Gastrointestinal Flashcards
The (sympathetic/parasympathetic) nervous system is stimulatory to the GI tract
Parasympathetic
What is the primary role for the myenteric plexus
Movement
What is the primarily role for the submucosal plexus in the GI tract?
Secretion and blood flow
What glands are found in the body of the stomach?
- Parietal Cells
- Enterochromaffin-like Cell
- Chief Cells
What glands are found in the antrum of the stomach?
- G Cell
2. D Cell
What is the source of gastrin?
- G cells of the gastric antrum
What stimulates gastrin secretion?
- Stretch
- Nerves of the gastric mucosa
- Vagal stimulation → Gastrin-Releasing Peptide - Peptides
- Amino Acids → Phenylalanine and Tryptophan are the big players
What cells does gastrin act on?
- Parietal cell
2. Enterochromaffin-Like Cells
What are the actions of gastrin?
- Endocrine*
1. Stimulate enterochromaffin like cells to secrete histamine
2. Stimulate parietal cells to secrete HCl
What are the three secretagogues involved in parietal cell activation?
- ACh
- Bind M3 receptors → cause increase in intracellular Ca - Gastrin
- Bind CCK-B receptors and cause increase in intracellular Ca - Histamine
- Binds to H2 receptors → increases cAMP
- Most potent stimulant of parietal cell
What inhibits HCl secretion by parietal cells?
- Secretin
- CCK
- Prostaglandins
- Dopamine
- Somatostatin
- GIP
- Peptide YY
- Enteroglucagon
Where does pepsinogen come from?
- Chief Cells
What is the stimulus for pepsinogen secretion by Chief Cells?
- ACh
- Via the vagus nerve → stimulated by stretch - HCl
What is the function of pepsinogen?
- Precursor for pepsin → protein digestion
Where does somatostatin come from?
- D Cells
What is the stimulus for somatostatin secretion?
- Lipids
- Protein
- Bile
What are the functions of somatostatin?
- Paracrine*
1. Decrease gastrin secretion - Endocrine*
2. Decrease parietal cell acid secretion - Neurocrine*
3. Decrease gastric motility
- Inhibits CCK release
- Inhibits secretin release
- Inhibits gallbladder contraction
What are the phases of gastric secretion?
- Cephalic - 30%
- Gastric - 60%
- Intestinal - 10%
What are the contributors to the cephalic phase of gastric secretion?
- Smell/sight of food
- ACh → Vagus n.
- Gastrin → G cells
- Histamine → ECL cells
What are the contributors to the gastric phase of gastric secretion?
- Gastric digestion and release of peptides
- Stretch → vasovagal reflexes, local enteric reflexes
- Gastrin → G cells
What are the contributors to the intestinal phase of gastric secretion?
- Gastric emptying
- Decreases intestinal and gastric antral pH
- Somatostatin → D cells
- Secretin → S cells
- CCK - I cells
What are the cells of origin for gastrinomas?
- Malignant transformation of pancreatic delta cells
What is the underlying reason for the clinical signs seen in gastrinomas?
Due to hypergastrinemia
- Esophageal and Gastroduodenal erosions and ulcerations
- Enzymatic maldigestion
- Gastric antral hypertrophy → delayed gastric emptying, gastric outflow obstruction
What are the clinical signs seen with gastrinomas?
- Vomiting*
- Weight loss*
- Depression
- Lethargy
- Anorexia
- Diarrhea
- Steatorrhea
* → most common
What changes on a CBC can be found with gastrinomas?
- Regenerative anemia
2. Leukocytosis → mainly due to stress
What changes on a chemistry can be found with gastrinomas?
- Hypochloremic, metabolic alkalosis → because the parietal cells are releasing a lot of H, Cl, and K
- Mild liver enzyme activity +/- hyperbilirubinemia
- May be due to metastasis
- Common bile duct obstruction - +/- alterations in blood glucose due to secretion of other hormones
How can gastrinomas be diagnosed?
- Fasting serum gastrin → want to see at least >3x the reference range but there are a lot of things that can also increase gastrin levels so its best for it to be >10x
- Histopath is the treatment of choice
Gastrin concentrations were found to be significantly (higher/lower) in CKD cats
Higher but there was a lack of uremic gastropathy lesions → no indication for gastroprotectants
What is the mechanism of action of Octreotide?
Somatostatin Analog
- Inhibit gastric acid release from parietal cells
- Inhibit gastrin release → reduce 25-50% of pretreatment values
- Decrease tumor load (gastrinomas)
- Reduce enterochromaffin-like cell hyperplasia
What is the source of Ghrelin?
