Lecture 34

Question 1

Describe the cephalic phase of digestion

Answer 1

feedforward = anticipatory response to stimulus
responds to gustatory/visual/thoughts of food
increase PNS stimulation
increase salivary, pancreatic, gastric secretions
increase gallbladder contractions
relax sphincter of Oddi

Question 2

Describe the oral phase of digestion

Answer 2

mechanical digestion = chewing to create softened bolus and increase SA
chemical digestion = salivary amylase breaks starches to maltose

Question 3

what is the purpose of salivation, where does it occur?

Answer 3

parotid, sublingual, submandibular glands
lubricates and moistens the bolus
solubilizes the material
digestion of starch
antibacterial actions: lysozymes and immunoglobins

Question 4

Describe the swallowing reflex

Answer 4

bolus pushes against soft plate, this causes closing of nasopharynx and sends signal via cranial nerve IX to swallowing center in medulla
breathing stops
larynx moves upwards and forwards to close the trachea
Upper/lower esophageal sphincters open
tongue directs bolus down esophagus via peristalsis

Question 5

What are the two main functions of the esophagus

Answer 5

protective/propulsive

sphincters protect airway from swallowed material/gastric reflux

Question 6

Describe the gastric phase of digestion

Answer 6

Mechanical: rugae of stomach break down food, increase SA, mix with gastric acid to produce chyme

chemical: break down of proteins
storage: regulated release of chyme by negative feedback
protection: acidic environment destroys pathogens

Question 7

List the different secretions into the stomach lumen

Answer 7

mucus from mucus cell; tonically regulated or via mucus irritation; provides physical barrier between lumen and epithelium
bicarbonate from mucus cell; secreted with mucus; neutralizes stomach acid
HCl from parietal cell; acetylcholine/PNS stimulation; activates pepsin, destroys pathogens
pepsinogen and gastric lipase from chief cell; acetylcholine/PNS; breaks proteins to polypeptides, digests fats

Question 8

How is HCl secreted?

Answer 8

Via H+/K+ ATPase, K+ leaves via leak cell
loss of H+ pulls CA equation to right, bicarbonate leaves through basolateral membrane into the bloodstream via exchanger with Cl- which leaves apical membrane through leak channel

Question 9

How are stomach ulcers formed?

Answer 9

when acid and pepsin get through stomach lining and creates a hole in the mucus
caused by having a colony of the Heliobacter pylori (most people do have this) but it creates an immune response and produces chronic superficial gastritis
also, taking NSAIDS (non-steroidal anti-inflammatory drugs) reduces mucus and bicarbonate production