Gastrointestinal Physiology Flashcards
what does uveitis correlate with
gut inflammation (ex. crohn’s disease)
why is the gut important to optometry
in the sense of nutrition’s effect on the eye
what is digestion
mechanical and chemical breakdown of food into molecular constituents
absorption of nutrients goes from the digestive tract lumen to the….
blood and lymph
what is motility
mixing of food for digestion and absoption
propulsion of food through digestive tract (GI tract)
what is taste
chemical sensitivity to food
what are the different organs that have associated lymphatic tissues (ALTs)
gut ALT (GALT)
mucosal (MALT)
conjunctive (CALT)
what are peyer’s patches
wehre is the highest concentration
aggregates of immune cells in the gut
highest concentration in the distal ileum
what cells are meant to prevent food allergies
certain cells which line the gut are meant to prevent food allergies
from which development layer are the myenteric plexus and meissner’ plexus derived
neural crest
why does a gut have “a nervous system unto itself”
it operates w/o much input from the CNS
where is the myenteric (Auerbach’s) plexus located
btwn circular and longitudinal muscle layers
-part of muscalaris externa
where is the meissner’s plexus
just inside the inner circular layer of muscle
-part of submucosa
what are the accessory organ
liver
gall bladder
exocrine pancreas
what are the componenets of the small intestine
duodenum
jejunum
illeum
what are the components to the large intest
cecum ascending colon transverse colon descending colon sigmoid colon rectum anus
what is the epithelium of the mucosa used for
secretion and absorption
what are the components to mucosa
epithelium
lamina propria
muscularis mucosa
what are the components of the muscularis externa
inner circular/outer longitudinal
auerbach’s (myenteric) plexus
what does the muscularis mucosa do
contract fairly continuous
gently agitates surface ep, allowing for “enhanced contact” btwn epithelium and food in the lumen
any neuron outside of the CNS is _____ derived
everything else is ____ Derived
neural crest
neural tube
how do the layers of the histological organization go from inner to outer
epithelial cells lamina propira muscularis mucosa mucosa submucosa muscularis externa serosa
what are smooth muscle cells linked by
what does this allow for
what do most gut muscles act as
gap junctions
allows for electrical syncitium
most gut muscles act as unitary muscles
what kind of cells are interstitial cells of cajal
what are they produced by
pacemaker cells
produced by inactivation and activation of Na-K-ATPase
electrical slow waves are everywhere, what plays an important role in this
ca influx plays an important role in action potential mediation
what produce muscle contraction
the magnitude is proportional to what
caused by an influx of what
spike potentials
- magnutude proportional to spike #
- caused by influx of Ca
- number of spikes is influenced by various nts
what are insterstial cells of cajal produced by
inactivation and activation of Na-K-ATPase
electrical slow waves may trigger action potentials, what channel mediates this?
what can happen when these are used to treat cardiovascular disorders?
L-type Ca channels
-diordered GI motility may be side effect of treating cardiovascular disorders w/ L-type channel blockers
what is the enteric NS
-what kind of neurons can it control
extension of CNS that controls GI tract independently of CNS control
-controls more than a million neurons: sensory, motor, interneuron
what are the 3 patterns of GI motility
- propulsion
- trituration
- mixing
what is propulsion?
how does this help push food along in one direction
movement of ingested food, liquids, GI secretions and sloughed cells
peristalsis: alternating contraction/relaxation of smooth circular and longitudinal muscles
what is emesis
technical term for vomiting
what is trituration
- where does this take place
- once complete, where does the food leave through
crushing and griding of food in the stomach
- crashing together of waves moving in opp directions in the stomach
- takes place in the ANTRUM with the pylorus closed (retropulsion)
- once complete, leaves through the opened pylorus
what is mixing
blending various secretions (pancreatic, biliary, intestinal) w/ nutrients
what are the 2 gastroenteric reflexes and what do they do
what are gastroenteric reflexes
gastroilial: empties the terminal portion of the ileum
gastrocolic: movements in colon
- distension of the stomach initiates reflex that increases the rates of peristalsis and secretion along the small intestine
what is the rectoanal reflex
what muscle does this
when rectum is distended, there is reflex relaxation of internal anal sphincter
-puborectalis muscle of the pelvic floor (tail wagging)
what muscle is the puborectalis a part of
part of levator ani muscle
-when it relaxes, defacation occurs
what is hirschsprung’s dieaese
congenital blockage of the large intestine due to improper muscle movement in the colon
-nerves of the myenteric and meissner’s plexi haven’t migrated into the right positions to stimulate the appropriate msucles for propulsion
congenital megacolon is associated w/ waht
down syndrome 10% of pts
what is the current theory of hirschsprung’s disease
may be caused by failed migration of colonic ganglion cells during gestation
-most cases not familial
in hirschsprung’s what causes the bowel and abdomen to swell
intestinal contesnts build up behind the blockage, causing the bowel and abdomen to swell
-if the condition if severe, the newborn may fail to pass stool and may vomit
what is the salivary gland secretion regulated by
what is its baseline secretion
parasympathetic nervous system
30 ml/hr
-needed even when not eating, for dental health
how does salivary gland secretion lubricate food
acinar cells in the glands produce the more watery components of secretions
salivary gland secretion begins digestion, how?
