Alimentary System (Bolts)

Alimentary System (Bolts)

1. John Bolton

   • URT Pathology
     • Dysphagia
       • Difficulty Eating
         • Prehension
         • Mastication
         • Swallowing
         • NOT UNWILLINGNESS
       • Associated with Oropharyngeal/Oesophageal Disease
       • Gag Reflex
         • Normal Defence Mechanism
           • vs. Foreign bodies
         • From intraoral stimulation
           • CN V, IX, X to brain
             • impulse elevatese soft palate and constricts pharynx
         • Dysphagia can provoke gagging, but gagging not necessarily dysphagia
       • Clinical Signs
         • Reduced/no food intake
         • Ptyalism (saliva)
         • Halitosis
         • Gagging
       • Evaluate Prehension > Mastication > Swallow
         • Lips, Face, incisor, teeth, tongue = Prehension
           • CN V, VII, XII = motor
           • CN VII, IX, X (taste), I (smell), II (sight), V (feel) = sensory
         • Teeth, tongue, jaws, muscles = Mastication
           • CN V, IX = sensory
           • CN VII, XII = motor
         • Pharyngeal and oesophageal function = Swallowing
           • Voluntary Phase (Oral)
           • Involuntary Phase (Everything below the pharynx)
             • Oesophagus
               • Dogs and Ruminants: striated
               • Horse/Cat/Pig, striated to smooth
               • Innervated by vagus, and sympathetic nerves
               • Oesophageal Disease
                 • Inflammation: Infectious
                   • Viral: Same as mouth/pharynx
                     • BVDV
                 • Toxic
                   • Corrosive agents
                 • Trauma
                   • Foreign bodies/iatrogenic
                     • Intraluminal Obstructions
                     • Pressure causing necrosis/ulceration
                 • Neoplasia
                 • Developmental/Degenerative
                   • Vascular Ring anomalies
                   • Congenital/Acquired motility disorder
                   • Megaoesophagus
                 • Extraluminal Obstructions also possible
                   • Persistent Right Aortic Arch
           • CN: V, VII, IX, X, XII = Sensory
           • Pharyngeal Dysfunction
             • Pharyngeal Paralysis: Neuro
               • Nasal discharge
               • Aspiration Pneumonia
             • Achlasia
               • Failure of upper oesophageal sphincter to open
               • Uncommon
               • Acquired (polymyopathy) or Congenital
         • Pathology affecting Function (DAMNITV)
           • Toxic
             • Uremia/Corrosive Chemicals
           • Trauma
             • Bones, Wire, Grass seeds, poor dentition
           • Inflammation: Infectious
             • Bacteria
               • Actinobacillus ligniersi
                 • Wooden Tongue
               • Fusobacterium necrophorum
                 • Necrotic stomatitis/calf diphtheria
             • Viral
               • Feline rhinotracheitis virus
               • Calicivirus
               • Vesicular Stomatitides
                 • FMD, VS
               • Erosive Stomatitides
                 • BVDV, Rinderpest, MCF
             • Fungal
           • Neoplasia
             • Lymphosarcoma
             • Fibrosarcoma
     • Regurgitation + Vomiting
       • Regurgitation
         • Usually with oesophageal disease
         • Followed by retch/gag
         • Passive expulsion from pharynx/oesophagus
         • NO nausea/abdominal contraction, conscious effort, bile
       • Vomiting
         • Nausea, Retching
         • Forceful expulsion of stomach contents
         • Antiperistalsis (SI) into stomach, and Retrograde Giant Contractions (RGC)
         • Initiates in Emetic centre in Medulla
           • Not a distinct entity (pharmacologic)
           • Stimulated by:
             • Bacterial toxins
             • Upper GI irritation/distension
             • Indirectly via other pathways
           • Efferent: Vagus, Phrenic, Spinal nerves to abdominal muscles
         • Consequences
           • Malnutrition
           • Dehydration/Hypovolemia
           • Hypochloremia
           • Hypokalemia
           • Metabolic alkalosis
   • Intestines
     • Obstruction
       • Simple obstruction
       • Closed Loop Obstruction
         • External
           • e.g incarcerated umbilical hernia
         • Internal
           • e.g incarcerated small intestine in epiploic foramen
         • Both stretch and chemical receptors
       • Strangulation Obstruction
         • Examples
           • SI Torsion
           • Colonic torsion
           • Caecal torsion
           • Left Displaced Abomasum
           • GDV
           • Right Sided Abomasal Torsion
         • e.g. Torsion/Pedunculated lipomas
       • Mechanisms
         • Mechanical
           • Obturation obstruction
             • Typically minimal vasc. damage to wall
             • Sometimes pressure necrosis
             • Ingested foreign bodies/phytobezoars
               • Phytobezoars (fibre/plant material), trichbezoars = hairballs
                 • Activates Stretch receptors
             • Distended intestine proximal to obstruction
             • Intussusception
               • "Telescoping"
