Question

What is the glomerular filtration rate? What is the normal filtration force in humans?

Answer 1

Hint: Nephrons, in kidneys, are the primary structures for blood filtration. Each nephron consists of double epithelium bound glomerulus surrounding a bunch of fine capillaries bringing the blood in and initiating the filtration.

Complete answer:
Nephrons are small , highly coiled tubular structures that contain a ‘renal corpuscle’ from where the blood plasma is filtered and a ‘renal tubule’ into which the filtrate enters and passes through. A renal corpuscle, in turn, consists of a small cup- like structure bounded by two layers of epithelium known as Glomerular or Bowman’s capsule. This capsule surrounds the glomerulus or capillary network which is a labyrinth of fine capillaries. Blood plasma is filtered in the Bowman’s capsule and the filtered fluid then enters the renal tubules of the nephron. The amount of filtrate formed per minute in the renal corpuscles of both kidneys is referred to as the glomerular filtration rate or GFR. In males, it amounts to 125 mL/min while in females, it is 105mL/min.
- Interlobular brings blood into the kidney and branches into different arterioles which take the blood to the glomerulus.
- Water and other small molecules like ions or salts move from the capillary network or the glomerulus to the inside of the glomerular capsule under the glomerular blood pressure.
- Large molecules like formed elements are unable to pass through the capillary wall just like in any filtration process. Thus, afferent arteriole leaving the glomerulus contains the non- filtrate i.e large molecules and the renal tubules contain filterable components like water, nutrients, ions and nitrogenous wastes.
- On average, the daily volume of glomerular filtrate is 150 litres in females and 180 litres in males. But more than 99% of this filtrate is returned to the bloodstream via tubular reabsorption, so only 1-2 litres of urine is excreted on an average by an adult.

Note: GFR increases when more blood flows into the glomerular capillaries. So, by adjusting the blood flow into and out of the glomerulus or by altering the glomerular capillary surface area available for exchange and filtration, GFR is regulated and maintained. These functions are controlled by three mechanisms namely autoregulation, neural regulation and hormonal regulation.