Question

The glomerular filtration rate would be decreased by (a) Constriction of the efferent arteriole (b) An increase in afferent arteriolar pressure (c) Compression of the renal capsule (d) An increase in the renal blood flow

Short answer

The glomerular filtration rate would be decreased by compression of the renal capsule (c).

Step-by-step solution

Understanding the process of GFR

The glomerular filtration rate is the process by which the kidneys filter blood, removing excess wastes and fluids. This function depends on the effective pressure within the glomerulus and the health of the filtration barrier.

Identifying effects of each factor

(a) Constriction of the efferent arteriole: Constricting the efferent arteriole decreases the blood flow away from the glomerulus. This will increase the blood pressure in the glomerulus and hence increase GFR, contradicting the statement. (b) An increase in afferent arteriolar pressure: An increase in the afferent arteriole pressure would increase the blood flow into the glomerulus, which would also increase the GFR, not decrease it. (c) Compression of the renal capsule: If the renal capsule is compressed, it would physically obstruct the normal filtration process, likely decreasing the GFR. (d) An increase in the renal blood flow: Increasing renal blood flow generally increases the pressure in the glomerulus, and hence, the GFR.

Key concepts

Efferent Arteriole

The efferent arteriole plays a crucial role in regulating the blood pressure within the glomerulus. Located at the exit of the glomerular capillaries, it helps maintain an optimal pressure for filtering blood. When the efferent arteriole constricts, it reduces the blood flow out of the glomerulus, causing an increase in the glomerular pressure.
This action boosts the glomerular filtration rate (GFR), as more blood is retained within the glomerulus for filtration. However, prolonged constriction can lead to excessive pressure, potentially damaging the delicate structures of the kidney.

• Constricted efferent arteriole: increases glomerular pressure, raises GFR
• Potential risk: prolonged constriction may harm kidney structures

Understanding the effect of the efferent arteriole is vital for comprehending how different factors influence the GFR and by extension, how the kidneys function effectively.

Afferent Arteriole

The afferent arteriole carries blood into the glomerulus. It is a gateway that determines how much blood enters the glomerular filtration process. When it dilates, more blood can flow into the glomerulus, enhancing the filtration process and increasing GFR.
Conversely, constriction of the afferent arteriole reduces blood flow into the glomerulus, thereby decreasing the GFR. This delicate balance controlled by the afferent arteriole is crucial for kidney health.

• Dilated afferent arteriole: increases blood flow, raises GFR
• Constricted afferent arteriole: reduces blood flow, lowers GFR

Changes in the pressure or tone of the afferent arteriole can thus directly affect how well the kidneys filter blood, impacting overall kidney function.

Renal Blood Flow

Renal blood flow is the volume of blood delivered to the kidneys per unit time. It is a critical factor that affects the glomerular filtration rate. Increased renal blood flow enhances the delivery of blood to the kidneys and raises glomerular pressure, thereby increasing the GFR.
On the other hand, reduced renal blood flow decreases glomerular pressure and thus lowers the GFR. Thus, ensuring adequate renal blood flow is essential for optimal kidney function and filtration.

• High renal blood flow: boosts glomerular pressure, increases GFR
• Low renal blood flow: reduces glomerular pressure, decreases GFR

This balance of renal blood flow is vital for maintaining the filtration capacity of the kidneys, ensuring they effectively remove waste and excess fluid from the blood.

Renal Capsule

The renal capsule is a fibrous covering that encases the kidney, providing structural support and protection. Its role goes beyond just a protective layer; it influences the internal pressure of the kidney. Any compression or restriction of the renal capsule can obstruct normal kidney function by altering the pressure dynamics.
Compression of the renal capsule can physically impede the normal expansion of the kidney during filtration, reducing the space available for blood flow and lowering the glomerular filtration rate (GFR).

• Compression: obstructs kidney function, decreases GFR
• Normal condition: supports kidney structure, maintains healthy GFR

Understanding the importance of the renal capsule helps in identifying conditions or injuries that might compromise kidney filtration efficiency by altering pressure or physical space in the kidney.