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237 Cards in this Set
- Front
- Back
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What does ruminant saliva contain?
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NaHCO3: buffer acid produced by bacterial fermentation.
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What innervation controls all activities of the GI tract? (2 exceptions)
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Autonomic control of everything except swallowing and external anal sphincter
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What autonomic innervation is in charge most of the time?
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Parasympathetic mostly, stimulates motility and secretion
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What does the sympathetic system do mostly?
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Inhibits the parasympathetic system to decrease motility and secretion
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What is pseudoptyalism
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Inability to swallow saliva
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What is ptyalism
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Over production of saliva
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What do parasympathetic nerves use and act on?
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Secrete ACh onto Muscarinic receptors
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What do sympathetic nerves use and act on?
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Secrete NE onto Adrenergic receptors
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What effect would ACh have on salivary secretion?
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Cholinergic effects increase secretion (adrenergic inhibit it)
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What are the three functions of Saliva? (fourth in ruminants)
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Facilitate mastication and deglutition
Initiate starch and lipid digestion Evaporative cooling Enable microbial digestion in the forestomach |
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What is Deglutition?
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The act of swallowing
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What are the three phases of deglutition?
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Oropharyngeal (oral, pharyngeal and cricopharyngeal)
Esophageal Gastroesophageal |
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Which phase of deglutition is voluntary?
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Oral stage of oropharyngeal
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What separates the stages?
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Oropharyngeal from esophogeal: Upper Esophogeal Sphincter (UES)
Pharyngeal from cricopharyngeal: Lower Esophageal sphincter (LES) |
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What is Dysphagia?
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Difficulty swallowing or chewing
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Define Regurgitation
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Effortless expulsion of ingesta from the esophagus, a passive process that occurs without warning; only neural reflex involved is gag
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What is Regurgitation the cardinal sign of?
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Esophageal disease
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What is Halitosis?
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foul odor to the breah
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Functions of the esophagus?
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transport ingesta
eructation egestion (birds) regurgitation |
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4 Consequences of an obstructed esophagus in a ruminant
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Gas Bloat*
Saliva spilling over Can't ruminate Acidosis |
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Which animals have smooth muscle in their esophagus and where?
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Cat, Horse, Pig
Caudal 1/3rd |
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What is the clinical significance of a skeletal muscle esophagus?
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Dog/Cow are at risk for diseases like myasthenia gravis
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What is the difference in the nerve physiology of the skeletal muscle esophagus?
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Parasympathetic nerves secrete ACh onto nicotinic receptors
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How does one visualize the esophagus?
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NOT normally on Rads!
Contrast with fluoroscopy, endoscopy |
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3 Most common sites of esophagus obstruction?
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Thoracic inlet, base of the heart, diaphragm
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What are the two ways peristalsis is initiated in the esophagus?
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Primary waves: initiated by swallowing
Secondary waves: initiated by local distension |
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How does the vagus nerve vary from a dog to a cat?
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Dog: muscular esophagus- ACh onto nicotinic receptors
Cat: smooth muscle, ACh onto muscarinic |
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What makes up the UES?
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2 pharyngeal muscles, relaxes only to pass bolus or gas
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Describe the LES
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Physiologic rather than anatomic sphincter, prevents gastric reflux via enlargement of the gastric fundus and positive intrabdominal pressure
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How would you treat Gastroesophageal reflux?
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Low-fat diet
avoiding late night meals Metoclopramide: increases LES tone |
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Which animals have smooth muscle in their esophagus and where?
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Cat, Horse, Pig
Caudal 1/3rd |
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What is the clinical significance of a skeletal muscle esophagus?
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Dog/Cow are at risk for diseases like myasthenia gravis
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What is the difference in the nerve physiology of the skeletal muscle esophagus?
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Parasympathetic nerves secrete ACh onto nicotinic receptors
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How does one visualize the esophagus?
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NOT normally on Rads!
Contrast with fluoroscopy, endoscopy |
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3 Most common sites of esophagus obstruction?
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Thoracic inlet, base of the heart, diaphragm
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What are the two ways peristalsis is initiated in the esophagus?
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Primary waves: initiated by swallowing
Secondary waves: initiated by local distension |
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How does the vagus nerve vary from a dog to a cat?
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Dog: muscular esophagus- ACh onto nicotinic receptors
Cat: smooth muscle, ACh onto muscarinic |
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What makes up the UES?