               • Common in young animals
               • Usually secondary to non--obstructive disease (parasties)
                 • Hypermotility/irritability
             • Retained Meconium (Failure to pass feces in neonates)
             • Enteroliths/Faecaliths
               • Accumulations of mineral salts, or faeces
               • Block Colon in horses
             • Impaction
               • Many Causes
               • Severe constipation (LI) in dogs
               • Sand impaction in horses
               • Activates Stretch receptors
           • Narrowing of Gut Lumen: Intrinsic lesions on wall
             • Congenital
               • Atresia
               • Stenosis of pylorus (rare)
             • Acquired
               • Inflammatory lesions
               • Benign/malignant tumors
               • Post anostomotic stenosis
           • Narrowing of Gut Lumen: Extrinsic Lesions on wall
             • Adhesions
               • Previous surgery
               • Previous peritonitis
             • Herniae
               • External (umbilical/inguinal)
               • Internal (epiploic forman)
             • Extraintestinal masses:
               • Abscesses
               • Tumours
               • Fat Necrosis
             • Small intestinal Volvulus (Volvulus/Torsion)
             • LI/Colonic Torsion/Displacement
               • esp,. Horses
             • Left Displaced Abomasum (Cows)
             • Gastric Dilation Volvulus (Dogs)
             • Right sided Abomasal Torsion (Cows)
         • Paralytic Ileus
           • "Functional" obstruction
           • Fails to propel contents
           • Can affect either SI or LI
           • Often follows GI Sx
           • Also associated with Electrolyte imbalance, peritonitis, toxemia
           • Stretch receptors: pain
         • Vascular Bowel Disease
           • "Functional" obstruction
           • Associated with arteritis: S. vulgaris parasite
           • Severe cases: Segmental infarct of colon
           • Uncommon now with antiparasitics
       • Other Signs
         • Reflex Reduced intestinal motility
         • Emptying intestine distal to obstruction
         • Reduced/Intestinal Borborygmi
           • Distension of intestine with fluid/gas
           • Reflex Neural Inhibition
           • Reduced blood supply
           • Hypovolemia, electrolyte disturbances
           • Endotoxemia
         • Abdominal Distension
           • Accumulated gas/fluid proximal to obstruction
             • Fluid in small intestine accumulates, may reflux
             • Horses cannot vomit, fluid causes pain/rupture
             • Vomiting in dogs
               • HCl Loss
                 • Metabolic alkalosis
           • Continued fermentation with gas production
           • Tympany (esp. horses) large intestine
             • Caecal gas cap "ping"
         • Tachycardia
         • Hypovolemic/Endotoxic Shock
         • Diagnostic Tests
           • Changes in peritoneal fluid
           • Abdominal Ultrasound Examination
   • Abdominal Pain
     • Neural Pathway
       • Extreme Stretch and Chemo nociceptors
         • Spinothalamic Pathway
         • Stretch Receptors
           • Hollow Organs: Muscular layers b/w muscularis mucosa and submucosa
           • Solid Organs: In serosa
           • Mesentery: w/ large blood vessels
           • Activation
             • Distension of Hollow organs
               • e.g GI Obstruction
             • Forceful muscular contractions
               • Urolithiasis/cholelithiasis, intestinal spasms
             • Stretching of solid organ serosa or capsule
               • Hepatic Congestions
             • Stretching of mesentery or mesenteric vessels
               • Neoplasia/Volvulus
         • Chemoreceptors
           • Hollow organs: Within mucosa/submucosa
           • Activation
             • Inflammation
               • Peritonitis/Abscess/Pancreatitis/G
             • Ischemia/Necrosis
               • Volvulus/GDV/Infarct/splenic torsion
             • by substances and ions
     • Clinical Manifestations
       • Vary: Episodic to Continuous
       • Tends to be more severe with BOTH stretch and chemical
       • Pain varies with lesion
       • Species differences
         • Horses: Obvious
           • Agitated, grinding teeth, sweating
             • Restlessness, inappetance
               • Lateral Recumbency/Dog sitting
         • Ruminants: Hard to determine
           • Non-specific: anorexia/depression
             • Kicking at abdomen, restless, grunting
           • TEST: Positive Grunt Test
         • Dogs: Range (depression, growling to grunts and tense abdomen)
   • Diarrhea
     • Refresher
       • Surface Area is super important in digestion
       • Crypts + Cells
         • Produce Enterocytes
           • Migrate up to villi
             • Die and slough into lumen
         • Secretory
       • Villous Cells
         • Absorptive
       • Enterocytes
         • Cells joined to one another tightly
           • Transport
             • Intracellular
               • Through cell
             • Transcellular
               • Between the cells
       • Digestion
         • Carbohydrates
