Gastrointestinal Physiology Flashcards
Use to locate the appendix
TAEnia Colin
ANTRUM
G cells
Parietal cells (IF, HCL)
Fundus
Vitamin C & iron are absorbed
Duodenum
All nutrients are absorbed
Jejunum
Vitamin B12, IF, ADEK, Bile salt, Bile acids are absorbed
Ileum
Folate
Jejunum
Vagus nerve found
Transverse colon
Absorption of water
Proximal colon
Storage of feces
Rectum
Distal Colon
Basic GI Layers
Mucosa
Submucosal
Muscularis
Serosa
Smooth muscle cells controlling the epithelium
Muscularis Mucosa
Collagen, elastin, glands and blood vessels
Submucosa
Decreases diameter of the lumen
Inner Circular Muscle Layer
Shortens segment of the GIT
Outer Longitudinal Muscle Layer
Aka adventitia or mesothelium
Serosa
between inner circular & outer longitudinal muscle layers For motility (inner circular & outer longitudinal muscle layers)
Myenteric Plexus / Auerbach Plexus
Which layer is NOT seen in the esophagus?
Serosa
Strongest layer of the esophagus?
Submucosa
3 muscle layers are found in the stomach instead of two. What are these muscle layers?
Inner Oblique
Middle Circular
Outer Longitudinal
The Myenteric Plexus is mainly excitatory EXCEPT for which regions?
Pyloric Sphincter & Ileocecal Valve
Esophageal to upper large intestines
vagus nerve
Lower large intestines to anus
Pelvic nerves
Secretion & absorption
Meisner plexus/ Submucosal Plexus
Motility
Auerbach plexus/ Myenteric Plexus
For retropulsion of food
Inner oblique
G cells, stomach, Antrim
Gastrin
Stimulus: small peptides, stomach Distention, vagus nerve via GRP; inhibited by H & somatostatin
Gastrin
Increases gastric H secretion
Stimulates growth of gastric mucosa
Gastrin
S cells
Duodenum
Secretin
Stimulus: H in duodenum
Fatty acids in duodenum
Secretin
Increases Pancreatic HCO3 secretions
Increases Biliary HCO3 secretion
Decreases effect of gastric on gastric mucosa
Secretin
I cells
Duodenum & Jejunum
CCK
Cholecystokinin
Monoglycerides, FA, small peptides and AA
CCK
Cholecystokinin
Stimulates GB contraction, sphincter of Oddi Relaxation
Increases Pancreatic enzyme & HCO3 secretion
Increases growth of exocrine pancreas and gallbladder
Inhibits gastric emptying
CCK
Cholecystokinin
K cells
Duodenum
Glucose - dependent Insulinotropic Peptide
Stimulus: Oral glucose, fat, AA
Glucose - dependent Insulinotropic Peptide
Increases Insulin secretion
Inhibits Gastric Emptying (only above normal physiologic levels)
Glucose - dependent Insulinotropic Peptide (GDIP)
M cells
Duodenum
Jejunum
Motilin
stimulus: Fasting
Motilin
Stimulates
Motilin
Most potent stimuli for gastric secretion
phenylalanine
Tryptophan
Methionine
Neurocrine from vagus nerve to G cells
GRP/Bombesin
GI hormone classifies as an INCRETIN
GIP
GLP 1
GI hormone responsible for the interdigestive myoelectric complex
Motilin
Secreted by pancreas in response to CHO, CHON, lipids
Pancreatic Polypeptide
Inhibits pancreatic HCO3 and enzymes
Pancreatic Polypeptide
Secreted by intestinal cells in response to hypoglycemia
Enteroglucagon
Stimulates glycogenolysis and gluconeogenesis
Enteroglucagon
Secreted by L-cells of small intestines
Glucagon-Like Peptide 1 (GLP-1)
Stimulates insulin secretion
Glucagon-Like Peptide 1 (GLP-1)
Secreted by cells throughout the GIT in response to H
Somatostatin
Inhibits release of ALL GI hormones
Somatostatin
Inhibits gastric H secretion
Somatostatin
