L29 - Digestion 2

Question 1

What occurs during the cephalic phase?

Answer 1

digestive reflexes triggered by stimuli are received in the medulla oblongata e.g. sight, sound, smell of food
feeds forward through to the PNS so that ENS activity is increased

Question 2

Where does mechanical digestion begin?

Answer 2

in the mouth

Question 3

What is mechanical digestion (mastication)?

Answer 3

chewing which involves slicing, tearing, grinding and mixing of food by the teeth

Question 4

What is the role of saliva?

Answer 4

softens and lubricates food, mucus provides lubrication, lysozyme destroys bacteria

Question 5

What is chemical digestion?

Answer 5

amylase activity which begins carbohydrate digestion

some lipase activity which begins fat digestion

Question 6

What occurs during swallowing?

Answer 6

respiration is inhibited, the glottis and epiglottis close, the upper esophageal sphincter opens and the lower esophageal sphincter relaxes

Question 7

What is the swallowing reflex?

Answer 7

1. tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex 2. upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways 3. food moves downward

Question 8

What propels food down the esophagus?

Answer 8

propelled by peristaltic waves and aided by gravity

Question 9

What enables peristalsis to occur?

Answer 9

esophageal intraluminal pressures at different sites during swallowing
after a swallow, the “pressure wave” moves sequentially down the esophagus

Question 10

Our gastroesophageal sphincter is normally closed to prevent…

Answer 10

gastric contents from refluxing into the esophagus

Question 11

What is the role of the gastroesophageal sphincter?

Answer 11

separates esophagus from stomach, prevents reflux of stomach contents, relaxes to allow entry of food

Question 12

What are characteristics of gastroesophageal sphincter disorders?

Answer 12

failure of relaxation: swallowing difficulties

ineffectiveness: reflux esophagitis “heartburn”

Question 13

What are the three general functions of the stomach?

Answer 13

storage (and control of exit)

protection: acid environment destroys bacteria and other pathogens, stomach must also protect itself from “autodigestion”
digestion: enzymes, acid assists

Question 14

How does the stomach digest?

Answer 14

mechanical: mixing (peristaltic waves)
chemical: enzymes, acid assists
absorption: no food, some water

Question 15

What is going to increase the rate of emptying of stomach contents into the duodenum?

Answer 15

volume of chyme in the stomach

Question 16

What is going to decrease the rate of emptying of stomach contents into the duodenum?

Answer 16

presence of fat and acid in the duodenum, volume of chyme in the duodenum, having a bad day

Question 17

Which factors increase emptying and motility?

Answer 17

volume of chyme in stomach, also influences strength of contraction

Question 18

Which factors decrease emptying and motility?

Answer 18

most important control: presence of fat, acid, hypertonicity or distension within duodenum
sadness, fear or intense pain (increased sympathetic activity)

Question 19

What is the typical emptying rate of gastric contents?

Answer 19

fluids: minutes
ordinary meal: 2-3 hours
fatty meal: 4-6 hours

Question 20

What is the role of the gastric gland?

Answer 20

mucous neck cells within the gastric gland secrete mucus and bicarbonate
enables the formation of a protective layer between the stomach cells and the highly acidic stomach lumen

Question 21

What is the role of chief cells in the gastric gland?

Answer 21

secrete the inactive protease pepsinogen which is activated upon leaving the protective barrier between the stomach cells and the lumen
prevents autodigestion

Question 22

What allows for the conversion of pepsinogen to pepsin?

Answer 22

H+ ions in the stomach lumen convert pepsinogen to pepsin

Question 23

What is the function of acid?

Answer 23

activates pepsinogen to active enzyme pepsin
provides acid medium for optimal pepsin activity
aids in breakdown of connective tissue and muscle
denatures protein
kills microorganisms ingested with food

Question 24

Acid is secreted by which type of cells?

Answer 24

parietal cells

Question 25

What is the role of the parietal cell?

Answer 25

secretes acid into the stomach
intracellular pH 7.2: stomach lumen as low as pH 1
pumping H+ against gradient 2.5 million x more concentrated

Question 26

How does the parietal cell allow for the formation of HCl in the stomach lumen?

Answer 26

bicarbonate is exchanged for chloride in the interstitial fluid and H+ is exchanged for K+ in the lumen of the stomach (proton pump)
chloride is secreted into the lumen of the stomach

Question 27

What would have the greatest impact on decreasing gastric acid secretion?

Answer 27

inhibiting the proton pump (H+/K+ ATPase)

Question 28

What are G cells stimulated by and what do they produce?

Answer 28

the vagus nerve and the ENS
gastrin which activates ECL cells with acetylcholine to release histamine and all of these chemicals stimulate parietal cells to produce H+

Question 29

What does increased H+ stimulate that results in increased digestion?

Answer 29

the ENS which stimulates chief cells to release pepsinogen -> converted into pepsin by H+ which is used to digest the amino acids / peptides that set off the ENS

Question 30

What does increased H+ stimulate that results in decreased digestion?

Answer 30

D cells which secrete somatostatin

somatostatin inhibits G cells, chief cells and parietal cells

Question 31

What are gastric ulcers caused by?

Answer 31

H. pylori which disrupt the gastric mucosal barrier (more than 80% of ulcers)

Question 32

How are gastric ulcers treated?

Answer 32

antibiotics and/or H2 histamine blockers e.g. ranitidine, and/or proton pump inhibitor e.g. omeprazole