           • Amylase
           • Glucose, Fructose, Galactose
         • Protein
           • Pepsin + Pancreatic proteases
           • Amino Acids
           • Multiple Digestive Pathways
             • Luminal Enzymes digest proteins to AA for absorption
             • Luminal enzymes digest proteins, brush border enzymes digest to AA for absorption
             • Luminal enzymes digest proteins to oligopeptides, taken by enterocytes, broken to AA and absorbed intracellularly
         • Lipids
           • Lipase + Co-lipase + Bile Salts
           • FFAs + Monoglycerides
     • Intestinal Fluid Balance
       • Water/Electrolyte balance
         • Secretion/Absorption > Input/Output
         • Efficiency of absorption increases down the tract
         • Sodium Transport
           • Nutrient Coupled Na Transport
             • Downhill gradient from Na/K pump
             • Cl absorbed passively (paracellular)
               • other ion gradient
             • Na - Glucose transporter SGLT1
             • Small Intestine
           • Sodium Hydrogen Exchanger
             • Small Intestine + Colon
             • Na exchanged for H
               • NHE3 transporter
               • Down gradient from Na/K pump
           • // Na H and Cl HCO3 exchange
             • In Ileum and Proximal colon
             • Na absorbed, coupled to Cl-
             • HCO3- produced intracellularly
             • H+ and HCO3 released
               • Na and CL absorbed
           • Electrogenic Na Absorption
             • Distal Colon
             • via Na+ specific, aldosterone sensitive ion channel
             • Down Na gradient by Na/K pump and K channel
             • Cl- absorbed passively (paracellular)
               • other ion gradient
         • Chloride Secretion
           • Both SI and LI
           • Secreted from crypt cells
           • Paracellular movement of Na
           • Cl secretion drives fluid secretion
           • Main source of Cl for Cl-HCO3 anion exchanger
           • Secretion regulated by second messengers
           • Stimulation by secratogogues >>> Opening/addition of new Cl channels (Secretory diarrhea)
         • Short Chain Fatty Acids/VFAs
           • Colon
             • Generated by bacterial fermentation
           • Acetate/Proprionate/Butyrate
           • Rapid absorption in colon = more Na/fluid resorption
           • SCFAs upregulate NHE3 expression
             • Enhances entry of SCFA into cells
               • Cl butyrate and SCFA HCO3 exchangers coupled to Na/H exchange
                 • Promote Na/Cl absorption
         • Nett Balance (Small Intestine)
           • Absorption
             • Water
             • Na (active)
             • K (passive)
             • Cl (exchange for HCO3)
             • Non-electrolytes
               • Glucose/AA/Lipids/Bile Salts
           • Secretion
             • Bicarbonate
         • Nett Balance (Large Intestine)
           • Absorption
             • Water
             • Na
             • Cl
             • SCFAs
             • NO NON-ELECTROLYTES absorbed. These are fermented
           • Secretion
             • K
             • HCO3-
         • Water Absorption
           • Passive (respond to salts)
           • Freely permeable upper small intestine
             • Most paracellular
           • Very large amounts
     • Pathological Mechanisms
       • Maldigestion/Malabsorption
         • Ingestion of poorly absorbed solutes
         • Villous atrophy (Loss of Surface Area)
           • Different types of atropy (Rotavirus/Parvovirus/TGE)
         • Epsom Salts/Sodium Sulfare poorly absorbed
           • Maldigesta in intestines
             • Causes water to move into lumen (osm D+)
               • Maldigested material ferments, increased osmotic drag
             • Also poor digestible milk replacer/lactose intolerant puppies
             • EPI, or Hepatic Insufficiency
         • LOW VOLUME
       • Secretion
         • Bacterial toxins
           • Enterotoxigenic e.Coli (Non-invasive)
         • Inflammatory Mediators
         • Endogenous laxatives
         • Increased ion transport mechanisms (esp. Cl-)
           • Both SI and Colon
           • No demonstrable intestinal lesions
             • Biochemical lesion
           • Fluid overload of large intestine
             • HIGH VOLUME DIARRHEA
               • Diarrheal fluid is isotonic
         • HIGH VOLUME
       • Changes in intestinal Permeability
         • Acute inflammation
           • Enteroinvasive Salmonella/e.coli
         • Chronic Inflammation
           • Eosinophilic enteritis (Horses)
             • Eosinophils infiltrate gut wall
               • Thickened gut wall
             • Infiltrates mesenteric LN
             • Variable granuloma formation in mucosa
           • Johne's Disease (Cows)
             • Chronic D+/emancipation/hypoproteinemia
             • Mycobacterium avium/ss. paratuberculosis
           • Histiocytic Ulcerative Colitis (Boxers)
             • Granulomas/ulceration in colon
             • infiltration with mØs with PAS+ material
         • Often associated with loss of protein
           • Protein-losing enteropathies