Primarily the stomach (parietal cells)
- Can also come from intestine, pancreas (epsilon cells), and hypothalamus
What is the stimulus for Ghrelin?
- Fasting
What is the action of Ghrelin?
- Stimulate growth hormone secretion from the pituitary
- Stimulate appetite, body growth, and fat deposition
- Anti-inflammatory properties → decreases production of inflammatory cytokines
- Increases rate of gastric emptying
What is the MOA of Entyce (Capromorelin)
- Ghrelin agonist
* Has also shown that there is a transient increase in growth hormone and sustained increase in IGF-1 concentrations in adult healthy beagles
What are the most common adverse effects of Entyce?
- Vomiting
2. Diarrhea
What is the source of leptin?
Adipocytes
What is the stimulus for leptin secretion?
Increased adipose tissue
What are the actions of leptin?
- Decreased production of appetite stimulators in the hypothalamus
- Neuropeptide Y
- Agouti-related protein (AGRP) - Activation of POMC neurons
- α-melanocyte stimulating hormone
- Activation of melanocortin receptors - Increase sympathetic activity → increase metabolic rate → increase energy expenditure
- Decrease insulin secretion (pancreatic β cells)
- Increase TNF-α production and macrophage activation
What is the source of secretin?
- S cells
What is the stimulus for secretin release?
- Low duodenal pH
What are the actions of secretin?
- Inhibit acid secretion by parietal cells
- Slow gastric emptying
- Secretion of HCO3 rich pancreatic fluid (ductal cells)
- Trophic to the exocrine pancreas
What is the source of cholecystokinin?
I cells
What is the stimulus of cholecystokinin?
- Intraduodinal fatty acids, amino acids, H+ ions
What are the actions of cholecystokinin?
- Pancreas*
1. Potentiates secretin
2. Pancreatic enzyme secretion (acinar cells)
3. Stimulation of pancreatic growth - Gallbladder*
1. Gallbladder contraction
2. Relaxation of the sphincter of oddi - Stomach*
1. Inhibit gastric emptying
What are the functions of the following pancreatic cells?
- Acinar Cells
- Ductal Cells
- Secrete digestive enzymes (amylase, lipase, and trypsinogen)
- Secrete H20 and HCO3
What converts trypsinogen to trypsin?
The brush border enzyme enterokinase
What is the role of ACh in regulation of pancreatic secretions?
- Secreted by parasympathetic nerve endings in vagus and enteric nerves (stretch)
- Digestive enzymes
- Small quantities of bicarbonate poor water/electrolyte solution
What is the role of cholecystokinin in pancreatic secretion regulation?
- Large quantities of digestive enzymes
2. Small quantities of bicarbonate poor water/electrolyte solution
What is the role of secretin in pancreatic secretion regulation?
- Large quantities of bicarbonate rich water/electrolyte solution → important because it allows for carrying the digestive enzymes to the duodenum
What are the phases of pancreatic secretion?
- Cephalic - 20%
- Gastric - 5-10%
- Intestinal - 70-75%
What contributes to the cephalic phase of pancreatic secretion?
- Pavlov*
1. Sight, smell, taste, or thought of food
2. Vagal fibers → ACh
3. Vagal fibers → Gastrin → acinar cells (potency 50-100% of CCK)
4. Little fluid, so little enzyme makes it to the intestine
What contributes to the gastric phase of pancreatic secretion?
- Vagal and enteric fibers → ACh
- G cells → Gastrin → acinar cells
- Little fluid, so little enzyme makes it to the intestine
What contributes to the intestinal phase of pancreatic secretion?
- HCl acid (pH <4.5-5.0, important for enzyme activity) in small intestine
- S cells → Secretin → bicarbonate rich fluid, low chloride
- I cells → CCK
What % of bile acids are reabsorbed for recycling? What % are excreted?
- 95%
2. 5%
What are the most common secondary bile acids?
- Deoxycholic acid
2. Lithocholic acid
What amino acid are bile acids conjugated to in the liver?
- Taurine»_space;» glycine
- Cats can only do taurine, dogs can do taurine and glycine
Where are bile acids reabsorbed? How?
- Ileum
2. Active transport via a Na-K ATPase
What is the source of Gastric inhibitory peptide?
- K cells
What is the stimulus for gastric inhibitory peptide release?
- Intraduodenal fatty acids, amino acids»_space; carbohydrates
What are the actions of gastric inhibitory peptide?
