Proximal Convoluted Tubule

• Active Reabsorption– Nutrients (glucose, amino acids, Vitamins)– Ions (K+, Na+, Cl-, Ca2+)– Small plasma proteins– Some urea and uric acid

~70% of Filtrate is reabsorbed in PCT

Question: How are these Reabsorbed?

Reabsorption of Na+ :

First – simple diffusion:

Then – 1o active transport:

Na+ is Actively Reabsorbed:

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.

• Deeper into medulla, more H2O 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 tubules

e.g., K+, H+ and HCO3-

Secretion – DCT a key site.

• Fine-tuning - eliminate unwanted items.

• This filtrate in tubules is destined to be

urine unless reabsorbed in collecting ducts.

• 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

Renin-Angiotensin-Aldosterone

_______________________

______________(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)

Rate

pH

Osmolarity

Cells

Na+, K+

Large Pro-

Small Pro-

Glucose

Urea

Volume

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.

Normal Healthy Kidney

Polycystic kidneys

Enlarged Polycystic kidneys (16 to 18 pounds combined).

1. Infectious organisms.

Variety of Causes of Renal Failure:

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, sepsis

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

Variety of Causes:

4. Obstruction of urine flow.

5. Insufficient renal blood flow.

- Kidney stone (calcium oxalate, uric acid 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.

Possible Treatments for Renal Failure:

Dialysis

Kidney Transplant

Stop or Treat the Cause

Overall Processes of the Nephron