L29 - Digestion 2 Flashcards
What occurs during the cephalic phase?
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
Where does mechanical digestion begin?
in the mouth
What is mechanical digestion (mastication)?
chewing which involves slicing, tearing, grinding and mixing of food by the teeth
What is the role of saliva?
softens and lubricates food, mucus provides lubrication, lysozyme destroys bacteria
What is chemical digestion?
amylase activity which begins carbohydrate digestion
some lipase activity which begins fat digestion
What occurs during swallowing?
respiration is inhibited, the glottis and epiglottis close, the upper esophageal sphincter opens and the lower esophageal sphincter relaxes
What is the swallowing reflex?
- 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
What propels food down the esophagus?
propelled by peristaltic waves and aided by gravity
What enables peristalsis to occur?
esophageal intraluminal pressures at different sites during swallowing
after a swallow, the “pressure wave” moves sequentially down the esophagus
Our gastroesophageal sphincter is normally closed to prevent…
gastric contents from refluxing into the esophagus
What is the role of the gastroesophageal sphincter?
separates esophagus from stomach, prevents reflux of stomach contents, relaxes to allow entry of food
What are characteristics of gastroesophageal sphincter disorders?
failure of relaxation: swallowing difficulties
ineffectiveness: reflux esophagitis “heartburn”
What are the three general functions of the stomach?
storage (and control of exit)
protection: acid environment destroys bacteria and other pathogens, stomach must also protect itself from “autodigestion”
digestion: enzymes, acid assists
How does the stomach digest?
mechanical: mixing (peristaltic waves)
chemical: enzymes, acid assists
absorption: no food, some water
What is going to increase the rate of emptying of stomach contents into the duodenum?
volume of chyme in the stomach
What is going to decrease the rate of emptying of stomach contents into the duodenum?
presence of fat and acid in the duodenum, volume of chyme in the duodenum, having a bad day
Which factors increase emptying and motility?
volume of chyme in stomach, also influences strength of contraction
Which factors decrease emptying and motility?
most important control: presence of fat, acid, hypertonicity or distension within duodenum
sadness, fear or intense pain (increased sympathetic activity)
What is the typical emptying rate of gastric contents?
fluids: minutes
ordinary meal: 2-3 hours
fatty meal: 4-6 hours
What is the role of the gastric gland?
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
What is the role of chief cells in the gastric gland?
secrete the inactive protease pepsinogen which is activated upon leaving the protective barrier between the stomach cells and the lumen
prevents autodigestion
What allows for the conversion of pepsinogen to pepsin?
H+ ions in the stomach lumen convert pepsinogen to pepsin
What is the function of acid?
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
Acid is secreted by which type of cells?
parietal cells
What is the role of the parietal cell?
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
How does the parietal cell allow for the formation of HCl in the stomach lumen?
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
What would have the greatest impact on decreasing gastric acid secretion?
inhibiting the proton pump (H+/K+ ATPase)
What are G cells stimulated by and what do they produce?
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+
What does increased H+ stimulate that results in increased digestion?
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
What does increased H+ stimulate that results in decreased digestion?
D cells which secrete somatostatin
somatostatin inhibits G cells, chief cells and parietal cells
What are gastric ulcers caused by?
H. pylori which disrupt the gastric mucosal barrier (more than 80% of ulcers)
How are gastric ulcers treated?
antibiotics and/or H2 histamine blockers e.g. ranitidine, and/or proton pump inhibitor e.g. omeprazole