L3 Glomerular Filtration (P2 Hard)

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Questions and Answers

Which structure forms the primary barrier for filtration in the glomerulus?

Basement membrane (correct)

Bowman's capsule

Podocytes

Endothelial cells

How does the permeability of glomerular capillaries compare to other capillaries in the body?

It is 50 times more permeable.

It is 100 times more permeable. (correct)

It is 10 times more permeable.

It is less permeable.

What component of the basement membrane contributes to its negative charge?

Endothelial cells

Podocytes

Collagen

Glycoproteins (correct)

What is the approximate rate of glomerular filtration per minute in healthy adults?

125 ml/min Signup and view all the answers

What happens to the liquid that is filtered through the glomerular membrane?

It passes extracellularly through the basement membrane. Signup and view all the answers

What is the primary function of the glomerular filtration rate (GFR)?

To measure the efficiency of the kidneys in filtering plasma Signup and view all the answers

Which of the following correctly represents the equation for filtration fraction?

Filtration Fraction = GFR / RPF Signup and view all the answers

If the GFR is measured at 125 ml/min, what percentage of renal plasma flow (RPF) does this value represent?

20% Signup and view all the answers

Which process is NOT involved in the formation of urine?

Extracellular metabolism Signup and view all the answers

Which of the following statements about the efferent arterioles is accurate?

They leave the glomerulus carrying 80% of the plasma that was not filtered. Signup and view all the answers

How does an increase in colloid osmotic pressure affect the glomerular filtration rate (GFR)?

It decreases GFR. Signup and view all the answers

What effect does severe sympathetic stimulation have on renal blood flow (RBF) and GFR?

Decreased RBF and GFR. Signup and view all the answers

What is the relationship between the diameter of the afferent arteriole and GFR?

Increased diameter decreases resistance and increases GFR. Signup and view all the answers

How does the hydrostatic pressure in Bowman's capsule affect GFR in the presence of ureteric stones?

It decreases GFR. Signup and view all the answers

What happens to GFR with high protein intake?

GFR increases. Signup and view all the answers

Which factor is directly proportional to GFR?

Glomerular capillary permeability. Signup and view all the answers

What effect does an increase in the diameter of the efferent arteriole have on GFR?

Increases GFR initially but ultimately decreases it. Signup and view all the answers

Which property of inulin makes it suitable for measuring GFR?

It is non-toxic, freely filtered, and not secreted or reabsorbed. Signup and view all the answers

What is the primary function of the filtration slits between podocyte foot processes?

To act as a barrier to plasma proteins Signup and view all the answers

Which of the following statements accurately describes the properties of glomerular capillaries?

They feature high capillary hydrostatic pressure. Signup and view all the answers

What is the net filtration pressure in the glomerulus?

10 mmHg Signup and view all the answers

Which force acts as a reabsorbing force in the glomerulus?

Plasma colloid osmotic pressure Signup and view all the answers

What is the primary determinant of renal blood flow?

Glomerular filtration rate stability Signup and view all the answers

Which component of the glomerulus plays a crucial role in the formation of filtration slits?

Foot processes of podocytes Signup and view all the answers

What substances can freely pass through the filtration barrier of the glomerulus?

Water and small solutes under 4 nm Signup and view all the answers

What is the role of the basement membrane in the filtration process?

Acts as a charge-selective barrier Signup and view all the answers

How does the diameter of the afferent arterioles compare to that of the efferent arterioles?

Afferent arterioles are larger than efferent arterioles Signup and view all the answers

What is the primary charge characteristic of the basement membrane in the glomerulus?

Negatively charged Signup and view all the answers

Which statement regarding inulin clearance is true?

Inulin clearance is less than G.F.R if reabsorption occurs. Signup and view all the answers

What is the significance of the clearance value of a substance being less than that of inulin?

The substance is completely reabsorbed by the kidneys. Signup and view all the answers

How is the glomerular filtration rate typically calculated?

Using the equation C = U * V / P. Signup and view all the answers

What happens to the clearance rate of glucose in the kidneys?

It becomes zero when completely reabsorbed. Signup and view all the answers

Which of the following best describes the factors influencing the filtration force in the glomerulus?

It involves both colloid osmotic pressure and hydrostatic capsular pressure. Signup and view all the answers

What does a clearance value higher than 700 ml/min indicate about a substance?

The substance is secreted from the renal tubules. Signup and view all the answers

What is the expected normal value of glomerular filtration rate (G.F.R)?

