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psl201: physiology > 4 week 21 > Flashcards

4 week 21 Flashcards

1
Q

T or F: absorption is maximized only when nutrients are needed

A

false: absorption is maximized regardless of whether nutrients are needed

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2
Q

what is the enteric nervous system? (3)

A
  • 1) submucosal plexus
  • 2) myenteric plexus
  • 3) reflexes mediated through ENS control many GI
    functions
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3
Q

describe endocrine regulation of GI function

A
  • GI hormones are secreted from endocrine cells in the stomach and small intestine
  • examples: gastrin, CCK, secretin, GIP, GLP1
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4
Q

diff bw short vs long reflex pathway?

A
  • short: stimulus, receptors, ENS, endocrine cells, hormone, blood, effector cells, response
  • long: stimulus, receptors, CNS (influenced by things like emotions, smell), ANS, ENS, endocrine cells, hormone, blood, effector cells, response
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5
Q

what are the 3 phases of GI regulation?

A
    1. cephalic phase: thoughts, taste, and smell – preps for food entering the stomach
    1. gastric phase: enhances activity of the stomach
    1. intestinal phase: enhances digestion and absorption in small intestine + inhibits activity of the stomach
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6
Q

how is saliva secretion regulated? (2)

A
  • sensory info sent to the medulla salivary center
    1. parasympathetic activation: watery saliva (main)
    1. sympathetic activation: protein-rich, viscous saliva
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7
Q

how is the secretion of acid and pepsinogen regulated? (2)

A
  • pepsinogen (secreted by chief cells) is cleaved by HCl (secreted by parietal cells) to get pepsin
  • pepsin breaks down proteins in the lumen
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8
Q

describe the production of stomach acid (6)

A
  • parietal cells produce HCl
  • carbonic anhydrase catalyzes production of bicarbonate and H+
  • H+ is actively secreted into lumen of the stomach
  • bicarbonate is transported into interstitial fluid (and later blood) for Cl–
  • Cl– diffuses into lumen of the stomach through channels
  • net result = acid production
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9
Q

describe cephalic phase direct vs indrect

A
  • direct: sight/smell/taste of food = +parasympa activity = +acid and pepsinogen secretion (chief/parietal cells)
  • indirect: sight/smell/taste of food = +parasympa activity = G cells secreting gastrin and plasma gastrin = +acid and pepsinogen secretion (chief/parietal cells)
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10
Q

describe gastric phase in more detail

A
  • proteins, peptides, and amino acids in the stomach
  • distension of stomach
  • stimulate acid, pepsinogen and gastrin secretion via short and long reflex pathways
  • later:
  • exit of food from the stomach removes stimuli for secretion
  • increased acidity inhibits gastrin release
  • reduced acid and pepsinogen secretion
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11
Q

describe intestinal phase in more detail

A
  • food enters duodenum
  • increased osmolarity, fat and acid, distension
  • long and short reflex pathways inhibit acid and pepsinogen secretion
  • e.g. intestinal hormones cholecystokinin (CCK) and secretin released during the intestinal phase reduce acid secretion and stomach motility
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12
Q

how is the secretion of pancreatic juice and bile regulated via CCK and secretin at the pancreas vs at the liver/gall bladder?

A
  • pancreas: CCK stimulates acinar cells to secrete enzymes, potentiates secretin effects. secretin stimulates duct cells to secrete bicarbonate, potentiates CCK effects
  • liver/gall bladder: CCK stimulates gallbladder contraction + relaxation of sphincter of Oddi. secretin stimulates bile secretion from liver
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13
Q

so ultimately, what does secretin vs CCK do?

A
  • secretin = neutralizes acid (+bicarbonate)
  • CCK = +protein, fat, carb digestion
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14
Q

function of glucose-dependent insulinotropic peptide (GIP)?

A
  • stimulated by glucose/fatty acids/amino acids
  • increases insulin secretion (= gastric emptying/acid when levels high)
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15
Q

function of glucagon-like peptide-1 (GLP-1)?

A
  • stimulated by fatty acids/carbohydrates in small intestine
  • increases feelings of satiety, insulin, and beta cell growth but decreases glucagon and gastric emptying/acid
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16
Q

what is motility primarily caused by?

A

contractions of the muscularis externa (outer muscle layers)

17
Q

diff bw multi-unit and single-unit smooth muscle?

