Renal Physiology: Glomerular Filtration
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Questions and Answers

Which of the following substances are excluded from moving through the glomerular filtration barrier?

  • Low-molecular-weight organic solutes
  • Inorganic ions
  • Plasma proteins (correct)
  • Water

    • The glomerular filtration rate (GFR) in a normal young adult male is approximately 180 L/day.

    True

    What is the primary site of glomerular filtration?

    Bowman's capsule

    The equation to express urinary excretion rate is: Urinary excretion rate = Filtration rate - _____ + Secretion rate.

    <p>Reabsorption rate</p> Signup and view all the answers

    Match the renal processes with their definitions:

    <p>Glomerular filtration = Bulk flow of fluid into Bowman's capsule Tubular reabsorption = Substances moving from tubules back into blood Tubular secretion = Substances moving from blood into tubules Urinary excretion = Final product eliminated from the body</p> Signup and view all the answers

    How many times is the total plasma volume filtered by the kidneys in a day?

    <p>60 times</p> Signup and view all the answers

    All substances that are freely filtered by the glomerular capillaries are also completely reabsorbed.

    <p>False</p> Signup and view all the answers

    What happens to the composition of glomerular filtrate as it passes through the renal tubules?

    <p>It is modified by reabsorption and secretion.</p> Signup and view all the answers

    What happens to substances that are freely filtered and totally reabsorbed from the tubules?

    <p>Their excretion rate is zero.</p> Signup and view all the answers

    The total area of glomerular capillary endothelium across which filtration occurs is approximately 0.8 m².

    <p>True</p> Signup and view all the answers

    What condition occurs when proteins, like albumin, are filtered into the urine due to a loss of negative charge on the basement membrane?

    <p>Proteinuria or albuminuria</p> Signup and view all the answers

    The glomerular capillary membrane consists of three major layers: endothelial cells, the basement membrane, and ______.

    <p>epithelial cells (podocytes)</p> Signup and view all the answers

    Match the following substances with their excretion rates:

    <p>Amino Acids = Zero Organic Acids = Filtration rate plus tubular secretion rate Electrolytes (sodium, potassium) = Less than filtration rate Glucose = Zero</p> Signup and view all the answers

    Which statement correctly describes the role of mesangial cells in the glomerulus?

    <p>They remove trapped material from the basement membrane.</p> Signup and view all the answers

    Podocytes do not have a significant negative charge.

    <p>False</p> Signup and view all the answers

    The thickness of the basement membrane in the glomerular capillary membrane is about ______.

    <p>50 nm</p> Signup and view all the answers

    What is the maximum diameter of neutral substances that can freely pass through the glomerular membrane?

    <p>4 nm</p> Signup and view all the answers

    Most plasma proteins are effectively filtered through the glomerular membrane.

    <p>False</p> Signup and view all the answers

    What is the typical filtration fraction (FF) in the kidneys?

    <p>0.2 or 20 percent</p> Signup and view all the answers

    The net filtration pressure is the algebraic sum of the four ______ pressures.

    <p>Starling</p> Signup and view all the answers

    Match the following pressures to their respective roles in filtration:

    <p>Glomerular hydrostatic pressure = Forces Favoring Filtration Bowman's capsule hydrostatic pressure = Forces Opposing Filtration Bowman's capsule colloid osmotic pressure = Forces Opposing Filtration Glomerular capillary colloid osmotic pressure = Forces Opposing Filtration</p> Signup and view all the answers

    Which statement about the electrical charge of the glomerular membrane components is correct?

    <p>They are all negatively charged.</p> Signup and view all the answers

    The Glomerular filtration rate (GFR) can be calculated using the formula GFR = Kf x net filtration pressure.

    <p>True</p> Signup and view all the answers

    What is the equation used to determine the net filtration pressure in the glomerulus?

    <p>Forces Favoring Filtration - Forces Opposing Filtration</p> Signup and view all the answers

    What is the normal glomerular filtration rate (GFR)?

    <p>125 ml/min</p> Signup and view all the answers

    Increased Bowman's capsule hydrostatic pressure leads to an increase in GFR.

    <p>False</p> Signup and view all the answers

    What does Kf represent in the context of glomerular filtration?

    <p>The filtration coefficient or hydraulic conductance of the glomerular capillary wall</p> Signup and view all the answers

    The normal Kf is calculated to be about _____ ml/min/mm Hg of filtration pressure for both kidneys.

    <p>12.5</p> Signup and view all the answers

    Match the factors with their effects on GFR:

    <p>Increased glomerular capillary hydrostatic pressure = Increases GFR Constriction of afferent arteriole = Decreases GFR Increased glomerular capillary colloid osmotic pressure = Decreases GFR Decreased Kf = Decreases GFR</p> Signup and view all the answers

    Which factor does NOT contribute to a decrease in GFR?

    <p>Increased glomerular hydrostatic pressure</p> Signup and view all the answers

    The Kf of renal capillary glomeruli is significantly lower than that of most other capillary systems in the body.

    <p>False</p> Signup and view all the answers

    What are two factors that can lead to an increase in GFR?

    <p>Increased glomerular capillary hydrostatic pressure and increased efferent arteriolar resistance</p> Signup and view all the answers

    What is the primary effect of angiotensin II on renal arterioles?

    <p>Vasoconstriction</p> Signup and view all the answers

    Prostaglandins act as vasodilators in the kidneys, countering the effects of the sympathetic nervous system and angiotensin II.

    <p>True</p> Signup and view all the answers

    What is the role of dopamine at low levels in the treatment of hemorrhage?

    <p>Dopamine dilates arterioles in critical organs and protects blood flow.</p> Signup and view all the answers

    The _____ is the most potent vasoconstrictor that is produced by endothelial cells.

