GI Tract - structure and motility

Question 1

Alimentary canal

Answer 1

Hollow organs from mouth to anus
Separated by sphincters
Mouth, oropharynx, oesophagus, stomach, SI, LI, rectum, anus
Accessory structures: salivary glands, liver, GB, pancreas

Question 2

Structure of digestive tract wall

layers - innermost to outermost

Answer 2

Mucosa - epithelial cells, lamina propria, muscularis mucosa
Sub-mucose - connective tissue
Muscularis externa - circular and longitudinal muscles
Serosa - connective tissue

Question 3

Circular muscle contraction

Answer 3

Inner layer

Lumen becomes longer and narrower

Question 4

Longitudinal muscle contraction

Answer 4

Outer layer

Lumen becomes shorter and fatter

Question 5

Slow waves

Answer 5

Driven by ICC cells - between circular and longitudinal layers
Contraction only occurs if AP is present.
The greater the number of AP’s fired, the more intense the contraction
stomach ~ 3 per min
duodenum ~ 12 per min
ileum ~ 8 per min
Proximal LI ~ 8 per min
Distal LI ~ 16 per min

Question 6

Peristalsis

Answer 6

Co-ordinated wave of contraction behind a bolus of food
Relaxation ahead of the bolus of food
Food bolus propelled along GI tract from oral -> anal

Question 7

Peristalsis - behind bolus of food

Answer 7

Circular muscle contraction

Longitudinal muscle relaxation

Question 8

Peristalsis - infront of bolus of food

Answer 8

Circular muscle relaxation

Longitudinal muscle contraction

Question 9

Segmentation

Answer 9

Mixing and churning the food
Occurs in the SI in the fed state
Occurs in the LI (haustration)

Question 10

Principle site of digestion

Answer 10

Small intestine