Exotics renal anatomy and physiology Flashcards
Describe nitrogenous waste in aquatic organisms
excrete ammonia directly
Describe nitrogenous waste of terrestrial organisms
Mammals, terrestrial amphibians - urea
Birds, reptiles - Uric acid (uricotelism)
Describe the features of uric acid
Made in liver
Highly insoluble:
- water conservation
- storage in eggs
Tubular secretion via reptilian-type nephrons
Excretion is independent of:
- urine flow rate
- tubular water reabsorption
- hydration state
Describe the causes of gout in birds and reptiles
Hyperuricemia (excess uric acid) => precipitates out of blood into organs and joints => gout (visceral and articular)
Causes:
- renal disease
- high dietary protein - too many AAs => more uric acid
- dehydration - urates produced which cannot be flushed => renal gout
- nephrotoxic drugs - damages renal tubules
Describe the composition of urates in birds and reptiles
Precipitate:
- uric acid
- protein
- Na+ (carnivorous)
- K+ (herbivorous)
Enters cloaca and mixes with faecal material
Why are birds and reptiles able to excrete urates even when dehydrated?
Uric acid crystals precipitate => no osmotic pressure so does not draw water out with it
Why is urinalysis useless in birds and reptiles?
Due to mixing of urine, urate and faecal material
Describe the use of the renal portal valve in exotics
Normal:
Valve closed (ACh): limbs => renal portal veins => kidney => caudal vena cave
Stressed or dehydrated:
Valve open (adrenaline): limbs => caudal vena cava
How does the renal portal system in exotics protect against ischemic necrosis of the kidney?
Blood from tail/caudal body travels to the heart via the kidney
Portal system ensures blood flow to tubules (does not supply glomerulus)
Describe the clinical implications of the renal portal system in exotics
Drug pharmacokinetics:
- if drugs injected into caudal region, goes to kidneys first => damage or excretion
Caudal mesenteric vein:
- contributes to renal portal system
- disease of GIT => kidneys
- toxins from gut
Label the fish nephrons
Label the freshwater glomerular teleost nephron
Label the marine glomerular teleost nephron
Label the marine aglomerular teleost nephron
Label the reptilian nephron
Describe the key difference between fish/reptile and mammalian nephrons
fish/reptile nephrons have no LoH
Describe the avian nephrons
70-90% Reptile type nephrons:
- no LoH
- Cortex only
10-30% Mammalian type nephrons:
- LoH
- cortex -> medulla
Limited urine concentration
Describe the avian response to dehydration
Aginine vasotocin (avian ADH equivalent)
- stimulated by increased plasma osmolarity
- constricts afferent arteriole (renal portal system maintains perfusion)
-controls tubular water permeability
Urine can be retropulsed from the urodeum into the colon and caecum for sodium-linked water reabsorption
Describe sodium linked water reabsorption in the avian/reptilian colon and caecum
Active transport of Na out of colon
Cl ions follow Na
Water follows via osmosis
Describe the reptile response to dehydration
Arginine vasotocin => afferent arteriole constriction and increased tubular water permeability
Reverse peristalsis of urine from urodeum => rectum/colon
Describe post-renal urine modification in exotics
Cloaca, colon, bladder:
- ions
- water
- protein
- Na+, K+
- urates
Voided urine not reflective of renal function
Label the breeding and non-breeding avian urinary system (male)
Why can kidney disease cause paralysis in avian species?
Kidneys closely associated with lumbar and sacral plexus - spinal nerves run through kidney parenchyma
Kidney disease => renomegaly => pressure on nerve plexi => paralysis or lameness
Describe lizard renal anatomy
Caudal aspect of kidneys fused in many species
Only some species have a bladder
Describe the anatomy of the avian kidneys
Paired
Retroperitoneal
Large
Describe snake renal anatomy
Right kidney cranial to left
No bladder - urine stored in distal colon or flared ends of ureters
Describe chelonian renal anatomy
Kidneys in caudal coelom
No pelvis, pyramids, cortex or medulla
Fewer nephrons
Lower GFR
Poorly developed glomeruli
No LoH (can’t concentrate urine)
Describe chelonian bladder anatomy
Bladder may have paired accessory bladders
Bladder is osmotically permeable (give baths before hibernation to fill accessory bladder)
Describe the sexual segment in some male squamates
Cells between distal tubule and collecting duct
Cells change at breeding system:
- cuboidal => columnar
- increase in size
- large eosinophilic granules secreted into lumen
Describe the salt glands of some avian and reptile species
Modified nasal/lacrimal/salivary glands
Excretion of salt without water loss
Excreted by burrowing, sneezing, tongue protrusion
Dries to white powder (can be confused as fungal infection)
High salt exposure => hyperplasia/hypertrophy
Describe fish renal anatomy
Single kidney
Length of coelom
Cranial division:
- endocrine
- haematopoietic
Caudal division:
- filtration (nephrons)
No LoH => hypo-osmotic urine
Describe fish osmoregulation and nitrogenous waste
Water movement by osmosis across skin and gills
Nitrogenous waste (ammonia) excreted by gills, some in urine
Describe freshwater fish osmoregulation
Ion loss/water gain across gills and skin
Kidney excretes water - high GFR
Gills:
- NaCl active uptake
- excrete ammonia
Dietary intake NaCl
Describe saltwater fish osmoregulation
Lose water across gills and skin
Drink seawater to replace
Gills:
- excrete NaCl
- excrete ammonia
Kidneys:
- small or no glomeruli
- remove excess divalent ions (Mg2+)
Describe amphibian renal anatomy
Renal portal veins:
- blood from hindlimbs => kidney => heart
Caecilians (legless, wormlike lizards):
- one kidney
- full length coelom
Caudates (salamanders, newts) and anurans (frogs, toads)
- paired kidneys
- posterior kidneys
- retroperitoneal
Describe the amphibian cloacal bladder
Outpouching of cloacal wall
No direct connection with excretory ducts
Urine seeps into cloaca and is forced into bladder for urine storage
Cloacal opening is closed by sphincter muscle
Describe osmoregulation of aquatic amphibians
Skin water permeable - prone to evaporative water losses
Kidney must excrete excess water
Excrete ammonia through gills/skin
Describe osmoregulation of terrestrial amphibians
Water conservation important
Evaporative losses
Urinary bladders stores water (aquaporins control movement)
Decreased GFR with reduced water
Most excrete urea
Describe the clinical relevance of aquatic species osmoregulation
Skin is important for fluid balance and respiration:
- disease/damage can be catastrophic for health
- no surgical scrubbing (destroys mucous coating)
- sensitive to environmental contaminants
- minimise handling
- can administer fluids and meds by putting them in water
- water quality very important
What is the issue here?
Articular gout = uric acid deposits in synovial capsules and tendon sheath of joints
Describe the murexide test
Used to confirm gout
Joint aspirate mixed with nitric acid and dried
Ammonia added
If turns mauve = uric acid present = gout
What are the causes of decreased uric acid secretion?
What causes increased uric acid production
excess dietary protein
What does pink shell lesions suggest in aquatic species?
septicaemias
How can you prevent septicaemia in aquatic species?
Keep enclosure clean
Clean water thoroughly
Test water quality regularly
Remove things that could cause injury
Ensure correct temps
Balanced diet
Reduce stress
