GI phys overview Flashcards
define Bolus
rounded mass of food ready to swallow
define Borborygmi-
abdominal rumbling sounds.
define Chyme
semifluid mass of partly digested food passed from the stomach to the duodenum
Define Diverticulum
outpouching of GI wall
define Eructation
belching
Define Peristalses
propulsion of food through the esophagus and intestines
Define Postprandial
after feeding
Define Sitophobia
fear of eating
DEfine Steatorrhea-
fatty stools
small intestine prefix
ileo
large intestine prefix
colo
rectum prefix
proct
Upper GI structures
Oral Cavity, Pharynx, Esophagus, Stomach, Small intestine
Lower GI structures
large intestine
what are the parts of the small intestine
duodenum,jejunum, ileum
what are the parts of the large intestine
cecum,colon,rectum,anus
What are the accessory organs of GI tract?
Salivary glands (parotid, submandibular, sublingual)
Exocrine Pancreas
Liver- Hepatic system
Gallbladder- Biliary system
What spincters are voluntary control?
external anal and upper esphageal
pylorus sphincter connects what?
stomach to the small intestine
what does the sphincter of oddi connect?
the galbladder to the small intestine
what does the small intestine have to increase surface area?
villus and crypts
what does the colon have to increase surface area?
just crypts
what are special about the GI epithelial cells?
constant renewal, stem cells at the base of the crypts divide, differentiate and migrate to the tips of the villi
Why is it important that GI epithelial cells renew every 3-6 days?
Prevent the accumulation of mutations due to toxin exposure
What are the 4 major GI wall types?
Mucosa, submucosa, muscularis externa, serosa
What does the muscularis externa contain in its layer
circular muscle (mechanical digestion), myenteric nerve plexus, longitudinal muscle for propulsion
what is a diverticulum?
single pouch protruding from alimentary tract. Usually false not true. inflammation due to lack of fiber, can progress to diverticulitis
What are some characteristics of mucus? Secreted by?
viscous, hydroscopic gel, goblet cells
How are mucin monomers combined into plexes?
by disulfide links,
2 layers in the stomach and colon, 1 layer in small intestine
What protects the protein core of the mucus?
- Glycosylation protects the protein core from proteases (pepsin) in the stomach
What are enterocytes coated with
transmembrane mucins
what are the 4 basic processes faciliation caloric uptake?
Digestion, Absorption – excess capacity (95% of diet lipids)
Secretion, Motility – under neural and hormonal control
What does the teeth do for digestion?
mastication
What does the salvia do?
lubricates and breaks down, with chewing creates the bolus
What does the stomach do for digestion?
movements and pepsin digests food into chyme
what does the duodenum do for digestion?
brush border enzymes from pancrease and bile salts from liver
Where are amino acids, monosaccharides, and
lipids absorbed
small intestine-duodenum and jejunum
where are cobalamine (B12) and bile salts/acids absorbed?
small intestine-ileum
What absorbs water and electrolytes
small and large intestines
What does absorption depend on?
Splanchnic Circulation, 1-5 litersAt depending on vasomotor tone
At rest, how much CO goes to the gut?
21%
what is the blood flow from the intestine?
portal vein to the liver allowing for detoxification.
Where does the liver get its blood from?
1/4 blood from hepatic artery, 3/4 blood form portal vein
by how much can flow increase during increased gut activity?
4-5 Liters
What happens to blood flow to the GI tract during exercise and emergencies
massive vasoconstriction shunts blood away from the gut.
what does the enterohepatic circulation do
Recycling of bile salts/acids from the ileum, can alter drugs (what body goes to Rx), some metals get secreted into feces
What are the metabolic vasodilatiors that increase blood flow?
CO2, H+, K+, adenosine, etc
Chylomicrons are too large to pass through the capillary cells, so what happens to them?
they get absorbed through lacteals which empty into blood stream via thoracic duct
what is mesenteric ischemia due to?
occlusive mechanisms like thombi, or
non-occlusive mechanisms including prolonged reflex vasoconstriction (due to hypovolemia, heart failure) or abnormal levels of circulating vasoconstrictors (e.g, epinephrine, angiotensin II)
what are the effects of mesenteric ischemia?
Postprandial Pain, Sitophobia (fear of eating)
Necrosis of the tips of the villi
Loss of barrier function of the wall of the gut and uptake of vasodilator toxins (endotoxin) from the gut resulting in Septic Shock
The fluid environment of the GI tract is supplied by what
organs that drain into the GI tract and GI epiethlial
What does the fluid in the GI tract contain
ions, digestive enzymes, mucins, and bile
Where are majority of the fluids reabsorbed
reabsorbed in the small intestine with nutrients
What regulares secretion of the GI system?
