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The Reptile Kidney: FromAnatomy to Clinical Medicine
Mark A. Mitchell DVM, MS, PhDUniversity of Illinois
College of Veterinary Medicine
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Introduction Renal Disease
Lizards
Green iguanas For decades SNHP a
problem in juveniles
Long term effectsPTH?
Living longer? Chelonians
How to manage? Anatomy, Physiology
Diagnostics
Treatment considerations
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Anatomy
Paired Lobulated
Squamates
Elongated
Location
Pelvic canalCoelomic cavity
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Anatomy
Ureters
Urogenital papillae
Urodeum
Urethra Urinary bladder
Absent in crocodilians
and snakes Chelonians water
resorption
Urine flow
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Anatomy
Blood supply
To kidneys
Arterial blood- renal artery
Venous blood- renal portal
veins From kidneys
3-5 efferent renal veins
Paired renal veins
Posterior vena cavae
Renal portal system
Caudal vein drains intoRPS
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Histology Metanephric kidneys
Fewer nephronsthan mammals
No ansa nephroni
Well developedglomeruli
Nephrons at right >to kidney long axis
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Histology
Nephron= Glomerulus
Thin ciliated neck segment
Proximal tubule Narrow ciliated intermediate segment
Short distal tubule
Sexual segment
Collecting duct
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Physiology of the Reptile Kidney
Kidney Regulate extracellular volume and composition
Filtration Selective reabsorption Secretion
Hormonal control Renin Urodilatin Dopamine
Kallikrein Prostaglandins
Erythropoietin Vitamin D
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Physiology of the Reptile Kidney
Uricotelic
Uric acid salts primarily excreted Monosodium urates most common
Uric acid excreted in the proximal tubule
Urine isosmotic with varying amounts ofprotein
Urine concentration does not exceed plasmaUric acid excreted in colloidal suspension
Relatively insoluble- minimize insensible water
loss
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Extra-renal physiology
Secondary sites ofextracellular fluidregulation
BladderCloaca
Nasal salt glands
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Renal Disease
ACUTE VS. CHRONIC
Anamnesis
Physical examinationDiagnostics
Therapeutic considerations
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Anamnesis
Iguanas 3-6 year old adults
High protein/purine diets
Free-ranging
Cats
Excess vitamin andmineral supplementation
Limited water access, lowhumidity
Lack of UVB SNHP
Parathyroid: nephrotoxic
Multifactorial
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Anamnesis
Chelonians 1-5 years old
High protein/purinediets
Excess vitamin andmineralsupplementation
Limited/no wateraccess
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Physical Examination
Be thorough:
Common findings: Muscle tremors
Dehydration Wasting (CRF)
Anorexia
Weak and depressed
Palpable kidneys
Digital- cloaca
Externally
Constipation
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Diagnostic Testing
CBC PCV
Dehydration
Leukocytosis
Inflammation Always
infectious?
Reference ranges?
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Diagnostic Testing
Calcium-
phosphorus Normal ratio >1-1.5
Inverse ratio
Indications?
