Exam 2: Digestive System Flashcards
alimentary canal
continuous muscular tube that digest food and absorbs nutrients
accessory organs
- organs that aid in digestion
- produce secretions to help breakdown food
functions of GI tract
provides body with water, electrolytes, and nutrients
(maintain function and growth)
- long “tube” from top of mouth down to anus
GI tract requires what
- movement of food
- break down food to absorbable material
- absorption of digestive material
- neural control (intrinsic and extrinsic)
major actions of the GI tract
- absorption - nutrients/water
- digestion- breakdown of food into absorbable molecules
- propulsion/motility- propel ingested food from mouth to rectum
- secretion- enzymes and fluid for digestion/absorption
epithelial cells in GI tracts
`line entire GI tract and serve as primary barrier
- specialized epithelial cells secrete and absorb compounds to/from lumen
alimentary (GI) canal layers
(lumen)
- mucosa
- submucosa
- muscularis externa
- serosa/adventitia
small intestine vs large
- most nutrients is absorbs in the small intestine
- large is more for movement and dealing with water for balance
mucosa
inside layer of the alimentary canal (lining the lumen)
- secretes mucus
- absorb digestive end-products
- protect against disease
submucosa
supports the mucosa (areolar connective tissue)
- rich supply of blood
- lymphatic vessels
- lymphoid follicles
- nerves
muscularis externa
mostly smooth muscle
- moves things down
- peristalsis and segmentation
abdominopelvic cavity
contains digestive organs
lined by serous membrane (serosa)
peritoneal cavity
fluid-filled sac
- visceral - inner
- parietal - outer
mesentary in the peritoneal cavity
double-walled peritoneum
- rich blood upply
retroperitoneal
anything outside of the peritoneal cavity is retroperitoneal
- this is lined with adventitia vs serosa
serosa
freely moving - fluid between layers
- only on organs in the peritoneal cavity
- outermost layer of the alimentary canal
adventitia
rigid and binding - not moving
- only on organs that are retroperitoneal
ex. esophagus (stuck in place)
splanchnic circulation
blood supply for digestive organs
- arteries branch directly from abdominal aorta
- hepatic portal vein takes blood from organs to the liver before emptying into interior vena cava
myenteric nerve plexus
muscular layer -> contraction
- between circular and longitudinal muscle layers
submucosal nerve plexus
stimulating glands to excrete
- in submucosa
parasympathetic NS fibers
preganglionic fibers are long and synapse in ganglia INSIDE the wall of the GI tract
sympathetic NS fibers
preganglionic fibers are short and synapse in ganglia OUTSIDE of the GI tract
GI extrinsic PNS
PNS is supplied by the VAGUS N. and the PELVIC N.
vagus N of the GI extrinsic PNS
innervates the UPPER GI tract
- upper third esophagus w/ striated muscle
- wall of stomach
- small intestine
- upper colon
pelvic N of the GI extrinsic PNS
innervates the LOWER GI tract
- striated muscle of anal canal and walls of lower colon
GI intrinsic/enteric NS
- intrinsic/enteric NS directs all functions of the GI tract
- located in gangli in the myenteric and submucosal plexus
- controls contractile, secretory, and endocrine functions of GI
enteric/intrinsic NS
has both long and short reflex arcs
GI neurocrines
neurotransmitters and neuromodulators in the GI tract in the enteric NS
neuromodulators
modulate activity of neurotransmitters
GI neurocrines
- acetylcholine - cholinergic neurons
- contract smooth muscle
- increase salivary, gastric, pancreatic secretion - norepinephrine - adrenergic neurons
- relaxation of smooth muscle
- salivary secretion
GI system regulatory substances
GI peptides are classified as hormones (endocrine), paracrine, or neurocrines
- based on whether peptide is released from an endocrine cell or a neuron from the GI tract
autocrine, paracrine, and endocrine
autocrine- communicates w/ your own activity
paracrine- nearby cell secretion, no bloodstream
endocrine- bloodstream HAS to be involved
GI peptides functions
- contraction and relaxation of smooth muscle
- secretion of enzymes for digestion
- secrete fluid and electrolytes on tissues
- some regulate secretion of other GI peptides
ex. somatostatin inhibits secretion of all the GI hormones
somatostatin
INHIBITS secretion of all the GI hormones
neurocrines (action potentials)
substances synthesized in neurons of GI tract and are released after an AP
- after released, they diffuse across synapse and act on target cell
- in GI tract: ACh and norepinephrine
endocrine (secretion)
