Exam 4 GI Flashcards
what are the segments of the GIT
the mouth, pharynx, esophagus, stomach, small and large intestines and the sphincters in between
what are the layers of the GIT
the serosa, longitudinal muscle, myenteric (Auerbach’s) nerve plexus, circular muscle, submucosa, submucosal (Meissner’s) plexus, muscular mucosa, mucosa and epithelial lining.
neural control is both intrinsic and extrinsic. what systems are associated with these
intrinsic, the enteric NS, which is made of the myenteric and submucosal plexus
extrinsic, the ANS, (PNS and SNS)
which stimulates and which inhibits with the use of what hormones
the SNS inhibits with NE and the PNS stimulates with ACh.
myenteric plexus is part of what NS, and where does it go from. between what layers is it found
enteric. goes from the esophagus to the anus. between the circular and longitudinal SM layers.
what is the function of the myenteric plexus. what are its stimulatory and inhibitory influences
to control GI motility.
stimulatory influences: increased tonic contraction (tone), increased contraction frequency and intensity (increased propulsion)
inhibitory influences: decreased sphincter tone (relaxation of the sphincters)
you need two things to pass food along. What two things does the myenteric plexus do to help food move along
increase the contraction and frequency of muscles, and also relax the sphincters.
what is the submucosal plexus location and function
between the esophagus to the anus. and it controls the local control (secretion, absorption, contraction of the muscularis mucosa)
why is the contraction of the muscularis mucosa important
this controls the SA of the epithelium, so this also determines the amount of absorption.
where do we get influence from the extrinsic NS of the GIT
the parasympathetic is from the cranial (vagal) nerves and the sacral nerves
the sympathetic is through the 4 plexus’s (superior cranial, celiac, superior and inferior mesenteric)
blood that courses through the gut, spleen and pancreas flow to the liver via the ___. in the liver, blood passes through the millions of minute liver sinusoids and finally leaves the liver via ___. this blood flow through the liver allows the reticuloendothelial cells to do what
- portal vein
- hepatic veins, then eventually to the vena cava
- remove bacteria and other particulate matter. it filters the blood
after a meal, what happens to GI blood flow
increased 2-3x for 3-6 hours after a meal
what are some causes of activity induced blood flow
vasodilation hormones (gastrin, secretin and CCK) vasodilator kinins low O2, high aldosterone.
what I the nervous control of the GI blood flow. gives examples
PNS: increases gut activity, and increases blood flow
SNS: directly decreases blood flow, like during auto-regulatory escape, exercise and shock
why do you get cold after eating
in the extremities, you get cold because the blood is shunted away from the extremities to the gut
arterial and venous blood flow are in ___ directions. what does this mean for blood flow and the tips of the villi. what percent of blood is shunted this way
opposite. this allows most blood O2 to diffuse from the arterioles to the venules without the O2 being carried to the tip of the villi. 80%
what happens in diseases like circulatory shock to the blood flow in villi
the blood flow to the gut becomes curtailed, and the tips of the villi become O2 deficient, leading to ischemic death and disintegration which will lead to greatly diminished absorptive capacity.
all endocrines are hormones, and all hormones are
peptides.
where are these hormones released
into the blood, travel in the circulation to get to their destination
are all neurocrines (NT’s) peptides?
no, some are peptides, like VIP and others are not like ACh and NE.
how are neurocrines released
nerves release them and they travel to target cells
how are paracrines released and on what kinds of cells do they act
released by endocrine cells and diffuse to the target cells. they act on endocrine cells via positive and negative feedback
are paracrines peptides
some are like somatostatin and other are not like histamines
what are the two structurally related families of GI hormones
gastrin and CCK and then secretin, GIP, VIP and glucagon.
