Question

The net pressure gradient in the kidney that causes the fluid to filter out of the glomeruli into the capsule is
(a) 50 mm Hg
(b) 75 mm Hg
(c) 10 mmHg
(d) 30 mm Hg

Answer 1

Hint: The kidneys help in the formation of urine, starting from the blood flowing through glomerular capillaries to excreted from the urinary bladder. Due to a net filtration rate, about 20% of the plasma fluid is filtered out into the Bowman's capsule. The resulting filtration is promoted by a pressure gradient of 10 - 15 mm Hg.

Complete Step by Step Answer:
We all know that the structural and functional units of the kidneys are the nephrons. A glomerulus is a tuft of capillaries present in nephrons which is a capillary network of complex anastomosing plexus of vessels and not of independent capillary loops. Through an afferent arteriole, blood enters the glomerulus and leaves it through an efferent arteriole. After that blood plasma filters out from glomerulus into the glomerular capsule. When glomerular (blood) hydrostatic pressure exceeds the hydrostatic pressure of the glomerular capsule and the blood colloid osmotic pressure glomerular filtration occurs. The sum of both osmotic and hydrostatic pressure results in a net filtration pressure (NFP).

$$\begin{gathered} NFP=GlomerularBloodHydrostaticPressure(GBHP) \\ -[capsularhydrostaticpressure(CHP) \\ +bloodcolloidosmoticpressure(BCOP)] \\ =10mmHg \end{gathered}$$
$NFP=55-(15+30)=10mmHg$.
So. The correct answer is, ’20 mmHg.’

Additional information:
1) In a day, the entire volume of the blood is filtered through the kidneys about 300 times, and 99 percent of the water filtered is recovered.
2) Under resting conditions the heart pumps about 5 L of blood per min from which approximately 20 percent or one liter enters the kidneys to be filtered. This liter results on average in the production of about 125 mL/min filtrate produced in men (range of 90 to 140 mL/min) and 105 mL/min filtrate produced in women (range of 80 to 125 mL/min) .
3) Increased fluid retention in the interstitial spaces and cells of the body; can be seen as swelling over large areas of the body, particularly the lower extremities are called systemic edema.
4) Inulin is a plant polysaccharide that is injected to determine glomerular filtration rate(GFR) ; is neither secreted or absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate.

Note: For clinicians, changes in glomerular dynamics are important factors to consider when evaluating the effects of diverse pathologies on the kidney. For patients with diabetes or heart failure, one of the most commonly used medications is an ACE inhibitor which reduces the formation of angiotensin II, in turn, it decreases GFR by preventing the constriction of different arterioles. Care should be taken in patients with chronic kidney disease undergoing anesthesia to maintain renal perfusion pressures as certain agents are known to decrease the GFR and cause renal injury such as methoxyflurane.