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2 pharyngeal muscles, relaxes only to pass bolus or gas
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Describe the LES
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Physiologic rather than anatomic sphincter, prevents gastric reflux via enlargement of the gastric fundus and positive intrabdominal pressure
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How would you treat Gastroesophageal reflux?
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Low-fat diet
avoiding late night meals Metoclopramide: increases LES tone |
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What is the cardinal sign of esophageal disease?
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Regurgitation
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How do you distinguish between vomiting, expectoration and regurgitation?
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Physical exam, history, observing the animal eat
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What are the two causes of regurgitation?
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Obstruction and motility disorder (myasthenia gravis)
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Is the skeletal muscle esophagus under voluntary control?
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NO (ACh onto nicotinic receptors)
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What is myasthenia gravis?
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Autoimmune disease where nicotinic receptors are attacked
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Describe the recovery ability of the esophagus
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Very unforgiving!
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What is the normal pH of the stomach?
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1-2
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What are the 6 products of the stomach?
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Hydrogen ions: kills, convert pepsinogen into pepsin
Pepsinogens: digest protein Mucus: lubricate, protect Bicarb: protect Intrinsic factor: B12 absorption Water: dissolve, dilute |
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What does Gastrin do?
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Stimulates acid secretion
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What does Somatostatin do?
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Inhibits gastrin secretion
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What region secretes mucus and bicarbonate?
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Cardiac mucosa
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What do Parietal cells do?
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Produce H+, and intrinsic factor in dogs
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What do Chief cells do?
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Produce pepsinogen
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What do ECL cells do?
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produce histamine
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What do D cells do?
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Produce somatostatin
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What do G cells do?
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produce gastrin
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What are the three main mediators of gastric HCl secretion?
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Gastrin (G receptors)
Histamine*(H2 receptors!) Acetylcholine (Muscarinic receptors) |
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What is the significance of the proton pump in parietal cells?
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It is ACTIVE and creates the Alkaline tide
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What stimulates Gastrin release?
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Vagus nerve
Gastric distention Protein in the lumen (somatostatin inhibits) |
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What are the three vagus nerve stimuli?
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Cephalic phase: anticipation
Gastric phase: gastric distention and protein in the lumen Intestinal phase: food in the duodenum |
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Explain the significance of Histamine on the Parietal cell
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Histamine is stimulated by ACh and gastrin
cAMP synergizes with Ca++ to stimulate HCl secretion |
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Why do drugs like Tagamet, Zantac and Pepcid AC work so well?
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They target H2 receptors to inhbits gastric acid secretion and H2 receptors are only found in the stomach so no side effects
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What is at the apical end of the parietal cell?
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Active H+-K+ pump
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What are the most potent and complete inhibitors of gastric acid secretion?
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Those that inhibit the proton pump
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Where does Somatostatin come from and what does it do?
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From D cells
inhibits the proton pump by inhibiting gastrin release from G cells and histamine from ECL cells |
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Would somatostatin levels be high at low or high pH?
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At a low pH somatostatin would be high because we no longer need the proton pump to be active
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How do prostaglandins protect the stomach?
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Increase mucosal blood flow
Inhibit cAMP Stimulate mucus and bicarbonate secretion |
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What do NSAIDs do to put us at risk for gastric ulceration?
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They inhibit endogenous prostaglandin synthesis
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What should NSAIDs never be combined with?
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Corticosteroids
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How does Misoprostol (Cytotec) work?
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It is synthetic PGE2, so helps prevent gastric ulcers
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What are likely causes of Gastric Ulcers?
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NSAIDs or corticosteroids
fasting/anorexia- horses neoplasia foreign body |
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What is the afferent limb of the vomiting reflex?
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Stimulus
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What is the efferent limb of the vomiting reflex?
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Response
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What are 4 major stimuli of the vomiting center?
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Chemoreceptor trigger zone*
Vestibular apparatus Abdominal Viscera Cerebral cortex |
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How does the glottis closing function in vomiting?
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creates negative intrathoracic pressure around the esophagus
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Where is the chemoreceptor trigger zone?
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Floor of the 4th ventricle
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What drug induces vomiting in a dog?
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Apomorphine
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What drug induces vomiting in a cat?
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Xylazine
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How does Cerenia (aka Maropitant) work?
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Acts on NK1 receptors in the abdominal viscera, chemoreceptor trigger zone and vomiting center to prevent vomiting
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How does Zofran (Ondansetron) work?