GIP
glucose dependent insulinotropic peptide
VIP`
vasoactive intestinal peptide
what does gastrin do when secreted
promotes H+ secretion by gastric parietal cells (1500x more potent then histamine)
what is the tropic activity of gastrin
stimulates the growth of the oxyntic mucosa of the stomach, the duodenal mucosa and the colon mucosa
why does surgical removal of the Antrum cause atrophy
because that is where the G-cells are located that release gastrin
what do patents with gastrin secreting tumors have
mucosal hyperplasia and hypertrophy
where is gastrin released from
from the G-cells in the Antrum and duodenum
what stimulates the release of gastrin
- protein digestion products like small peptides and AA
- nervous, physical distention
- calcium, decaf coffee, wine
- high pH (when gastrin is released, it releases H ions, which will lower the pH)
what inhibits the release of gastrin
acidification of the Antrum (when the pH is low, it is negative feedback to stop secreting gastrin)
response to a meal. within and between meals
with in a meal: large amount of G-17 are released from the Antrum, the small gastrin.
between meals, small amount of G-34 are released from the duodenum (big, secreted between meals)
Gastrinoma- Zollinger- Ellison Syndrome
gastrin secreting tumor, either in a non beta cell tumor of the pancreas (80%) or G-cell tumor in the duodenum (10-15%) continually secretes gastrin into the blood which will cause hyper secretion of acid. The increased parietal cell mass and stimulation of hyperplastic mucosa as well as the increased H secretion by parietal cells and hypertrophy of the gastric mucosa.
what are the symptoms of Gastrinoma- Zollinger- Ellison Syndrome
duodenal ulcers, diarrhea, steatorrhea, hypokalemia
Gastrinoma Summary
there is hyperglastrinemia, which causes an increase in parietal cell mass and acid secretion, which causes intestinal hyperacidity. This leads to peptic ulcers or a decrease in bile salts and a decrease in lipase activity (because lipase needs a high pH to work). the decrease in bile salts and the decrease in lipase activity will cause the diarrhea, steatorrhea and hypokalemia.
how do we get steatorrhea and hypokalemia from gastrinoma
steatorrhea, the low pH will inactivate the pancreatic lipase, which causes bile salts to precipitate.
hypokalemia results from the loss of GI secretions in the stool.
CCK. what does it do, where is it released from
cholecystokinin. promotes fat digestion and absorption. released from the I-cells in the duodenum and jejunum
what causes the release of CCK
- fatty acids or monoglycerides (not TG)
- peptides and single AA
- acid (weak)
what are the 4 major actions of CCK
- emptying the gallbladder by contracting it and relaxing the sphincter of Oddi (contents can move from gallbladder to the intestines)
- secretion of pancreatic enzymes (potent stimulator) and HCO3 (weak stimulator)
- inhibits gastric emptying (gives more time to digest the fat)
- tropic effects (exocrine pancreas and gallbladder mucosa)
what is the principle stimuli for the delivery of pancreatic enzymes and bile to the small intestines
CCK
where is secretin released from, and what is its stimuli for release
from the S-cells of the duodenal mucosa and stimulus is acid in the duodenum (when the pH is below 4.5) and fatty acids int eh duodenum
what are the physiologic effects of “nature’s antacid” (secretin)
- inhibits gastric acid secretion (enterogastrone)
- stimulates pancreatic and bile bicarbonate secretion, needed for fat digestion
- tropic effects of exocrine pancreas
what family is GIP (glucose-dependent insulinotropic peptide) a member of
secretin
what stimulates GIP (glucose-dependent insulinotropic peptide) release and from where
released from K-cells of duodenum and primal jejunum
any major nutrient and oral glucose, but not IV glucose (incretin)
what is the only GI hormones that is released in response to all major nutrients
GIP (glucose-dependent insulinotropic peptide)
what are the physiologic effects of GIP (glucose-dependent insulinotropic peptide)
stimulates the release of insulin (AKA gastric inhibitory peptide) and inhibits gastric acid secretion
motilin: where is it secreted from and what does it do
from the upper duodenum during fasting. will increase GI motility and initiates the inter digestive myoelectric complexes that occur in 90 min intervals
pancreatic polypeptide: where is it secreted from and what does it do
from the pancreas in response to the ingestion of PRO, CHO and lipids. inhibits pancreatic secretion of HCO3 and enzymes
enteroglucagon: where is it secreted from and what does it do
from the intestinal cells in response to a decrease in blood glucose concentration and stimulates the live to increase glycogenolysis (glycogen is broken down into gluc -1- phosphate) and gluconeogenesis (new glucose from non-CHO source)
glucagon-like peptide-1 (GLP-1): what is it produced from and where is it secreted by and what does it do
produced from proglucagon and secreted by L-cells of the small intestine. incretin
where are paracrines synthesized
in the endocrine cells of the GIT
do paracrines enter the systemic circulation
no, they act locally
somatostatin. where is it secreted and in response to what. what does it do
from the D-cells of the GI mucosa in response to the lower pH (more acidic)also secreted by the hypothalamus and delta cells of the endocrine pancreas. it inhibits the secretion of GI hormones and inhibits gastric H+ secretion .
