Flashcards in Exotics Deck (56)
What are the different forms of nitrogenous waste organisms can produce?
- Uric acid
What organisms are ammonotelic?
- Fish, aquatic amphibians
What organisms are ureotelic?
Mammals, terrestrial amphibians
What organisms are uricotelic?
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?
- 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
- 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?
- 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
- 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
- Posterior kidneys
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)
- 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
- Cannot concentrate urine
- Make up 70-90%
What are mammalian type nephrons in the avian kidneys?
- LoH present
- From cortex to medulla
- 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