Secreted by mast cells of gastric mucosa
Histamine
Increases H secretion; potentials gastric and Ach action
Histamine
Action of Ach
Contraction of smooth muscle in wall Relaxation of sphincter a Inc salivary secretion Inc gastric secretion Inc pancreatic secretion
Source of Ach
Cholinergic neurons
Action of NE
Relaxation of smooth much in wall
Contraction of sphincters
Inc salivary secretion
Source of NE
Adrenergic Neurons
Actions of VIP Vasoactive intestinal Peptide
Relaxation of smooth muscle
Inc intestinal secretion
Inc pancreatic secretion
Source of VIP
Neurons of mucosa and smooth muscle
Action of Gastrin-Releasing (GRP) or Bombesin
Inc gastric secretion
Source of GRP or Bombesin
Neurons of gastric mucosa
Actions of Enkephalins (Opiates)
Contraction of smooth muscle
Dec intestinal secretion
Source of Enkephalins
Neurons of mucosa and smooth muscle
Actions of neuropeptide Y
Relaxation of smooth muscle
Dec intestinal secretion
Source of Neuropeptide Y
Neurons of mucosa and smooth muscle
Action of substance P
Contraction of smooth muscle
Inc salivary secretion
Source of Substance P
Consecrated with Ach
Inhibits appetite
Found at the Ventromedial Hypothalamus
Satiety Center
Stimulates appetite
Found at the Lateral Hypothalamic Area
Appetite/Hunger Center
Sends signals to Satiety & Hunger Centers
Arcuate Nucleus
Releases POMC to decrease appetite
Anorexigenic Neurons
Releases Neuropeptide Y to increase appetite
Orexigenic Neurons
Stimulates Anorexigenic neurons, inhibits orexigenic neurons
leptin (fats cells), Insulin, GLP-1
Inhibits Anorexigenic neurons
Gherkin (gastric cells)
Inhibits gherkin
Peptide Y
Constant level of contraction or tone without regular periods of relaxation
Tonic contractions
Due to subthreshold slow waves
Tonic contractions
Orad (upper) region of the stomach and in the lower esophageal, Ileocecal and internal anal sphincter so
Tonic contractions
Periodic contractions followed by relaxation
Phasic Contractions
for mixing and propulsion
Due to spike potentials
Phasic Contractions
Seen in the esophagus, gastric Antrum, small intestines
Phasic Contractions
Not true action potential
Slow waves
Due to GI pacemaker Intertitial cell of cajal
Slow waves
Slowest frequency
Stomach
Fastest frequency
Small intestines
True action potential
Spike potential
What is the most common stimulus for GI peristalsis?
Distention
What is the Myenteric Reflex
Muscles Upstream contract, muscles downstream exhibit receptive relaxation
What is the Law of the GUT?
Myenteric Reflux + anal direction of peristalsis
How long does it take to transfer material from pyloric to Ilecocecal valve, and ileocecal valve to colon, respectively?
3-5 hours, 8-15 hours
The law of the gut is due to what phenomenon?
Peristaltic reflex
Receptive relaxation
Begins CHO digestion
Amylase
Swallowing center
Medulla
Triggers reflex when food is at the pharynx
Oral phase
Soft palate pulled upward (closes nasopharyngeal), glottis covered (prevents aspiration), upper esophageal sphincter a relaxes
Pharyngeal Phase
UES close, primary and secondary esophageal peristalsis occurs
Esophageal Phase
Capacity of stomach for food
Amount of water absorb in proximal colon
Amount of gastric secretion
1.5 L
Able to bypass the pyloric sphincter
Water
Who of the following is a possible effect of bago tony on gastric emptying?