- what does amylase break polysaccharides into
- what does lingual lipase break down triglycerides to
carb and fat digestion begins in the mouth
- amylase breaks down polysaccharides to oligosaccharides and maltose
- lingual lipase: breaks down triglycerides to fatty acids and glycerol
salivary gland secretion has an immune function, what is involved
IgA is the secreted immunoglobulin
-salivary glands, mammary glands, lacrimal glands, lining of GI and respiratory tracts
Lysozyme and lactoferrin: antibacterial enzymes
-lysozome breaks down bacterial cell walls
what does epidermal growth factor do to salivary gland secretion
promotes healing of the mucosa in the mouth and stomach
prevents and heals ulcers
saliva is hypotonic, what are the ions
higher K and HCO
-pumped into the acinar duct lumen (saliva)
-aldosterone stimulates K removal from tissue and into the lumen
low Na and Cl
-pumped out of saliva
-water can’t follow Na out bc of the properties of the duct cells
chloride shift
-cl leaves in exchange for HCO3
-keeps saliva relatively basic
-neutralizes stray stomach acid/protects the bottom of the esophagus
in gastric secretion, the stomach absorbs water and lipid soluble substances, what are they
alcohol, glucose, aa, medium chain fatty acids, drugs
gastric secretion prepares _____ for digestion
chyme (food slurry)
oxyntic glands are in the fundus and corpus (body) of the stomach and parietal cells in the glands secrete _____
- this and vit _____ are required for ______
- what results ffrom poor absorption of this vit
intrinsic factor and HCl
- intrinsic factor complexes w/ vit B12 and is required for B12 absorption in the distal ileum
- pernicious anemia results from poor B12 absorption
histamine acts on parietal cells to promote _____
acid production
-binds to parietal H2 receptors
chief cells produce ____ and _____
what do these do
gastric lipase and pepsinogen
- gastric lipase continues fat digestion
- pepsin digests proteins and is derived from pepsinogen+acid
pyloric glands are in the antrum and pyloric regions, what kind of cells are here and what do they do
neuroendocrine cells: release hormones that act in the gut
- G cells: in antrum, release gastrin (hormone that stimulates acid production)
- parasympathetic innervation by vagus to parietal cells promotes acid release
- D cells: produce somatostatin and inhibits gastrin secretion
what are the 4 ways to promote stomach acid production
- G cells release gastrin which acts on parietal cells
- parasympathetic innervation of parietal cells (via acetylcholine)
- parasym stimulation of G cells => #1
- histamine secreting stomach cells release hisatmine, which binds to H2 receptors, which cause parietal cells to promote acid production
carbonic anhydrase in parietal cells results in generation of what
H and HCO3
H is pumped out in exchange for K, this involves ATPase
-Cl follows H out to form HCl in the stomach
chloride ions are brought into the cells via ______
what is the movement of cells
chloride shift
- cl in from the blood, HCO3 out
- btwn blood and parietal cells
- an “alkaline tide” into the blood (thought to protect cells from the acid on the other side)
what is zollinger-ellison syndrome caused by
what can this lead to
cuased by gastrin secreting tumor of the pancrease; leads to peptic ulcers (most actually in duodenum)
what kind of drugs retulates stomach acid secretion
- H2 receptor blockers
- ex. zantac, pepcid, cimetidine (tagamet) - Ach/Muscarinic blockers
- ex. atropine - proton pump inhibitors
- block H/K ATPase
ex. omeprazole (prilosec)
proton pump inhibitor use is linked w/ increased susceptibility to bacterial infections, how
reduce the acidity/effectiveness of stomach acid in destroying pathogens
what are the 3 phases of stimulation of acid secretion after ingesting a meal
- cephalic
- thinking about food gets things going
- via vagus stim of parietal and G cells - gastric
- due to physical distension (by food entry)
- mediated by local reflexes - intestinal
- stimulated by aa in the blood
what stimulates secretion
what inhibits secretion
stim: vagal stimulation, histamine, and gastrin
inhibits: chyme in duodenum; directly and via gastric inhibitory peptide (GIP) and secretin produced in duodenum
once you’re in the duodenum, material will come into contact w/ pancreatic secretions, how
secretions via sphincter of oddi
what pH do pancreatic enzymes work best at
neutral pH
- pancreatic secretions have the same osmolarity of plasma (more basic)
- neutralize acidic chyme
what do acinar cells release
some ions and enzymes
-small volume containing Na and Cl ions and enzymes
ductal cells are like the stomach acid secreting cells in reverse, an “acid tide”
-what kind of system does this use? what occurs
antiporter system, fueled by entry of Cl from the lumen into the cell -exchanged for HCO3 -no ATPase involvement in this antiport Na/K antiport btwn duct cell and blood -Na to blood -K to the cell -uses NA/K ATPase
where is the cystic fibrosis transmembrane conductance reulator located at? what does it secrete? -what does it allow re-entry of waht do mutations in the gene cause? what are the signe?