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Acts on 5HT3 receptors in the abdominal viscera (dogs) and the vomiting center (cats) to prevent vomiting
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How does Metoclopramide (Reglan) work?
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Acts on D2 (dopamine) receptors in the chemoreceptor trigger zone to prevent vomiting
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What two drugs work opposite one another in the dog?
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Reglan/Metoclopramide and Apomorphine both act on D2 receptors (apomorphine stimulating them to induce vomiting)
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What two drugs work opposite one another in the cat?
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Chlorpromazine/Compazine and Xylazine both work on Alpha2 (NE) receptors in the cat (xylazine induces vomiting)
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Which animals can vomit readily?
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Carnivores, omnivores
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How do ruminants vomit?
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Internally, abomasul contents into rumen
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How do horses vomit?
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extremely rare due to LES tonus, only happens during gastric rupture
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2 Categories of vomiting in small animal
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Extra-GI (not part of GI tube directly)- liver failure, kidney, etc
GI- obstruction, dietary, parasites, etc |
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Metabolic consequences of a ruminant vomiting
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Metabolic alkalosis (loss of HCl)
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Metabolic consequences of monogastric animal vomiting
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Metabolic acidosis normally (duodenal vomiters)
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What is a metabolic alkalosis pathopneumonic for in a duodenal vomiter?
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Pyloric obstruction
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What stimulates gastric motility?
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Gastrin in response to feeding
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What causes gastrin's release from G cells?
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Gastric distention, protein products in the gastric lumen and vagal stimulation
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What inhibits gastric motility?
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Duodenal receptors detect excessive hypertonicity or acidity, releasing secretin (acid/distention response) or CCK (lipid response)
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What causes Cholecystokinin to be released?
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High lipid content in the duodenal lumen
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What causes secretin to be released?
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High distention or acidity in the duodenal lumen
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What is hematamesis?
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Vomiting blood
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What is Melena?
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Blood in stool from an upper GI bleed, dark tarry
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What parts of the stomach are most at risk for ulceration?
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Stratified squamous epithelium which is non glandular
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Why is a low fat diet good for a patient with reflux?
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Low fat means that there is decreased secretion of CCK, which means that gastric emptying will increase and food/acid will not reflux
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What is Hematochezia?
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Fresh blood in the stool, colon bleed
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What is significant about the pancreas' location?
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It has close proximity to many organs so swelling or pancreatitis can affect many systems
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Where does the dogs pancreatic duct open?
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On the major duodenal papilla next to the bile duct
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Where does the cats pancreatic duct open?
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On the major duodenal papilla WITH the bile duct
Puts cats at risk for triaditis |
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What is triaditis?
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Bacterial infection resulting in inflammation of the duodenum, the pancreas and the biliary tree
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What species has an important accessory pancreatic duct?
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Dogs
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What are two common diseases of the exocrine pancreas?
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EPI: exocrine pancreas insufficiency
Pancreatitis |
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What are inactive precursors called?
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Zymogens
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What pancreatic enzyme acts on proteins?
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Trypsinogen->trypsin
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What pancreatic enzyme acts on Fats?
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Procolipase->Lipase
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What pancreatic enzyme acts on Carbohydrates?
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Amylase
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What is pancreatic secretory trypsin inhibitor?
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secreted by acinar cells and packaged with zymogens to neutralize any inadvertantly activated trypsin
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What does increased lipase and amylase indicate?
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In blood, indicates pancreatitis due to inappropriate leakes from tissue
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What is the name of the proteolytic enzyme that activates zymogens?
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Enteropeptidase or enterokinase (in brush border)
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What is enteropeptidase most effective at converting?
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Trypsinogen->trypsin
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What is primarily responsible for activating most zymogens?
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Trypsin! "The Warden"
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Does the pancreas completely break things down?
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No, brush border enzymes do the final stage
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Why doesn't the pancreas digest itself? 4 reasons
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1- Zymogens are inactive
2- Enzymes are membrane bound 3- Intracellular trypsin inhibitor from acinar cells 4- enterokinase/peptidase is in the lumen not the pancreas |
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Signs of EPI?
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maldigestion, weight loss, osmotic diarrhea, polyphagia
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How do we diagnose EPI?
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TLI: trypsin like immunoreactivity, blood trypsin is abnormally low
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How is pancreatic secretion controlled?