Parasympathetic, hormonal, and enteric nerves
What is transmural water movement driven by?
osmotic gradients
How does water move across the epithelium?
through the cells (transcellular route) perhaps with the help of specific water channels (aquaporins) and between cells (paracellular route) according to osmotic gradients driven by active electrolyte transport.
What is conductivity defined by in regards to the epithelia
leakiness, depends on the variable presence of absense of tight junction
What coupled activity mediates fluid uptake?
electroneutral NACL absoprotion with NA/H exhanged on the apical side, CL/HCO3- exchange in apical membrane
what is secretory diarrhea
infection-increases CL secretion drwaring water into lumen
what is osmotic diarrhea
small bowel overgrowth leads to production of organic acids suffiencet enough to pull water from blood stream via osmosis
What does fluid flux depend on?
surface area available for ion transport and residence time in the lumen
What is the action of some antidiarrheal in regards to fluid flux
slows transit to increase fluid absorption
What controls the length of time food takes for digestion and absoprotion?
motility
Time spent in the Esophagus
10 seconds
time spent in the stomach
4-5 hours
time spent in the SI
2.5-3 hours
time spent in the LI
30-40 hours
total time it takes food to digest?
36-48 hiours
What is most of the GI tract made up of?
SMOOTH MUSCLE
What are the exceptions to most of the GI tract being made of muscle
striated muscle in upper third of esophagus, pharynx, external anal sphincter
GI smooth muscle contractile characteristics- describe the rhythmic
Rhythmic “phasic” (seconds) contractions and long “tonic” contractions (minutes to hours)
How is basal tone maintained in regards to Gi smooth muscle?
bassal resting tone is maintained w/o elevation in intraceullar CA2+ and without energy expenditure. (sphincters)
What can GI smooth muscle do in response to stretching?
DEPOLARIZE! leading to contraction
Proximal pressure on a sphincter causes the sphincter to do what?
relax
distal pressure a sphincter causes the sphincter to do what?
contract
The slow waves electrical activity is initiated by
interstitial cells of Cajal are phasic and propagated over a few centimeters
What are the slow waves due to?
increase in calcium followed by repolarization by K+ channels
What can change in the slow waves-amplitude or frequency?
AMPLITUDE! by signals releasing calcium from internal stores or opening Ca++ channels on plasma membrane
Parasympathetics release of AcH binds to what receptor? and causes what?
Myscarinic-increase of CA into cell, phophorylation of myosin and increase ATP actvity by increase myosin/actin binding. this leads to contraction
What do peristaltic contractions do to the bolus of food?
propel intestinal contents forward, longitindal
wha do Segmenting contractions do to the bolus of food?
contractions of circular muscles in small and
large intestine that locally mix contents (churning), nonpropulsive
What controls the migrating motor complex?
motiln
what is the migrating motor complex?
relaxation of sphincters and contractions in stomach and small intestine occurring during fasting
what is also know as the mini brain?
the enteric nervous system,can operate independently of CNS! but control of secretion and motility may be less than optimal.
Where are the submucosal nerve plexus?
small and large intestine, sensory and blood flow, Meissner’s
Where is the myenteric nervous plexus?
between circular and longitudinal muscle layer from esophagus to internal anus
Auerbach’s
changes in GI tract are detected by what?
intrinsic sensory receptors including: stretch receptors, osmoreceptors, and chemoreceptors
Do Chemosensitive taste receptors always evoke taste?
NO! they are other places in the body besides the mouth
What excites the afferent sensory neurons of the enteric nervous system?
distension of the gut wall or chemical signals from the lumen of the gut transmitted to sensory neurons.-like 5HT
many of the sensory neurons are stimulated by serotonin (5-HT) released from what kind of cells?
mucosal enterochromaffin cells (ECL) - respond with a few action potentials followed by hyperpolarization (adaptation)
What transfers the info about the gut environment?
the myenteric plexus- relays signals up and down the gut
The enteric efferent motorneurons are found where? what kind of neuron are they?
myenteric plexus, unipolar
What excites the efferent motorneurons?
Fast ESPS’s, respond to sustaintined trains of AP
What does the efferent motorneurons carry?
information to GI smooth muscle, vascular smooth muscle, GI exocrine secretory cells and GI endocrine secretory cells
What do the excitatory motorneurons release?
release acetylcholine, neurokinin A and substance P
what do the inhibitory fibers release
vasoactive intestinal peptide (VIP) and nitric oxide (NO) on smooth muscle cells.
Long neural reflexes involve?
CNS AND ANS
short neural reflexes invovle?
only nerves of the enteric plexus
Nutrients activate what neural reflexes?
both autonomic nervous system and enteric nervous system promoting secretion and motility.
