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e. Kidney Function (1) Glomerulus: filtration (2) PCT: tubular reabsorption (3) Loop of Henle (a) descending loop: filtrate concentrates (b) ascending loop: filtrate dilutes Constant recycling of salt creates “standing salt gradient” in kidney medulla. DCT. GLOM. PCT. CD. - PowerPoint PPT Presentation
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24-1
e. Kidney Function
(1) Glomerulus: filtration
(2) PCT: tubular reabsorption
(3) Loop of Henle
(a) descending loop: filtrate concentrates
(b) ascending loop: filtrate dilutes
Constant recycling of salt creates
“standing salt gradient” in kidney medulla
24-2
PCT DCT
LOOP
CD
GLOM
24-3
300
NaCl H2O
24-4
300
1000
700
400
100300
600
900
1200
1400
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
24-5
300
1000
700
400
100300
600
900
1200
1400
300
600
900
1200
1400
NaCl
NaCl
NaCl
24-6
(4) Distal convoluted tubule
both active absorption and secretion
(a) control ion concentrations in filtrate
e.g., Na+, Cl-, K+, HCO3-, H+
regulates blood pH and ion composition
(b) removes wastes from blood by secretion
At end of DCT, filtrate is back to 300 mosm/L
24-7
300
1000
700
400
100
300
300
600
900
1200
1400
NaCl H2O
24-8
(5) Collecting Duct
Filtrate in CD passes down through standing salt gradient in medulla ECF
Water will leave filtrate by osmosis
Water picked up by blood and returned to general circulation
Salts and wastes remain behind to form a concentrated urine
24-9
(6) Summary
All kidneys:
elimination of wastes
conservation of needed salts and nutrients
Looped kidneys (birds and mammals only):
self generating osmotic gradient gives ability to concentrate urine
massive savings of water in animals with high waste production and water
loss
24-10
f. Control of kidney function
Control water reabsorption in collecting duct
Neurohypophysis/neural lobe
arginine vasopressin (AVP) in mammals
arginine vasotocin (AVT) in all others
9 amino acid peptide
Control: endocrine reflex arc
24-11
Decreased BloodPressure
Increased BloodOsmolarity
AorticBaroreceptors
CNSChemoreceptors
AVP RELEASE
+
+ +
+
24-12
AVP action
increase permeability of cells to water
via cAMP, induces production of proteins
“water channels”
works in kidney, bladder, skin
kidney
increases permeability of cells of collecting duct to water
24-13
300 mosm 300 mosm
300 mosm
NO AVPlow water
permeability
Large amountsof dilute urine
DIURESIS
HIGH AVPhigh water
permeability
H2O to circulation
1200 mosm
Small amounts ofconcentrated urine
ANTIDIURESIS
AVP = AntiDiuretic Hormone (ADH)
ECF
300
800
1200
24-14
2. Bladder
homeotherms
storage organ for hyperosmotic urine
poikilotherms
epithelium is thin, contains ion pumps
Na+, Cl-, pumped to blood, H2O follows
H2O permeability controlled by AVT
AVT increases, water uptake increases
24-15
3. Integument (skin)
barrier to environment
most vertebrates: impermeable to salts, H2O
waxy coating, dead cells, scales, mucus
amphibians: no barrier to H2O
lose H2O rapidly
can take up H2O along with ions
AVT: increases skin permeability
24-16
4. Salt Glands
marine elasmobranchs: rectal gland
marine reptiles and birds: facial
24-17
All drink sea water to gain water
no freshwater access
high salt load
no looped kidney: dilute urine
Excrete salt load from salt glands
concentrated saline solution excreted
active transport of Na+/Cl- to outside
2-3 X osmolarity of blood plasma
24-18
5. Gut
primary location for water and salt uptake
ion pumping into animal
water entry by osmosis
24-19
6. Gills
pump ions in or out
water follows by osmosis
24-20
C. Osmoregulatory Environments
1. Sea water (1000 mosm/L)
Problem: if blood pOs does not equal water pOs
then water and solutes will diffuse across gill
2 strategies:
a. conform
let blood osmolarity = environment
hagfish: plasma = 1000 mosm salt
sharks: plasma = 500 mosm salt, 500 mosm urea
kidney must still regulate blood composition
24-21
b. Regulate at 300-350 mosm/L
gill in salt water:
osmotic H2O loss from blood
passive salt gain from environment
response of marine fish:
(1) drink sea water
gain H2O and salt in gut
(2) excrete Na+, Cl- by pumping out at gills
(3) divalent ions, wastes excreted in urine
24-22
Marine fish kidney
adapted to minimize water loss in urine
very low glomerular filtration, down to 0
Overall strategy:
gain water and salt by drinking
excrete salt gained
conserve water at all locations
24-23
2. Fresh water (<100 mosm/L)
All animals regulate at 300-350 mosm/L
Problem
diluting: lose salt, gain H2O at gills
Solution
don’t drink
gain salt through diet
conserve salt
pump in at gills
reabsorb from bladder
24-24
Freshwater fish excrete excess water at kidney
adapted to maximize water loss in urine
very high glomerular filtration, no loop
“copious amounts of dilute urine”
24-25
Additional osmoregulatory problem
disposal of nitrogenous wastes
protein catabolism makes ammonia
increases osmotic pressure of blood
toxic
24-26
All fish
ammonia highly soluble in water
diffuses out of blood at gills
Fish are “ammonotelic”
excrete ammonia as nitrogenous waste
24-27
3. Terrestrial Environments
a. Take up as much water as possible
(1) Drink
(2) Eat
H2O trapped in food as humidity
H2O generated by biochemical breakdown of complex nutrients
“metabolic water”
60 ml H2O/100 g dry barley
(3) Absorb: amphibian skin, bladder
24-28
b. Reduce water loss
(1) Avoid hot environments (nocturnal)
(2) Impermeable skin
(3) Kidney
Produce a concentrated urine: loop
Kidney water conservation ability:
U/P ratio = urine osmolarity
plasma osmolarity
reptiles: no loop, U/P up to 1
birds: small loop, U/P up to 6
mammals: great loop, U/P up to 25
24-29
(4) Respiratory system
nasal labyrinth
inhale: air warmed and humidified
exhale: H2O condensed by cooling
Respiration still primary H2O loss in xeric environments
24-30
(5) Nitrogenous wastes
terrestrial: retain and detoxify ammonia
Mesic environments:
ammonia converted to urea in liver
less toxic
concentrated in urine
“ureotelic”
24-31
Xeric environments
urea still requires too much water
ammonia is converted in liver to uric acid
precipitates as insoluble salt after kidney
“uricotelic”
Huge water savings
Ammonia: 500 mls H2O to excrete 1 g N
Urea: 50 mls H2O to excrete 1 g N
Uric Acid: 10 mls H2O to excrete 1 g N
24-32
Ammonia
fish
aquatic amphibian larvae
crocodilians
Urea
mesic reptiles and amphibians
mammals
Uric acid
birds
xeric reptiles and amphibians
24-33
d. Store H2O: amphibians
store H2O in bladder and lymph
tolerate dehydration
draw water out of lymph
draw water out of urine from bladder
allow blood osmolarity to rise to 600