the reptile kidney

8/2/2019 The Reptile Kidney

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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
http://www.abaxis.com/veterinary/vetscan_vs2.html


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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
http://www.abaxis.com/veterinary/vetscan_vs2.html


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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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the reptile kidney

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