Proximal Convoluted Tubule• Active Reabsorption

– Nutrients (glucose and amino acids)– Ions (K+, Na+, Cl-)– Small plasma proteins– Some urea and uric acid

Na+ is actively reabsorbed:

First – simple diffusion:

Then – 1o active transport:

~70% of Filtrate is reabsorbed in PCT

Na+ linked 2o Active Transport

Symport with:– Glucose– Amino acids – Ions (e.g., Ca2+)

Passive Transport of Water:– As Na+ pumped out, H2O follows by osmosis.

(passive)

Transcytosis of Proteins:– Small proteins can get into filtrate, due to size

they are reabsorbed via vesicular transport.

Passive Transport of Urea:– As other solutes leave lumen, [urea] higher than ECF, thus passively diffuses into ECF.

Reabsorption of Urea

Transporter Characteristics

A substance can exceed renal threshold,e.g., glucosuria.

– Saturation (# of carriers):

– Competition:

– Specificity:glucose, fructose, tyrosine, valine, etc, all have own carriers.

maltose instead of glucose – takes a seat, but not transported.

limited # of carriers to transport solutes back into body.

• First, Na+ transported out of filtrate.

H2O Reabsorption – Loop of Henle a key site.

• Collecting duct also a key site for H2O reabsorption – (role of ADH).

• Osmolarity of ECF gets higher.

• As loop gets deeper into renal medulla, more H2O is drawn out.

• Filtrate becomes Very concentrated!

• Region is impermeable to H2O.

Ascending Loop of Henle

• Thus, H2O can no longer leave filtrate in this region, so Osmolarity becomes lower again at start of DCT.

• Active Transport into nephron tubulese.g., K+, H+ and HCO3

-

Secretion – DCT a key site.

• 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.

• Reabsorption of Na+

Final Modification: Collecting Ducts

• After collecting duct, filtrate now called urine (no longer modified).

• Reabsorption of H2O

• Under Endocrine Control – ADH (vasopressin)

Mictruition Reflex

Autoregulation of Renal System

_______________________

______________(inactive)

(_____________)

_________________________________

___________

____________(activated)

_____

_______________

Liver Kidneys LungsAdrenalCortex

Na+ _______

H2O _______Thirst StimulationVasoconstriction Reabsorption of H2O

Kidneys

(active)

Anti Diuretic Hormone (ADH)

Angiotensinogen(inactive)

(Vasopressin)

Angiotensin Converting Enzyme (ACE)

Aldosterone

Angiotensin I(activated)

Renin

Angiotensin II

Liver Kidneys LungsAdrenalCortex

Na+ retention

H2O retentionThirst StimulationVasoconstriction Reabsorption of H2O

Kidneys

(active)

Comparison of FluidsPlasma Filtrate UrineBloodSubstance

(parameter)

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.

Polycystic kidneys (16 to 18 pounds combined).

1. Infectious organisms.

Variety of Causes:

2. Toxic agents.

3. Inflammatory immune response (allergic).

- Blood borne microbes- UTI’s

- lead, arsenic, pesticides, additives, medications- long-term exposure to high aspirin doses

- glomerulonephritis- e.g., after strep throat (streptoccocus)

Variety of Causes:

4. Obstruction of urine flow.

5. Insufficient renal blood flow.

- Kidney stone (uric acid-calcium crystals)- Tumors- Enlarged prostate gland

All create back pressure, decreasing GFR

- 2o to heart failure- Hemorrhage (e.g. shock)- Atherosclerosis

Leads to inadequateFiltration pressure

1. Uremic Toxicity

Potential Ramifications:

2. Metabolic Acidosis

3. Potassium (K+) retention

- Caused by retention of toxins/waste products in blood.

- From inability of kidneys to secrete H+.

- Inability to secrete K+ (effects RMP).

4. Na+, Ca2+ and phosphate and Imbalances

5. Loss of plasma proteins

6. Anemia

- Inability of kidneys to regulate ion reabsorption and secretion.

- Result of increased leakiness of glomerulus.

- Inadequate erythropoiten production.

7. Depressed immune system- Increased toxic waste and acidic conditions.