2. Proximal Convoluted Tubule
Active Reabsorption
Nutrients (glucose and amino acids)
Ions (K+, Na+, Cl-)
Small plasma proteins
Some urea and uric acid
~70% of Filtrate is
reabsorbed in PCT
Na+ is actively reabsorbed:
First – simple diffusion:
Then – 1o active transport:

3. Na+ linked 2o Active Transport
Symport with:
Glucose
Amino acids
Ions (e.g., Ca2+)

4. Passive Transport of Water:
As Na+ pumped out, H2O follows by osmosis (passive)
Passive Transport of Urea:
As other solutes leave lumen, [urea] higher
than ECF, thus passively diffuses into ECF.
Transcytosis of Proteins:
– Small proteins can get into filtrate, due to size
they are reabsorbed via vesicular transport.

5. Reabsorption
of Urea

6. Transporter Characteristics
Specificity:
glucose, fructose, tyrosine, valine, etc, all have own carriers.
Competition:
maltose instead of glucose – takes a seat, but not transported.
Saturation (# of carriers):
limited # of carriers to transport solutes back into body.
A substance can exceed renal threshold,
e.g., glucosuria.

7. H2O Reabsorption – Loop of Henle a key site.
First, Na+ transported out of filtrate.
Osmolarity of ECF gets higher.
As loop gets deeper into renal medulla, more H2O is drawn out.
Filtrate becomes Very concentrated!
Collecting duct also a key site for H2O reabsorption – (role of ADH).

8. Ascending Loop of Henle
Region is impermeable to H2O.
Thus, H2O can no longer leave filtrate in this region, so Osmolarity becomes lower again at start of DCT.

9. Secretion – DCT a key site.
Active Transport into nephron tubules
e.g., K+, H+ and HCO3-
Fine-tuning of filtrate; getting rid of what body needs to eliminate.
All that remains in tubules is destined to be
urine unless reabsorbed in collecting duct.

10. Final Modification: Collecting Ducts
Reabsorption of Na+
Reabsorption of H2O
Under Endocrine Control – ADH (vasopressin)
After collecting duct, filtrate now called
urine (no longer modified).

12. Mictruition Reflex

13. Autoregulation of Renal System

14. Liver
Kidneys
Lungs
Adrenal
Cortex
___________
_________________________________
_____
______________
(inactive)
____________
(activated)
_______________
(active)
Kidneys
_______________________
(_____________)
Na+ _______
Vasoconstriction
Reabsorption of H2O
Thirst Stimulation
H2O _______

15. Liver
Kidneys
Lungs
Adrenal
Cortex
Aldosterone
Angiotensin Converting Enzyme (ACE)
Renin
Angiotensinogen
(inactive)
Angiotensin I
(activated)
Angiotensin II
(active)
Kidneys
Anti Diuretic Hormone (ADH)
(Vasopressin)
Na+ retention
Vasoconstriction
Reabsorption of H2O
Thirst Stimulation
H2O retention

16. Comparison of Fluids
Substance
Blood
Plasma
Filtrate
Urine
(parameter)

17. Renal Failure
When kidney function disrupted to the point they are unable to perform regulatory and excretory functions sufficient to maintain homeostasis.
Acute – sudden onset with rapid reduction in urine formation
(less than 500ml/day minimum being excreted).
Chronic – slow, progressive, insidious loss of renal function.
Up to 75% of function can be lost before detected.

19. Polycystic kidneys (16 to 18 pounds combined).

20. Variety of Causes: 1. Infectious organisms. 2. Toxic agents.
- Blood borne microbes
- UTI’s
2. Toxic agents.
- lead, arsenic, pesticides, additives, medications
- long-term exposure to high aspirin doses
3. Inflammatory immune response (allergic).
- glomerulonephritis
- e.g., after strep throat (streptoccocus)

21. Variety of Causes: 4. Obstruction of urine flow.
- Kidney stone (uric acid-calcium crystals)
- Tumors
- Enlarged prostate gland
All create back pressure, decreasing GFR
5. Insufficient renal blood flow.
- 2o to heart failure
Leads to inadequate
Filtration pressure
- Hemorrhage (e.g. shock)
- Atherosclerosis

22. Potential Ramifications:
1. Uremic Toxicity
- Caused by retention of toxins/waste products in blood.
2. Metabolic Acidosis
- From inability of kidneys to secrete H+.
3. Potassium (K+) retention
- Inability to secrete K+ (effects RMP).

23. 4. Na+, Ca2+ and phosphate and Imbalances
- Inability of kidneys to regulate ion reabsorption
and secretion.
5. Loss of plasma proteins
- Result of increased leakiness of glomerulus.
6. Anemia
- Inadequate erythropoiten production.
7. Depressed immune system
- Increased toxic waste and acidic conditions.