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Neurally and hormonally
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What stimulates pancreatic secretion?
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Vagus nerve (cephalic, gastric and intestinal phases)
CCK (cholecystokinin) Secretin |
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What does CCK cause the pancreas to do?
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Secretes enzymes from acini
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What does secretin cause the pancreas to do?
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Secretes bicarbonate rich fluid
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Why is the vagal influence on the pancreas important for dogs with pancreatitis
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If the dog sees/smells food it will stimulate pancreatic enzymes synthesis/secretion, worsening the proble
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How does the vagus nerve affect the pancreas?
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Stimulates pancreatic enzyme synthesis and secretion
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What three functions does the bicarbonate rich fluid of the pancreas serve?
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1- neutralizes gastric acid
2- provides optimal pH for brush border enzymes 3- increases solubility of fatty and bile acids |
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What two cells are involves in the alkaline tide? (creating and balancing)
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Gastric parietal cell creates
Pancreatic centroacinar cell resolves |
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How do cats vary in their exocrine pancreas function?
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Cats pancreas' secrete intrinsic factor which is necessary for B12 absorption
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What does B12 do?
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Used for cell proliferation, affects intestinal crypts and bone marrow when deficient
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Where are receptors for intrinsic factor-B12 complexes located?
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Exclusively on the lumen of the ileum
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Name three causes for cobalamin (B12) deficiency
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1- EPI(cats since dogs release intrinsic factor in the stomach too)
2- Small intestinal bacteria overgrowth (due to EPI usually) because bacteria use B12 themselves 3- Malabsorptive disease of the ileum (receptors damaged) |
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What would occur if we removed an animals pancreas?
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1- Diabetes mellitus
2- EPI 3- B12 deficiency (esp. in cats) |
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How would we feed an animal with pancreatitis?
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fed intravenously or through duodenum
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Liver function in GI?
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Synthesis of Bile Acids
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Describe the liver's vascular supply
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Dual: Hepatic artery and portal vein
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What is the % of blood flow from the hepatic artery?
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20% of flow, 50% of 02 (80% from portal vein)
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Describe a congential portosystemic vascular anomaly
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Connects the portal vein to the caudal vena cava directly, results in Hepatic Encephalopathy
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How would you treat a congential portosystemic shunt?
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Low-protein diet, give antibiotics, and laxatives (helps trap NH3 as NH4+)
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When is surgical ligation of a shunt an option?
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Only in congenital. Acquired develops multiple
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Describe the differences in Congenital and Acquired shunts
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Congenital: <1 year, no Ascites, surgically correctible, NORMAL portal pressure
Acquired: >4 years, ascites, high portal pressure |
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How does a low protein diet help hepatic shunts?
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Reduces NH3 formation in the gut
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How do antibiotics help a hepatic shunt?
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Reduce bacterial metabolism of protein to NH3
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How does Lactulose help a hepatic shunt?
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Increase transit of food and trap NH3 as NH4+
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What does Bile do?
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Provides bile acids for fat assimilation
excretory route for fat-soluble substances contains electrolytes and water |
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What causes jaundice?
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Failure to excrete bilirubin
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What is bilirubin?
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Waste product of hemoproteins that is excreted by liver into bile
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What are the causes of icterus (3)?
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Pre hepatic: hemolysis of RBCs
Hepatic: stasis of bile within liver Post-Hepatic: obstruction of bile duct |
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What would you see if the bile duct was 100% obstructed?
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Acholic feces: white feces
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Where are bile acids synthesized exclusively?
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Liver
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Primary bile acids like cholic and chenodeoxycholic acids are synthesized from what?
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Cholesterol (rate limiting step is 7-alpha hydroxylation)
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What is the purpose of conjugation of bile acids?
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They become positively charged so they stay in the hepatocyte
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What conjugates primary bile acids?
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Taurin in dog and cat
Glycine in dog |
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What is an essential amino acid in the cat?
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Taurine
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What would you observe in a cat with taurine deficiency
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cardiomyopathy and retinal degeneration
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How are conjugated bile salts secreted into the bile duct?
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They are actively transported
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What is ursodeoxycholic acid?
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Synthetic bile acids
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What is enterohepatic circulation?
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circulation of conjugated bile acids
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How does Cholecystokinin act in bile acid secretion?
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CCK stimulates the gall bladder to contract->releases bile acids, but it also relaxes the greater hepatoduodenal papilla
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How does Secretin work in bile acid secretion?
