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What are the different forms of nitrogenous waste organisms can produce?

- Uric acid
- Urea
- Ammonia


What organisms are ammonotelic?

- 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