L2 Renal Circulation (P1 Mid)

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Questions and Answers

What is the first structure that blood enters when it enters the kidney?

  • Glomerulus
  • Renal artery (correct)
  • Interlobular arteries
  • Afferent arteriole

What percentage of cardiac output is represented by renal blood flow?

  • 10-15%
  • 25-30%
  • 20-25% (correct)
  • 15-20%

Which component is primarily responsible for the filtration process in the kidney?

  • Collecting duct
  • Glomerulus (correct)
  • Distal tubule
  • Peritubular capillaries

What is the primary function of the peritubular capillaries?

<p>Reabsorption of substances (B)</p> Signup and view all the answers

How is renal plasma flow calculated?

<p>Using para-aminohipuric acid clearance (D)</p> Signup and view all the answers

What does the term 'plasma clearance' refer to?

<p>The volume of plasma cleared of a particular substance per minute (C)</p> Signup and view all the answers

In renal circulation, what comes after the glomerulus?

<p>Efferent arteriole (C)</p> Signup and view all the answers

Which of the following correctly describes the renal fraction?

<p>The portion of cardiac output that passes to the kidneys (C)</p> Signup and view all the answers

Which of the following accurately describes how PAHA is processed in the kidneys?

<p>PAHA undergoes glomerular filtration and tubular secretion. (B)</p> Signup and view all the answers

What does the clearance of a substance indicate?

<p>The volume of plasma cleared of that substance. (B)</p> Signup and view all the answers

To calculate the effective renal plasma flow (ERPF), which of the following is used?

<p>ERPF = U × V/P (A)</p> Signup and view all the answers

What percentage of arterial plasma PAHA is typically excreted in urine?

<p>90% (B)</p> Signup and view all the answers

Which processes contribute to the handling of plasma in the kidneys?

<p>Filtration, reabsorption, and secretion (A)</p> Signup and view all the answers

What is the glomerular filtration rate (GFR) derived from a 625 ml/min plasma flow?

<p>125 ml/min filtered into the Bowman’s capsule (C)</p> Signup and view all the answers

Which factor does NOT contribute to the regulation of renal blood flow (RBF)?

<p>Concentration of electrolytes in urine (B)</p> Signup and view all the answers

What happens to capillary pressure with an increased diameter of the afferent arteriole?

<p>Capillary pressure increases, enhancing GFR. (A)</p> Signup and view all the answers

What is the primary aim of extrinsic control in the kidney?

<p>To control arterial blood pressure (D)</p> Signup and view all the answers

How does extrinsic control affect glomerular filtration rate (GFR)?

<p>It decreases GFR through afferent arteriolar vasoconstriction (A)</p> Signup and view all the answers

Which baroreceptors are involved in detecting changes in arterial blood pressure?

<p>Aortic arch and carotid sinus baroreceptors (A)</p> Signup and view all the answers

What effect does generalized arteriolar vasoconstriction have on renal blood flow?

<p>It decreases renal blood flow (B)</p> Signup and view all the answers

What is one way extrinsic control overrides autoregulation?

<p>By inducing sympathetic activity (C)</p> Signup and view all the answers

What is the relationship between cardiac output and renal blood flow (RBF)?

<p>RBF constitutes about 1/4 of cardiac output (B)</p> Signup and view all the answers

Which component is directly affected by changes in glomerular capillary blood pressure?

<p>Glomerular filtration rate (C)</p> Signup and view all the answers

What does the clearance of a substance refer to in the context of renal function?

<p>The volume of plasma that is cleared of the substance per minute (D)</p> Signup and view all the answers

What is the primary aim of autoregulation in the kidneys?

<p>To maintain constant renal blood flow and glomerular filtration rate (B)</p> Signup and view all the answers

Which mechanism is involved in the myogenic response of autoregulation?

<p>Stretch-induced contraction of smooth muscle in response to increased pressure (A)</p> Signup and view all the answers

What happens to the afferent arteriole during autoregulation when arterial blood pressure increases?