Decreased emptying of solids
Back and forth movement with no net forward motion
Segmentation Contraction
Mixes chyme with pancreatic enzymes
Segmentation Contraction
Propels chyme towards large intestines
Peristaltic contraction
Mouth and stomach
Bonus
Small intestine
Chyme
Large ins testiness
Feces
Saclike segments due to segmental contractions of the large intestines
Haustra
For absorption of water
Proximal colon
For storage of feces
Distal colon
Occurs 1-3x a day to move colonic contents over long distances (from transverse colon to sigmoid colon)
Mass movement
Color of feces is due to
Stercobilin
Food in the stomach increases peristalsis in the ileum and relaxation of the Ileocecal sphincter
Gastroileal Reflex
Food in the stomach increases peristalsis in the colon and frequency of mass movement mediated by the Parasympathetic NS, CCK, gastrin
Gastrocolic Reflex
Vomiting center
Medulla
Incomplete vomiting
Closed UES
Retching
Submucosal of duodenum
Brunner’s gland
Produce initial saliva
High Na, Low K
Acinar Cells
Reabsorption Na K
Stimulated by aldosterone
HCO3, K
Ductal Cells
Serous secretion
Parotid gland
Mixed secretion
Submandibular gland
Sublingual gland
Effect of Parasympathetic NS
Increases salivation
Effect of Sympathetic NS
Decreases salivation
Initial Saliva is high in
Na, Cl
Final saliva is high in
HCO3, K
Hormone involved in absorbing Na at the ductal cells
Aldosterone
At high flow rates, saliva has
High Na, Cl, Low K & High HCO3
At low flow rates, saliva has
Low Na, Cl, High K & Low HCO3
For proteins
HCL and Pepsinogen
For Vitamin B12 absorption
Intrinsic factor
For protection of gastric mucosa against HCL
Mucus
Body
HCL, intrinsic factor
Parietal cells
Body
Pepsinogen
Chief cells
Antrum
Gastrin
G cells
Antrum
Mucus, Pepsinogen
Mucus cells
Contains mucus neck cells, parietal cells and chief cells
Oxen tic glands (body)
Contains G cells, Mucus cells
Pyloric glands (antrum)
Secreted Mucus and HCO3
Mucus cells, Mucus Neck cells
Secreted Hcl and IF
parietal cells/oxyntic cells
Secretes gastrin
G cells
Secretes serotonin
Enterochromaffin cells
Secretes Histamine
Enterochromaffin-like Cells ECL
Secretes Pepsinogen
Chie/Peptic cells
Which of the following is the site of secretion of intrinsic factor?
Gastric Fundus of parietal cells
What are the 3 substances that stimulate HCL secretion?
Histamine (paracrine) - acting on H2 receptors
Ach (Neurocrin) - act on M3 receptors
Gastrin (GI hormone) - act on CCKb receptors
What are the inhibitors of HCL secretion?
Low pH (<3.0) of the stomach
Somatostatin
Prostaglandins
Give examples of anti-Muscarinic drug
Atropine
Example of H2-blocker
Cimetidine
S/e gynecomastia
PPI
Omeprazole -most effective
Stimuli of cephalic phase - 30%
Sight, smell, taste, thought of food
Stimuli of Gastric phase - 60%
Stomach Distention, AA, small peptides, alcohol, caffeine
Stimuli of Intestinal Phase - 10%
AA, peptides
What substances protects the mucosa from HCL and pepsin?
HCO3, Mucus
What are the protective factors against PUD?
Prostaglandins, mucosal blood flow, growth factors
What are the damaging factors?
H, pylori, NSAIDS, stress, smoking, alcohol
A patient with a duodenal ulcer is treated successfully with the drug cimetidine. The basis for cimetidine’s inhibition of gastric H secretion is that it
Block H2 receptors on parietal cells
Secreted by S cells
Secretin
Acts on ductal cells
Increases HCO3 secretion
Secretin
Secreted by I cells
CCK
Acts on CCKa receptors in actin are cells and ductal cells
Potentials effect of secrets in increasing HCO3 secretion
CCK
Acts on Muscarinic receptors in actin are cells and ductal cells
Also potentials effect of secretin in increasing HCO3 secretion
Ach
Via vagovagal reflexes
Ach
Most common component of Bile
Water
Active component of bile
Bile salts
Primary bile acid
Chenodeoxycholic acid
Secondary bile acid
Deoxycholic acid
Store bile
Gall bladder
Create bile
Liver
Causes Gall bladder contraction
CCK & Ach
Causes sphincter of ODDI relaxes
CCK
94% bile salts are recirculated back to the liver using
Na-Bile salt cotransporter in the terminal ileum (enterohepatic circulation)
Digestion of carbohydrates in the Mouth
Ptyalin
Digestion of carbohydrates in the Small intestine
Pancreatic amylase, brush-border enzymes, disaccharidases
How do you absorb Glucose and Galactose from lumen to intestinal cell
SGLT-1
How do you absorb Fructose from lumen to intestinal cell?
