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
lizard kidneys
- caudal aspect of kidneys fused in many species (horseshoe)
- renal portal system
- may or may not have a urinary bladder
kidneys in snakes
- right kidney cranial to left
- 25-30 lobules
- no bladder, urine stored in distal colon or flared ends of each ureter
chelonian renal anatomy
- kidneys in caudal coelom
- bladder: single central structure +/- paired accessory bladders (important in hibernation)
- bladder osmotically permeable (can reabsorb water) (important for hibernation)
- in aquatic turtles a bouyancy aid and resorbs Na
microscopic renal anatomy in reptiles
- no pelvis, pyramids, cortex, medulla
- a few thousand nephrons
- lower GFR than mammals
- poorly developed glomeruli, few capillaries
- no loop of henle (cant concentrate urine)
what are salt glands
- some birds and reptiles have them, marine and desert animals only
- for when salt consumption > renal clearance
- excretion of salt without water loss
- hyperplasia/hypertrophy with high salt exposure
- countercurrent exchange
- modified nasal/lacrima/salivary glands (located eye, nose or tongue)
- excreted by burrowing, sneezing, tongue protrusion
- dries to white poweder
fish renal anatomy
- single kidney length of coelom
- divisions: cranial = endocrine and hematopoietic, caudal = filtration
- size and number of glomeruli varies
- +/- renal portal veins
- no loop of henle = hypo-osmotic urine
- water movement by osmosis over skin and gills
- nitrogenous waste = ammonia via urine or gills
explain osmoregulation in freshwater fish
- ion loss/water gain
- fish more salty than water, suck in water
- kidney excretes water (high GFR)
- gills responsible for active NaCl uptake and excretion of ammonia
- dietary intake of NaCl
explain osmoregulation in marine fish
- water more salty than fish
- lose water across gills and skin
- drink seawater to replace (angiotensin 2)
- gills excrete NaCl and ammonia
- kidneys small or have no glomeruli and remove excess divalent ions (Mg)
compare osmoregulation in fish
which kind of fish (salt or fresh) is at most risk of gaining water from their surroundings
freshwater
what type of fish (fresh or salt) has the higher GFR
freshwater
in which fish (salt of fresh) are the glomeruli small/absent
salt
which fish produces the most dilute urine
fresh
which fish (salt or fresh) drinks the most water
salt
amphibian renal anatomy and physiology
- urine: kidney -> ducts -> cloaca -> urinary bladder
- renal portal veins but not in caecilians
- caecilians = one kidney full length of coelom
- caudates and anurans paired posterior retroperitoneal kidneys
- cloacal bladder not true bladder (outpouching or diverticulum of cloacal wall, no direct connection with excretory ducts, opening closed by sphincter mm.
- nitrogenous waste type depends on lifestage and environment (aquatic = ammonia, terrestrial = urea or uric acid)
- hypo-osmotic urine
- aquatic amphibians skins extremely permeable to water and prone to evaporative losses. kidney must excrete excess water
- terrestrial amphibians important water conservation. evaporative loss. urinary blader stores water and can reabsorb. decrease their GFR with reduced water. most excrete urea
what is the clinical relevence of aquatic species and their renal phys
- skin is important for fluid balance and respiration
- diseases/damage can be catastrophic for health
- very sensitive! (environmental contaminats, cant scrub for sx, minimise handling, wear gloves, water quality very important
- can administer fluids/meds through water
