Renal categories 

Aim to show systematic approach to move through quickly.

Functions of the kidney

1)    H20 balance

2)    Electrolytes

3)    Waste

a.     Urea

b.     Uric acid

c.     Creatinine

d.     Hb

e.     Drugs

4)    Endocrine

a.     Vit D EPO,protsglandins 

5)    RBC

6)    Gluconeogenesis

7)    Blood pressure 

How does the kidney establish a concentration gradient?

1)    Countercurrent multiplier

2)    Counter current exchanger

3)    Role of urea

Handling of acid

1)    Reabsorption of bicarb

2)    Titrateable acid PO4 and organic acid excretion

3)    Ammonium

Factors that govern GFR

1)    Filtration barrier

a.     Endothelium fenestrations

b.     Basement membrane 

c.     Podocyte foot processes

2)    Molecule

a.     size

b.     Electrical charge

3)    Starling forces

a.      Flow         =                Kf [(PGC  –  PBS) -  s (PGC  -  PBS)]

The net movement of H2O in the glomerular capillaries = GFR 

PGC :          Glomerular capillary hydrostatic pressure

• High and does not decrease much along length of capillary

• Arterial end 60mmHg, venous end 58mmHg
• increased by:         afferent arteriole vasodilation

                                    efferent arteriole vasoconstriction

                                    increased MAP (although autoregulation keeps GFR fairly constant)

• ­ PGC = ­ GFR

PBS :           Bowman’s space hydrostatic pressure

• 15mmHg

• increased by: obstruction to urine flow

• ­ PBS = ¯ GFR

PGC :         Glomerular capillary oncotic pressure

• Because of large fluid loss and impermeabilty to protein, Pc increases along the length of the capillary

• Arterial end = 21mmHg, Venous end = 33mmHg

• increased by decreased RBF

• ­ PGC = ¯ GFR

PBS :          Bowman’s space osmotic pressure

• 0mmHg (Glomerular capillaries essentially impermeable to protein)

• increased by: disease states causing increased membrane permeability

• ­ PBS = ¯ GFR

Kf:             high (due to high H2O permeability)

Kf = product of: 

                  Surface area for filtration

                  Glomerular capillary hydraulic conductivity (permeability to H2O)

• increased by – relaxation of mesangial cells (angiotensin II contracts mesangial cells and reduces K thus reduces GFR)

s sigma: relfection coefficient

                  high ~1.0 as glomerular capillaries are essentially impermeable to protein 

At arterial end of capillary:

Flow          =                K (PGC  –  PBS) -  s (PGC  -  PBS)

                  =                (60 - 15) – (21 – 0)

                  =                45 – 21

                  =                24mmHg (net fluid out)

At venous end of capillary:

Flow          =                K (PGC  –  PBS) -  s (PGC  -  PBS)

                  =                (58 - 15) – (33 – 0)

                  =                43 – 33

                  =                10mmHg (net fluid out)

There is a net outward filtration pressure along the whole length of the capillary

4)    Other

a.     Autoregulation myogenic

b.     TG feedback

c.     SNS, AT2, ANP