GFR and RBF

Definitions

100

A normal GFR is _________, while below 60 for over 3 months indicates chronic kidney disease.

90–120 mL/min

200

Glomerular Filtration Rate measures how well your kidneys filter waste from your blood. Usually estimated via a blood test (eGFR) measuring _______ levels, it determines kidney function stage. 

creatinine

300

Renal blood flow is the volume of blood delivered to the kidneys, accounting for ________ of cardiac output to ensure proper waste filtration and oxygenation.

20-25%

Calculations

100

A patient's lab results are as follows:

- Urine Inulin Concentration (15 mg/mL)

- Urine flow rate (1 mL/min)

- Plasma Inulin Concentration (0.1 mg/mL)

Calculate the GFR in mL/min.

GFR = 150 mL/min

Explanation: (15 mg/mL x 1 mL/min) / (0.1 mg/mL)

200

Given a patient has:

- GFR = 125 mL/min

- FF = 0.2

- Hct = 0.45 

Calculate the RBF in mL/min. 

RBF = 1136 mL/min

Explanation: First, calculate RPF. 

RPF = (125 mL/min) / 0.2 = 625 mL/min

RBF = (625 mL/min) / (1 - 0.45) = 1136 mL/min

300

Given the following:

- RPF = 5 mL/min

- GFR = 2 mL/min

Calculate the filtration fraction.

FF = 40%

Explanation: FF = (2 mL/min) / (5 mL/min) = 0.4 = 40%

Mechanisms

100

In tubuloglomerular feedback, the ________ in the distal tubule senses increased ________ delivery (often due to high GFR), which triggers ________ of the afferent arteriole, reducing GFR to normalize sodium excretion.

macula densa, NaCl, vasoconstriction

200

The _______ mechanism in the kidney is a rapid, intrinsic autoregulatory process where ________ arteriole smooth muscle contracts when stretched by increased blood pressure and relaxes when blood pressure drops.

myogenic, afferent

300

RBF is tightly autoregulated to remain constant between _________ mean arterial pressure.

50–150 mmHg