GIT Flashcards
Muscle fibers are electrically connected with one another allowing low resistance movement of ions from one muscle to the next
gap junction
When an AP is elicited anywhere within muscle, it generally travels in all directions
syncytium
Activity of GI smooth muscle
1 slow wave
2 spike
continual, slow, intrinsic electrical activity
Rhythm determined by frequency Not action potentials Slow, undulating changes in RMP 5-15 mv ; 3-12 freq per minute 3 in the stomach 12 in duodenum 8-9 in ileum
Slow wave
Electrical pacemakers for smooth muscle cells controlling slow waves
Undergo cyclic change in membrane potential due to unique ion channels that periodically open and produce inward (pacemaker) currents to generate slow wave
Interstitial cells of Cajal
Slow waves only cause contraction in
They mainly excite appearance of intermittent
stomach
Spike potentials that inturn actually excite ms contraction
True action potentials
Automatic when RMP of GI sm becomes more + (-50/-60 -> -40mv)
Each time peaks of slow waves become more + than -40, these appear
The higher the slow wave potential, the frequency becomes:
Spike potential
greater
AP of GI sm are
1
2
Than nerve fibers
longer 10-40x
run by calcium-sodium channels (slower to open and close) therefore longer AP
Ca ion is responsible for contraction
Cranial parasympathetic
Mouth Pharyngeal region Esophagus Stomach Pancreas First half of large intestine -vagal
Sacral parasympathetic
2nd, 3rd, 4th sacral segment of spinal cord
Pelvic nerves
Distal half of large intestine to anus
-defecation
Postganglionic neurons of GI parasympathetic system are located in
myenteric and submucosal plexus
inc activity of entire enteric system
Depolarization of membrane is triggered by
1 stretching of muscle
2 stimulation by acetylcholine from parasympathetic nerves
3 stimulation by GI hormone
Hyperpolarization of membrane is caused by
1 NE and Epi on fiber membrane
2 sympathetic nerve stimulation by NE
Slow waves are propelled by these ions
sodium
Spike potentials from slow wave are generated by these ions
calcium
Continuous, lasting minutes to hours increasing or dec in intensity but still continues
Caused by continuous repetitive spike potentials or hormones that bring about continuous partial depolarization of smooth muscle without action potential
Calcium entry without change in membrane potential
Tonic contraction
Outer plexus between longitudinal and circular ms layer
Controls mainly GI movement
Myenteric Auerbach’s plexus
In submucosa
Inner plexus
Controls mainly GI secretion and local blood flow
Submucosal meissner’s plexus
Myenteric Auerbach’s plexus generate
1 inc tonic contraction
2 inc intensity of rhythmical contraction
3 inc rate of rhythm of contraction
4 inc velocity of conduction of excitatory waves (peristaltic)
But not entirely excitatory bec has inhibitory fxn through transmitter
Inhibitory trasmitter secreted by Myenteric Auerbach’s
Vasoactive intestinal peptide
Act on the pyloric and ileocecal valve
Submucosal Meissner’s plexus regulates
1 secretion
2 absorption
3 contraction
of submucosal muscle (infolding)
Excites GI activity
acetylcholine
Inhibits GI activity
norepinephrine
epinephrine
Neural control of gut (3)
1 post sympathetic/pre paraganglionic
2 enteric
3 sensory (to enteric the prevertebral ganglia and spinal cord)
Sympathetic fibers run from
T5-L2 Preganglionic fibers enter sympathetic chain lateral to spinal column Celiac ganglion, mesenteric ganglia Post ganglionic sympathetic neurons Secrete NE and EPI
Afferent sensory fibers are stimulated by
1 irritation of mucosa
2 distention of gut
3 specific chemical substances in gut
80% of vagal nerve fibers are
afferent
GI reflexes (3)
1 integrated within gut wall enteric NS (secretion, peristalsis, mixing, contraction)
2 gut to prevertebral sympa and back to GI (gastrocolic, enterogastric, colonoileal)
3 from gut to spinal cord and brain stem and back to GI (pain, gastric moror and secretion, defacation)
Signal from stomach cause evacuation of colon
Gastrocolic reflex
Signal from colon and SI to inhibit stomach motility and secretion
Enterogastric reflex
