NURS 6501: MIDTERM EXAM: Please contact Your Favorite Professor for help with NURS 6501: Midterm Exam or any other assignment. Email: professorrobertphd@gmail.com   A patient with normal renal function suddenly experiences an increase in systemic blood pressure. Which intrinsic mechanism is most likely to occur to maintain a constant glomerular filtration rate (GFR)? Group of answer choices

• Tubuloglomerular feedback resulting in increased sodium reabsorption in the distal tubule
• Tubuloglomerular feedback leading to efferent arteriole constriction
• Tubuloglomerular feedback leading to dilation of the afferent arteriole
• Tubuloglomerular feedback leading to afferent arteriole constriction

  The correct answer is: Tubuloglomerular feedback leading to afferent arteriole constriction. Explanation: Tubuloglomerular feedback (TGF) is a mechanism by which the kidneys maintain a relatively constant glomerular filtration rate (GFR) despite fluctuations in systemic blood pressure.

• When blood pressure increases, it leads to an increase in glomerular filtration pressure, which could increase the GFR if not regulated.
• The macula densa, which is located in the distal convoluted tubule (close to the glomerulus), senses the increased sodium chloride (NaCl) delivery due to the higher filtration rate.
• In response, the macula densa releases signals that cause the afferent arteriole (the blood vessel leading to the glomerulus) to constrict. This constriction of the afferent arteriole reduces the blood flow into the glomerulus, helping to normalize the filtration pressure and thus maintaining a constant GFR.

Why the other options are incorrect:

• Tubuloglomerular feedback resulting in increased sodium reabsorption in the distal tubule: While sodium reabsorption is important, this mechanism isn't the primary way to regulate GFR. The feedback primarily adjusts the afferent arteriole size to regulate blood flow and GFR.
• Tubuloglomerular feedback leading to efferent arteriole constriction: Constriction of the efferent arteriole can increase the glomerular filtration pressure, but this is typically not the primary mechanism activated by TGF to regulate GFR in response to an increase in systemic blood pressure.
• Tubuloglomerular feedback leading to dilation of the afferent arteriole: Dilation of the afferent arteriole would increase the blood flow to the glomerulus, which would increase GFR, rather than stabilize it in response to increased systemic blood pressure.

Conclusion: The primary response to increased blood pressure in the kidneys is affecting the afferent arteriole through tubuloglomerular feedback, leading to constriction of the afferent arteriole to maintain a constant GFR.