1. Animal Physiology – Osmoregulation & Excretion
Chapter 44

2. Osmoregulation Def – MGT of body’s water & solute concentration
Osmoregulation depends on the environment the organisms lives in
Marine Vertebrates (Fish) – face dehydration pressures from the sea (salt H2O)
So they are in a hypertonic solution
What happens to H2O inside the fish? – Exits
Fish lose great amounts of water via gills & skin
To combat this loss, fish produce little urine & consume large amounts of sea H2O combined with active transport of salts

3. Osmoregulation (Page 2)
Freshwater vertebrates (fish)
Environment is hypotonic, so need to counter osmotic pressure
Active transport of salts into body
Excrete substantial amounts of dilute urine

4. Excretory Systems Terrestrial Organisms
Evolved mechanisms that expel wastes into the environment & retain water as well
Different organisms = different mechanisms
Protista = Contractile vacuole
Platyhelminths = Protonephridia/Flame-bulb system
Annelids (Earthworm) = Metanephridia
Insects & Terrestrial Arthropods = Malpighian Tubules
Humans = Nephrons (Kidneys)

5. Excretion (Page 2) Def – removal of metabolic wastes
Wastes include:
CO2 & H2O (Respiration wastes)
Nitrogenous waste (from protein metabolism)
Ammonia, urea, or uric acid
Excretion Organs (Humans)
Skin, lungs, kidneys, & liver (site of urea production)

6. Nitrogenous Wastes Ammonia Urea Uric Acid
Highly toxic, but water soluble
Generally excreted by waterborne organisms
Urea
Not as toxic as ammonia
Humans & Earthworms excrete
In mammals, ammonia is decomposed into urea in liver
Uric Acid
Pastelike substance that you have seen on the outside of your car
NOT water soluble; Least toxic form
Deposited by birds (and reptiles) – minimum of H2O loss

8. Urine Production in 4 Easy Steps
1. Filtration
Pressure-filtering of body fluids
Removal of water & solutes
Cells, proteins, & large particles remain
2. Reabsorption
Reclaims valuable substances from the filtrate
Glucose, vitamins, & hormones
3. Secretion
Adds other substances (toxins & excess ions) to the filtrate
4. Excretion
Altered filtrate leaves the body

9. Human Kidney Dual functionality: Osmoregulation & Excretion
Renal = kidney
Renal vein, renal artery, renal nerve, renal failure
Kidneys are the body’s filters
Kidneys filter 1,000 – 2,000 L blood per day
Produce 1.5 L urine per day

10. Human Kidney (Page 2)
Humans need to conserve water, but also remove toxins
Kidney adjusts volume & concentration of urine due to animal’s intake of water & salt
Fluid intake is high & salt intake low = dilute (hyposmotic) urine
Fluid intake low & salt intake high = concentrated (hyperosmotic) urine

12. Nephron

13. Pathways Blood: Filtrate (urine):
Renal artery  (afferent & efferent) aterioles  peritubular capillaries  renal vein
Filtrate (urine):
Glomerulus OR tubule OR Loop of Henle  ureters  Bladder  urethra

14. The Nephron Functional unit of the kidney
Each kidney contains ~1 million nephrons
Vocab:
1. Tubule (Proximal & Distal)
2. Glomerulus – Ball of capillaries
3. Bowman’s capsule – End of tubule that surrounds the glomerulus
4. Loop of Henle – Descending & Ascending limbs

15. Nephron Particulars Renal Cortex
Glomerulus – tightly packed ball of capillaries
Bowman’s Capsule – encapsulates the glomerulus
Actual site of blood filtration
Proximal Tubule – site of substantial secretion & absorption
Distal Tubule – another important site of secretion & absorption

16. 6 Main Steps in the Nephron
1. Filtration from glomerulus in Bowman’s Capsule
2. Proximal (near) tubule – secretion & reabsorption
Changes the volume & composition of the filtrate
3. Descending Loop of Henle – reabsorption of H2O continues
4. Ascending Loop of Henle – Reabsorption of salt (NaCl) w/o giving up H2O = dilution of urine
5. Distal (far) tubule – K+ and NaCl levels are regulated
6. Collecting Duct – filtrate becomes more concentrated as more water is reabsorbed

17. Nephron Steps Filtration Passive (diffusion) & nonselective
Blood pressure forces fluid from the glomerulus into the Bowman’s Capsule
Bowman’s Capsule contains specialized cells which increase the rate of filtration
Anything small enough to filter out does so
Glucose, salts, vitamins, wastes such as urea, other small molecules
From Bowman’s Capsule, the filtrate travels to the proximal tubule, the loop of Henle, distal tubule, then to the collecting duct or tubule
From the collecting tubule, filtrate trickles into the ureter & finally the urinary bladder (temp storage)  Urethra  out

18. Nephron Steps (Page 2) Secretion Reabsorption Active & Selective
Uptake of molecules that did not get filtered into Bowman’s Capsule
Occurs in Proximal tubule
Reabsorption
Water & solutes (glucose, amino acids, & vitamins) that entered the tubule during filtration are returned to peritubular capillaries then to the body
Proximal tubule, Loop of Henle, and to collecting tubule

19. Nephron (Page 3) Excretion
Loop of Henle – Acts as a countercurrent exchange mechanism
Maintains a steep salt gradient surrounding the loop
This gradient ensures that water will continue flowing out of collecting tubule of the nephron
Creates hypertonic urine
Conserves water
Longer Loop of Henle = More water reabsorption
Excretion
Removal of metabolic wastes (nitrogenous wastes)
Everything that passed into the collecting tubule is excreted from the body

20. Kidney Dialysis
-- When the kidney(s) fail, patients must undergo dialysis (artificial mechanical filtration)

21. Nephron Particulars (Page 2)
Renal Medulla
Loop of Henle
Descending limb – Impermeable to Salt, but permeable to water
Filtrate becomes increasingly concentrated
Ascending limb – Impermeable to water, but permeable to Salt
NaCl diffuses out of the lower part, increasing salt concentration of the surrounding tissue

23. Nephron Particulars (Page 3)
Collecting Duct
Carries the remaining filtrate through tissue that has high osmolarity (salt concentration)
ADH (Anti-Duretic Hormone) – Determines whether water is removed here or not
If ADH is present, collecting ducts become permeable to water & filtrate = hypertonic urine
If ADH is NOT present, collecting ducts’ walls remain impermeable to water = hypotonic urine

24. Hormonal Control of Kidneys
Under the control of Nervous & Endocrine systems
Hence, kidney can quickly respond to the changing requirements of the body
ADH (Anti-Diuretic Hormone)
Produced by the hypothalamus
Stored in the Posterior Pituitary
Targets the collecting tubule of the nephron
Hypothalamus has osmoreceptor cells that monitor blood concentrations of salts
On a feedback loop to maintain homeostasis of fluid concentration

25. Work
When body’s salt concentration is too HIGH, ADH is released into the blood
ADH increases permeability of the collecting tubule
So more water is collected from the urine, and urine volume is decreased
When body’s salt concentration is too LOW (dilute), due to water intake being too high or salt intake too low, ADH is reduced = more urine production
EtOH = ADH inhibition = excessive urine production
May lead to dehydration