urinary system in exotics Flashcards
what is the form of nitrogenous waste in aquatic organisms
ammonia
mammals and terrestrial amphibians excrete nitrogenous waste in the form of
urea
birds and reptiles excrete nitrogenous waste in the form of
uric acid
what is uric acid
- made in the liver
- highly insoluble
- good for water conservation, can be stored in eggs without becoming toxic to fetus
- secreted via tubular secretion (reptilian type nephrons
- amount excreted independent of urine flow rate, tubular water reabsorption and hydration state
what is gout in birds and reptiles
hyperuricemia (in joints or visceral)
- renal disease in which they cannot excrete uric acid
- can be due to very high dietary protein, dehydration (urates produced but cant be flushed) or nephrotoxic drugs (damage to renal tubules)
what are urates
white to yellow colloidal suspension
precipitate:
- uric acid
- protein
- Na
- K
uric acid crystals precipitate because there is no osmotic pressure (wont draw water out with it
what is the renal portal system and what animals have one
- in reptiles, birds, amphibians and most fish
- has both cranial and caudal portal veins
- blood goes to kidney from heart and again from legs
- protects against ichemic necrosis (when GFR reduced
- portal system ensures blood flow to tubules
- does not supply the glomerulus
- default is closed under ACh control. Limbs -> renal portal veins -> kidney -> caudal VC
- open under adrenaline control and diverts to mammalian system: blood from limbs goes straight to caudal VC
what are some clinical implications of the renal portal system
- drug pharmacokinetics -> nephrotoxic drugs injected into hind limbs go straight to kidney, or secreted from tubules and peed out.
- caudal mesenteric vein contributes to renal portal system. alimentary tract disease affects kidneys. toxins from the gut go straight to kidney
what structure is missing from fish and reptile nephrons
loop of henle
no urine concentrating ability
discuss avian nephrons
- 70-90% are reptile type (no loop of henle, cortex only)
- 10-30% mammalian type which have loop of henle spanning cortex and medulla
- limited urine concentration
discuss avian osmoregulation in terms of hehydration
- decrease GFR and urine flow rate
- under action of arginine vasotocin (rather than ADH)
- stimulated by increase in plasma osmolarity
- constriction ogf afferent arteriole and perfusion maintained by renal portal system
- controls tubular water permeability
- urine goes into urodeum and is reabsorbed into colon and caeca
- sodium linked water reabsorption (sodium goes out, followed by Cl then water)
- decreased with stress polyuria
how do reptiles respond to dehydration
- similar to birds (arginine vasotocin action)
- reabsorption of water by reverse peristalsis: urodeum, urine into rectum/colon
- high tolerance for severe dehydration and high salt load
is urinalysis useful for testing kidney function in reptiles? why or why not
no
urine undergoes a lot of modification after kidneys, excretion not same as what comes out of kidneys.
in cloaca, colon and bladder, lots of modification to ions, water, proteins, Na and K and urates
what is the morphology and location of avian kidneys
- paired retroperitoneal (large)
- caudal edge borders lungs (caudal synsacrum)
- close association with lumbar and sacral plexus
- spinal nerves run through kidney parenchyma
- near abdominal air sac diverticulum
inflammation or neoplasia in the kidney of a bird can led to …….. why
lameness/paralysis
because spinal nerves run through kidney parenchyma