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GI 1 > Phys 4 > Flashcards

Phys 4 Flashcards

1
Q

Gastrointestinal regulation hormones (8)

A
  1. gastrin
  2. cholecystokinin
  3. secretin
  4. Gastric inhibitory peptide
  5. Motilin
  6. Somatostatin
  7. Serotonin
  8. Histamine
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2
Q

Gastrin

  • secreted by what
  • secreted when
A
  • secreted by gastric enteroendocrine cells
  • secreted in response to:
  • peptides and aa
  • distention of stomach
  • vagal stimulation
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3
Q

Gastrin

  • action
  • inhibited by
A

stimulates:
- gastric glands to release gastric acid (excites ECL cells which release histamine which parietal cells respond to)

inhibited by:

  • acid in stomach
  • somatostatin
  • secretin
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4
Q

Cholecystokinin

  • secreted by what
  • secreted when
A
  • enteroendocrine cell of duodenal mucosa

- fatty chyme, peptides, aa in duodenum

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5
Q

Cholecystokinin

  • action
  • inhibited by
A

Action:

  • increased pancreatic output of enzyme-rich juice
  • gallbladder contraction and bile release
  • relaxation of sphincter of Oddi
  • augments secretin action

Inhibited by:
- lack of stimulus as digestion products transit through system

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6
Q

Secretin

  • secreted by what
  • secreted when
A
  • S cells of upper SI mucosa

- in response to acidic chyme, peptides, aa, fats

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7
Q

Secretin

- action

A

Action in stomach

  • decrease gastric gland activity
  • decrease gastric motility during gastric phase

Action in pancreas
- increase bicarb-rich watery juice from duct cells

Action in liver:
- increase bile production (but not release)

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8
Q

Secretin inhibited by what

A

alkaline content in duodenum

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9
Q

Gastric inhibitory peptide

  • aka
  • secreted by what
  • secreted when
A
  • glc-dep insulinotropic peptide
  • produced by K cells of duodenum and jejunum
  • secreted when there is (glucose and fatty) chyme in the duodenum
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10
Q

Gastric inhibitory peptide

  • Action
  • inhibited by what-
A

Action in stomach

  • decrease gastric gland secretion
  • gastric motility during gastric phase

Action in pancreas
- stimulate insuline secretion

Inhibited by lack of stimulus as digestion products transit through the system

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11
Q

Motilin

  • secreted by what
  • action
A
  • secreted by chromaffin-like cells in stomach
  • action
    1. acts on GPCR of myenteric ENS neurons
    2. increase contraction of smooth muscle of stomach and SI between meals
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12
Q

Somatostatin

  • aka
  • secreted by what
A 
- aka growth hormone inhibiting hormone
Secreted by:
- Hypothalamus
- D cells of pancreatic islet cells
- GI mucosa
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13
Q

Somatostatin

- stimulated by what

A
  • food in stomach

- SNS activity (don’t want to digest during SNS activation)

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14
Q

Somatostatin

- action

A
  • stomach: decrease all gastric secretions, motility, and emptying
  • pancreas: decrease secretions
  • gall bladder: decrease contraction and bile release
  • SI: decrease GI blood flow and intestinal absorption
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15
Q

Serotonin

  • produced by what in GI system
  • in response to what
  • action
A
  • produced by stomach mucosa
  • in response to food in stomach
  • action: stomach contraction
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16
Q

Histamine

  • produced by what in GI system
  • in response to what
  • action
A
  • stomach mucosa
  • response to food in stomach
  • action: parietal cell secretion of gastric acid
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17
Q

Enteric nervous system

  • location
  • three types of neurons
A
  • wall of digestive tract from esophagus to anus
  • Afferent: receptors in mucosa sense chemical, mechanical, osmotic changes
  • Motor: control smooth muscle motility, arteriolar diameter, glandular secretion, absorption
  • Interneurons
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18
Q

How is ENS connected to CNS?

A
  • via ANS fibers
  • operates independently
  • neurotransmitters: Ach, serotonin, NE, GABA, ATP, CO, NO
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19
Q

Two ENS neural plexuses list

A
  1. Myenteric (Auerbach) plexus

2. Submucosal (Meissner’s) plexus

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20
Q

Myenteric plexus

A
  • between long and circular smooth muscle layers

- primary motor control: smooth muscle activity, propulsion along GI tract

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21
Q

Submucosal plexus

location

A

between circular muscle and luminal mucosa

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22
Q

Submucosal plexus

innervation

A
  • glandular epithelium: increase mucous secretion
  • intestinal epithelial cells: endocrine secretions
  • submucosal blood vessels: increase GI blood flow by releasing vasodilators (VIP/vasoactive intestinal peptide & NO)
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23
Q

Extrinsic innervation of GI

A
  • primarily parasympathetic
  • vagus and sacral outflow
  • generally increases intestinal smooth muscle activity
  • synapses to cholinergic fibers of both ENS plexuses
24
Q

Sympathetic nervous system in GI

A
  • generally decreases activity

- post-gan fibers synapse on both ENS plexuses, directly to smooth muscle, blood vessels (vasoconstriction)

25
Q

Control of food intake factors

A
  • food preferences
  • emotions
  • environment
  • lifestyle
  • circadian rhythms (cortisol increase in am leads to hunger)
  • many hormones that direct GI function have and effect on behavior also
26
Q

