Exotics

Question 1

describe lizard kidneys (2)

Answer 1

1. paired kidneys located in caudodorsal/intrapelvic
2. paired ureters enter urodeum at cloaca, then urethra leaves the cloaca and enters the bladder in SOME species on lizards

Question 2

describe snake kidneys (4)

Answer 2

1. paired kidneys located in caudal 1/3 coelom, 75-95% SVL
2. paired ureters enter the urodeum at the cloaca!
3. NO BLADDER
4. kidneys have a sexual segment in the distal convoluted tubule

Question 3

describe chelonian kidneys (2)

Answer 3

1. paired kidneys in caudodorsal coelom
2. paired ureters enter the urodeum at the cloaca and then the urethra leaves the cloaca and enters the bladder in ALL chelonians!

Question 4

do reptile kidneys have a loop of henle? if not, how does the body adapt? give other species that have this blood supply

Answer 4

no loop of henle in reptiles!! compensate by including a portal venous supply in the renal vasculature to maintain a high overall renal blood flow but keep glomerular blood flow low

reptiles can turn their glomeruli on and off/bypass glomeruli while still supplying blood to kidneys (will then use bladder to concentrate urine/reabsorb water as needed)

loop of henle allows urine concentration via water reabsorption, so no loop of henle would mean no way to excrete solutes or reabsorb water so can bypass glomerulus with venous blood supply and not make filtrate

birds, amphibians, and fish also have this dual blood supply!

Question 5

describe the reptilian metanephric kidney (3)

Answer 5

1. only thousands of nephrons, versus millions in mammals
2. glomerulus, proximal convoluted tubule, and distal convoluted tubule all same
3. has an intermediate segment between proximal and distal; no loop of henle!

Question 6

identify the main products for urinary excretion of nitrogen in birds, reptiles, amphibians, and fish

Answer 6

lizards and snakes: mainly uric acid (predisposed to gout)

chelonians: mainly uric acid but also higher concentrations of urea than lizards and snakes

aquatic turtles and crocodiles: mainly urea and ammonia

birds: primarily uric acid (predisposed to gout)

amphibians: ammonia is species with gills, urea in most adults without gills

fish: mainly ammonia (KIDNEYS NOT RESPONSIBLE, THE GILLS DO THIS)

Question 7

describe uric acid excretion in reptiles

Answer 7

1. independent of GFR but dependent on blood and nephron ultrafiltrate flow
2. active transport from ECF into renal cell, then diffuses into tubules down concentration gradient
3. if tubular flow stops due to decreased GFR, urates accumulate in tubule lumen and prevent diffusion, resulting in increase in cellular uric acid increase and renal gout

Question 8

what determines GFR in reptiles? (2)

Answer 8

1. is proportional to functional renal mass
2. decreased by arginine vasotocin (AVT; similar function to ADH in mammals), turns individual nephrons on or off

Question 9

describe osmoregulation in reptiles (4)

Answer 9

1. reptiles can tolerate a hella wide range of osmolarity (256-492)
2. like mammals, kidneys, skin, and intestinal tract all contribute to osmoregulation
3. some reptiles have salt glands to secrete high concentrations of NaCl and K
4. post-renal modification of urine by cloaca/bladder

Question 10

describe post-renal modification of urine osmolarity by the bladder.cloaca in reptiles

Answer 10

reptiles use urine as a water reservoir; usually wait to urinate until it is raining and they know they can replenish their water supply; otherwise will NOT urinate, no matter how dehydrated they are, and will continue to squeeze water out of the bladder and into the blood for water retention

Question 11

describe avian kidneys (5)

Answer 11

1. paired, retroperitoneal within the ventral fossa of the synsacrum (fused pelvis and lumbar vertebrae)
2. intimately associated with the lumbar/sacral plexus nerves and veins, meaning that renal disease can result in lameness if the kidneys swell and compress those nerves
3. relatively large and often divided into cranial, middle, and caudal divisions by veins
4. no obvious demarcation between cortex and medulla
5. no renal pelvis

Question 12

describe avian nephrons (2 types)

Answer 12

1. cortical nephrons are similar to reptiles: these are the most common and are confined to the cortex; perform uric acid excretion by the glomerulus and proximal convoluted tubular secretion, but do not have a loop of henle so cannot concentrate urine
2. medullary nephrons are similar to mammals: these are less common and are located in both cortical and medullary regions AND have a loop of henle! so they can concentrate urine, but since there are so few birds still have poor urine concentration capability and rely on uric acid to concentrate urine and secrete water

Question 13

describe avian dual renal blood supply

Answer 13

1. high pressure renal arteries supply each kidney division, controlled by hydration and AVT
2. low pressure external iliac veins branch to form caudal renal portal veins, providing 2/3 of renal blood flow to supply to proximal convoluted tubule (but NOT glomeruli); this blood flow is controlled by innervation of smooth muscle valve controls that are normal closed to direct blood flow to the kidneys but can close with symp stimulation to direct blood to brain and heart

Question 14

describe avian ureters

Answer 14

ureters drain to the dorsal urodeum of the cloaca which directs urine into the rectum/colon via retroperistalsis for reabsorption of water and mixing with feces

BIRDS HAVE NO BLADDER

Question 15

describe avian nasal glands

Answer 15

all have nasal or salt glands above the eye

marine species: glands excrete excess salt from the salt water they consume

arid species: glands remove salt from blood, pass it down the nasal passages, and it can be sneezed out

Question 16

describe avian osmoregulation

Answer 16

droppings have 3 components
1. liquid urine: minor concentration, but 90% of glomerular filtrate is reabsorbed by renal tubules
2. semi-solid uric acid
3. feces

nitrogenous waste!
urea (minor excretion and contribution to osmoregulation)
uric acid: major excretion and contribution to osmoregulation

Question 17

describe amphibian kidneys and bladder

Answer 17

kidneys are mesonephric! have a nephrostome, or a direct connection between the coelom and the nephron, meaning that renal disease can cause fluid accumulation in the abdomen

bladder serves are a water reservoir/reabsorption pool and performs Na+ reabsorption and K+ secretion

Question 18

describe amphibian osmoregulation

Answer 18

1. main excretory products are ammonia and urea
2. cannot concentrate urine above that of plasma (like reptiles)
3. in freshwater: water influx and ion loss occurs across gills via osmosis, so they excrete large volumes of dilute urine
4. out of water: arterial flow/GFR are decreased; AVT decreases water excretion, water is reabsorbed from the bladder by osmosis, and Na/K exchange occurs across the skin and bladder

Question 19

describe fish kidneys (2 types)

Answer 19

1. cranial/head kidney: hemopoietic, immune function; no renal function
2. caudal/tail kidney: metanephric, osmoregulatory/renal function with a dual renal portal supply

Question 20

describe fish osmotic regulation in freshwater and saltwater

Answer 20

in freshwater:
osmotic INFLUX of water and LOSS of ions occurs through skin and gills, so they excrete large volumes of dilute urine and actively reabsorb sodium, magnesium, chloride, sulfate

in saltwater: osmotic LOSS of water and INFLUX of ions occurs through skin and gills, so they excrete small volumes of isotonic urine (reduced/absent glomeruli) and excrete magnesium, calcium, and sulfate

main nitrogenous waste for ALL is ammonia, which is highly toxic and must be removed immediately; is excreted by diffusion from the gills and the kidneys PLAY NO PART IS NITROGENOUS WASTE EXCRETION IN FISH