Afferent information leaving GI tract is carried by ?
Extrinsic Autonomic Nervous System-para and sympathetics
parasympathetics relsease what in the GI tract?
AcH! AGAIN! via vagus nerve
parasympathetics activate what in the GI tract?
REST AND DIGEST! stimulates activity of the enteric plexuses, increases GI motility and secretory activity.
Sympathetics mostly relese in the GI tract
andregerics-epi,
Sympathetics inhibits what in the GI tract? other actions?
DECREASES ACTIVITY! inhibits activity of the enteric plexuses, decreases GI motility, contracts GI sphincters, constricts GI microvasculature
What does the vaso-vagal efferent response do?
coordinate excitatory and inhibitory activity within the Enteric Nervous System to mediate peristalsis
What does the vaso-vagal afferent go?
to autonomic centers in the medulla
What are the neurotransmitters of the enteric nervous system?
AcH, gastrin releasing peptide, substance P, Vasoactive intestinal peptide, NO
Who releases AcH? Where does it go?
primary excitatory transmitter from sensory cells and from motoneurons to muscle, epithelium, secretory cells and at interneuronal junctions. intracellular Ca++
Who releases Gastrin releasing peptide? function?
released from vagal nerve endings to stimulate G cell secretion of gastrin
When is substance P released? and usually with who?
an excitatory transmitter generally co-released with acetylcholine
Vasoactive Intestinal Peptide (VIP) action is?
DILATION! Promotes motility
Relaxes smooth muscle in esophagus and stomach
Stimulates fluid secretion and promotes dilation of the GI vasculature. increases cAMP
What kind of neurotransmitter is NO? What is it usually corealsed with?
inhibitory transmitter co-release with VIP from inhibitory motoneurons, hydrophobic- intracellular targets.
What are the primary Gastro-Intestinal Hormones
Gastrin, Cholecystokinin (CCK) , Secretin, Gastric Inhibitory Peptide or Glucose-Dependent Insulinotropic Peptide (GIP), and Motilin
Gastrin is released from what cells?
G cells in antrum of stomach (vagus_
what does gastrin detect?
detect amino acids leading to pepsinogen and H+ release.
CCK is released from what kind of cells? Due to what? Stimulates what?
- I cells in D/J detectdetect fat and amino acids, secretion of pancreatic enzymes and bile salts involved in fat uptake
Secretin is released from what kind of cells? Due to what? Stimulates what?
S cells primarily in D/J detect acid stimulates secretion of pancreatic juice including bicarbonate and inhibits gastric motility.
GIP s released from what kind of cells? Due to what? Stimulates what?
K cells in D/J detect carbohydrates and fat to inhibit gastric acid secretion and stimulate insulin release from pancreas.
Motilin is released from what kind of cells? Due to what? Stimulates what?
secreted by endocrine cells; released cyclically during fasting state to initiate Migrating Motor Complex
Histamine in the GI tract is from what kind of cells and does what?
(ECL cells) , endocrine regulartor
Somatostatin in the GI tract is from what kind of cells and does what?
(D cells)- paracrine regulators
Where are digestive enzymes store?
specialized cells and and products are packaged into zymogen granules and stored.
How do digestive enzymes get released
Secretion usually involves a stimulus-induced increase in either cAMP or [Ca+2]i (or both) … which then leads to zymogen granule docking and dumping.
T/F because of all the bacteria we have in our guy, its equivalent to being outside of our body
TRUE
How is gas produced?
some of it is swallowed when eating, neutralization of gastic acid by bicarbonate generates CO2, Gas byproducts of fermentation of fiber in colon can be used by other bacteria, excreted by lungs, and evacuated
Borborygmi, “stomach rumble” is actually?
CREATED BY GAS IN THE BOWELS!
Why do people have flammable gas?
because of methenobrevibacter smithii
bacterial overgrowth syndrome occurs because of
delayed small intestine transit and diverticulum
what are side effects of bacterial overgrowth syndrome
Gas and bloating fromfermentation, Compete for B12 uptakeleading to anemia, Deconjugate bile acids leading to steatorrhea, Produce toxins altering epithelium
How do you diagnose bacterial overgrowth syndrome
Diagnose with hydrogen breath test
What are properties of the GI tract that limit growth of bad bugs
Saliva contains lactoferrin, lysozyme, and secretory IgA
Acidic environment in stomach
More lymphocytes in GI than the circulating immune system
Mucus- IgA, lysozyme, lactoferrin
Paneth cells secrete antimicrobial peptides
Digestive enzymes cleave bacteria
Diarrhea
Vomiting
Microflora prevent colonization of pathogenic microorganisms (probiotics and prebiotics, <pH)
Peristalsis, Ileoceccal valve