Hormones that control food intake list

A
  1. Leptin

2. Ghrelin

27
Q

Leptin

  • where produced
  • action overview
A
  • produced by apidose

- controls fast reserves: inhibits hunger when fat reserves are met

28
Q

Leptin

  • what receptors does it target
  • action details
A
  • targets receptors in arcuate nucleus of hypothalamus
  • inhibits hunger by counteracting effects of neuropeptide Y, potent hunger promotor
  • stimulates satiety by promoting a hunger suppressant alpha-MSH
29
Q

Ghrelin

  • produced where
  • in response to waht
A
  • produced by stomach, pancreas, and adrenal glands

- response to empty stomach: increases right before meal, decreases after meal

30
Q

Ghrelin

- targets

A
  • hypothalamus
  • increase hunger, increase food intake
  • nucleus accumbens
  • center for motivation, pleasure, reward, reinforcement
  • stomach
  • increase gastric acid secretion and GI motility
31
Q

What inhibits ghrelin

A

leptin

32
Q

Peristalsis

A
  • contractions along length of GI tract
  • reflex response to wall distention: local stretch activates myenteric plexus
  • contraction behind stimulus (Act, sub P) and relaxation in front of stimulus (NO, VIP)
  • rate increased/decreased by intrinsic innervation (depending on location, colon is slower, stomach is faster)
33
Q

Segmentation and mixing

A
  • ENS mediated pattern of contraction at both ends of a segment with contraction in the middle (mixing)
  • impedes forward progress, slows transit time, increases mixing, digestion, and absorption
34
Q

Basic Electrical rhythm

  • describe
  • mediated by what
A
  • spontaneous rhythmic fluctuations in membrane potential
  • rate varies by location (stomach vs. duodenum)
  • mediated by “interstitial cells of Cajal” which are pacemaker cells
35
Q

Basic electrical rhythm

  • cause what
  • overall goal
  • nervous input
A
  • spike potentials at peak of BER create contraction
  • coordinates peristalsis and segmentation
  • Vagus input increases and adrenergic input decreases
36
Q

Migrating motor complex

  • describe
  • initiated by what
  • duration
A
  • GI motility under fasting conditions (inter digestive maintenance)
  • initiated by motion q 100 mins
  • duration is 5 minutes
37
Q

Migrating motor complex

- 3 phases

A

Phase 1: quiescent, no activity
Phase 2: irregular electric and mechanical activity that does not propagate
Phase 3: motilin peaks, wave of contraction sweeps along length of tract

38
Q

What does food ingestion do to motilin, BER, and peristalsis

A

inhibits motilin

returns BER and peristalsis

39
Q

Mastication

A

mechanical bd of food, mixes with saliva, forms bolus with tongue and cheek

40
Q

Swallowing

A
  • reflex triggered by afferent impulses to CNs V, IX, X
  • integration of motor impulses in thalamus
  • soft palate elevates to close nasopharynx
  • glottis covers trachea
  • peristalsis draws bolus to esophagus
41
Q

Lower esophageal sphincter

A

Internal

  • closed sphincter
  • relaxes upon swallowing

External

  • skeletal diaphragm muscle encircles lower esophagus
  • phrenic innervation allows coordination of respiration and intraabdominal pressure to prevent backflow
42
Q

Motility of stomach

A
  • funds relaxes to accept food
  • astral systole: contractions of distal stomach
  • secretions are released, mixing and churning occurs
  • lasts 3-4 hours
43
Q

Compare the time in stomach of:
carbs
protein
fatty meal

A

Carbs < protein < fat

**Fat = satiety

44
Q

Process of stomach emptying

A
  • wave of coordinated contraction
  • antrum to pylorus to upper duodenum and relaxation of pyloric sphincter
    = controlled drip of chyme into duodenum
45
Q

Motility of Small intestine

A
  • peristalsis moves material distally
  • BER: faster proximally (jejunum) slower distally (ileum)
  • segmentation allows mixture of chyme with pancreatic and intestinal secretions and bile
46
Q

Colon motility

  • goal
  • timing
A
  • dehydration and compaction

- material enters 4-8 hours post meal, elimination 9-12 hours post meal

47
Q

Ileocecal valve

A
  • part of ileum, projects into cecum
  • remains closed to prevent retrograde contamination of small intestine from bowel
  • valve opens as pressure in ileum increases
48
Q

Colon motiliy

- two types of movement

A 
Peristalsis
- slower in colon
- moves material to rectum
Segmentation
- gives time for water absorption to occur
- 1-2 L fluid reduced to loss of 200 mL
49
Q

Colon mass movements

A
  • simultaneous contraction of large confluent areas (vs. peristalsis which is local)
  • 3-4 qd
  • occur during or just postprandial (activated by food in stomach)
  • moves material through colon
50
Q

how does fiber affect mass movements in colon

A

increases strength of contraction, gives contraction something to work against

51
Q

Gastroileal reflex

A
  • gastric peristalsis stimulates ileal peristalsis, pushing small intestine contents towards colon
52
Q

Defecation reflex

  • initiated by what
  • neural input
A
  • initiated by distention of rectum

- Parasympathetic sacral outflow (relaxation of anal sphincters, rectum contraction)

53
Q

What happens to defecation reflex if evacuation is delayed

A
  • rectum relaxes
  • sphincters contract
  • reflex occurs again at next mass movement
  • allows for more time
54
Q

What pressure causes involuntary evacuation

A

55 mmHg

55
Q

During evacuation what happens

A
  • rectal contraction
  • valsalva increases intra-abdominal pressure
  • internal and external anal sphincters relax
  • levator ani mostly relax, lowering rectal pressures (decrease curvature)
  • feces leaves the body
56
Q

Gastrocolic reflex

A

distention of stomach causes contractions of rectum and desire to defecate

GI 1 (16 decks)

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