Upper GI tract structure and function

Question 1

Whats in saliva?

Answer 1

• Water: 99% of secreted fluid. Softens, moistens, dilutes particles. Solvent
• Mucins: Major protein component. Mucins + water = mucus. Viscous solution - lubricant function, prevents damage to oesophagus
• α-Amylase: Catalyses breakdown of polysaccharide (starch, glycogen) into disaccharide (maltose) + glucose
• Electrolytes: controls tonicity/pH before it continues down GI tract
• Lysozyme: Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

Question 2

Describe the effect of sympathetic and parasympathetic stimulation on salivation?

Answer 2

Parasympathetic
o Cranial nerves VII (facial) & IX (glossopharyngeal)
o Stimulation ==> profuse watery salivary secretion
Sympathetic
o Stimulation ==> small volume, viscous salivary secretion
o High mucus content (caused by α1 adrenoceptors stimulation)
o High amylase content (caused by β2 adrenoceptors stimulation)

Question 3

What 3 things control salivation?

Answer 3

Sympathetic NS
Parasympathetic NS
Reflex control

Question 4

Where are the glands found in the wall of the oesophagus?

Answer 4

Submucosa

Question 5

What type of muscle is found predominantly in different areas of the muscularis externa of the oesophagus?

Answer 5

upper 1/3 (superior) = skeletal muscle

lower 2/3 (inferior) = smooth muscle

Question 6

What type of muscle make up the upper and lower oesophageal sphincters?

Answer 6

Smooth muscle

Question 7

Describe the anatomy of the stomach as food enters and leaves

Answer 7

Oesophagus ==> gastroesophageal (cardiac) opening (lower oesophageal (cardiac) sphincter) ==> cardiac region ==> fundus ==> body (greater and lesser curvature) ==>pyloric region ==> pyloric opening (pyloric sphincter) ==> duodenum

Question 8

Where in the GI tract is there 3 layers in the muscularis externae?

Answer 8

Muscularis externae = three layers: longitudinal (outer), circular (middle), oblique (inner, mainly in bottom area for squeezing/twisting motion for gastric emptying)

Question 9

What cell types are found in the lumen of the stomach?

Answer 9

Mucus cells (mucus)
Parietal cells (HCl + intrinsic factor) 
Chief cells (pepsinogen)

Question 10

What are the 5 functions of the stomach?

Answer 10

Temporary store of ingested material
Dissolve food particles and initiate digestive processes
Control delivery of contents to small intestine
Sterilise ingested materials
Produce intrinsic factor (vitamin B12 absorption)