1. OSMOREGULATION & EXCRETION
Chapter 44

2. OVERVIEW Osmoregulation Excretion
Relative concentrations of water and solutes must be maintained in a variety of environments (land, freshwater, marine)
Excretion
Metabolism creates waste that must be expelled from the body
Proteins and nucleic acids present a problem because ammonia (primary waste product) is toxic

3. 44.1 ~ OSMOREGULATION
Balancing the uptake and loss of water and solutes over time. If they don’t osmosis will cause animal cells to swell and burst or shrivel and die.
Isoosomotic = two solutions with the same osmolarity
Hyperosmotic = solution with the greater concentration of solutes
Hyposomotic = solution with the more dilute concentration of solutes
Water flows from a hyposomotic solution to a hyperosmotic one.

4. TWO BASIC SOLUTIONS
#1 (only available to marine animals) is to be isoosomotic with the environment.
Osmoconformer
Does not adjust its internal osmolarity
Live in water that is fairly stable
#2 (available to any animal) is to control its internal osmolarity because body fluids are NOT isoosmotic with the outside environment.
Osmoregulator
Body fluids are not isoosomotic with surroundings
Enables animals to live in diverse environments
Has an energy cost (active transport of solutes)

5. COST OF OSMOREGULATION
Depends on:
How different osmolarity is from the surroundings
How easily water & solutes move across the animal’s surface
How much work is required to pump solutes across the membranes
Ranges from 5% to 30% of total resting metabolic rate

6. STENOHALINE VS. EURYHALINE
Stenohaline – narrow salt; Most animals cannot tolerate substantial changes in external osmolarity
Euryhaline – broad salt; Animals that can survive large fluctuations in external osmolarity.
Examples: Salmon, Talapia

7. MARINE ANIMALS Most marine invertebrates are osmoconformers
Marine vertebrates and some invertebrates are osmoregulators
Ocean is strongly dehydrating because it is much saltier than than internal fluids and water is lost by osmosis
Balance water loss by drinking large amounts of seawater
Salt is actively pumped out of gills and passed through urine

8. FRESHWATER ANIMALS Problems are opposite those of marine animals
Freshwater animals are constantly gaining water by osmosis and losing salt by diffusion
Maintain water balance by excreting large amounts of very dilute urine and taking in salt by the gills

10. TEMPORARY WATERS
Anhydrobiosis “life without water” – animals can survive in a dormant state when their habitats dry up
Water bears
Survive for a decade or more in inactive state

11. LAND ANIMALS
Desiccation “drying up” is a huge problem for land animals
Adaptations that help land animals avoid drying up:
Waxy layers of insects exoskeleton
Shells of land snails
Layers of dead keratinized skin
Nocturnal
Drinking and eating moist foods
Using metabolic water (water produced during cellular respiration)

12. 44.2 ~ NITROGENOUS WASTES
When proteins and nucleic acids are broken down nitrogenous wastes are produced
When these macromolecules are broken apart for energy ammonia (NH3) is produced which is very toxic
Three forms of ammonia that animals secrete
Ammonia
Urea
Uric acid

13. AMMONIA
Very soluble but only tolerated at low concentrations so must be released in lots of water
Aquatic species (fish)

14. UREA
Substance produced in the vertebrate liver by metabolic cycle that combines ammonia with carbon dioxide
System carries urea to kidneys where it is excreted
Mammals, adult amphibians, sharks, marine bony fishes, turtles
Advantage: low toxicity and requires less water
Disadvantage: expend energy to produce it from ammonia

15. URIC ACID
Largely insoluble in water and can be excreted as a semi solid paste with very little water loss
Insects, land snails, reptiles, birds
Relatively non-toxic
Requires considerable ATP to produce (more than Urea)

17. EVOLUTION & ENVIRONMENT ON WASTE
Uric acid can be stored within the reptilian egg as a harmless solid left behind when the animal hatches
Type of waste produced by vertebrates depends on habitat

18. 44.3 ~ STEPS OF URINE PRODUCTION
1. Filtration – body fluids are filtered to keep the good stuff in the body fluids and put the bad stuff in the filtrate
2. Reabsorption – filtering the filtrate to make sure none of the “good stuff” is kept in the filtrate (active transport to reclaim valuable substances in body fluids)
3. Secretion – filtering the body fluid to make sure all of the “bad stuff” is in the filtrate
4. Excretion – filtrate leaves the body (urine)

20. Good stuff: cells, proteins, large molecules, valuable solutes such as glucose,
Bad stuff: water, small solutes such as salts, sugars, amino acids, and nitrogenous wastes. Nonessential solutes and wastes

21. SURVEY OF EXCRETORY SYSTEMS
Protonephridia: Flame-bulb system
Flatworms
Functions in osmoregulation (wastes diffuse out through body surface)

22. Metanephridia
Annelids

23. Malpighian Tubules
Insects and terrestrial arthropods

24. Vertebrate Kidneys
Function in osmoregulation and excretion

25. 44.4 ~ MAMMALIAN KIDNEY
Site of water balance, salt regulation and excretion
Pair of kidneys
Each 10 cm long (kidney bean shaped)
Supplied with blood by a renal artery and drained by a renal vein
Urine exits through ureter and drains into urinary bladder
Urine is excreted from urinary bladder through the urethra

26. STRUCTURE & FUNCTION OF NEPHRON
2 regions to the kidney
Outer renal cortex
Inner renal medulla
Functional unit of the kidney is the nephron – consists of single long tubule and a ball of capillaries called the glomerulus
Bowman’s capsule – cup shaped swelling that surrounds the glomerulus
Each human kidney contains a million nephrons

28. Filtration happens as blood pressure forces fluid from the blood in the glomerulus into the Bowman’s capsule.
Filtration is nonselective and filtrate contains: salts, glucose, amino acids, vitamins, nitrogenous wastes and other small molecules
Pathway of filtrate – see figure 44.14

30. Nephrons process about 180 L of initial filtrate
Between 1,100 to 2,000 L of blood flows through a pair of human kidney’s each day.
Nephrons process about 180 L of initial filtrate
Nearly all sugar, vitamins, other organic nutrients and about 99% of the water are reabsorbed into the blood leaving only about 1.5 L of urine to be voided per day
4 steps are completed in:
Proximal tubule
Descending limbo of the loop of Henle
Ascending limb of the loop of Henle
Distal tubule
Collecting duct

31. 44.5 ~ WATER CONSERVATION IS A KEY TO TERRESTRIAL ADAPTATION
As the filtrate flows in the collecting duct past interstitial fluid of increasing osmolarity, more water moves out of the duct by osmois, thereby concentrating the solutes, including urea, that are left behind in the filtrate.

32. REGULATION OF KIDNEY FUNCTION
If a lot of salt is brought in with low water availability the mammal can excrete urea and salt with little water loss in hyperosmotic urine.
If salt is scarce and fluid intake is high the kidney can get rid of the excess water with little salt loss by producing large volumes of hypoosmotic urine
Regulated through nervous and hormonal controls
ADH – antidiuretic hormone
RAAS – renin-angiotensin-aldosterone system
ANF – atrial natriuretic factor

34. ADH is a response to an increase in the osmolarity of the blood – when the body is dehydrated.
RAAS – responds when a situation that causes an excessive loss of both salt and body fluids (injury, severe diarrhea)

35. 44.6 ~ DIVERSE ADAPTATIONS