- located on the luminal side of the membrane
- secrete Cl ions out of the cells
- allows re-entry of Cl to fuel antiport for the acid tide
- mutattions in this gene cause cystic fibrosis
- signs: salty tasting skin, poor growth and weight gain, thick and sticky mucus, frequent chest infections, coughing, shortness of breath
how does secretin and VIP retulate pancreatic secretion
secretin and VIP: secreted by endocrine cells in the duodenum in response to acid
- acts on ductal cells to increase HCO3 secretion to neutralize chyme
- responsible for water and electrolytes
how does CCK regulate pancreatic secretion
acts on gallbladder and pancrease
stimulates bile, enzymes, etc
pancreatic acinar cells secrete ____ which break down nearly anything
why can pancreatitis be deadly?
enzymes
- very unpredictable
- massive enzyme release
- local breakdown in the post body wall
what is bile composed of
bile salts, pigments (bilirubin), cholesterol, phospholipids, proteins
what is bile produced by
where is it concentrated in
can a person live w/o a gallbladder?
what stimulates gallbladder contraction
hepatocytes and concentrated in the gallbladder
- a person can live w/o a gallbladder, but has to be more attentive of fat intake
- CCK stimulates gallbladder contraction
what are the functions of biliary secretion
- absorption of lipids (bile acids)
- cholic and deoxycholic acids
- forms micelles to digest lipids
- reabsorbed in the distal ileum - excretion of cholesterol and bilirubin
what is jaundice
certain liver diseases interfere w/ normal production and discharge of bile
-pigments deposit in sclera, skin, tissues, some fluids=> yellowish pigmentation
bilirubin is a major component of bile pigments
-breakdown product of what?
breakdown product of Hb
how do CCK and secretin work in regulation of bile production
CCK: release stimulated by presence of fatty acids or aa
- causes contraction of gall bladder and indirectly relaxes spincter of oddi (like vagus nerve)
secretin: release from intestinal mucosa stimulated by presence of acid - stimulates bicarbonate production by bile duct cells (like pancreatic duct cells)
- this is how bile contributes to neutralization of acid in duodenum
when do gallstones form
form when bile has too little bile salts or too much cholesterol or billirubin
how does gastrin stimulate bile secretion
directly and indirectly by increasing acid production
what do steroids do to bile secretion
inhibit
what are some other fucntions of the liver
- plasma protein secretion
- anything ending in “inogen” - nutrient store formation
- metabolite conversion
- detoxification
- cytochrome P450: breaks down toxic molec
- converts ammonia to urea
in carbohydrates where does digestion start
- what does this form
- what does the brush border membrane break down
- what does glucose and galactose absoroption depend on
starts w/ salivary amylase, then pancreatic amylase
- forms disaccharides and oligosaccharides
- brush border membrane breaks down disaccharides
- glucose and galactose absorption depends on Na dependent carrier (fructose uptake by facilititate transport)
where does protein digestion start
pepsinogen is converted to ______ in stomach
trypsinogen to ______
-what is this converted by
- starts in stomach, then small intestine
- pepsinogen converted to pepsin in stomach
- trypsinogen to trypsin
- converted by enteropeptidase
- trypsin activates other enzymes
essential fatty acids are _______
-omega 3 and omega 6 have what kind of bond at
unsaturated
double bond at 6 and 3 from the end of the molec
which omega 3’s are essential for normal development of vision of newborns
eicosapentaenoic (EPA) and docosahexaenoic (DHA)
where does digestion of lipids start in
using what kind of cells
starts in mouth w/ lingual lipase, followed by stomach w/ acid lipase (chief cells)
pancreatic lipase forms ____ and ____ to be stored in adipocytes
monoglyceride and 2 fatty acids
phosphlipase digests _____
cholesterol esterase breaks down ____
phospholipids
cholesterol
how do bile salts emulsify fats
by forming micelles which enhance delivery to, and absorption by, brush border
what do micelles transport
what do they prodivde for digestion of lipids
- transport poorly soluble monoglycerides and fatty acids
- provide increased surface area for digestion of lipids in the micelles
the gut secretes chylomicrons and VLDLs
- where are the absorbed fats reassembled
- how are they packaged for easier transport
- transported out of the gut via what
in the enterocyte (lining cells of the gut)
- packaged into chylomicrons for easier transport
- transported out of the gut via the lymphatic system
what are the fat soluble vitamins
-how are they absorbed
A, D, E, K
-absorbed passively and incorporated into chylomicrosn
iron is an important component of heme and also participant in many enzymatic rxns
-how is it transported in the blood
iron is actively transported in the blood via transferrin after being converted to ferritin by binding w/ apoferritin
