Physiology and Biochemistry of GI tract

Question 1

Describe the structure of the layers that make up the GI tract

Answer 1

Question 2

What are the three phases of swallowing?

Answer 2

oral

pharyngeal

oesophageal

Question 3

What stage of swallowing is voluntary?

Answer 3

oral

Question 4

Where do the neurons originate that control the involuntary phase of swallowing?

Answer 4

medulla and lower pons

Question 5

Where does the food travel to beyond the mouth?

Answer 5

oropharynx ===> laryngopharynx ===> oesophagus

Question 6

What cranial nerve passes information from mechanoreceptors in the pharynx to sensory nuclei in the brain?

Answer 6

CN IX - glossopharyngeal

food stimulates mechanoreceptors in the pharynx

information from sensory nuclei passess via interneurons to the motor nucleus ambiguus in the medulla

motor impulses travel from the motor nuclei in the brain stem to the muscles of the pharynx, palate and upper oesophagus via glossopharyngeal and vagus nerves

(lesions in these nerves could result in dysphagia)

Question 7

What happens if the wave of peristaltic contraction fails to propel the food bolus to the stomach?

Answer 7

distention of the oesophagus initiates a vago-vagal reflex which triggers a secondary peristaltic wave

Question 8

Which cell type is responsible for histamine secretion in the stomach?

Answer 8

Enterochromaffin-like cells (ECL cells)

Question 9

What are the principal secretions of parietal cells?

Answer 9

hydrochloric acid and intrinsic factor

Question 10

What do chief cells secrete?

Answer 10

pepsinogen

Question 11

What hormone do D cells produce?

Answer 11

somatostatin

Question 12

What hormone do G cells produce?

Answer 12

gastrin

-stimulates secretion of gastric acid (HCl)

Question 13

How does gastrin exert its effects?

Answer 13

• binds to CCK_B receptors in enterochromaffin-like cells
• histamine is released
• histamine induces the insertion of K+/H+ ATPase pumps into the apical membrane of parietal cells