histamine: where is it secreted, and what does it do
secreted by endocrine cells of the GI mucosa. along with gastrin and ACh (PNS), histamine stimulates the H+ secretion by gastric parietal cells.
Neurocrines are ___ that are released by
neurotransmitters that are released by terminal nerve endings.
examples of neurocrines
NE, ACh, VIP, GRP
which is parasympathetic and which is sympathetic and what do they do to digestion. ACh and NE
ACh is PNS, and it increases digestion and contracts. NE is SNS and decreases digestion, and relaxes
what does it mean when you say the GI smooth muscle is a syncytium
the larger areas of smooth muscle contract as a single unit, much like the heart.
what is the purpose of gap junctions in the GI SM
to make it act like a syncytium became there are spaces for ions movement of low resistance, and they are between bundles of cells and layers of SM. There is a single AP propagation from cell to cell and it can spread within and between muscle layers. when one cell becomes depolarized, so do the others.
what happens when circular muscle contracts
the diameter of the lumen decreases because of the smooth muscle contracting around it
what happens when longitudinal muscle contracts
the segment decreases in length
what are phasic and tonic contractions of the SM
phasic means they are periodic and have relaxation, and tonic means that there is a constant tone and no regular periods of relaxation
what happens when a food bolus stretches the intestines
the SM circular contracts behind the bolus, pushing it forward and then the longitudinal will contract as well
when the bolus is in the stomach and moves with gastric juices what is it called
chyme
when the chyme passes through the small intestine to the large what is it called
feces
what are slow waves
rhythmic changes int he membrane potential that are caused by variation of the sodium conductance. oscillating depolarization kinda like the SA node. these are not AP’s.
what kind of cells make slow waves and what is it about their frequency
the interstitial cells of Cajal are the pacemaker cells that are in the myenteric plexus that make these slow waves. depending on where you are, they are about 3-12 waves per minute and this will dictate the maximum frequency of SM contraction. frequency RTS and is fixed
what is the story with the amplitude of the slow waves. what happens with an increased amplitude
its variable. its affected by nervous and hormonal stimuli. an increased amplitude increases the spike potential frequency and increases the strength of the contraction
what are spike potentials. when do they happen. what ion is responsible for contraction.
true AP’s. they happen with the slow waves reach the threshold (-40) and this causes the SM to contract. Ca.
explain the frequency of spike potentials
they are affects by nervous and humoral control. an increase in frequency means an increase in contraction, but the increase in frequent does not increase the maximum frequency of contraction.
describe the membrane potential. when it doesn’t reach threshold? when you have stimulation by stretch, ACh, PNS
slow waves don’t reach threshold, (-40) there are no spike. there are still constant periods of contraction and relaxation happening during resting state.
stimulation… threshold is met and a spike occurs.
what does the SNS (NE) do to the spike potentials
it hyper polarizes the membrane and brings the resting membrane potential way down
what is the relationship between electrical and mechanical activity
the mechanical always follows the electric (with a slight delay)
what is the purpose of chewing
to break down cells and break apart ingested cellulose. you want to increase the SA of the food and decrease the particle size. you also want to mix the food with saliva
what does saliva do
begins to digest starches (alpha amylase, lingual lipase) and lubricates the food for swallowing
describe how swallowing works
its initiated voluntarily in the mouth and then there is an involuntary swallowing set in motion by the swallowing center int he medulla. There are three stages
what are the three stages of swallowing
- oral phase (voluntary): initiates the swallowing process
- pharyngeal (involuntary): passage of food from the pharynx to the esophagus
- esophageal (involuntary); food from pharynx to stomach
there are 4 steps of the esophageal phase, what are they
- the UES opens and the swallowing reflex allows food to travel from the pharynx to the esophagus. the UES will close to prevent reflux.
