02.1 Glomerular filtration and blood flow

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Questions and Answers

What is the approximate renal blood flow (RBF) to the kidneys in mL/min?

800 mL/min

1,100 mL/min (correct)

1,200 mL/min

900 mL/min

Which statement about renal plasma flow (RPF) is accurate?

RPF is equal to RBF at 1,100 mL/min.

RPF is usually higher than the glomerular filtration rate (GFR).

RPF is unaffected by haematocrit levels.

RPF is approximately 605 mL/min after accounting for haematocrit. (correct)

What is the normal glomerular filtration rate (GFR) in mL/min for adults?

150 mL/min

175 mL/min

125 mL/min (correct)

100 mL/min

Which factor does NOT contribute to the determination of the glomerular filtration rate (GFR)?

Heart rate Signup and view all the answers

During ultrafiltration, which substance is typically absent from the ultrafiltrate?

Proteins Signup and view all the answers

What is the filtration fraction in relation to renal plasma flow (RPF)?

About 20% Signup and view all the answers

How does prolonged hypotension affect the kidneys?

It can lead to acute kidney injury (AKI). Signup and view all the answers

Which diagnostic approach is typically used to estimate glomerular filtration rate (GFR)?

Serum creatinine measurement Signup and view all the answers

How does increasing resistance of the efferent arteriole influence the glomerular filtration rate (GFR)?

It increases GFR by enhancing the net filtration pressure. Signup and view all the answers

Which factors specifically oppose filtration in the glomerulus?

Hydrostatic pressure in Bowman’s space and oncotic pressure in glomerular capillaries. Signup and view all the answers

What is the likely effect of high-dose diuretics on renal perfusion if not monitored carefully?

They may reduce renal perfusion leading to potential injury. Signup and view all the answers

In what situation is proteinuria most likely to be observed?

Nephrotic Syndrome resulting from glomerular damage. Signup and view all the answers

What does a higher serum creatinine level indicate regarding kidney function?

Reduced kidney function. Signup and view all the answers

Which of the following correctly describes the role of NSAIDs in renal perfusion?

They constrict the afferent arteriole, reducing GFR. Signup and view all the answers

How does the filtration fraction typically vary under pathological conditions?

It can fluctuate significantly depending on the underlying renal condition. Signup and view all the answers

What is the primary determinant of glomerular filtration rate as indicated by Starling forces?

The balance of hydrostatic and oncotic pressures. Signup and view all the answers

Study Notes

Glomerular Filtration and Renal Blood Flow

Renal blood flow (RBF) is approximately 1100 mL/min, 22% of cardiac output. Kidneys are highly perfused for metabolic needs and use oxygen at twice the rate of the brain.
Renal plasma flow (RPF) is calculated as RBF x (1 - hematocrit). A typical hematocrit is 45%, leading to an RPF around 605 mL/min.
Glomerular Filtration Rate (GFR) is the rate at which plasma is filtered into Bowman's capsule, typically 125 mL/min in normal adults.
The filtration fraction is about 20% of RPF.
Ultrafiltration occurs as fluid moves across the glomerular filtration barrier into Bowman's space. It lacks proteins and blood cells. The process is influenced by Starling forces.

Key Concepts

Starling Forces are the balance of hydrostatic and oncotic pressures influencing glomerular filtration.
- Glomerular hydrostatic pressure (PGC) promotes filtration.
- Bowman's space hydrostatic pressure (PBS) opposes filtration.
- Glomerular oncotic pressure (πGC) opposes filtration.
Net Filtration Pressure (NFP) is the combined effect of these forces driving fluid into Bowman's space.

Pathophysiology

Filtration Barrier: The glomerular capillaries filter based on size and charge, allowing small, positively charged molecules to pass more readily.
Starling Forces influence the direction and rate of fluid movement across the glomerulus.

Pharmacology

Vasodilators: Drugs like ACE inhibitors or angiotensin II receptor blockers reduce efferent arteriolar resistance, decreasing glomerular pressure and GFR.
Diuretics: Used to manage fluid balance but high doses might reduce renal perfusion.
NSAIDs: These drugs can constrict afferent arterioles which reduces GFR and RBF.

Clinical Applications

Case Study: Prolonged hypotension due to hemorrhage can lead to renal dysfunction and needs assessment of GFR and RBF dynamics.
Diagnostic Approach: Serum creatinine is measured to estimate GFR, and ultrasound assesses renal blood flow.
Treatment options include restoring blood pressure with fluids or vasopressors and using diurétics to balance fluids.
Complications/Management: Acute kidney injury (AKI) can arise from prolonged ischemia, resulting in reduced GFR and RBF. Management focuses on addressing the underlying cause and optimizing renal perfusion.

Differential Diagnosis

Acute Kidney Injury (AKI): Reduced GFR and oliguria often from hypotension or nephrotoxins.
Chronic Kidney Disease (CKD): Gradual loss of GFR over time often related to electrolyte and fluid overload.
Nephrotic Syndrome: Characterized by proteinuria related to damage in the glomerular filtration barrier.

Investigations

Serum Creatinine: A marker for GFR, with higher levels indicating reduced kidney function.
Creatinine Clearance Test: Estimating GFR based on urine creatinine levels.
Imaging (Ultrasound): Useful for assessing renal blood flow and identifying blockages.

Questions for Clarification

Question 1: How does efferent arteriole constriction affect glomerular filtration rate (GFR) in short-term and long-term conditions?
Question 2: What pathological conditions lead to increased Bowman's capsule hydrostatic pressure?

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Description

This quiz covers the key concepts of glomerular filtration and renal blood flow, including the calculations for renal plasma flow and filtration rate. Understand the influence of Starling forces on the filtration process and the physiological significance of these parameters.