Colon to inhibit emptying of ileal content to colon
Colonoileal reflex
Secreted by G cells in antrum, duodenum, jejenum
Stimulated by protein, distention, nerve
Inhibited by acid
Gastrin
Gastrin stimulates
gastric acid secretion
mucosal growth
Secreted by I cells of duodenum, jejunum, and ileum
Stimulated by protein, fat and acid (proteoses, peptone and long chain FA
Cholecystokinin
CKK stimulates
inhibits
pancreatic bicarbonate secretion
pancreatic enzyme secretion
gallbladder contraction
growth of exocrine pancreas
gastric emptying
Secreted by S cells of duodenum, jejunum and ileum
Stimulated by acid and fat
Secretin
Secretin stimulates
Inhibits
pepsin secretion
pancreatic bicarbonate secretion
biliary bicarbonate secretion
growth of exocrine pancreas
gastric acid secretion
Secreted by K cells of duodenum and jejunum
Stimulated by protein, fat and carbohydrate
Gastric inhibitory peptide
Gastric inhibitory peptide stimulates
Inhibits
insulin release
gastric acid secretion
Secreted by M cells of duodenum and jejunum during fasting
Stimulated by fat, acid and nerve
Motilin
Motilin stimulates
gastric motility
interdigestive myoelectric complexes
intestinal motility
Types of movements of GI tract
1 propulsive forward food movement
2 mixing
Contractile ring around the gut that moves anything in front forward
Stimulus:
Peristalsis
distention of gut
chemical and physical irritation
parasympathetic signals
Law of gut
Peristaltic reflex to anal direction of movement
Receptive relaxation propelling food toward anus
Kinins released that promote vasodilation
Kallidin
Bradykinin
Adenosine
Stages of swallowing
1 voluntary
2 pharyngeal
3 esopahgeal
Control of stomach emptying resides in
1 inhibitory feedback signals from duodenum (enterogastric)
2 CCK
Gastric empyting is slowed by
1 too much chyme is already in small intestine
2 chyme is acidic
3 too much fat or hypertonic or hypotonic
4 irritating
Hormones that promote peristalsis in intestine
gastrin CCK insulin motilin serotonin
hormones that inhibit small intestinal motility
secretin
glucagon
Single celled, secrete mucus in response to irritation of epithelium and act as lubricant to protect surface from excotiation and digestion
Mucus goblet glands
Invagination of epithelium into mucosa
Deep, contain secretory cell
pits
crypts of Lieberkuhn
Acid and pepsinogen secreting gland of stomach and upper duodenum
Oxyntic gland
Tubular
Secretion of glands is stimulated by
1 tactile stimulation
2 chemical irritation
3 distention of gut wall
Sympathetic effect on glandular secretion (2)
1 slightly inc secretion
2 superimposed sympa on para significantly reduces secretion bec of vasoconstrictive reduction of blood supply
Basic Mechanism of secretion
1 diffusion of nutrient material or active transport to capillary into base of gland
2 oxidative energy ATP from mitochondria utilized by gland
3 synthesis of secretory substance from ATP and substrate in ER and golgi
4 formation of proteins in secretion by ribosome
5 transport of secretion from ER to golgi (20 mins)
6 modification, concentration and discharge of secretion into cytoplasm in form of secretory vesicle in apical end
7 vesicle storage until use (inc in cell membrane perm by control signal to calcium, ca entry causing vesicle fusion with apical membrane -> exocytosis
Daily secretion of saliva
Saliva contains large amounts of ions
800-1500 ml
K (acini primary secretion along with ptyalin) and bicarbonate (duct by passive exchange of bicarbonate for chloride)
sodium chloride conc are several times less in saliva than in plasma
Net result: under resting conditions, NaCl conc is about 15 meq/L while K is at 30 meq/L bicarbonate at 50-70 meq/L
Saliva two types of protein
1 ptyalin - serous, alpha amylase for starch dig
2 mucin - mucus for lubrication and protection
Parotid glands secrete
While submandib and sublingual secrete
Buccal glands secrete
Saliva pH
serous secretions
both serous and mucus
mucus only
6-7 favorable for ptyalin
Saliva contains enzymes that destroy bacteria
1 lysozyme -attacks bacteria
2 thiocyanate ions - bactericidal, digest and help remove bacteria support
3 antibody
Primary secretion
Secondary secretion
