1. Water Balance & Excretion

2. Osmoregulation
active regulation of the osmotic pressure of bodily fluids and cells
osmotic pressure = pressure resulting from a difference in solute concentration across a selectively permeable membrane

3. Osmoregulation hyperosmotic hypoosmotic isoosmotic
hyperosmotic (hypertonic)
hypoosmotic (hypotonic)
isoosmotic (isotonic)

4. Unicellular Organisms
water balance is often maintained by contractile vacuoles
video of Paramecium:

5. Excretion eliminating waste is important for all living organisms
(Image from:

6. Types of Waste wastes are eliminated through various organs:
lungs (CO2)
large intestine (solid wastes)
liver (transforms toxins for removal)
kidneys (soluble wastes)

7. Nitrogenous Wastes mostly from deamination
animals that live in water can remove ammonia with lots of water
mammals, some reptiles, most amphibians form urea
birds and some invertebrates produce uric acid
Ammonia (NH3) is highly toxic

8. Human Excretory System
Image from:

9. Renal Blood Flow)
blood is brought to the kidneys by the renal arteries
filtered blood leaves the kidneys through the renal veins
(Image from:

10. The Urinary System
kidneys can hold up to 25% of the body’s blood at a time
kidneys filter the blood
urine (with wastes and toxins) is conducted to the bladder through the ureters

11. Kidney Structure Basic structure: cortex medulla renal pelvis
(Image from:

12. Nephron the functional unit of the kidney is the nephron
there are about 1 million nephrons in each kidney

14. Review Kidney Structure…

15. Image from: http://commons. wikimedia

16. Be able to label

17. Image from :http://kcfac. kilgore. cc. tx
Label the diagram

18. Explain the production of Urine
(Image from:
Afferent Arrives…Efferent Exits
Explain the production of Urine

19. How is urine formed?

20. Urine Formation filtration reabsorption secretion
Simple overview of urine formation:
(Image on previous slide from: ,-Sterile.html

21. Filtration higher blood pressure in glomerulus
water, ions, smaller dissolved molecules (glucose, amino acids, urea) can move through the walls of the glomerulus
your kidneys filter your entire blood plasma 65 times every day!
glucose, NaCl, H+ ions, amino acids,

22. Reabsorption ion pumps reabsorb Na+, K+, Cl- (active)
active transport proteins reabsorb amino acids, glucose
filtrate becomes hypoosmotic to interstitial fluid, so water is reabsorbed by osmosis and through aquaporins
If you produced 120 mL of urine a minute…
(your bladder’s stretch receptors signal to your brain when there is 200mL of urine; can hold up to )
Osmotic gradient created by glucose, amino acids moves water back to blood.

23. Where? a lot of reabsorption occurs in the proximal convoluted tubule
filtrate with high concentration of urea and other wastes enters loop of Henle and then distal convoluted tubule:
more water and ions (Na+& Cl-)are reabsorbed

24. Where (cont’d)?
collecting ducts are permeable to water but not salt ions, so more water is reabsorbed
at bottom of medulla, urea is reabsorbed through passive urea transporters (increasing concentration gradient…more water reabsorbed)

25. Secretion
H+ ions (active) to adjust blood pH (HCO3- is also reabsorbed to balance)
products of detoxified poisons (passive)
water-soluble drugs (passive)
nitrogen-containing wastes (such as small amounts of NH3)
in the proximal and distal convoluted tubules

26. Animations
Narrated animation on urine formation; good amount of detail:
Narrated animation of structure & function; quite detailed:

27. Other links…
Khan academy…this video starts off with the structure of the kidney & nephron, then goes into detail about the formation of urine (covered in 9.5)