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Questions and Answers
What effect does a drop in arterial blood pressure (ABP) below 80mmHg have on glomerular filtration rate (GFR)?
What effect does a drop in arterial blood pressure (ABP) below 80mmHg have on glomerular filtration rate (GFR)?
Which condition leads to an increase in GFR due to a decrease in πGC?
Which condition leads to an increase in GFR due to a decrease in πGC?
How does severe constriction of the efferent arterioles affect GFR?
How does severe constriction of the efferent arterioles affect GFR?
What physiological response occurs when the tubular fluid flow rate increases in the nephron?
What physiological response occurs when the tubular fluid flow rate increases in the nephron?
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Which of the following conditions can decrease the glomerular filtration rate (GFR)?
Which of the following conditions can decrease the glomerular filtration rate (GFR)?
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What effect does nephritis have on glomerular capillary permeability and GFR?
What effect does nephritis have on glomerular capillary permeability and GFR?
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What happens to the GFR when there is obstruction in the urinary tract?
What happens to the GFR when there is obstruction in the urinary tract?
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Which factor directly correlates with the permeability of the glomerular capillaries?
Which factor directly correlates with the permeability of the glomerular capillaries?
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Study Notes
Factors Affecting Glomerular Filtration Rate (GFR)
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Changes in Glomerular Capillary Pressure (PGC)
- Normal GFR remains consistent despite changes in blood pressure unless it exceeds 160 mmHg or falls below 80 mmHg.
- A decrease in blood pressure below 80 mmHg can stop GFR, causing anuria (complete urinary suppression).
- A significant increase in blood pressure above 160 mmHg increases GFR resulting in increased urine output, known as pressure diuresis.
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Afferent Arteriolar Constriction
- Decreases GFR by reducing PGC.
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Efferent Arteriolar Constriction
- Mild constriction increases GFR by increasing PGC
- Severe constriction decreases GFR by decreasing PGC.
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Changes in Glomerular Capillary Oncotic Pressure (πGC)
- Hypoproteinemia (low blood protein) increases GFR by decreasing πGC.
- Dehydration increases πGC, which decreases GFR.
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Changes in Tubular Pressure (PT)
- Edema of the kidney increases hydrostatic pressure in the tubules, reducing GFR.
- Obstruction of the urinary tract increases PT, which decreases GFR.
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Changes in Surface Area
- A decrease in the surface area available for filtration reduces GFR.
- This can occur due to:
- Decreased number of functional nephrons, as seen in chronic renal failure or after nephrectomy.
- Contraction of mesangial cells.
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Changes in Permeability
- GFR is directly proportional to glomerular capillary permeability.
- Increased permeability, as in nephritis, increases GFR.
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Sympathetic Stimulation
- Mild stimulation does not impact GFR due to auto-regulation.
- Strong stimulation causes vasoconstriction in glomerular arterioles, reducing both renal blood flow (RBF) and GFR.
Tubulo-Glomerular Feedback
- When tubular fluid flow rate increases in the distal part of the nephron (ascending loop of Henle and distal convoluted tubule), GFR in the same nephron decreases and vice versa.
- Mechanism:
- Increased tubular flow rate delivers large amounts of fluid, sodium, and chloride to the distal tubules.
- Na+ and Cl- enter the macula densa cells.
- Increased Na+ concentration stimulates Na+-K+ pump activity.
- Increase in adenosine triphosphate (ATP) hydrolysis leads to the formation of more adenosine.
- Adenosine acts on adenosine A1 receptors, causing release of calcium.
- Calcium causes contraction of smooth muscle in the afferent arterioles, leading to their constriction and decreased GFR.
Measuring Glomerular Filtration Rate
- Can be measured using inulin or creatinine clearance.
- Inulin and creatinine are freely filtered in the glomeruli, and the filtered amount is excreted.
- Neither is reabsorbed or secreted in the renal tubules, meaning the amount excreted per minute equals the amount filtered per minute.
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Description
This quiz explores the various factors that influence the Glomerular Filtration Rate (GFR), a critical aspect of kidney function. It covers the effects of changes in glomerular capillary pressure, arteriolar constriction, oncotic pressure, and tubular pressure on GFR. Understanding these factors is essential for comprehending renal physiology and pathophysiology.
