Renal anatomy of exotics

Question 1

How do aquatic organisms excrete ammonia?

Answer 1

As ammonia which is relatively toxic but aquatic animals more tolerant as it can be diluted quickly.
It requires lots of water to produce

Question 2

How do mammals and terrestrial amphibians excrete their nitrogenous waste?

Answer 2

As urea which requires less water for excretion

Question 3

How do birds and reptiles excrete their nitrogenous waste?

Answer 3

As uric acid which requires very little water to excrete and is highly insoluable

Question 4

How many kidneys do fish have?

Answer 4

Fish have a single kidney the length of the coelom which is dived into two sections (which can be separate)
Cranial: endocrine & hematopoietic
Caudal: filtration (nephrons)

Question 5

Do freshwater fish have more glomeruli?

Answer 5

Yes and longer

Question 6

Why do fish lack a loop of henle?

Answer 6

They are surrounded by water which moves salts via osmosis.

Question 7

How do fish excrete their nitrogenous waste?

Answer 7

The nitrogenous waste is excreted by urine and via the gills (majority).

Question 8

In freshwater ion loss and water gain occurs across the ………….. so they…
How do they maintain their salt levels?

Answer 8

The gills
so they also produce much more and more diluted urine (so subsequently have a high GFR).
In order to maintain their saltiness above the water freshwater fish actively take up NaCl via the gills and excrete ammonia.

Question 9

In saltwater fish they lose water across their gills so…

Answer 9

They have to drink seawater to replace it, their gills excrete NaCl (actively) and ammonia (passively) to maintain saltiness. Subsequently the kidneys are small with no glomeruli and just remove excess divalent ions eg Mg2+.

Question 10

How do amphibians remove urine from their kidneys?

Answer 10

In amphibians the urine travels from the kidney via the ducts to the cloaca and the urinary/cloacal bladder

Question 11

In amphibians the blood from the hindlimbs travels by the…

Answer 11

Amphibians have renal portal veins where blood from the hind limbs travels via the kidney before reaching the heart.

Question 12

Do amphibians have one or two kidneys?

Answer 12

Caecilians have one kidney that is the full length of the coelom whereas caudates and anurans have paired posterior kidneys that are positioned retroperitoneal.

Question 13

Amphibians have ………-osmotic urine

Answer 13

Hypo-osmotic

Question 14

The skin of aqueous amphibians is highly permeable so passive absorption of water occurs readily, what does this mean for the kidneys?

Answer 14

The kidney must excrete excess water and lose ammonia via the gills.

Question 15

Amphibian bladders can…

Answer 15

reabsorb water

Question 16

Where do bird kidneys lie?

Answer 16

They lie near the abdominal air sac diverticulum and are divided into Cranial, middle, caudal divisions.

Question 17

Most of the avian nephrons are of what type?

Answer 17

Reptilian type: so have no loop of henle and are only in the cortex
Th other 20% are mamalian type with a loop of henle and span the cortex and medulla

Question 18

What do birds do if they get dehydrated?

Answer 18

If birds become dehydrated they decrease their GFR and urine flow rate

Question 19

In birds what kicks in when they sense increased plasma osmolarity?

Answer 19

Arginine vasitocin (which controls tubular water permeability)

Question 20

Birds have some degree of Na linked water reabsorption but this is reduced by…

Answer 20

Decreased by stress and polyuria

Question 21

What is the purpose of the urine reflux into the colon of birds?

Answer 21

Na and Cl are pumped out of the colon and H2O follows

Question 22

How can renal disease cause non-weight bearing lameness in birds?

Answer 22

Lumbar and sacral plexus associated with kidneys

Renal disease puts pressure on the nerve plexus which leads to non-weight bearing lameness

Question 23

What species produce uric acid and where is it made?

Answer 23

Uric acid is produced by terrestrial reptiles and birds, it is made in the liver and secreted by the reptilian type nephrons.

Question 24

Uric acid secretion is independent, what does this mean?

Answer 24

This excretion is independent of urine flow rate and is excreted 8-16x more than GFR and therefore independent of hydration state

Question 25

What causes gout in the bird?

Answer 25

Birds can get hyperuricemia which leads to goat, it is caused by high dietary protein and dehydration

Question 26

How do birds excrete even more salt?

Answer 26

Birds also have a salt gland (supraorbital gland) which drains into the nostrils because salt consumption is higher than the renal clearance so the salt gland provides extra renal excretion of NaCl. They are especially common in aquatic birds and desert birds and the gland hypertrophies with high salt exposure

Question 27

How does the salt gland control Na conc?

Answer 27

If a bird drinks seawater then Na+ goes into the blood and the solute conc of the blood increases so water moves out of the cells and ECFV increases so the salt gland excretes salt.

Question 28

Do reptiles have one or two kidneys?

Answer 28

In lizards the caudal aspect of the kidneys is fused and they may lack a urinary bladder

Question 29

What is the snake renal system like?

Answer 29

In snakes the left kidney is caudal to the right and consists of 25-30 lobules.
The reptile kidney has no pelvis, pyramids, cortex and medulla, it only contains a few thousand nephrons.
They have no bladder so urine is stored in the distal colon or in the flared ends of each ureter.

Question 30

Where do chelonian kidneys lie?

Answer 30

Chelonians have kidneys in the caudal coelom and their bladder is a single central structure with or without paired accessory bladder

Question 31

Do reptiles have a portal system like birds?

Answer 31

Yes
They may have a valves similar to birds so when the valve is closed blood goes from the hindlimbs to the kidneys to the heart and when the animal is stressed the valve opens and the blood goes straight to the heart.

Question 32

What is the sexual segment?

Answer 32

Cells between distal tubule and collecting duct that are cuboidal and become columnar there is a 2-4x increase in size
Large eosinophillic granules secreted into lumen
Regress after castration (androgen control)
They function to separate urine and semen and aids the formation of a copulatory plug.

Question 33

Reptiles secrete their uric acid along with…

Answer 33

Reptiles secrete their nitrogenous waste as uric acid complexed with protein and Na (carnivores) or K+ (herbivores), it is secreted with mucoid substances, glycoprotein/mucopolysaccharides

Question 34

How do reptiles reabsorb protein from their urine?

Answer 34

In the In urodeum there is urineflow into the rectum (reverse peristalsis) so that protein can be absorbed and recycled

Question 35

Reptiles uric acid secretion into the proximal tubule requires what ion?

Answer 35

K+

Question 36

Why does urate secretion increase if blood pH drops in reptile?

Answer 36

Urate secretion increases if blood pH drops this is because H+ ions secreted into bladder (if present) and uric acid precipitates

Question 37

What is the reptile response to dehydration?

Answer 37

The afferent arteriole constricts (arginine vasotocin), the glomerulus closes, the tubule collapses and this decreases GFR and decrease excretion.

Question 38

What are the additional functions of the kidney in reptiles and birds?

Answer 38

Reptile & Bird:convert 25-hydroxycholecalciferol to active forms of D3
Reptile: Vitamin C synthesis