Exotics Flashcards
What are the different forms of nitrogenous waste organisms can produce?
- Uric acid
- Urea
- Ammonia
What organisms are ammonotelic?
Aquatic
- Fish, aquatic amphibians
What organisms are ureotelic?
Mammals, terrestrial amphibians
What organisms are uricotelic?
Birds, reptiles
What are the advantages and disadvantages of ammonotelic excretion?
- Requires a lot of water (not a problem as are aquatic)
- Little energy required to produce ammonia
What are the advantages and disadvantages of ureotelic excretion?
- Moderate amount of water required for excretion
- Moderate amount of energy required to produce urea
What are the advantages and disadvantages of uricotelic excretion?
- Very little water required for excretion
- High amount of energy needed for produciton
- Very stable, can be stored within eggs without damage to the embryo
Describe uric acid as an excretion molecule
- Made in liver
- Tubular secretion from repitilian type nephrons
- Independent of urine flow rate
- Rate of uric acid clearance approx 8-16x GFR
- Independent of tubular water reabsorption
- Independent of hydration state
What is unusual about excretion in reptiles?
- Uric acid complexed with protein and Na+ (carnivorous diet) or K+ (herbivorous)
- High levels of protein in urine
- Are able to reabsorb protein from urine
- Passes from urodeum to rectum by reverse peristalsis in order to do this
What happens to uric acid in reptiles following reabsorption in the bladder?
- Actively secreted into proximal tubules
- Needs K+ for this
What happens to urate secretion in reptiles if blood pH drops?
- Increases
- H+ ions secreted into bladder (if present) and uric acid precipitates
What are reptiles prone to in situations of severe dehydration?
- Gout in kidneys
- Not enough water to flush things out
Describe the fish renal anatomy
- Single kidney length of coelom
- Retroperitoneal
- May be separate or joined, but cranial and caudal divisions
- Cranial: endocrine and haematopoietic
- Caudal: filtration (nephrons)
- May or may not have renal portal veins (supply renal tubules then back to heart, no supply to glomerulus)
Describe the nephrons found in fish
- No glomeruli in some species
- Freshwater: many (larger) glomeruli
- No LoH
How is the ammonia removed from the fish’s body?
- Urine
- Gills (most excretion from the gills)
Describe osmoregulation in freshwater fish
- Higher conc. ions in fish than out, so water moves in by osmosis
- Ions out of fish
- Both of these through gills (and skin)
- Kidney excretes water
- Gills active NaCl uptake, excrete ammonia
- Dietary intake of NaCl
Describe the excretion of water by freshwater fish
- Kidney
- High GFR
- Most segments of kidney reabsorb vitamins and minerals
- Distal tubules also reabsorb ions
- Dilute urine produced
Describe osmoregulation in marine fish
- Conc. ions higher outside than inside
- Water out of fish by osmosis, ions in
- Lose water across gills and skin
- Drink seawater to replace lost water (angiotensin II)
- Gills excrete NaCL and ammonia
- Kidneys remove excess divalent ions (Mg2+), only small/no glomeruli
Describe urinary tract anatomy of amphibians
- Kidney -> ducts -> cloaca -> urinary (cloacal) bladder
- Cloacal bladder is outpuching/diverticulum of cloacal wal (no connection to excretory ducts)
- Cloacal opening controlled by sphincter muscle
- Have renal portal veins (not caecilians)
Describe the kidneys of caecelians
- One kidney
- Full length of coelom
Describe the kidneys of caudates and anurans
- Paired
- Posterior kidneys
- Retroperitoneal
Compare the excretion methods of aquatic vs terrestrial amphibians
- Aquatic excrete ammonia (also larval stage)
- Terrestrial excrete urea or uric acid
- Some adults may be flexible depending on water availability
Outline osmoregulation in aquatic amphibians
- Skin water permeable
- Passive absorption of water
- Kidney excretes excess water
- Excretion of ammonia through gills/skin
Outline osmoregulation in terrestrial amphibians
- Water conservation important
- Evaporative loss
- Urinary bladder to store water (or reabsorb)
- Controlled by arginine vasotocin (AVT)
- Aquaporins
- Decrease GFR with reduced water
- Excrete urea (can store until water is available to facilitate excretion)
What are the similarities between aquatic and terrestrial amphibian excretion?
- High GFR
- Filter coelomic and/or vascular fluid
- Hypo-osmotic urine
- urinary bladder stores urine after formation
Describe avian renal anatomy
- Paired kidneys (large)
- From caudal edge of lungs to ccaudal synsacrum
- 3 divisons of kidney (cranial, middle caudal)
- Renal lobules with cortex and medullary cones
- Reptilian and mammalian type nephrons
- Limited urine concentration
What are reptile type nephrons in the avian kidneys?
- No LoH
- cortex only
- Short
- Cannot concentrate urine
- Make up 70-90%
What are mammalian type nephrons in the avian kidneys?
- LoH present
- From cortex to medulla
- Longer
- Concentration of urine takes place here
What is the significance of the lumbar and sacral plexi in relation to the kidneys?