- Inhibition of gastric acid secretion
2. Stimulation of pancreatic insulin release during hyperglycemia
What is the source of glucagon like peptide 1?
L cells of the ileum and colon
What is the stimulus for glucagon like peptide 1?
- Intraluminal glucose and lipid
What are the actions of glucagon like peptide 1?
- Inhibit gastric acid secretion
2. Pancreatic islet (β) cells → stimulate insulin secretion
What is an incretin?
A hormone secreted from the intestine in response to nutrients that potentiate insulin secretion
What are the main incretins?
- GLP-1 → L cells
2. GIP → K cells
What is the incretin effect?
Oral glucose will cause a significantly increased release of insulin compared to IV administration
*responsible for 25-70% of insulin secretion
How do GLP-1 and GIP stimulate insulin secretion?
- Stimulation of insulin biosynthesis
- Stimulation of β-cell proliferation
- Promotion of β-cell resistance to apoptosis
- Enhanced β-cell survival
- GLP-1 important for control of fasting hyperglycemia
- GLP-1 inhibits glucagon secretion by α-cells
What is the source of peptide YY?
- L Cells in Distal Ileum and Colon
What is the stimulus for peptide YY secretion?
- Fatty Acids
2. Carbohydrates (lesser degree)
What are the actions of peptide YY?
- Ileal brake
- Inhibition of CCK and secretin
- Proliferation of gut mucosa
- Slows gastric emptying
What is the MOA of slentrol (dirlotapide)?
- Microsomal membrane transfer protein inhibitor
- Block the assembly and release of lipoproteins in the bloodstream → decreases fat absorption - Increases peptide YY (and GLP-1) in rats
- Increases satiety signals
What is the purpose of using slentrol (dirlotapide)? What are the most common adverse effects?
- Utilized for weight loss
2. Emesis, loose feces
What is the ileal brake?
- Lipid and glucose in the ileum → release of Peptide YY
2. Peptide YY → causes stomach relaxation and slow gastric emptying
What is the gastrocolic reflex?
- Distention of the stomach → causes colon to defecate
What is GI segmentation?
- Random contraction of circular muscles
- Mixes food with digestive enzymes and brings nutrients in contact with absorptive surfaces
- Slows transit time
What is GI peristalsis? What controls cranial contraction and caudal relaxation?
- Short wave of constriction moving aborally over a short segment of intestine
- Moves contents aborally
- Cranial contraction → ACh, substance P
- Caudal relaxation → nitrous oxide, VIP
What is the migrating motility complex?
- “Housekeeper” that clears the gut of undigested residue and prevents overgrowth of bacteria during the fasting state
- Occurs every 90 minutes
- Not present in cats and rabbits → they have a migrating spike complex - Starts in the stomach and propagates to the ICJ (includes the gallbladder)
What are the phases of the migrating motility complex?
- Phase 1 → quiescence
- ~1 hour - Phase 2 → Intermittent contractions
- Similar to that with feeding
- 15-40 minutes - Phase 3 → Intense propulsive motility
- 4-8 minutes
- Motilin
What is the source of Motilin?
- M cells in the stomach, small intestine, and colon
What is the stimulus of Motilin secretion?
- H+ and lipid in fed stae
- Most important in fasting (inter digestive) state
- Episodically released into serum during fasting → causes phase 3 of the migrating motility complex
What are the actions of Motilin?
- Initiates phase 3 of the migrating motility complex
What are the sources of serotonin in the GI tract?
- Enterochromaffin like cells
2. Enteric neurons throughout the GI tract
What are the actions of serotonin in the GI tact?
- Stimulates GI smooth muscle contraction
2. Intestinal electrolyte secretion
What are intestinal carcinoids?
- Tumors of endocrine cells of the GI tract
2. Contain secretory granules → contain SEROTONIN, secretin, somatostatin, and gastrin
At what point are clinical signs seen in EPI?
- When 90% of pancreatic function is lost
What is the underlying etiology for EPI? What is the most common in dogs? cats?
- Pancreatic Acinar Atrophy → most common in dogs
- Chronic Pancreatitis → most common ind cats
- Pancreatic Hypoplasia
- Pancreatic Neoplasia
Describe how B12 is absorbed from the diet
- B12 from the diet is bound to HAPTOCORRIN (R factor) in the STOMACH
- HAPTOCORRIN-B12 enters the DUODENUM and the haptocorrin is digested by pancreatic enzymes
- B12 then binds to INTRINSIC FACTOR
- INTRINSIC FACTOR-B12 goes to the ILEUM where it is endocytose by epithelial cells
- B12 dissociates and binds to TRANSCOBALAMIN
- TRANSCOBALAMIN-B12 then exits the epithelial cell and transits to the liver
What kind of anemia is the result of a B12 deficiency?