secreted, pass through liver, enter systemic circulation to target cells (can either be in GI or elsewhere) (hormones)
- gastrin
- cholecystokinin (CCK)
- secretin
- GIP
paracrine (diffusion)
secreted by enteric (intestine) cells of the GI tract
- act locally within the SAME tissue that secretes them
- do NOT go into the bloodstream
- somatostatin = inhibitory
- histamine = stimulates H+ secretion (acid where digestion occurs)
gastrin
secreted by G cells of the stomach
- stimulates growth of gastric mucosa
- stimulates H+ secretion and is inhibited by a low pH of the gastric contents
secretin
secreted by S cells of duodenum in response to H+ and fatty acids in the lumen of the small intestines
- secreted when pH is < 4.5 in SI
- promotes secretion of pancreatic and biliary HCO3- which neatralizes H+ in the lumen
- neutralization of H+ is necessary for fat digestion
GIP
secreted by K cells in the duodenum and jejunum mucosa
- increases insulin and decreases H+ secretion
- has amino acids in common with secretin and glucagon
CCK
secreted by I cells of duodenum and jujenum in response to monoglycerides/fatty acids and peptides/amino acids (not triglycerols)
- improves digestion by slowing down the emptying of food from the stomach
- stimulates production of bile in liver as well as gall bladder
- ensures pancreatic enzymes and bile salts are secreted
CCK major actions
- contraction of gallbladder
- secretion of pancreatic enzymes
- secretion of bicarbonate from the pancreas
- growth of pancreas and gallbladder
- inhibition of gastric emptying
CCK contraction of gallbladder
relaxtion of the sphincter of Oddi ejects bile from gallbladder into the lumen of the small intestine
- bile is needed for emulsification of dietary lipids
CCK secretion of pancreatic enzymes
pancreatic lipases digest ingested lipids to fatty acids, monoglycerides, and cholesterol to be absorbed
pancreatic amylase vs protease
amylase- digests carbohydrates
protease- digests proteins
CCK growth of pancreas and gallbladder
CCK has an effect on pancreas and gallbladder bc these are major target organs
CCK inhibition of gastric emptying
slows gastric emptying and increases gastric emptying time
- critical for fat digestion and absorption
- CCK slows delivery of chyme (partially digested food) from stomach to small intestine ensuring time for good digestion and absorption
what does secretin inhibit?
inhibits the effects of gastrin on the parietal cells (H+ secretion and growth)
- gastrin produced HCL after a meal into bloodstream, secretin blocks how much acid is being produced
whats unique about GIP
only GI hormone that is secreted in response to all three types of nutrients
- glucose
- amino acids
- fatty acids
stimulation and inhibition of GIP
- GIP stimulates insulin secretion by the pancreatic B cells
- GIP inhibits gastric H+ secretion and gastric emptying
types of paracrines (substance secreted by a cell)
somatostatin and histamine
somatostatin paracrine
secreted by D cells in the GI mucosa in response to decreased lumin pH
- inhibits secretion of other GI hormones and gastric H+ secretion
- secreted by hypothalamus and pancreas cells
histamine paracrine
secreted by endocrine type (ECL) cells of the GI mucosa
- stimulates H+ secretion by the gastric parietal cells
histamine vs somatostatin
histamine stimulates H+ secretion
somatostatin inhibits H+ secretion
satiety (feeling of being full)
satiety and feeding center
hypothalamus in satiety
controls feeding and appetite
- contains nuclei with neurons that project onto the satiety/feeding centers
satiety center
inhibits appetite
located in the ventromedial hypothalamus
ex. ventromedial hypothalamic lesions = obesity
feeding center
located in the lateral hypothalamus
ex. lateral hypothalamic lesions = anorexia
anorexigenic neurons
release pro-opiomelanocortin (POMC) which DECREASES appetite
orexigenic neurons
release neuropeptide Y and cause and INCREASE in appetite
muscles in the GI tracts
muscles are unitary smooth muscle
- electrically coupled gap junctions allows cell-to-cell spread of action potentials that provide smooth contractions
peristalsis (motility)
circular and longitudinal muscle
circular muscle
contracts and results in shortening of a ring of smooth muscle
- decreases diameter of that segment
longitudinal muscle
contracts and results in shortening
- decreases the length of that segment
ex. think of a catipillar moving
steps of peristalsis
- contraction of circular muscles behind the food mass
- contraction of longitudinal muscles ahead of food mass
- contraction of circular muscle layer forces food mass forward
