can increase time to 6 hours or more carbohydrate-rich chume moves quickly through duodenum

Question 5

Sphincters of the stomach

Answer 5

Work to control the passage

1. lower oesophageal (cardiac) sphincter
2. pyloric sphincter

Question 6

Ulcers

Answer 6

• peptic or gastric ulcers
• can cause erosions in stomach wall, if erosions perforate wall, can lead to peritonitis and haemorrhage
• most ulcers caused by bacterium: helicobacter pylori
• can also be caused by non-steroidal anti-inflammatory drugs like aspirin

Question 7

Stomach histology

Answer 7

• mucosa consists of 3 layers
  simple columnar epithelium cells called surface mucosa cells
  lamina propria (areolar connective tissue)
  Muscularis mucosa (smooth muscle)
• The lamina propria: contains blood and lymphatic vessels to reabsorb nutrients from Gi tract supports mucosal epithelium
• contains mucosa associated tissue -> protection against disease

Question 8

Mucosa

Answer 8

• consists of simple columnar epithelium
• entirely composed of mucous cells: secrete two-layer coat of alkaline mucus
  Contains gastric pits, that leas into gastric glands
  Gastric juice = water, hydrochloric acid and pepsin

Question 9

Gastric protection

5 mechanisms

Answer 9

The stomach has several mechanisms to protect it from the acis and pepsin, these are:

1. mucus layer
2. bicarbonate secretion
3. epithelial tight junctions
4. mucosal blood flow
5. prostaglandins

Question 10

Muscosal barrier

Answer 10

• harsh digestive conditions require stomach to be protected

- mucosal barrier protects stomach and is created by

Question 11

Mucosal barrier protects stomach and is created by:

Answer 11

• Thick layer of bicarbonate-rich mucus
• Tight junctions between epithelial cells prevent juice seeping underneath tissue
• Mucosal blood flow contributes to protection by supplying the mucosa with oxygen and HCO3, and by removing H+ and toxic agents diffusing from the lumen into the mucosa and support the healing process and prevents superficial lesions from developing into deep ones
• Prostaglandins inhibit acid secretion, stimulate mucus and bicarbonate secretion

Question 12

Microscopic anatomy of the stomach

Answer 12

• Stem cells: rapid division and supply of new cells
• types of gland cells: glands in fundus and body produce most gastric juice
• glands include secretory cells:
  1. mucous neck cells
  2. parietal cells
  3. chief cells
  4. enteroendocrine cells

Question 13

Parietal cells

Answer 13

• secretions include:
• hydrochloric acids: pH 1.5-3.5: denatures protein, activated pepsin, breaks down plant cell walls and kills many bacteria
• intrinsic factor: glycoprotein required for absorption of Vitamin B12 in small intestine

Question 14

Chief cells

Answer 14

• secretions include:
• pepsinogen: inactive enzyme that is activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)
• Pepsin: digestive enzyme which breaks down proteins into peptides
• lipase: digested 15% of lipids
• location of the HCl acid producing parietal cells and pepsinogen secreting chief cells in a gastric gland
• HCl activated pepsinogen to active form pepsin

Question 15

Enteroendocrine cells

Answer 15

• secrete chemical messengers into lamina propria
• acts as paracrine: serotonin and histamine
• hormones: somatostatin and gastrin
• low pH inhibits gastrin secretion: occurs between meals and during digestion as negative feedback mechanism

Question 16

Control of acid secretion

Answer 16

• g cells (in the pyloric antrum of the stomach) release Gastrin
• Gastrin (peptide hormone) stimulates secretion of gastric acid b the parietal cells of the stomach activating Enteroendocrine cells = release of histamine
• neurones -> acetylcholine -> increase release of gastrin, histamine, HCl
• more HCl gets somatostatin releasing cells to release somatostatin -> negative feedback

Question 17

Stomach acids

Answer 17

• Approx 2L of gastric acid is produced by the stomach every day
• stomach pH: 1.5-2.5
• the acid is important for:
  1. killing bacteria
  2. aiding digestion
  3. optimal pH for pepsin