Which of the following is false regarding glomerular capillaries (AIIMS NOV.2011)
|A||Oncotic pressure is higher in the blood column than that in glomerular capillaries|
|B||Constriction of the afferent arteriole produces fall in capillary BP|
|C||Concentration of glucose is equal in glomerular capillaries and ultrafiltrate|
|D||Hematocrit is raised in the glomerular capillaries|
I. The factors governing filtration across the glomerular capillaries are the same as those governing filtration across all other capillaries, that is, the size of the capillary bed, the permeability of the capillaries, and the hydrostatic and osmotic pressure gradients across the capillary wall.
III. Kf, the glomerular ultrafiltration coefficient, is the product of the glomerular capillary wall hydraulic conductivity (ie, its permeability) and the effective filtration surface area. PGC is the mean hydrostatic pressure in the glomerular capillaries, PT the mean hydrostatic pressure in the tubule (Bowman's space), πGC the oncotic pressure of the plasma in the glomerular capillaries, and πT the oncotic pressure of the filtrate in the tubule.
a. Now the oncotic pressure of the glomerular capillaries is the same as in any other systemic capillary i.e. 25 mm Hg
b. Constriction of the afferent arteriole causes a fall in capillary BP resulting in decreased GFR
c. Due to filteration of plasma, RBC are more in glomerular capillaries, so the GFR increases
IV. Concentration of all freely filtered substances like glucose are equal in glomerular capillaries and ultrafiltrate