    <p>endothelin</p> Signup and view all the answers

    Match the substance with its effect on renal arterioles:

    <p>Angiotensin II = Vasoconstriction Prostaglandins = Vasodilation Endothelin = Increased arteriolar resistance Nitric Oxide = Vasodilation</p> Signup and view all the answers

    How do NSAIDs affect renal function?

    <p>Inhibit prostaglandin synthesis</p> Signup and view all the answers

    Nitric oxide is released by endothelial cells in response to increased shear stress or pressure and is a potent vasoconstrictor.

    <p>False</p> Signup and view all the answers

    What happens when renin-angiotensin system is activated during hemorrhage?

    <p>It causes an increase in angiotensin II levels and vasoconstriction, leading to decreased renal blood flow.</p> Signup and view all the answers

    Study Notes

    Glomerular Filtration

    • The bulk flow of fluid from the glomerular capillaries into Bowman's capsule
    • The filtrate contains most inorganic ions and low-molecular-weight organic solutes
    • The glomerular filtration rate (GFR) is the volume of filtrate formed per unit time
    • In a normal young adult male, the GFR is an incredible 180 L/day (125 mL/min)
    • Urine formation results from glomerular filtration, tubular reabsorption, and tubular secretion
    • Urinary excretion rate = Filtration rate - Reabsorption rate + Secretion rate

    Renal Handling of Substances

    • Some substances are freely filtered, but neither reabsorbed nor secreted, therefore excretion rate = filtration rate
    • Some substances are freely filtered, but partly reabsorbed, therefore urinary excretion rate is less than filtration rate
    • Some substances are freely filtered and totally reabsorbed, resulting in a zero urinary excretion rate
    • Some substances are freely filtered and not reabsorbed, but are secreted, therefore excretion rate = filtration rate + tubular secretion rate

    Structure of Glomerular Capillary Membrane

    • The glomerular capillary membrane has three major layers:
      • Endothelial cells: Perforated by large fenestrae ("windows") and rich in fixed negative charges
      • Basement membrane: About 50nm thick, contains glycoproteins and proteoglycans, and has a net negative charge.
        • In minimal change nephropathy, the negative charges are lost leading to proteinuria or albuminuria
      • Epithelial cells: Contain podocytes with pedicels which interdigitate forming slits through which the filtrate enters Bowman's space. Podocyte membranes also have a high density of negative charge
    • The glomerulus also contains mesangial cells, which act as phagocytes and can contract

    Factors Affecting Filtration

    • The glomerular capillary membrane is thicker than most other capillaries, but more porous
    • Filtration rate of any substance depends on:
      • Molecular size: Freely passes neutral substances up to 4nm, but almost completely excludes those greater than 8nm
      • Electrical charge: Negatively charged molecules are impeded by electrostatic repulsion; positively charged molecules are favored
    • Filtration fraction (FF): The fraction of the renal plasma flow that is filtered, averaging about 0.2

    Determinants of GFR

    • The pressures driving fluid movement across the glomerular capillary wall are the Starling forces:
      • Glomerular hydrostatic pressure (PG): Pressure within the glomerular capillary
      • Bowman's capsule hydrostatic pressure (PB): Pressure within Bowman's capsule
      • Glomerular capillary colloid osmotic pressure (πG): Pressure due to proteins in the glomerular capillary
      • Bowman's capsule colloid osmotic pressure (πB): Pressure due to proteins in Bowman's space
    • GFR = Kf x net ultrafiltration pressure
    • Net filtration pressure = Forces Favoring Filtration - Forces Opposing Filtration
      • Forces Favoring Filtration: PG (60 mmHg) and πB (0 mmHg)
      • Forces Opposing Filtration: PB (18 mmHg) and πG (32 mmHg)
    • Net filtration pressure = [(60 + 0) - (18 + 32)] = 10 mmHg

    Filtration Coefficient (Kf)

    • Kf is the water permeability of the glomerular capillary wall
    • Kf is calculated from GFR and net filtration pressure
    • Normal Kf is about 12.5 ml/min/mm Hg
    • Kf of renal capillary glomeruli is 400 times higher than other capillary systems

    Factors Decreasing GFR

    • Decreased Kf
      • Uncontrolled hypertension
      • Diabetes mellitus (thickening of glomerular basement membrane)
    • Increased Bowman's capsule hydrostatic pressure
      • Obstruction of urine flow (e.g., ureteral stone)
    • Increased glomerular capillary colloid osmotic pressure
    • Constriction of the afferent arteriole

    Factors Increasing GFR

    • Increased glomerular capillary hydrostatic pressure
      • Increased arterial pressure
      • Increased efferent arteriolar resistance
    • Increased sympathetic nerve activity
      • Vasoconstriction of afferent and efferent arterioles
      • Reduced renal blood flow
    • Prostaglandins (e.g., PGE2, PGI2)
      • Vasodilation of afferent and efferent arterioles
    • Dopamine (low doses)
      • Vasodilation of cerebral, cardiac, splanchnic and renal arterioles
    • Nitric oxide (NO)
      • Vasodilation of afferent and efferent arterioles
      • Released by endothelial cells in response to increased shear stress or pressure
    • Endothelin
      • Potent vasoconstrictor of endothelial origin
      • Implicated in the nephrotoxicity of some drugs (e.g., cyclosporine)

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    Description

    Explore the processes of glomerular filtration and renal handling of substances in this quiz. Understand concepts like the glomerular filtration rate (GFR) and how various substances are filtered and reabsorbed by the kidneys. Test your knowledge on urine formation and the dynamics of substance handling in renal physiology.

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