- Closely associated
- Renomegaly can increase pressure on nerve plexi, leading to non-weight bearing lameness
Describe the elimination of uric acid in birds
- White/light yellow colloidal suspension
- Precipitate: uric acid, Na+/K+, protein
- Uric acid crysta precipitate has no osmotic pressure, no water drawn with it for elimination
- Eliminated as urates suspended within spheres complexed with protein (or K+ if herbivorous) and sodium
- Small volume of water needed
- Mixed with faecal material
Describe the urinary anatomy of lizards
- Caudal aspect of kidneys fused in many species
- +/- urinary bladder
Describe the urinary anatomy of snakes
- Right kidney cranial to left
- 25-30 lobes
- No bladder
How is urine stored in snakes?
- No bladder
- Stored in distal colon or flared ends of each ureter
Describe the urinary bladder in chelonians
- Kidneys in caudal coelom
- Bladder is single central structure +/- paired accessory bladders
What is unusual about the bladder of chelonians?
- Is osmotically permeable
- Can reabsorb wateer
- In aquatic turtles acts as buoyancy aid and reabsorbs Na+
Describe reptile microscopic renal anatomy
- No pelvis, pyramids, cortex, or medulla
- A few thousand nephrons
- Poorly developed glomeruli
- Few capilaries
- No LoH
What is the sexual segment in squamates?
- Males
- Between distal tubule and collecting duct
- Enlarges dramatically in breeding season
- Cells go from cuboidal to columnar
What occurs in the sexual segment?
- Cells go from cuboidal to columnar
- Large eosinophilic granules secreted into lumen
- Function largely unknwon, may be to separate urine and semen, or formation of copulatory plug
What are some additional functions of the kidney in reptiles?
- Conversion of 25-hydroxycholecalciferol to active vit D3
- Vitamin C synthesis
What is an additional function of the kidney in birds?
Conversion of 25-hydroxycholecalciferol to active vit D3
Describe gout formation
- Hyperuricaemia
- Can be caused by renal disease, high protein diet, dehydration, nephrotoxic drugs, damage to renal tubules
- Uric acid deposited in soft tissues (often kidney furthering problem)
What is the avian renal portal system?
- Second afferent lood supply from pelvic limbs to renal parenchyma
- Cranial and caudal portal veins
- Opened or closed by renal portal valve
- Does not supply glomerulus
- External iliac from hind limbs, valve at common iliac
Compare the open vs closed renal portal valve
- Closed: limbs to renal porta veins, kidney (Ach), normal conditions
- Open: limbs to caudal vena cava (adrenaline), valve smooth muscle relaxation so can bypass kidney
Discuss drug pharmacokinetics with respect to the renal portal system in birds
- Nephrotoxic drugs straight to kidney, more damage
- Tubular secretion: if drug can be eliminated by tubular secretion, will never reach rest of body
Describe the caudal mesenteric vein with respect to the renal portal system in birds
- Contributes to renal portal system
- Alimentary tract disease taken to kidney
- Toxins from gut (e.g. heavy metals) straight to kidney
Describe the renal portal system of reptiles
- Similar to birds
- Renal portal vein
- Bypasses glomerulus, perfuses renal tubules
- Can be valved similar to birds
List the osmoregulatory mechanisms used by birds in dehydration
- Decrease GFR
- Arginine vasotocin release (controls tubular water permeability)
- Sodium linked water reabsorption in the colon and ceca
Describe sodium linked water reabsorption in the colon and ceca
- In times of dehydration, urine refluxed to urodeum from proctodeum
- Then into colon and ceca
- Active transport of sodium into blood, chloride and water follow by diffusion
- Does not occur in times of stress (leading to polyuria)
- Produces concentrated uric acid, dry mixture with faeces
Describe reptilian responses to dehydration
- Afferent arteriole constriction (arginine vasotocin stimulates this)
- Glomerulus closes, tubule collapses
- GFR decreases
- Decreased excretion of nitrogenous waste and sodium
- Renal portal blood perfuses tubules
How are reptiles adapted to conserve water?
- Few nephrons
- Lower GFR
- Uric acid
- Cease GFR in times of stress
- Salt gland for excess Na+/K+ excretion
Where is the salt gland in reptiles and birds?
- Supraorbital gland
- Drains into nostrils
- Or above palate
In what birds is the salt gland found and why?
- Aquatic: high consumption of salt water
- Desert: need to conserve water so actively excrete salt
What is the function of the salt gland?
Removal of exess salt, when salt consumption exceeds the ability of the kdiney to remove it
How is salt removed by teh salt glands in birds?
- Countercurrent blood flow, paired gland, ots of lobes, each lobe has a duct and each duct has lots of capillaries
- Increased solute concentration in blood
- Water out of cells, increase ECF vol
- Increase blood plasma solute conc and ECFV leads to salt gland secretion
Describe the salt glands of reptiles
- Similar to birds
- Actively excrete Na+ and K+
- Near eye or nasal passages
- High plasma osmotic concentration stimulates this
- Sneeze excess salts
(looks like powder around nostrils once dried) - Sea turtles have modified tear glands
What are the 3 components of avian excreta?
- Urate (white)
- Faeces (brown)
- Urine (clear)