Ptyalin
Mucus
ECF
Na active absorption
Cl passive absorption
K active secretion
HCO3 secretion
Secrete HCl
Pepsinogen
Intrinsic factor
Mucus
On the body and fundus 80% proximally
Oxyntic
Gastric glands
Secrete mucus for protection of stomach mucosa and gastrin
Located on antrum 20% distal
Pyloric glands
Stomach oxyntic gland cell and secretion
1 mucous neck cell : mucus
2 chief cell : pepsinogen
3 parietal oxyntic : HCl and intrinsic factor
Factors that stimulate gastric secretion
1 acetylcholine (excites pepsinogen, mucus and hydrochloric acid secretion) 2 gastrin (HCl) 3 histamine (HCl)
Along with secretion of HCl parietal oxyntic cells also secrete this for VitB12 cobalamin absorption
Intrinsic factor
Absorption in ileum
ECL cells in recess of oxyntic glands release this in relation to the rate and amt of formation of HCl stimulated by gastrin
Histamine
When protein reaches antrum, this hormone is released by G cells and is then transported in the blood to ECL to release histamine
Gastrin
Pepsinogen secretion is mediated by
1 stimulation of chief cells by acetylcholine from vagus or enteric nerve
2 in response to gastric acid
Hormones in the SI that inhibit gastric secretion
Secretin
GIP (GDIP)
VIP
Somatostatin
Pancreatic enzymes digest all three major type of food. Most important are:
1 trypsin, chymotrypsin and carboxypolypeptidase for protein, peptides and AA
2 lipase for fatty acid and monogly
3 cholesterol esterase for hydrolysis
4 phospholipase for FA from phospholipid
Trypsinogen is activated by
Enterokinase
Trypsin from activated trypsinogen
Pancreas also secrete copious amounts of this ion to neutralize gastric acid
bicarbonate
Acetylcholine and cholecystokinin stimulate
meanwhile secretin stimulates
Large quantities of pancreatic enzyme but small water and electrolytes
secretion of water rich sodium bicarbonate soln
Secretin causes copious secretion of
While
CKK causes secretion of
pancreatic fluid water and bicarbonate also in the second part of bile secretion
pancreatic enzyme
Bile amount
Functions
600-1000ml
1 bile salt emulsify fat particles into minute particles for lipase
2 absorption of digested fat end product
3 excretion of waste bilirubin and cholesterol
Bile is concentrated by
Na Absorption and secondary chloride ion and water absorption
Bile salt formation
Cholesterol -> cholic and chenodeoxycholic acid
Acids combine with glycine and taurine -> glyco and tauroconjugates bile acid
Sodium salt secreted in bile
Compound mucus glands in the wall of duodenum secreting large amounts of alkaline mucus in resp to tactile or irritation and vagal stimulation and secretin
Inhibited by
Brunner’s gland of duodenum
pH 8 - 8.9
sympathetic stimulation
Crypts of Lieberkuhn in small intestine secrete
Watery fluid rich in Cl and bicarbonate creating sodium solute drag and osmotic movement of water
Digestive enzyme in small intestines
1 peptidase (AA) 2 sucrase, maltase, isomaltase, lactase (disach to monosach) 3 lipase (fat into glycerol and FA)
Regulation of small intestine secretion unlike the rest of the GI is through
local enteric nervous reflex
Protein fat and carbohydrate digestion mostly takes place in the
Small intestine
Fructose is absorbed in the small instestine by
Glucose is absorbed by
facilitated diffusion
Na-glucose co transport
Indole
Skatole
Mercaptan
Hydrogen sulfide
Odoriferous products
H pylori promotes stomach ulceration by
Burrowing into the gastric barrier
Producing ammonia that liquefies barrier and stimulates secretion of HCl digesting wall
Factors that inc mucosal ulceration
1 excess secretion of gastric juice esp initial portion of duodenum
2 smoking
3 alcohol
4 aspirin NSAID
Gluten destroys and blunts microvilli dec absorptive mucosa of twofolds when eating rye or wheat
Nontropical sprue
Celiac disease
Idiopathic sprue
Gluten enteropathy
Inflammation of intestinal mucosa from unidentified infectious agent occuring in tropics
Tropical sprue
Sprue complication
1 steatorrhea
2 severe nutritional def, wasting
3 osteomalacia bec of lack of Ca
4 inadequate blood coagulation bec of lack of Vit K
5 macrocytic anemia bec of B12 and folic acid