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Secretin stimulates the bile ducts to secrete bicarbonate which aids in neutralization of gastric acid
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In what feeders is the Sphincter of Oddi less defined?
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Continuous feeders, continuous secretion of hepatic bile into the intestinal tract
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How does Lipase function in TG breakdown?
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Lipase chews fatty acids off of TG's to create a Free fatty acid and BMG
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How does ALLI work?
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It inhibits lipase (essentially give you EPI) so you can't process fats
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What is ascites?
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Abnormal accumulation of serous fluid in the peritoneal cavity
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What is cirrhosis?
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Progressive disease of the liver characterized by diffuse damage to hepatic parenchymal cells
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How can we clinically measure liver function?
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Pre and Post-prandial serum bile acids, if liver function is bad then serum concentrations of bile acids increase after a meal due to inability to resorb them
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What does the screening test for liver function check?
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Screening test= serum biochemistry profile
A decrease in ALT,BUN, Albumin, Glucose or Cholesterol points to synthetic failure (>70% loss of function) |
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What type of nutrient site does the: dog, ruminant, and horse use for absorption?
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Dog- simple monogastric
Ruminant: foregut fermenter Horse: hindgut fermenter |
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What is absorbed/digested in the stomach?
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Digested: carbohydrates (salivery amylas), proteins (pepsin) and lipids (lipase)
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What is absorbed/digested in the Small Intestine?
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Digested: amylase, proteases, lipase all present
Absorbed: brush border absorbs glucose, amino acids and fatty acids |
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What is absorbed/digested in the Large intestine?
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Absorbed: SCFA's
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What is the path of cells in the villi, and how long does it take?
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Cells migrate up the villus as they mature, crypt to villus tip is 2-4 days
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What do crypt cells produce?
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They secrete Cl- and water, primarily secretory
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Are crypt cells secretory or absorptive?
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Secretory
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What do tip villus cells do?
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Primarily absorptive
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How are carbohydrates acquired in the diet?
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Simple monosaccharides, disaccharides and polysaccharides
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What are all dietary carbohydrates eventually broken down to?
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Glucose, Fructose or Galactose
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What type of receptors do mature villous epithelial cells have transporters for?
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Only for glucose, fructose or galactose (monosaccharides)
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Where are disaccharides split?
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By enzymes in the brush border membrane of villous epithelial cells
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How do mammals digest fiber?
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Mammalian enzymes cannot digest fiber, rely upon bacteria to ferment these to short chain fatty acids (SCFA's)
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How are monosaccharides transported?
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Coupled to the absorption of sodium and water
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What are ORS'?
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Oral rehydration solutions: contain simple monosaccharides.
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How does glucose absorption help rehydration?
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Absorption of glucose increases uptake of Na+ and water
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When are ORS not effective?
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They don't provide sufficient energy to meet needs
Won't stop diarrhea Ineffective if there is severe villous atrophy (because no glucose transporters are left) |
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What are the three phases of protein break down?
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1- intraluminal: enzymes by pancreas
2- surface- brush border peptidases 3-intracellular- of dipeptides (created by surface digestion) |
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What are the phases of fat digestion/absorption
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Lipoysis (pancreas)
Micellar solubilization (liver) Absorption (jejunal mucosa) Delivery (lymphatics) |
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What are the functions of small intestine motility?
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Propulsion
Mixing Reservoir function |
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What is "the pacemaker"?
|
Nerve like cells (cells of Cajal) that undergo spontaneous rhythmic depolarization in intestinal circular and longitudinal smooth muscle
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What is "the slow wave"
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cyclic depolarizations that are SUB-THRESHOLD (aka basal electric rhythm)
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What stimulates motile contraction?
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Neuroendocrine (vagal) stimulation that depolarizes a slow wave to threshold
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What limits contraction?
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neuroendocrine (sympathetic) nerves that hyperpolarize the slow waves away from threshold
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Why does slow wave frequency decrease down the GI tract?
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Ensure adequate time for digestion and absorption further down the tract
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Why are slow waves so frequent in the Duodenum?
