1. Osmoregulation and excretion
Mr. Abercrombie

2. Osmoregulation
Osmoregulation – ability to regulate the chemical composition of bodily fluids based upon uptake and loss of water and solutes
Ultimate goal is to maintain composition of cytoplasm in cells
Controlled movements of solutes  water follows by osmosis
Animals must remove metabolic wastes

3. Water balance and waste disposal depends on transport epithelia
Transport epithelia – layer(s) of specialized cells that regulate solute movements
Move specific solutes in controlled amounts in particular directions

4. Salt-excreting glands in marine birds

5. Spartina alterniflora is a salt marsh grass that exudes salt through specialized glands

6. Mangrove trees have adapted to a marine environment

7. An animal’s nitrogenous wastes are correlated with its phylogeny and habitat
Kinds of nitrogenous wastes excreted depends on:
Evolutionary history, habitat, water availability
Food type and amount
Ammonia – highly toxic, more suitable for aquatic organisms
Urea – produced in liver (combines CO2 + NH3)
100,000 X less toxic than NH3
safer to transport
Less water required for excretion
Energetically expensive
Uric acid – relatively non-toxic
Excreted as a paste, minimizes water loss
More energetically expensive than urea!
Precipitates out of solution, so can be stored in egg
Terrestrial turtles (uric acid) aquatic turtles (urea and ammonia)

8. In fish, most NH3 is lost as NH4+ across gill epithelium, with kidneys excreting very little.
Lost by diffusion
Requires ATP

9. Cells require a balance between osmotic gain and loss of water

10. Osmolarity
Osmolarity – total solute concentration expressed as molarity, or moles of solute per liter of solution)
Your book uses milliosmoles/L (mosm/L) in this chapter (10-3 M)
When two solutions differ in osmolarity, the one with the greater concentration of solutes is referred to as hyperosmotic, and the more dilute solution is hypoosmotic
Using these 2 terms, how do you think water flows?

11. Osmoconformer –does not actively adjust its internal osmolarity
Osmoregulators use energy to control their internal osmolarity; osmoconformers are isoosmotic with the environment
Osmoconformer –does not actively adjust its internal osmolarity
E.g. most marine invertebrates
Osmoregulator – must control its internal osmolarity because body fluids are not isoosmotic with surroundings

12. ~30% of Brine shrimp metabolic costs go towards osmoregulation

13. Ranges of osmolarity tolerance
Stenohaline – refers to an organism with a narrow range of osmolarity changes
Euryhaline – refers to an organism that can survive large changes in osmolarity
E.g. salmon
Tilapia – can live anywhere from fresh water to 2,000 mosm/L (2X that of seawater)

14. Osmoregulation in fish

15. What aspects of osmoregulation are different in marine sharks?
Salt is excreted by rectal gland or lost as feces.
Sharks do not lose a lot of water like other bony fish
Maintain high levels of urea and trimethylamine oxide (TMAO) in body fluids
Total osmolarity of shark bodily fluids is >1,000 mosm/L, which is slightly hyperosmotic to seawater!
Which direction does water move?

16. Anhydrobiosis: Tardigrades
Dehydrated:<2% water
Rehydrated: ~85% water

18. Most excretory systems produce urine by refining a filtrate derived from body fluids
Excretory systems typically involve two steps
1) Body fluid is collected
Filtration through selectively permeable membrane
Membranes retain cells, proteins, large molecules
Hydrostatic pressure forces water and small solutes into excretory system (filtrate)
2) Composition of collected fluid is adjusted by selective reabsorption or secretion of solutes
Active transport selectively reabsorbs valuable solutes (glucose, some salts, amino acids)
Nonessential solutes and toxins are left in filtrate for secretion

19. Flatworms have excretory systems called protonephridium

20. Annelids have tubular excretory systems called metanephridium
Earthworms take in water through osmosis, so excrete a dilute urine
Cilliated funnel

21. Insects and other terrestrial arthropods have malpighian tubules
The insect excretory system is one of several key adaptations that have contributed to their success on land

22. Kidney function overview

23. Two distinct regions of mammalian kidney: outer renal cortex and inner renal medulla

24. The nephron: the functional unit of te vertebrate kidney (~1 million in each kidney)
Consists of a single long tubule and a ball of capillaries called the glomerulus. With ~1 million nephrons, total tubule length is 80 km (~50 miles)
80%
20%
only mammals & birds

25. The nephron

26. Filtration of small molecules in the glomerulus is nonselective
The filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasma (salts, glucose, vitamins, nitrogenous wastes, etc.)

27. Pathway of the filtrate
From Bowman’s capsule, the filtrate passes through three regions of the nephron
The proximal tubule, the loop of Henle, and the distal tubule
Fluid from several nephrons
Flows into a collecting duct

28. From blood filtrate to urine: a closer look

29. Australian hopping mouse
Mammalian kidney’s ability to conserve water is a key terrestrial adaptation
The mammalian kidney can produce urine much more concentrated (1,200 mosmol/L) than body fluids (300 mosmol/L)
Australian hopping mouse
Lives in dry desert region
Can produce urine up to 9,300 mosmol/L
9X more concentrated than seawater
25X more concntrated as their body fluid

30. How the human kidney concentrates urine: the two-solute model
Countercurrent exchange
Exchange between opposing flows of descending and acending loops OVERCOMES the tendency for diffusion to even out salt concentrations throughout the kidney
Permeable to salt, BUT NOT WATER!!
Permeable to water, BUT NOT SALT!!

31. Countercurrent exchange maintains steep osmotic gradient, facilitates water retention, and nutrient reabsorption

32. Antidiuretic hormone (ADH) - Increases water reabsorption in the distal tubules and collecting ducts of the kidney
Osmoreceptor cells in hypothalamus monitor blood osmolarity
Osmolarity rises, ADH is released
ADH is on negative feedback if osmolarity lowers
This can decrease permeability of tubules and ducts  increased discharge of dilute urine

33. Renin-angiotensin-aldosterone system (RAAS)
Renin causes a plasma protein (angiotensinogen) to convert to a peptide called angiotensin II.
Adrenal gland releases aldosterone  distal tubules reabsorb more Na+ and H20  increasing blood volume and pressure
Angiotensin II hormone  increases blood pressure and blood volume.
Constricts arterioles  decreases blood flow
Stimulates proximal tubules to reabsorb more NaCl and H20
Reduces the amount of NaCl and water in urine  raising blood volume

34. Are ADH and RAAS the same thing?
No. Both increase water reabsorption, but they regulate different problems
ADH responds to increased osmolarity (dehydration, lack of water intake)
Injury or diarrhea will reduce blood volume without increasing osmolarity.
ADH will not detect this drop in volume and pressure, but RAAS will.

35. Atrial natriuretic factor (ANF)
Opposes RAAS – walls of the atria of the heart release ANF in response to an increase in blood volume and pressure.
ANF lowers blood pressure and volume
ANF inhibits:
release of renin from JGA
NaCl reabsorption by collecting ducts
Aldosterone release from adrenal glands

36. ADH, RAAS, and ANF
Comprise an elaborate system of checks and balances that regulate the kidney’s ability to control the osmolarity, salt concentration, volume, and pressure of blood.

37. Weird adaptation: The South American vampire bat
Kidneys offload much of the water absorbed from a meal by excreting large amounts of dilute urine
When roosting, kidneys switch to producing very hyperosmotic urine