1. Excretion
AP Biology
Unit 6

2. Osmolarity
Osmolarity = moles of osmotically active particles per liter of solvent
1 M Glucose = 1 Osmolar solution
1 M NaCl = 2 Osmolar solution
2 osmotically active particles because NaCl dissociates to become Na+ and Cl- in water

3. Question…
What would happen if your body did not maintain proper osmolarity?
You would either have an excess of water (bloated) or too little water (dehydrated)
Cells wouldn’t have the correct balance of solutes and H2O  won’t function properly

4. Osmoconformers
Animals whose internal osmolarity changes in relation to their external environment
Equilibrate with the environment
There are limits to this– too high or too low will cause death
Marine invertebrates
Ex. Brine Shrimp (Artemia)

5. Osmoregulators
Animals who can maintain their internal osmolarity at a particular level regardless of the external environment
Ex. Fish, humans, lots of other animals 

6. Question…
How does the environment one lives in affect how osmoregulation takes place?
Depending on the environment one lives in, osmoregulation can be very different

7. Saltwater Fish
Challenge: Prevent too much water from leaving the body (to go into the outside environment)
Higher osmolarity outside compared to inside of body
Solution…

8. Freshwater Fish
Challenge: Prevent too much water from coming into the body from the outside
Higher osmolarity inside body compared to outside
Solution…

9. Birds: Salt Glands
Many birds who live by the sea may take in sea water along with the food they eat
Get rid of the extra salt in by excreting it through nasal salt glands  sneeze or shake off the salt droplets

10. Nitrogen Waste
Nitrogenous wastes are a type of metabolic waste that must be removed from the body.
Carbohydrates broken down into CO2 and H2O
Fats broken down into CO2 and H2O
Proteins and Nucleic Acids broken down into NH2 groups (urea, ammonia, uric acid)

11. continuously excreted (keep internal levels low) OR
Ammonia
Ammonia is the most common nitrogen waste
Toxic at certain concentrations
To prevent toxicity to the animal ammonia must be
continuously excreted (keep internal levels low) OR
Converted to a nontoxic molecule (urea or uric acid) before excretion

12. Excretion in Aquatic Animals
For most aquatic animals, excreting ammonia is not an issue - why?
Ammonia is highly soluble in H2O, diffuses away rapidly (won’t stay concentrated around them)
Aquatic animals continuously lose ammonia from their bodies through diffusion across their gill membranes

13. Ammonotelic
Animals that excrete nitrogen waste mostly as ammonia are ammonotelic
Ex. Aquatic invertebrates, bony fish

14. Question…
Why don’t terrestrial animals and some aquatic animals just excrete dilute ammonia in liquid?
Since ammonia is toxic even at fairly low levels, it would have to use a lot of water to dilute it
Too much water loss = dehydration

15. Ureotelic
Animals that excrete nitrogen waste mostly as urea are ureotelic
Ex. Mammals (us!), amphibians, sharks, rays, some bony fish

16. Uricotelic
Animals that excrete nitrogen waste mostly as uric acid are uricotelic
Helps conserve H2O because it isn’t very soluble in water  semi solid
Ex. Birds, reptiles, insects, some amphibians

17. Excretory Process The main steps in producing urine (fluid waste) are:
Filtration
Selective Reabsorption
Secretion

18. Filtration
nonselective process in which water and small solutes are filtered across a membrane into the excretory system
Small solutes include salts, nitrogen wastes, sugars, amino acids
Filtrate = liquid produced from this step

19. Selective Reabsorption
Useful/”good” molecules are reabsorbed back into the body from the excretory system by active transport
Sugars, amino acids, some salts

20. Secretion
More waste (toxins, extra salts, etc) are transported into the filtrate
By active transport
Selective reabsorption and secretion also causes water to move in /out of filtrate
Urine = whatever is left of the filtrate after it has completed all 3 steps

21. Nephrons
The filtering units in the mammalian excretory system are the nephrons.
Random fact: there are approximately 1 million nephrons in each kidney

22. Major structures of the nephron
Glomerulus
Bowman’s Capsule
Proximal Tubule
Loop of Henle
Distal Tubule
Collecting Duct

23. Summary of Urine Creation
Urine is created as solutes are taken out of blood due to:
The differences in osmolarity in the tubules and the surrounding tissues
Differences in permeability in the tubule membranes
Random fact: each day you create approximately 2-3 liters of urine

24. Glomerulus & Bowman’s Capsule
Glomerulus = dense ball of capillaries
High pressure blood from arteries flows into the glomerulus
substances are filtered from the glomerulus into Bowman’s capsule due to the high pressure
Everything small enough gets across (red blood cells, proteins too big to fit through)

25. Selective Reabsorption
In the proximal tubule, many useful solutes are reabsorbed back into the body fluid
Glucose, amino acids, salts, some water

26. Loop of Henle
The main function of the is to reabsorb water from the urine
Ascending limb reabsorbs NaCl into the surrounding tissue; NOT permeable to H2O
Descending limb IS permeable to H2O H2O flows out of filtrate due to osmosis (high salt concentrations all around)
Descending limb
Ascending limb

27. Loop of Henle As NaCl is actively transported out osmolarity decreases
As H2O is reabsorbed from the filtrate, the osmolarity in the solution increases
As NaCl is actively transported out osmolarity decreases

28. Question…
Desert animals (kangaroo rats) usually have long loops of henle, while freshwater animals (beavers) have relatively short loops of henle. How does the environment one lives in relate to the length of the loop of henle?
Loop of henle is for water reabsorption. Living in a drier area means you need to save more water from urine  need a longer loop to do this

29. Distal tubule
More secretion and reabsorption takes place in the distal tubule

30. Collecting Duct
More water is reabsorbed in the collecting duct  urine is concentrated
Pathway of urine: kidney  ureter  bladder  urethra

31. Control of Excretion Processes
Antidiuretic hormone (ADH) increases the permeability of the collecting ducts to increase the reabsorption of water
Urine is concentrated further
Also called vasopressin

32. Control of Excretory Processes
Aldosterone also increases salt and water reabsorption in the distal tubule
Usually a response to low blood pressure/volume
The last step in a series of reactions involving other hormones

33. Interfering with ADH Caffeine and alcohol are diuretics
substances that cause more frequent urination
Caffeine and alcohol interfere with the actions of ADH  more urine produced
Alcohol = prevents ADH from being secreted
Caffeine = prevents ADH from binding to receptors on collecting duct