Glut 5
How do you absorb Glucose, Galactose, and Fructose from intestinal cell to the blood?
Glut 2
Digestion of proteins in the stomach
Pepsin, desaturation by HCL
Digestion of proteins in the Small intestine
Enterokinase, trypsin, chymotrypsin, Carboxypeptidases, peptidases
What is the optimum pH for pepsin activity?
Ph 1.0-3.0
Inactivated at pH >5.0 (ex in duodenum)
Digestion of Triglycerides in the mouth
Lingual Lipase secreted
Digestion of Triglycerides in the Stomach
Lingual lipase activated, gastric lipase activated, mechanical pulverized ion of fat, CCK decreasing gastric emptying
Digestion of Triglycerides in the small intestine
Emulsification by bile salts, pancreatic lipase activated
Micelles
From lumen to intestinal cell
For absorption from intestinal cell to lacteals
Chylomicrons
Bile salts inactivated pancreatic lipase. What pancreatic coenzyme is secreted to prevent this from happening?
Procolipase -> Colipase
What is the only product of TGA metabolism that is NOT hydrophobic?
Glycerol
What type of fatty acids go directly to the portal vein instead of the lacteals
Short-chain and medium-chain fatty acids
Main site for water absorption
Jejunum
Potassium is absorbed at the following sites
Small intestines
Potassium is secreted at the following sites
Large intestine
Primary ion secreted in the intestinal lumen
Chloride (Na, H2O follows)
Needed to absorb vitamin B12
Intrinsic factor
Needed to absorb calcium
1,25 (OH)2 cholecalciferol
Needed to absorb iron
Vitamin C
Part of the metabolism of these vitamins involved colonic flora
Vitamin K, Vitamin B1, Vitamin B2, Vitamin B12
Is absorbed in the SI via passive diffusion using Paracellular route
Potassium
Is secreted in the Colon similar to renal distal tubule
Potassium
ADP ribosylation of As subunit of Gs protein coupled to adenylyl Cyclades -> permanent activation -> water follows
V. Cholera
Increases Calbindin D-28K (calcium-binding proteins in the SI)
Calcitriol
Initiation digestion of fats starts in the
Stomach
Mechanism of transport associated with glucose absorption in the intestine via SGLT1?
Secondary active transport
Transport protein responsible for transport of glucose from the intestinal cells basement membrane to the blood?
glut 2
All of the following are absorbed through the intestine through secondary active transport except? A. Galactose B. Amino acids C. Bile salts D. Vitamin A E. Vitamin B
D. Vitamin A - fat soluble- simply diffuse
Which of the following is not an endopeptidase? A. Trypsin B. Chymotrypsin C. Elastase D. Aminopeptidase
D. Aminopeptidase
All of the following can hinder dietary absorption of calcium except? A. Excess fatty fooods B. phytic acid C. Oxalate from some vegetables D. Nota
D. Nota
Site of iron absorption in the gut?
Duodenum
All of the following assist in iron absorption except? A. Heme form of iron from meat B. Reduction of iron to Fe2 C. Vitamin C D. Alcohol E. Fructose F. None
F. None
Binding protein that assist in the absorption of vitamin B12 secreted in the saliva?
cobalophilin
Largest organ
Liver
2% of total body weight, receives 25% of cardiac output
Liver
Detoxification and excretion of waste products is using
Cytochrome P450 enzymes (Phase 1 reactions)
Conjugation (phase 2 reactions)
Fat soluble -> Glucoronic acid (polar)
UCB/IB
Urobilinogen -> stercobilin (yellow color feces)
CB/DB
Functional unit of the liver
Classic liver lobule
High O2 and nutrients
First to encounter toxins
Zone 1 / Periportal
Mid zonal
Zone 2
Low o2 and nutrients
Last to encounter toxins
Centrilobular/Zone 3
Are extremely effective in blood cleansing
Kuppfer cells
Kuppfer cells
Liver
Space of disse
Vitamin A storage
ITO cells
Liver sinusoids
APC
Kuppfer cells