Hirschprung’s disease results from lack of
ganglion cell in myenteric Auerbach’s plexus
Antiperistalsis Deep breath Raising of hyoid bone and larnyx to pull up esophageal sphincter open Closing of glottis Lifting of soft palate to close nares Contraction of diaphragm LES relaxation
Vomiting act
The liver receives percentage of CO
Pressure into the portal vein leading into liver is
27%
9mmHg indicating low resistance
inc if cirrhotic -> from fibrosis
Promotes liver regeneration
Inhibits liver
HGF
EDGF
TNF
IL6
TGFB
Liver role in protein metabolism
Deamination of amino acid
Formation of urea for excretion of ammonia
Forming plasma protein
Conversion of AA to other compounds (nonessential AA)
Vitamin stored in sufficient quantity in liver
A
D (good for 3-4 m)
B12 (at least 1 yr)
Test that differentiates unconjugated from conjugated bilirubin
Van den Bergh and
Negative urobilinogen in urine (obstructing jaundice)
Acetylcholine to gastric contraction
Stimulates
Gastrin to gastric contractions
Gastrin
Norepinephrine to gastric contractions
inhibits
Gastric emptying is slowest after a meal rich in
Fats
Factors that lead to increase emptying
Gastrin
Forceful retching
Hematemesis
Alcoholic
Mallory-Weis Tear in the GEJ
Increasing the intraabdomunal pressure against a closer glottis is otherwise known as:
Valsalva maneuver
Location of CTZ
Roof of the fourth ventricle
Area postrema
Medulla oblongata
Highly specific and selective serotonin 5HT3 receptor antagonist the nerve terminals of vagus peripherally and centrally in CTZ arew postrema
Low affinity for dopamine receptors
Ondansentron
Inhibits D2 and serotonin 5 HT3 receptors in CTZ
Administration leads to prokinetic effects via inhibitory actions on presynaptic and postsynaptic D2 receptora
Agonism of 5HT4
Antagonism of muscarinjc receptor inhibition
Enhances releae of acetylcholine, inc LES ang gastric tone accelerating gastric emptying
Metaclopromide
Most of the length of small intestine is from the
Ileum
In the duodenum secrete copious amounts of HCO3
Brunner’s glands
Emetogenic drugs such as chemotherapeutic agents promote vomiting by
Release of serotonin from the enterochromaffin cells of small intestine by causing degenerative changes of GI tract
Serotonin stimulates the vagal and splanchnic nerve receptors that project to medullary vomiting centers as well as the serotonin receptors in the area postrema thus initiating the vomiting reflex causinf nausea and vomiting
Splanchnic blood flow receives
about 25% of cardiac output
Blood from GI does not flow directly to IVC because it is shunted to
portal system
Contain secretory granules that release regulatory peptides and amines to hell regulate GI function
Enteroendocrine cells
Dopamine exerts this effect on GI tract
relaxant
Most frequent movement of SI
segmentation
Resection of this portion of the gut leads to impaired RBC maturation
Ileum t
Mucous neck cell secretes
Mucous
Parietal cells secrete
HCl
Chief cells secrete
Pepsinogen
Enterochromaffin cells secrete
Serotonin
Substance P
Enterochromaffin cells Kulchitsky cells produce
Serotonin
Enterochromaffin-like cells produce
Histamine Chromogranin A (Pancreastatin)
Destruction of parietal cells as seen in chronic gastritis is accompanied by decreased production of HCl and
Intrinsic factor
Pepsinogen maximal activity
pH 2.0
Pepsinogen inactivated at
pH 6.5
Pepsinogen is activated by
Zymogen HCl Acid pH
RBC production is defective caused by autoimmune attack against parietal cells
Pernicious anemia
Control of gastric acid secretion
3 physiologic agonists
Histamine
Ach
Gastrin
Elicit release of histamine from ECL cells
Gastrin
Endogenous antagonist to acid secretion
Somatostatin
Prostaglandin E Prostaglandlin I
Epidermal growth factor
The stomach secretes about
2 L of gastric juice
Most important of pancreatic enzymes for digesting proteins are
Trypsin
Chymotrypsin
Carboxypeptidase
Secreted by I cells
Stimulated by fats and protein
Promotes pancreatic enzyme secretion
Promotes pancreatic bicarbonate
Causes contraction of gallbladder -> release of bile
Cholecystokinin
Especially when fatty foods reach the duodenum after this long post meal
30 minutes