- the primary peristaltic contraction
the LES opens and the orad region of the stomach relaxes (receptive relaxation) to facilitate moment of the bolus into the stomach - secondary peristaltic wave, if the primary peristaltic contraction does not clear the bolus this happens
what is the receptive relaxation
the orad of the stomach will relax as food comes towards to so it can enter the stomach. the third step of the epspoageal phase of swallowing
what is primary peristalsis
the continuation of pharyngeal peristalsis, which is coordinated by the swallowing center of the medulla. Cannot occur after the vagotomy (striated muscle)
what is secondary peristalsis
the stretch related afferent sensory input to the ENS and the swallowing center. Occurs after vagotomy
what are some disorders of swallowing (dysphagia)
CVA/stroke: aspiration due to the UES and pharyngeal contractions not being coordinated. secondary peristalsis is still functional
muscular diseases: myasthenia gravis, polio, botulism
anesthesia: aspiration of stomach contents. food cannot leave because the sphincters. when the pressure is higher then the atmosphere, it wants to exit, prevented by UES. LES prevents it from going from stomach to esophagus. GERD is an example.
where are the orad and caudad regions of the stomach
orad is the first third and the caudad is the last 2/3
what prevents the gastric emptying from the stomach TO THE DUODENUM
the pyloris
what is the function of the gastric smooth muscle
relax to accommodate food in the orad region (receptive relaxation)
in the caudad region, the SM will mix food with gastric juice (retropulsion)
it will also propel the chyme through the pyloris to the duodenum
what happens as the meal empties
contractile activity and low amplitude contractions
what is receptive relaxation
the vasovagal reflex where vagal afferent carry impulses to CNS and efferent away from CNS to stomach.
what does gastric distensibility mean
CCk will increase and gastric emptying decreases, to give more time to digest Fat.
what are four factors that increase gastric emptying
- increase the tone of the orad stomach
- forceful peristaltic contractions
- decrease the tone of the pyloris
- absence of segmental contractions in the intestines (like receptive relaxation)
what are four factors that decrease gastric emptying when the receptors in the intestines are activated.
- relaxation of the orad stomach
- decreased forcible peristaltic contractions
- increase tone pyloric sphincter
- segmental contractions in the intestines (increase in P in the intestines, the harder it is to push food into the intestines)
the activation of intestinal receptors does what to gastric emptying
it decreases it
intestinal mucosa receptors are simulated by… and causes the triggering of…
high or low osmolarity, acid, fat, protein
triggers enterogastric reflex
what happens with the enterogastric reflex
fat and protein release CCK which increases gastric distensibility and decreases gastric emptying
acid will decrease gastric emptying by intrinsic neural reflexes and the involvement of other homers will decrease gastric emptying
how does small intestine motility contribute to digestion and absorption
it mixes the chyme with digestive enzymes, and circulation of chyme to achieve optimal exposure to mucosa, it also propels the chyme.
where are slow waves more frequent, the stomach or the small intestine
the small intestine
what are the two types of contractions in the small intestine and what are their functions
segmental contractions mix the chyme (circular- splits the bolus into two and allows mixing) and the peristaltic contractions propel the chyme (longitudinal).
what are the functions of the large intestine SM
anything that is not absorbed I the small intestine enters the large intestine and is called feces. the large intestine SM ties the chyme and enhances fluid and electrolyte absorption through haustral contractions. and propels the feces for mass movements.
what are haustral contractions
there are invaginations in the large intestine that contracts and causes movement helps to mix and propel
where do mass movements occur and what is the function. how often do they happen
occur in the colon and canton to move feces over long distances, such as from the transverse colon to the sigmoid. occur 1-3 x/day.
