2. Three Functions of Urine Formation
• Filtration – movement of fluids from the glomerular blood to the Bowman’s capsule
• Reabsorption – transfer of fluids from nephron back into peritubular capillaries
• Secretion – transfer of fluids peritubular capillaries into nephron

3. Filtration
Nutrients flow from glomerulus into Bowman’s capsule due to high blood pressure flow (of the artery)

4. Nutrient Flow of the following nutrients, which ones will flow out of the blood into the filtrate?
Solute
Glomerulus  Bowman’s Capsule?
water
NaCl
H+ ions
amino acids
glucose
plasma proteins
red blood cells (erythrocytes)
platelets

5. Reabsorption
Reabsorption saves us from having to continuously replenish our body with fluid.
20% of fluid flowing into kidney is filtered into nephrons
less than 1% of nephron fluid is used to make urine

6. Reabsorption vs. Secretion
carrier/channel proteins move nutrients into interstitial fluid and then back into blood
kidney tissue will only reabsorb a certain level of nutrients
carrier/channel proteins move wastes from blood to interstitial fluid to nephron

7. 1. Bowman’s Capsule
water and dissolved solutes leave glomerulus; enter Bowman’s capsule
water
Na+ H+
Cl-
glucose
amino acids
vitamins
minerals
urea
uric acid

8. selective reabsorption of nutrients (need transporters)
2. Proximal Tubule
HCO3-, K+
Na+, Cl-
H2O
amino acids
glucose
vitamins
selective reabsorption of nutrients (need transporters)
Urine pH determined by HCO3- reabsorption and H+ secretion H+
NH3

9. 3. Loop of Henle – Descending Limb
only permeable to H2O (osmosis)
impermeable to salt
solutions in tube are being concentrated
H2O

10. 4. Loop of Henle – Ascending Limb
only permeable to salt (need ionic transporters)
impermeable to water
NaCl

11. 5. Distal Tubule
selective reabsorption of nutrients (need transporters)
urine pH determined by HCO3- reabsorption and H+ secretion
HCO3-
Na+, Cl-
H2O H+ K+

12. 6. Collecting Duct urine formation by concentration nephron fluid
any urea and urine that is reabsorbed is less than that was filtered into nephron
NaCl
urea
water

14. Kidney Stones crystallization of some urine solutes
a 2 – 3 mm stone can obstruct flow to the ureter
Treatment:
increased water consumption
surgery

15. HOMEWORK Practice
Pg 454 #3,10
Pg 461 #32,33,34
Pg 462 # 54, 57