Phys 4 Flashcards
Gastrointestinal regulation hormones (8)
- gastrin
- cholecystokinin
- secretin
- Gastric inhibitory peptide
- Motilin
- Somatostatin
- Serotonin
- Histamine
Gastrin
- secreted by what
- secreted when
- secreted by gastric enteroendocrine cells
- secreted in response to:
- peptides and aa
- distention of stomach
- vagal stimulation
Gastrin
- action
- inhibited by
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
Cholecystokinin
- secreted by what
- secreted when
- enteroendocrine cell of duodenal mucosa
- fatty chyme, peptides, aa in duodenum
Cholecystokinin
- action
- inhibited by
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
Secretin
- secreted by what
- secreted when
- S cells of upper SI mucosa
- in response to acidic chyme, peptides, aa, fats
Secretin
- action
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)
Secretin inhibited by what
alkaline content in duodenum
Gastric inhibitory peptide
- aka
- secreted by what
- secreted when
- glc-dep insulinotropic peptide
- produced by K cells of duodenum and jejunum
- secreted when there is (glucose and fatty) chyme in the duodenum
Gastric inhibitory peptide
- Action
- inhibited by what-
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
Motilin
- secreted by what
- action
- 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
Somatostatin
- aka
- secreted by what
- aka growth hormone inhibiting hormone Secreted by: - Hypothalamus - D cells of pancreatic islet cells - GI mucosa
Somatostatin
- stimulated by what
- food in stomach
- SNS activity (don’t want to digest during SNS activation)
Somatostatin
- action
- 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
Serotonin
- produced by what in GI system
- in response to what
- action
- produced by stomach mucosa
- in response to food in stomach
- action: stomach contraction
Histamine
- produced by what in GI system
- in response to what
- action
- stomach mucosa
- response to food in stomach
- action: parietal cell secretion of gastric acid
Enteric nervous system
- location
- three types of neurons
- 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
How is ENS connected to CNS?
- via ANS fibers
- operates independently
- neurotransmitters: Ach, serotonin, NE, GABA, ATP, CO, NO
Two ENS neural plexuses list
- Myenteric (Auerbach) plexus
2. Submucosal (Meissner’s) plexus
Myenteric plexus
- between long and circular smooth muscle layers
- primary motor control: smooth muscle activity, propulsion along GI tract
Submucosal plexus
location
between circular muscle and luminal mucosa
Submucosal plexus
innervation
- 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)
Extrinsic innervation of GI
- primarily parasympathetic
- vagus and sacral outflow
- generally increases intestinal smooth muscle activity
- synapses to cholinergic fibers of both ENS plexuses
Sympathetic nervous system in GI
- generally decreases activity
- post-gan fibers synapse on both ENS plexuses, directly to smooth muscle, blood vessels (vasoconstriction)
Control of food intake factors
- 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
Hormones that control food intake list
- Leptin
2. Ghrelin
Leptin
- where produced
- action overview
- produced by apidose
- controls fast reserves: inhibits hunger when fat reserves are met
Leptin
- what receptors does it target
- action details
- 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
Ghrelin
- produced where
- in response to waht
- produced by stomach, pancreas, and adrenal glands
- response to empty stomach: increases right before meal, decreases after meal
Ghrelin
- targets
- hypothalamus
- increase hunger, increase food intake
- nucleus accumbens
- center for motivation, pleasure, reward, reinforcement
- stomach
- increase gastric acid secretion and GI motility
What inhibits ghrelin
leptin
Peristalsis
- 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)
Segmentation and mixing
- 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
Basic Electrical rhythm
- describe
- mediated by what
- spontaneous rhythmic fluctuations in membrane potential
- rate varies by location (stomach vs. duodenum)
- mediated by “interstitial cells of Cajal” which are pacemaker cells
Basic electrical rhythm
- cause what
- overall goal
- nervous input
- spike potentials at peak of BER create contraction
- coordinates peristalsis and segmentation
- Vagus input increases and adrenergic input decreases
Migrating motor complex
- describe
- initiated by what
- duration
- GI motility under fasting conditions (inter digestive maintenance)
- initiated by motion q 100 mins
- duration is 5 minutes
Migrating motor complex
- 3 phases
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
What does food ingestion do to motilin, BER, and peristalsis
inhibits motilin
returns BER and peristalsis
Mastication
mechanical bd of food, mixes with saliva, forms bolus with tongue and cheek
Swallowing
- 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
Lower esophageal sphincter
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
Motility of stomach
- funds relaxes to accept food
- astral systole: contractions of distal stomach
- secretions are released, mixing and churning occurs
- lasts 3-4 hours
Compare the time in stomach of:
carbs
protein
fatty meal
Carbs < protein < fat
**Fat = satiety
Process of stomach emptying
- wave of coordinated contraction
- antrum to pylorus to upper duodenum and relaxation of pyloric sphincter
= controlled drip of chyme into duodenum
Motility of Small intestine
- peristalsis moves material distally
- BER: faster proximally (jejunum) slower distally (ileum)
- segmentation allows mixture of chyme with pancreatic and intestinal secretions and bile
Colon motility
- goal
- timing
- dehydration and compaction
- material enters 4-8 hours post meal, elimination 9-12 hours post meal
Ileocecal valve
- part of ileum, projects into cecum
- remains closed to prevent retrograde contamination of small intestine from bowel
- valve opens as pressure in ileum increases
Colon motiliy
- two types of movement
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
Colon mass movements
- 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
how does fiber affect mass movements in colon
increases strength of contraction, gives contraction something to work against
Gastroileal reflex
- gastric peristalsis stimulates ileal peristalsis, pushing small intestine contents towards colon
Defecation reflex
- initiated by what
- neural input
- initiated by distention of rectum
- Parasympathetic sacral outflow (relaxation of anal sphincters, rectum contraction)
What happens to defecation reflex if evacuation is delayed
- rectum relaxes
- sphincters contract
- reflex occurs again at next mass movement
- allows for more time
What pressure causes involuntary evacuation
55 mmHg
During evacuation what happens
- 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
Gastrocolic reflex
distention of stomach causes contractions of rectum and desire to defecate
