1. Osmoregulation and Excretion
Ch 44 Notes

2. Osmoregulation
Process by which animals control solute concentrations and balance water gain and loss
Necessary for systems to function properly
Ions must remain at levels to allow muscles, nerves and body cells to work correctly
Essential for Homeostasis

3. Uptake vs Loss of Water Water uptake and loss must balance
If water uptake is excessive, animal cells can swell and burst
If water loss is substantial, cells can shrivel and die (plasmolysis)
Osmosis – passive process by which water enters and leaves cells
Occurs when two solutions differ in osmotic pressure (osmolarity)

4. Osmolarity Isoosmotic – two solutions with same osmolarity
No net movement of water (still moves, but at equal rates)
If two solutions differ in osmolarity:
Hyperosmotic – solution with more solutes (less water)
Hypoosmotic – solution with less solutes (more water)
Water flows from a hypoosmotic solution to a hyperosmotic one

6. Osmoconformer Animal that is isoosmotic with it’s surroundings
Marine Animals
No tendency to gain or lose water
Live in water that has a stable composition so have a constant internal osmolarity

7. Osmoregulator
Controls internal osmolarity independent of its environment
Animals can live in non-marine environments (fresh water, land) or marine
If they live in a hypoosmotic environment – must be able to get rid of excess water
If they live in a hyperosmotic environment – must take in water

10. Environmental Changes
Stenohaline – animals that cannot tolerate changes in external osmolarity (most animals)
Euryhaline – animals that can survive large fluctuations in external osmolarity
Animals in tidal areas, salmon

11. Marine Animals Most invert marine animals are osmoconformers
Must actively transport solutes to maintain homeostasis
Marine vertebrates and some inverts are osmoregulators
Ocean dehydrates these animals (lose water)
Balance water loss by drinking lots of seawater and pump out salts through active transport (gills or kidneys)

12. Freshwater Animals
Body fluid of freshwater animals is hyperosmotic to the fresh water
Water diffuses IN to the cells and salt leaves
These animals drink almost NO water
Urine is very dilute (lots of water in urine)
Salts are replenished by eating
Salmon - live in both environments and change their osmoregulation when they move

13. Temporary Water Some animals live in small ponds that dry out
Enter a dormant state called Anhydrobiosis

14. Terrestrial animals Animals on land always threatened with dehydration
Body covering reduces water loss
Waxy exoskeleton
Shells
Dead, keratinized skin
Nocturnal – many animals (esp. desert) are active at night to reduce evaporative water loss
All must drink and eat moist foods

15. Energetics of Osmoregulation
Costs energy to maintain an osmolarity difference with environment
Use active transport to maintain correct solute concentrations needed for homeostasis

16. Excretion
Process that gets rid of nitrogenous metabolites and other waste produces
Come from break down of nitrogen containing molecules (like proteins and nucleic acids) that release ammonia – very toxic to cells

17. Forms of Nitrogenous Waste
Ammonia
Very toxic to cells
Can only be tolerated in very small amounts
Animals that excrete ammonia must be surrounded by lots of water
Most common in aquatic species
Aquatic inverts – release ammonia across body surface
Fish – ammonia lost across gills

18. Forms of Nitrogenous Waste
Urea
Produced in the liver
Made by converting ammonia with carbon dioxide
Low toxicity
Can be transported in circulatory system and stored safely
Animals must expend energy to produce urea
Seen in mammals, most amphibs (adults), sharks, some marine bony fish and turtles

19. Forms of Nitrogenous Waste
Uric Acid
Relatively non toxic
Does not dissolve in water
Released as semi-solid paste
Very little Water lost
Needs even MORE energy to make than urea
Seen in insects, land snails, many reptiles and birds

21. Excretory Processes Urine – Fluid Waste made in four steps
1. Filtration - Body fluid comes in contact with selectively permeable membrane of a transport epithelium. Pressure drives a process where small solutes and water (filtrate) are driven across the epithelium (large molecules stay in body fluid)
2. Reabsorption – Filtrate becomes a waste product after useful molecules are recovered and returned to body fluid by active transport

22. Excretory Processes
3. Secretion – Non essential solids and wastes, toxins and excess ions are extracted from body fluids into the filtrate
4. Excretion – filtrate (urine) leaves the system and the body

23. Protonephridia Network of dead-end tubules connected to the outside
Flame bulbs are at end of each protnephridium
Cilia project into tubules and draw water and solutes from fluid
Filtrate moves through tubules and empties into external environment
Seen in flatworms (no coelom), rotifers

25. Metanephridia Open internally to the coelom
Each segment has a pair of metanephridia surrounded by capillaries
Cilia beat, draw fluid into collecting tubule with bladder
Urine moves through tube and solutes are reabsorbed
Waste is released to outside
Seen in Annelids (earthworms)

27. Malpighian Tubules
Extend from dead end tips immersed in hemolymph to openings in digestive tract
No filtration
Transport epithelium secretes solutes into tubule
Water follows by osmosis
Fluid passes to rectum
Solutes pumped back into hemolymph
Nitrogenous wastes eliminated as dry matter along with feces
Seen in insects, terrestrial arthropods

29. Kidneys Function in osmoregulation and excretion
Numerous tubules are highly organized and associated with capillaries
Also include ducts that carry urine from tubules out of kidney
Seen in vertebrates and some other chordates

30. Mammal Excretory System
Kidney – paired
Renal artery – brings blood to kidney
Renal vein – drains blood from kidney
Receives nearly 25% of blood exiting the heart
Ureter – urine exits kidney through this tube
Urinary Bladder – storage place for urine
Urethra – carries urine to the outside

32. Kidney Structure
Nephron – functional unit with long tubule and ball of capillaries called a Glomerulus
Bowman’s capsule - surrounds the glomerulus

33. Filtration of Blood
Occurs as blood pressure forces fluid from blood in the glomerulus into Bowman’s capsule
Capillaries are permeable to water and small solutes
Impermeable to blood cells and large molecules
Filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

34. Path of Filtrate From Bowman’s capsule to Proximal tubules
Recapture ions, water and valuable nutrients. Ammonia is synthesized and added to filtrate
To Descending Loop of Henle
Reabsorb water
To Ascending Loop of Henle
Impermeable to water
Contains ion channels
NaCl is reabsorbed
To Distal Tubule
Contributes to pH regulation by controlled secretion of H+ and reabsorption of HCO3
To Collecting Duct
Reabsorption of water can occur if needed
To Bladder