GIT

Question 1

order of structures

Answer 1

pyloric sphincter -duodenum-jejunum-oileum-ileucaeal sphincter-cecum-ascending colon- transverse colon - sigmoidal colon - distal colon - rectum - internal/external anal sphincter

Question 2

function of duodenum

Answer 2

• enzymatic digestion of food
• chyme triggered release of bile acids from the gall bladder
• neutralising acidity of chyme via bicarbonate release

Question 3

function of jejunum

Answer 3

main site of nutrient absorption

Question 4

function of the ileum

Answer 4

absorption of B-12 and bile salts

Question 5

Enzymes for food breakdown:
Fats
Protein
Carbohydrate

Answer 5

Lipase, Bile
Pepsin, endopeptidase, exopeptidase
amylase, brush border

Question 6

pharyngeal stage

Answer 6

1. bolus pushed into stomach by involuntary movement
2. Movement of bolus stimulates receptors in the oropharynx which signal to the deglutition centre in the MO and lower pons
3. brain signals soft palet and uvula to seal nasopharynx and the epiglottis to seal the larynx (prevents food entering the RT)
4. upper esophegal sphincter relaxes allowing bolus into oesophagus and contracts to prevent back fllow
5. lower oesophageal sphincter relaxes and food enters stomach.

Question 7

4 main functions of le stomach

Answer 7

• temporary reservoir for food
• mixing food and water with gastric secretory products
• grinding of food to reduce the size of particles
• regulating exit of chyme into the duodenum

Question 8

Large intestine primary function

Answer 8

• Absorption of water and concentration of waste

- occurs passively via osmosis and thus is determined by the active transport out of epithelial cells and into the lumen

Question 9

Passage of nutrients

Answer 9

• tight junctions between epithelial cells prevent paracellular transport
• for larger molecule transporters are thus required

Question 10

Mucousa

Answer 10

Innermost lining with 3 parts

1) mucous membrane
- simple columnar epithelium
- functions as a protective layer that is also implicated in absorption of nutrients and secretion of mucous
2) Lamina propria
- thin layer of connective tissue supporting the mucous membrane
- contains blood and lymph (fat absorption) vessels, nerve fibres and many supporting cells of the immune system (mast cells leukocytes macrophages)
- also contains ICC’s
3) Muscuarlis mucousa
- smooth muscle, highly folded to increase surface area, to form gastric pits. Specialised goblet cells in the mucousae secrete mucous.

Question 11

Submucousa and Submucousal Plexus

Answer 11

• highly vascularised with a thick layer of connective tissue which provides the digestive tract with distensibility and elasticity
• blood, lymph vessels and mucous secreting glands found in this layer
• submucousal plexus lines

Question 12

Muscularis Externa and myenteric plexus

Answer 12

• smooth muscle layer of the gut wall divided into an inner layer of circular smooth muscle and outer layer of longitudinal smooth muscle, myenteric plexus sits between the 2 muscle layers

Question 13

Serosa

Answer 13

• outermost layer of the GIT wall
• responsible for secreting water, serous fluid
• continuous with mesentery
• smooth muscle membrane which hold extrinsic muscle and nerve fibres

Question 14

Peristalsis

Answer 14

• ICC’s create slow wave potentials to produce phasic contractions in the stomach and small intestine
• slow waves begin spontaneously in the ICC’s and spread to adjacent smooth muscle cells via GAP JUNCTIONS
• threshold is not reached every cylce, when threshold is reached, contraction is graded
• circular smooth muscle contracts behind the bolus pushing it forward

Question 15

Order of structures in the gut wall

Answer 15

mucosa, lamina propria, muscularis mucousae, submucousal plexus, circular smooth muscle, myenteric plexus, longitudinal smooth muscle