125 ml/min Signup and view all the answers

What is the primary role of glomerular filtration in urine formation?

It initiates urine formation through filtration of plasma. Signup and view all the answers

Study Notes

Renal Module Details

Course code: IMP-07-20318
Phase: I
Year/semester: 2nd year / Semester 3
Credit hours: (not specified)
Course duration: 5 weeks

Lecture 3: Physiology of Glomerular Filtration Rate (GFR) and Affecting Factors

Intended Learning Outcomes (ILOs):
- Define glomerular filtration rate (GFR) and identify its value
- List factors affecting GFR
- Discuss GFR measurement methods

Glomerular Filtration

Process: A passive process (ultrafiltration)
Definition (GFR): The volume filtered by both kidneys per minute
Value (GFR): 125 ml/min
Relationship to Renal Plasma Flow (RPF): 20% of RPF (RPF = 625 ml/min)

Filtration Fraction

Definition: The fraction of plasma filtered through glomerular capillaries
Calculation: GFR / RPF = 125 ml/min / 625 ml/min = 20%
Importance: Indicates the efficiency of the filter bed

Basic Processes in Urine Formation

Glomerular filtration (GF)
Tubular reabsorption (TR)
Tubular secretion (TS)

Glomerular Filtration Membrane

Structure: Two cell layers
- Capillary endothelium (100 times more permeable than other capillaries)
- Podocytes (cells in Bowman's capsule; octopus foot processes encircling glomerular tuft)
Basement Membrane: Between the two layers; composed of collagen (support) and glycoprotein (negatively charged)
Filtration Process: Fluid passes through the layers extracellularly
- Between endothelial cells
- Through basement membrane
- Through filtration slits between podocytes' foot processes

Forces Acting on Glomerulus

Glomerular capillary hydrostatic pressure (HPgc): 55 mmHg (filtering force)
Plasma colloid osmotic pressure (OPpc): 30 mmHg (reabsorbing force)
Capsular hydrostatic pressure (HPc): 15 mmHg (reabsorbing force)
Net Filtration Pressure: 55 - (30 + 15) = 10 mmHg

GFR Regulation

Renal blood flow: Directly proportional to GFR
Arterial blood pressure (ABP): Within a range of 75-160 mmHg, autoregulation maintains GFR; outside this range, GFR is directly proportional
Glomerular Permeability: GFR is directly proportional to this
Sympathetic stimulation: Sever stimulation decreases renal blood flow (RBF) and GFR

GFR Regulation (continued)

Afferent Arteriole Diameter: Increased diameter reduces resistance, increases blood flow, and raises capillary blood pressure, thus increasing GFR.
Efferent Arteriole Diameter: Mild constriction increases resistance, blood flow, and glomerular capillary pressure, leading to higher GFR. Severe constriction initial results in raised GFR, but then falls markedly.

Factors Affecting GFR

Protein intake: High protein intake increases RBF and GFR
Number of functioning nephrons: Reduced functioning nephrons in conditions like chronic renal failure result in severely reduced GFR
Changes in glomerular colloid osmotic pressure: Increased OP (e.g., dehydration) decreases GFR; decreased OP increases GFR.
Hydrostatic pressure in Bowman's capsule: Increased pressure (e.g., ureteric stones) decreases GFR.

Measuring GFR

Inulin Clearance: used to assess GFR
- Inulin is nontoxic, not metabolized, and not stored in the kidneys.
- Freely filtered by the glomerular capillaries
- Neither reabsorbed or secreted by renal tubules.
- Normal value: 125 ml/min
- Calculation: (U x V)/P
  - U: inulin concentration in urine per ml
  - V: volume of urine excreted per min.
  - P: inulin concentration in plasma per ml

Importance of Inulin Clearance

Reference value
Renal tubular reabsorption
- Substances reabsorbed have lower clearance values than inulin (e.g., urea).
- Substances that are completely reabsorbed, e.g., glucose, have a zero clearance value.
Renal tubular secretion: Substances secreted have higher clearance than inulin.

Points to Remember

Glomerular filtration is the initial stage in urine formation, involving filtration of plasma.
Filtration force is glomerular hydrostatic pressure minus oncotic pressure and hydrostatic capsular pressure.
GFR is measured using inulin clearance and is normally 125 ml/min.

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Description

Test your knowledge on glomerular filtration and renal physiology. This quiz covers key concepts such as the structure of the glomerulus, glomerular filtration rate (GFR), and the role of the basement membrane in filtration. Understand how these factors relate to kidney function and filtration efficiency.