           • Electrolytes and protein move into lumen
             • Water moves into lumen/Osmotic D+
       • Changes in intestinal motility
         • Rarely a primary cause of disease
         • Increased motility can cause D+
           • secretory diarrhea
         • Decreased motility (SI), possibly SIBO
     • Osmotic Diarrhea
       • PART OF most D+ cases
       • Increased solute = more water into lumen
     • Role of Large Intestine
       • Compensated
         • Gut Flora = large reserve
         • Excess sugar = Converted to SCFA
           • Rapidly absorbed = no D+
       • Hypofermentation
         • NO developed flora (newborns)
         • Excess sugar not converted to SCFA
           • Less absorption = osmotic diarrhea
       • Hyperfermentation
         • Well developed flora
           • Overloaded with carbohydrates
         • Lactic acid produced (pH decreases)
           • Osmotic Diarrhea
   • Ruminants
     • Fermentation linked to Motility
     • Fermentation
       • Acidosis
         • Excess carbohydrate
           • Excess lactate
             • Osmotic diarrhea
               • Dehydration
                 • Hypovolemic Shock
             • Metabolic Acidosis
             • Even more bacteria/endotoxin
               • Endotoxic shock
             • Lactic acidosis
               • D-Lactate
                 • In rumen and blood
               • L-Lactate
                 • Used by host
               • Overwhelmss buffers --> Anion Gap
               • Also caused by poor perfusion
         • Death of "Good" bacteria
         • Diagnosis
           • Rumen Fluid Collection
             • Protozoa normally suspend the fluid, quick settling = protozoa are dead.
             • Analyse pH
             • gram stain
           • Presentations
             • Star Gazing
         • Consequences
           • Ruminal Stasis
             • Due to SCFAs
             • Caused by damaged ruminal wall, hypovolemia, metabolic acidosis and toxemia
           • Polioencephalomalacia
             • Destruction of thiamine producing bacteria
             • Thiamine deficiency
       • Ruminal Tympany (Bloat)
         • Free-Gas Bloat
           • Fermentation Normal
           • Acute
           • Chronic
           • Failure to Eructate
             • Blocked oesophageal opening
             • Obstruction of cardia
         • Frothy (Legume) Bloat
           • Fermentation Abnormal
           • Feeding lush pasture/legume
             • Chloroplast membrane protein = stable foam
               • traps gas, blocks eructation
           • No"ping"
           • Thorax compression, cardio failure, recumbency, death
     • Motility
       • Primary Cycle
         • Related to emptying/mixing
       • Secondary Cycle
         • Related to Eructation
       • Regulation via long vagovasal reflexes
         • Vagus nerve up to medulla
           • Vagus nerve down to smooth muscle
       • Abnormalities
         • Depression of Gastric Centers in CNS
           • anesthetics, drugs, pain, pyrexia
             • Traumatic Reticuloperitonitis (TRP/Hardware Disease)
               • Cow eats random hard stuff (esp in parturition/pregnancy)
                 • Collects in reticulum
                   • Penetrates wall
                     • Local peritonitis
                     • Generalised peritonitis
                     • Migrates through diaphragm: (myocarditic, thoracic abscess)
                   • Sits harmlessly and dissolves
                   • Reduce risk with a magnet
               • very common
               • Clinical Signs
                 • Decreased milk production
                 • Fever, Depression, Anorexia
                 • increased HR/RR
                 • Cranial abdominal pain (positive grunt test)
                 • Usually vague w/ localised TRP after 24hours
                   • Chronic = weight loss, poor lactation, rough hair, vagal indigestion
         • Lack of Excitatory Reflex inputs via tension receptors in forestomach
           • anorexia, vagus indigestion
             • Vagal Indigestion
               • Chronic, vague
               • Characterised by disruption to forestomach emptying
               • Failure of transport into/through omasum
               • Failure of abomasal emptying
               • Adhesions between forestomach and peritoneum
               • Often secondary to TRP or gut perforation
               • Usually no vagus nerve lesion
                 • mechanoreceptors?
                   • interferes with sensory signals to the brain
                     • Disrupted vagal motor signals for normal reticuloruminal motility
               • Clinical Signs
                 • Reduced feed intake, normal water
                 • Bradycardia, from vagovasal impulse
                 • Variable rumen sounds (absent/hypermotile)
                   • Usually increased but ineffective
                 • "Pearpple shape"
         • Blockade of motor pathways
           • secondary to drugs
             • atropine
           • hypocalcemia
         • Increased inhibitory reflex inputs via epithelial receptors in forestomachs
           • ruminal distension, acids, abomasal/small intestinal distension