Which of the following would reduce the glomerular filtration rate? O A) Vasoconstriction of the efferent arteriole OB) A drop in oncotic pressure O C) Vasodilation of the afferent arteriole O D) Vasoconstriction of the afferent arteriole E) An increase in osmotic pressure in the glomerular capsule
The Correct Answer and Explanation is :
The correct answer is D) Vasoconstriction of the afferent arteriole.
Explanation:
Glomerular filtration rate (GFR) refers to the rate at which blood is filtered through the glomeruli in the kidneys. GFR is influenced by the pressure difference between the glomerular capillaries and the Bowman’s capsule, as well as the resistance of the afferent and efferent arterioles. Let’s break down each option:
- A) Vasoconstriction of the efferent arteriole:
- Vasoconstriction of the efferent arteriole actually increases GFR. When the efferent arteriole constricts, it increases the pressure in the glomerular capillaries, thus enhancing the filtration of blood through the glomeruli. This is because the efferent arteriole is responsible for draining blood from the glomerulus; restricting outflow causes a buildup of pressure within the glomerular capillaries.
- B) A drop in oncotic pressure:
- A drop in oncotic pressure (the pressure exerted by proteins, such as albumin, in the blood) increases GFR. Oncotic pressure typically opposes filtration by pulling water back into the capillaries. A decrease in this pressure reduces the opposing force, allowing for greater filtration.
- C) Vasodilation of the afferent arteriole:
- Vasodilation of the afferent arteriole increases GFR. By dilating the afferent arteriole, more blood is allowed into the glomerulus, increasing the blood pressure and, consequently, the filtration rate.
- D) Vasoconstriction of the afferent arteriole (correct answer):
- Vasoconstriction of the afferent arteriole decreases GFR. When the afferent arteriole constricts, the amount of blood entering the glomerulus is reduced, leading to a decrease in glomerular pressure and a reduction in filtration.
- E) An increase in osmotic pressure in the glomerular capsule:
- An increase in osmotic pressure in the glomerular capsule decreases GFR. This would oppose filtration because the osmotic pressure in the capsule would draw fluid back into the glomerular capillaries, reducing the net filtration pressure.
Thus, vasoconstriction of the afferent arteriole decreases blood flow into the glomerulus, reducing the glomerular filtration rate.