A
  • multi-unit: individual cells contract
  • single-unit: cells connected by gap junctions (activation of one = electrical activity spreads to others, all contract)
18
Q

slow waves vs action potentials?

A
  • SLOW WAVES
  • spontaneous depolarization
  • generated in interstitial cells of Cajal and spread to rest of smooth muscle
  • BER varies in different areas of the GI tract and height of BER is affected by neural and hormonal input
  • parasympathetic → excitation
  • sympathetic → inhibition
  • ACTION POTENTIALS
  • cause muscle contraction when MP reaches threshold
  • frequency dependent on the slow wave
19
Q

2 main types of motility?

A
  1. segmentation: not unidirectional, at small/large intestine
  2. peristalsis: contents propelled down the GI tract
20
Q

what happens muscle-wise for segmentation vs peristalsis?

A
  1. segmentation: circular contracts / proximal or distal contracts
  2. peristalsis: at proximal segment circular contracts / longitudinal relaxes / diameter decreases vs at distal segment circular relaxes / longitudinal contracts / diameter increases
21
Q

T or F: chewing is completely voluntary

A
  • false – chewing is voluntary + involuntary
  • cyclical reflex: mouth closed = muscles active, food enters = muscles inhibited
22
Q

describe the processes involved in swallowing (9)

A
  1. tongue pushes bolus against soft palate and back of the mouth, triggering the swallowing reflex that is integrated in the swallowing centre of the medulla
  2. bolus descends in pharynx, pressing on epiglottis (covers glottis so food does not enter trachea + inspiration is inhibited)
  3. upper esophageal sphincter relaxes and bolus enters esophagus
  4. sphincter closes behind bolus
  5. bolus stretches esophagus, triggering peristalsis
  6. peristalsis propels bolus to stomach
  7. bolus arrives at stomach and triggers relaxation of lower esophageal sphincter and enters stomach
  8. swallowing center also initiates relaxation of stomach smooth muscle
  9. secondary wave moves bolus into stomach
23
Q

peristalsis waves strengthen as they approach the ___. why?

A
  • pylorus
  • to mix chyme (pyloric sphincter closed) , for gastric emptying (pyloric sphincter open)
  • stronger contractions open the pyloric sphincter
24
Q

how is gastric motility regulated at the cephalic, gastric, intestinal, and interdigestive states?

A
  1. cephalic-phase: stimulate: thinking of, tasting, smelling food, anger, aggression… inhibit: pain, fear, depression
  2. gastric-phase: stimulate: distension of stomach, gastrin
  3. intestinal-phase: inhibit: distension of duodenum and presence of chyme (osmolarity, acids, fat, etc), CCK, secretin, GIP
  4. interdigestive state: migrating motility complex: intense waves of peristalsis with opening of the pyloric sphincter
25
Q

What happens during vomiting? (6)

A
  1. stimulus to vomiting centre in medulla = enhanced salivation
  2. relaxation of the esophagus, LES, and body of the stomach
  3. contraction of the abdominal muscles and diaphragm both increase pressure in the abdominal cavity
  4. stomach and small intestine undergo reverse peristalsis
  5. breathing inhibited and epiglottis and soft palate close off the trachea
  6. stomach contents ejected from the mouth
26
Q

motility reflexes of the small intestine? (3)

A
  1. gastroileal reflex: presence of chyme in stomach increases motility in ileum
  2. ileogastric reflex: distension of ileum inhibits gastric motility
  3. intestino-intestinal reflex: injury or severe stress inhibits intestinal contractions
27
Q

what does the ileocecal (IC) valve do? what is it opened and closed by?

A
  • controls emptying of small intestine and prevents back flow
  • opened by distension of ileum and gastroileal reflex, closed by distension of the colon
28
Q

what are haustrations?

A
  • occur at proximal colon
  • like segmentation, but slower
  • mass movements 3-4x/day
29
Q

motility reflexes of the colon? (2)

A
  1. colonocolonic reflex: distension of colon in one area causes relaxation of other areas of colon
  2. gastrocolic reflex: food in stomach increases colonic motility
30
Q

what regulates defecation? (5)

A
  1. distension of colon activates stretch receptors
  2. smooth muscle of rectum contracts which increases pressure in rectum
  3. peristaltic contractions of sigmoid colon propel more fecal material into the rectum, increasing pressure
  4. internal anal sphincter relaxes simultaneously as external anal sphincter contracts
  5. when the external anal sphincter relaxes voluntarily = defecation

psl201: physiology (21 decks)

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