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It rapidly spreads out the acidic/high omsolarity fluid leaving the stomach
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What is the MMC?
|
Migrating myoelectric complex or "housekeeper"
A fasting motility pattern driven by the slow wave and directed by the enteric nervous system (doesn't require extrinsic innervation) |
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Describe a housekeeper contraction
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Powerful peristaltic contractions that originate in the stomach. Sweep retained solids, pooled liquid and bacteria into the colon
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What are the 3 phases of the interdigestive motility pattern
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Phase 1- no contractions
Phase 2- intermittent Phase 3- every slow wave is a contraction |
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Which phase of interdigestive motility has the most waves?
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Phase 3
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What drives the MMC in the stomach?
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Hormone called Motilin (mmc- migrating myoelectric complex)
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How does feeding affect MMC?
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Interrupts mmc cycling in carnivores and omnivores
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How do digestive motility patterns differ?
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These contractions occur intermittently and promote mixing to increase digestion and absorption
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How are carnivores and omnivores waves controlled?
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Stimulated by the vagus nerve in response to nutrients in the lumen of the proximal bowel
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How are ruminant waves controlled?
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The MMC is not interrupted by feeding, there is NO Digestive motility pattern. Duodenum receives a continuous flow of fermentation product
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How do ruminants compensate for the constant waves?
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They have a longer intestine
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What types of waves do all species have?
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Fasting/MMC/Housekeeper
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Why do dogs/cats have a digestive motility pattern?
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They have intermittent meals and so regulate the waves with vagal stimulation
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Why do sheep/horses have only housekeeper waves?
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They are constant grazers. Have a long GI to compensate for fast sweeping contractions
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What are the functions of the colon?
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Microbial Fermentation
Reabsorption of electrolytes and water Storage |
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Which species have microbial fermentation in their colon?
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All
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What energy source does colonic epithelium use?
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SCFA
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What do you need to benefit from hindgut fermentation?
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An enlarged colonic lumen (often haustra) and retention of buffered fluid
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What can/can't the colon absorb?
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Can absorb SCFA's
Can't absorb vitamins or amino acids |
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What is coprophagy and why would an animal do it?
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Eating own feces
Done in hindgut fermenters to obtain wasted protein and vitamins |
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How does the horse compensate for low digestive efficiency?
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By constantly eating
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How is colon motility designed in the horse?
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To retain material for fermentation
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Where is the horses' pacemaker?
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Pelvic flexure
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What type of contractions does the ventral colon have?
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Antiperistaltic to resist the flow of ingesta and retain fluid for fermentation
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What is a common site of impaction in the horse?
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Pelvic flexure due to narrowing of the lumen
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What does the dorsal colon do?
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Impedence of ingesta
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What is the motility pattern of animals without substantial colonic fermentation?
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designed for stroage and evacuation
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Where is the pacemaker for animals not relying on hindgut fermentation?
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In the transverse colon (at the right colic flexure)
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In Dogs/Cats where is the greatest overall absorption of water>
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Upper small intestine
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Where is the most efficient absorption of water?
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Descending colon (87%)
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How does the proximal colon absorb water?
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Surface epithelium absorbs NaCl and water (no nutrient transporters)
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What does crypt epithelium do?
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Secretes NaCl and water
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How is water absorbed in the distal colon?
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Under control of aldosterone epithelium absorbs NaCl and water (no nutrient transporters)
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How does water absorption in the horse small intestine vary?
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Very little water absorbed in the horse upper small intestine because large fluid volumes needed for fermentation
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What does horse ileum secrete?
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HCO3- rich fluid similar to ruminant saliva to buffer bacterial fermentation acid
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Where does the majority of horse water reabsorption occur?
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Distal large intestine, as mediated by the renin-angiotensin-aldosteron system
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What do the epithelium of the distal colon respond to?
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Aldosterone
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Explain the effect of SCFA's on the equine large intestine
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Increase mucosal prostaglandins which decrease water absorption
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What is hematochezia?
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Fresh blood in the stool= lower intestinal bleeding
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What is steatorrhea?
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Greasy stool due to the presence of malabsorbed fat
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What is dyschezia?
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Painful or difficult defecation
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What is the first step in diagnosing chronic diarrhea
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Determine small or large bowel origin
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What signs are associated with small bowel diarrhea?
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Weight loss
Polyphagia High volume Melena |
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What signs are associated with large bowel diarrhea?
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Increased frequence
Hematochezia Tenesmus (straining) |
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What is tenesmus?
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Straining to defecate
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What is a common GI cause of diarrhea?
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Maldigestion due to EPI (exocrine pancreas insufficiency) tested via TLI (trypsin like immunoreactivity)
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