<p>It constricts to decrease blood flow (B)</p> Signup and view all the answers

How does tubuloglomerular feedback contribute to autoregulation?

<p>By stimulating macula densa cells to release vasoactive chemicals (B)</p> Signup and view all the answers

What occurs at blood pressure levels outside the autoregulation range of 75-160 mmHg?

<p>Autoregulation becomes ineffective and GFR changes (D)</p> Signup and view all the answers

Which component of the nephron is involved in tubuloglomerular feedback?

<p>Distal convoluted tubule (D)</p> Signup and view all the answers

What is the result of afferent arteriolar vasoconstriction during autoregulation?

<p>Decreased glomerular filtration rate (B)</p> Signup and view all the answers

Which factor primarily influences glomerular capillary pressure?

<p>Net filtration pressure affected by arterial blood pressure (D)</p> Signup and view all the answers

What maintains the constant glomerular filtration rate (GFR) within the autoregulation range?

<p>Contractility of smooth muscle in afferent arterioles (C)</p> Signup and view all the answers

Why is constant GFR essential for normal kidney function?

<p>It ensures consistent filtration of waste products regardless of blood pressure changes (D)</p> Signup and view all the answers

Flashcards

What is PAH clearance?

PAHA is a substance that is completely removed from the blood during filtration by the kidneys. This process measures the total volume of plasma that is cleared from this substance.

What does 'clearance' mean in relation to kidney function?

The clearance of a substance refers to the volume of plasma that is cleared from that substance by the kidneys.

How is ERPF related to RPF?

The effective renal plasma flow (ERPF) is approximately 90% of the actual renal plasma flow (RPF).

What is glomerular filtration?

Glomerular filtration is the process of filtering blood through the glomerulus in the kidneys. It involves the movement of fluid and small molecules from the blood into Bowman's capsule.

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What is tubular reabsorption?

Tubular reabsorption is the process where filtered substances are reabsorbed back into the bloodstream from the renal tubules.

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What is tubular secretion?

Tubular secretion is the process of moving substances from the blood into the renal tubules.

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What are afferent and efferent arterioles?

The afferent arteriole is the blood vessel that carries blood to the glomerulus, while the efferent arteriole carries blood away from the glomerulus.

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How is renal blood flow regulated?

Renal blood flow (RBF) is regulated by both intrinsic (autoregulation) and extrinsic mechanisms. These mechanisms ensure a stable blood flow to the kidneys, which is essential for proper filtration.

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Renal circulation

The circulatory path through the kidneys, involving two sets of capillaries: glomerulus (filtration) and peritubular capillaries (reabsorption).

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Renal fraction

The percentage of total blood pumped by the heart (cardiac output) that flows specifically to the kidneys. Typically around 21%.

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Renal blood flow (RBF)

The amount of blood flowing through the kidneys per minute, usually around 1140 ml/min. Represents 20-25% of the cardiac output.

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Plasma clearance

The process of measuring the volume of plasma cleared of a substance by the kidneys per minute.

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PAH acid clearance

A technique to directly measure renal plasma flow using a specific compound like PAH. PAHA is filtered in the glomerulus but mostly excreted by the kidneys.

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Peritubular capillaries

Tiny blood vessels surrounding the nephron tubules, important for reabsorption of water and nutrients back into the bloodstream.

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Juxtaglomerular apparatus

A specialized structure located between the afferent and efferent arterioles in the nephron. It's crucial for regulating blood pressure and filtration.

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Autoregulation of renal blood flow

The process of maintaining a steady blood flow to the kidneys, even when blood pressure changes. Mechanisms within the kidneys ensure proper filtration.

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Autoregulation of GFR

The ability of the kidneys to maintain a relatively constant glomerular filtration rate (GFR) despite fluctuations in mean arterial blood pressure (ABP).

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Myogenic Mechanism

The process by which the afferent arteriole constricts in response to an increase in blood pressure, thereby reducing blood flow into the glomerulus and maintaining a stable GFR.