Macrocytic anemia (pernicious anemia)
What are the underlying causes of a B12 deficiency?
- Increased uptake by intestinal bacteria
2. Decreased intrinsic factor
Cats with EPI are (more/less) often cobalamin deficient than dogs
MORE
What produces intrinsic factor?
- Parietal cells of the stomach (dogs)
2. Pancreatic duct cells (dogs and cats)
Where is folate absorbed?
PROXIMAL small intestine
What % of dogs with EPI will have concurrent small intestinal bacterial overgrowth?
- 70%
Animals with EPI will likely have a (high/low) folate
low
Low serum folate suggests malabsorption in ____
Proximal small intestine
Low vitamin B12 suggests malabsorption in ____
Distal small intestine
Or decreased release of IF
Low or normal vitamin B12 together with a high folate suggests ____
Bacterial overgrowth
What are important qualities about serum TLI that need to be kept in mind when performing this test?
- Species and PANCREAS specific
2. It is eliminated by the kidneys → may be falsely elevated in patients with kidney disease
Serum TLI by radioimmunoassay has (high/low) sens and (high/low) spec for diagnosing EPI
- High
2. High
Fecal elastase has a (high/low) sens and a (high/low) spec for diagnosing EPI. This means it is good for ruling (in/out) disease.
- High
- Low
- Useful for ruling out disease
* Helpful for ruling out EPI in dogs with chronic diarrhea*
How is EPI treated?
- Non-enteric coated supplemental enzymes
- Antibiotics for SIBO
- Dietary modification → highly digestible, low fiber, low to moderate fat
- Cobalamine supplements
What kind of diet should be fed to animals with EPI?
- Highly digestible
- Low fiber
- Low to moderate fat
What is SIBO?
- Small intestinal bacterial overgrowth
- More of a pathogenic mechanism rather than a diagnosis
- When small intestinal bacteria are >10^5 CFU/mL
What is another term for idiopathic SIBO?
- Antibiotic responsive diarrhea
* Common in German shepherd dogs
* Not documented in cats
What are causes for secondary SIBO?
- Disease that results in excess substrate in the intestinal lumen
- EPI
- Motility disorder
- Blind loop - Disease the affects the clearance of bacteria
- Partial obstruction
- Abnormal motility
- Increased pH in the stomach or proximal SI (ie on PPIs) - Morphologic or functional derangement of the mucosa
What is the pathophysiology of SIBO?
Increased bacteria in the small intestine cause malabsorption or diarrhea due to:
- Compete for nutrients (bind cobalamin)
- Bacterial metabolism of nutrients can create products that promote diarrhea (reduced micelle formation)
- Bacteria metabolize undigested lipids due to #2 which produces hydroxylated fatty acids which act as detergents and damage the mucosal surface
- Bacterial degradation of carbohydrates → serve as osmotic agents → draw fluid into intestine
- Increased intestinal permeability
How is SIBO diagnosed?
- Aerobic and anaerobic culture of duodenal juice → GOLD STANDARD
- Hydrogen breath test
- Intestinal permeability assays → increased bacteria unconjugate bile acids which are then readily absorbed
- Response to antibiotics
What is the hydrogen breath test?
- When carbohydrates go to large intestine → fermented → short chain fatty acids → hydrogen goes up
- In SIBO → hydrogen levels go up sooner because bacteria are now adding to the fermentation process
How is SIBO treated?
- Antibiotics
- Tetracycline
- Metronidazole (anaerobes only)
- Tylosin (for chronic cases) - Diet
- Low fat, highly digestible - Parenteral B12
What are the causes of feline obstipation?
- Idiopathic megacolon - 62%
- Pelvic canal stenosis - 23%
- Nerve injury - 6%
- Manx sacral SC deformity - 5%
What is believed to be the underlying cause of feline idiopathic megacolon?
- One study showed a decrease sensitivity to neurotransmitters → dysfunction of smooth muscle
How is feline obstipation treated?
- Enemas
- Rectal suppositories (DSS, glycerin)
- Laxatives
- Hyperosmotics: Lactulose
- Bulk: Psyllium
- Lubricant: Mineral oil, petroleum - Prokinetics
- Cisapride
- Ranitidine
What is the MOA of cisapride?