Ca:P product (>70)
Human derived
Ionic vs. bound Role of pH
Protein
Hypoproteinemia Albumin losses
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Diagnostic testing Uric acid
Primarily eliminated tubularsecretion
Increase with severe disease Not a good indicator of renal
compromise
Chelonians (>10 mg/dl) Chronic dehydration
Primary gout Primary renal disease
Urea Chelonians
Creatinine Severe renal compromise >10 mg/dl
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Diagnostic Testing
Potassium
Increase in acute renaldisease
Sample processing
Cell leakage
Sodium and chloride
Dehydration
AST
Not specific (increase)
CK
Muscle wasting
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Diagnostic Testing
UrinalysisCystocentesis or catheter
Sample not sterile
Fecal/cloaca contamination
Culture: + or -
If primary bacterial problem suspected
Urine not concentrated- may be with renaldisease
Cytology Identify cell types
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Diagnostic Sampling: Urinalysis
Urinalysis: dipstick and cytology
Color- clear to straw
Green- biliverdin (liver)
Specific gravity
1.003-1.014
Increased with renal disease
pH: iguana- alkaline; carnivore- acidic
Cells- few RBC, few renal tubular, squamous, transitional
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Diagnostic Sampling: Urinalysis
Bilirubin, ketones:negative
Glucose, protein: none to low
Bacteria- common
Crystals- amorphous urates normal; calcium oxalates: renaldisease
Casts- renal compromise
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Diagnostic Testing Radiographs
Survey 2 views
Cranial extension ofkidney from pelvic canal
Negative contrast Air into coelomic cavity
(10ml/kg)
Ultrasound
7.5-10.0 MHz Scales Ultrasound gel or water
bath
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Diagnostic testing Biopsy
Anesthesia Propofol
10-15 mg/kg
Dissociative/Inhalant Ketamine: 5-10 mg/kg Telazol: 3-5 mg/kg
Lidocaine
Analgesics Opioids
Butorphanol 0.5-1 mg/kg
Carprofen 2 mg/kg
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Diagnostic Testing
Biopsy Transcutaneous tru-cut:
cranial
Cranial tail cut down:caudal
Endoscopy insufflation :cranial
Air
Exploratory coeliotomy:cranial
Collect multiplesamples
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Diagnostic Testing Histopathology
Leukocytic infiltrates Proteinaceous casts in
tubular lumens
Interstitial nephritis Glomerulonephritis
Pyelonephritis Glomerulosclerosis *Glomerulonephrosis *Tubulonephrosis
Associated metastaticmineralization
Generalized
* Common
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Suspected etiologies
Toxic compounds (e.g., aminoglycosides)
Nutritional High protein diets Limited water, humidity
Hypervitaminosis D
Amyloidosis Low molecular weight amyloid
Chronic antigenic stimulation Congo-red positive
Trauma
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Suspected etiologies Gout
Limit uric acid secretion Overwhelming production Severe dehydration
Bacterial diseases Gram-negative opportunists
Microthrombi Fungal Parasitic
Protozoa Cryptosporidiosis
Trematodes Nematodes
Viral IBD- snakes
Neoplasia
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Therapy
Stabilize patient
Correct problems
Protect remaining functional kidney
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Therapy
Correct environment and diet
Fluid therapy Assess dehydration: maintenance plus deficit
Maintenance: 25-30 ml/kg/day
Rate 1 ml/kg/hr (shock 5ml/kg/hr) Route: PO, SQ, IO, IV
Acute renal failure
May cause cardiac overload b/c delayed return tofunction
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Managing Dehydration
Measure
Sodium
PotassiumChloride
GlucoseUric acid/urea
Estimate osmolarity
osmolarity= 2(Na + K) + glucose + uric acidosmolarity= 2(Na + K)
Select fluids based on chemistries
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Therapy
Hypocalcemia
Consider Ca:P product: risk of mineralization
pH
Ionic contribution
treat with severe signs IO/IV: calcium gluconate (400 mg/kg/day)
Oral preferred when stabile
Phosphate binders Aluminum hydroxide (25 mg/kg PO BID)
Calcium carbonate (250 mg/kg PO BID)
Same risk as above
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Therapy
Hyperuricemia
Allopurinol (20 mg/kg PO SID)
Reduce hepatic production of uric acid
Probenecid (3 mg/kg PO SID)Block resorption in tubule= increase secretion
Nandralone anabolic steroid (5mg/kg q 28d)
Reduce protein catabolism
Lower protein diet
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Therapy
Vitamin D
Controversial Humans used to reduce PTH
Reduce renal toxicity without hypercalcemia
Calcium channel blockers?
Antimicrobials Culture and Sensitivity
Dialysis
Intracoelomic dialysis with hypertonic solution
Difficult because of relative insolubility of uric acid
Surgical Intervention
Blockage
Granuloma/abscess
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