water absorption occurs in the _____ making fecal contents semisolid and increases the difficulty to move
distal colon
mass movements lead to
bowel movements
two reflexes associated with defecation
rectospinchteric and gastrocolic
what is the rectospinchteric reflex
when the rectum fills with feces, the SM of the wall of the rectum contracts and the internal anal sphincter relaxes which is involuntary. but you won’t poop until the external anal sphincter relaxes which is voluntary
what is the gastrocolic reflex
distention of the stomach by food ingestion increases the motility of the colon and the frequency of mass movements
salivary glands have what appearance
a bunch of them looks like a bunch of grapes, but one singular one, an acinar, looks like a single grape.
salivary glands are stimulated by both branches of the ___
ANS
what is the difference between acinar cells and ductal cells
the acinar cells produce the primary secretion, similar to plasma (ptyalin, mucus, and ECF)
the ductal cells do what
modify the primary secretion (Na, Cl, K, HCO3)
the slower the rate of secretion, what will happen to the saliva
the slower the rate of secretion, the more the saliva will be modified and more time for the ductal cells to add stuff
acinar cells make isotonic solutions. how do they do this
they pull Na in, then back out. The Cl follows, which makes an electrochemical gradient. Duct cells also release HCO3 and K into the saliva
how does the PNS regulate saliva secretion
anything like conditioning, food, nausea and the smell of food increases the PNS and then secretes saliva.
things like dehydration, fear and sleep will decrease the PNS
why is it good to brush your teeth before bed
to kill bacteria. when you sleep, less saliva is made and saliva helps us kill bacteria.
what are the four main components of the gastric juice secreted by the gastric mucosa
HCL, pepsinogen, IF (to absorb B12), and mucus
the body of the stomach contains oxyntic glands which contain what two cells, and what do they secrete
- parietal cells, secrete HCL and IF
2. chief cells: secrete pepsinogen
the antrum of the stomach (last part of the stomach) contains pyloric glands which contain what two cells, and what do they secrete
- G-cells: secrete gastrin
2. mucus neck cells: secrete mucus, HCO3 and pepsinogen
pepsinogen turns to what in response to a low pH? what does it do then
turns to pepsin and starts to digest PRO
what are the three phases of gastric secretion
- cephalic phase (vagus): before you eat, visual, smell, increase gastric secretions.
- gastric phase: controlled by local reflexes, nervous secretory reflex, vagal, gastrin-histamine stimulation
- intestinal phase: when the chyme reaches the intestines, hormones.
oxyntic glands have what kinds of cells, and what do they secrete
parietal (IF, HCl) and chief (pepsinogen)
pyloric glands have what kinds of cells
G-cells (gastrin-not into the stomach, but into the circulation first) and mucus cells
two phases of the regulation of HCl Secretion
- cephalic phase, 30%, smell, taste, conditioning through vagus nerve
- gastric, 60%, distension, AA and peptides.
difference between gastric and duodenal ulcers
gastric, low H+ secretion with high gastrin levels, that hurts the gastric mucosa.
duodenal, high H+ levels and high gastrin
are there high or low H+ concentrations in Zollinger Ellison syndrome. what does this mean
high, means that there is high gastrin (tumor levels)
why does the stomach secrete mucus
for a protective barrier, to prevent cell erosion and death
what are some damaging factors to mucus
H pylori, H+ and pepsin, NSAIDS, stress, smoking and alcohol
what is peptic ulcer disease
starts with erosion of mucosa. it becomes a true ulcer when it goes down to tunica muscularis or even further down
acid from the stomach releases ___ from the wall of the duodenum and fats and AA cause the release of___
secretin and CCK
secretin causes
secretion of pancreatic fluid and bicarbonate
CCK causes secretion of
enzymes
describe bile secretion
the bile salts formed in the liver are stored int he gallbladder. when CCk is released in the presence of fat, the gallbladder contracts and the sphincter of Oddi relaxes, causing the contents of the gallbladder to go down the bile duct to the duodenum. At the ilium, the bile salts are reabsorbed through he portal circulation to the liver and recycled.
what happens when you have too much bile or it stays too longs and solidifies
gallstones
what are the four causes of gallstones
- too much absorption of water from the bile
- too much absorption of bile acids from bile
- too much cholesterol in the bile
- inflammation of the epithelium (not reabsorbed as well as you should, so cholesterol increases)
what can cause gallstones, and what is a potential hazard to gallstones
high fat diets, like fast food. can block the bile duct.