- 5HT2 and 5HT4 AGONIST
2. 5HT1 and 5HT3 ANTAGONIST
What is the MOA of ranitidine?
- H2 antagonist
What are the diagnostic criteria for abdominal fluid in a uroabdomen?
Abdominal fluid creat and K >2x serum
What are the diagnostic criteria for abdominal fluid in a septic abdomen?
Abdominal fluid glucose 20 LESS than serum
What metabolic causes should be ruled out prior to an idiopathic megacolon diagnosis in a cat?
- Hypokalemia
- Dehydration
- Hypercalcemia
How does the fluid in a septic abdomen hinder a patient?
- Decreases opsonins and thus phagocytosis
- Limits localization and walling off
- Intraabdominal hypertension can cause cardiopulmonary issues and urinary issues
What is the most common post-operative electrolyte abnormality in GDVs?
- Hypokalemia (after correcting for acidosis)
- Can be exacerbated with HYPOMAGNESEMIA
The majority of copper (40-60%) is absorbed where?
- Proximal small intestine
How is copper taken into the hepatocyte?
Copper transporter 1 (CTR 1)
What is the etiology of inherited copper storage disease in Bedlington terriers?
- AUTOSOMAL RECESSIVE*
1. DELETION of MURR1 → accumulation of copper in hepatocytes → chronic hepatitis
How is copper secreted into the bile?
MURR1
In what form is copper stored?
Metallothrein
What is the role of ceruloplasmin?
Converts Fe2+ to Fe3+ for transport
*This is a COPPER DEPENDENT oxidase
Where does copper accumulate in bedlington terriers?
Zone 3 (Centrilobular)
Where does copper accumulate in secondary copper accumulation disease? What is the underlying cause of secondary copper accumulation?
- Zone 1 (Periportal)
2. Cholestasis
When does copper start to accumulate in Bedlington terriers with the MURR1 mutation?
- 4-5 months
* In heterozygous carriers it will start to rise until 6-9 months where it then goes back to normal
What clinical signs are associated with copper storage disease in Bedlington terriers?
- Non-specific liver signs
2. HEMOLYSIS → ONLY HAPPENS IN BEDLINGTON TERRIERS
What is the treatment for copper storage disease?
- Penicillamine
- Trientine
- Vitamin C → enhances urinary excretion of copper
- Zinc
- Antioxidants → if hemolytic crisis occurs, in Bedlington’s only
What is the MOA of penicillamine?
- Mobilization of copper from tissues and excretion in urine
- May also increase synthesis of metallothionein
* Teratogenic and crosses placenta
What is the MOA of Trientine?
- Increases urinary excretion of copper
2. Decreases intestinal absorption of copper
What is the MOA of zinc in copper accumulation disorders?
- Reduces copper absorption from the diet
- Increases Metallothionein in intestinal mucosal cells → prevents absorption into the blood stream
* Takes 3 months to work
What is the most common form of IBD? Second most common?
- Lymphocytic/Plasmacytic
2. Eosinophilic enteritis
Which breed has a familial gluten sensitive enteropathy?
Irish Setter
*Mucosal permeability precedes development of disease
What is Basenji enteropathy?
- Severe hereditary form of LPE
- Has hyperglobulinemia and is prone to developing LSA
- Treatment is usually unsuccessful
Which breed develops familial PLE and PLN?
Soft Coated Wheaten Terriers
What are the biochem characeristics of Soft Coated Wheaten Terrier familial PLE and PLN
Eventually get both
- PLE: Panhypoproteinemia and hypercholesterolemia
- PLN: Hypoalbuminea, Hypercholesterolemia, Proteinuria, and Azotemia
What is unique about Boxer ulcerative colitis?
- PAS Positive
2. Responds to baytril
What is the best negative prognostic indicator for enteritis?
- Hypoalbuminemia
What are the forms of PLE that cause hypoalbuminemia but HYPERglobulinemia?
- Basenji enteropathy
- Histoplasmosis
- Lymphoma
Where does tritrichomonis foetus colonize? What does it cause?
- Distal ileum in cats
2. Large bowel diarrhea
How is t. foetus diagnosed?
Direct fecal smear
How is t. foetus treated?
- Resistant to metronidazole
2. Will spontaneously resolve in 2 years
What is the most common cause of PLE?
Lymphangectasia
What is lymphangectasia?
Dilatation and dysfunction of intestinal lymphatics → leak protein rich lymph into intestinal lumen
Which breeds are predisposed to primary lymphangectasia?
- Small Breeds (Yorkies, Maltese)
2. Norwegian Lundehund