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Tubulo-glomerular Feedback

The feedback loop involving the macula densa cells of the distal tubule and the afferent arteriole, which helps regulate GFR.

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Macula Densa Cells

Specialized cells in the distal tubule that sense changes in tubular fluid flow and solute concentration.

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Vasoactive Chemicals

Chemicals released by the macula densa cells to constrict the afferent arteriole, reducing blood flow into the glomerulus.

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Net Filtration Pressure

The pressure difference between the glomerular capillary pressure and the pressure in Bowman's capsule, driving filtration.

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Glomerular Capillary Pressure

The pressure inside the glomerular capillaries, which is the main driving force for filtration.

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Autoregulation Range

The range of mean arterial blood pressure (ABP) within which autoregulation can effectively maintain a constant GFR.

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Glomerular Filtration Rate (GFR)

The rate at which the kidneys filter blood, representing the amount of fluid and solutes passing from the blood into the nephron per unit time.

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Extrinsic GFR Control

Adjustments made to the glomerular filtration rate (GFR) that are independent of the intrinsic autoregulatory mechanisms of the kidneys.

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Sympathetic Nervous System Role in GFR

The sympathetic nervous system's influence on GFR, aiming to maintain blood pressure.

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Baroreceptors

Specialized sensors in the aortic arch and carotid sinus that detect changes in arterial blood pressure (ABP).

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Sympathetic Stimulation & Vasoconstriction

The sympathetic stimulation of the kidneys causes generalized vasoconstriction, which ultimately affects GFR.

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Afferent Arteriole Vasoconstriction

The process where sympathetic stimulation leads to constriction of the afferent arteriole in the kidneys.

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GFR Reduction from Afferent Vasoconstriction

Afferent arteriole vasoconstriction leads to a decrease in glomerular capillary blood pressure, ultimately reducing GFR.

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Extrinsic Control & Salt/Fluid Conservation

Extrinsic control overrides autoregulation to conserve fluid and salt, contributing to increased blood pressure.

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JGA & Vasodilators

The release of vasoconstrictors by the juxtaglomerular apparatus (JGA) counteracts the effect of extrinsic control to maintain adequate GFR.

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Study Notes

Renal Module Information

  • Course code: IMP-07- 20318
  • Phase: I
  • Year/semester: 2nd year/Semester 3
  • Academic year: 2022-2023

Lecture 2: Renal Circulation and Autoregulation of Renal Blood Flow

  • Speaker: Prof. Dr. Aziza Khalil
  • Lecture topic: renal circulation and autoregulation of renal blood flow

Intended Learning Outcomes (ILOs)

  • Describe renal circulation and its significance
  • Discuss regulation of renal blood flow
  • Identify plasma clearance and its measurement

Renal Circulation

  • Renal artery → interlobar arteries → arcuate arteries → interlobular arteries
  • Afferent arteriole → glomerulus → efferent arteriole (arterial blood)
  • Peritubular capillaries and vasa recta
  • Capillaries drain into interlobular vein → arcuate vein → interlobar vein → renal vein

Nephron and Tubules

  • Diagram shows the structure of a nephron, including the proximal tubule, juxtaglomerular apparatus, efferent and afferent arterioles, glomerulus, Bowman's capsule, loop of Henle, distal tubule, collecting duct, cortex, and medulla
  • Renal circulation details the flow of blood through a nephron.

Renal Circulation (Portal Circulation)

  • Renal circulation includes two capillary beds
  • Glomerulus is responsible for filtration
  • Reabsorption takes place in peritubular capillaries

Renal Blood Flow

  • 20-25% of cardiac output
  • 1140 ml/min
  • 90% of renal blood flow supplies the cortex

Renal Fraction

  • 21% of cardiac output goes to the kidneys

Renal Plasma Flow

  • 625 ml/min (55% of RBF)
  • Measured by para-aminohippuric (PAH) acid clearance

Plasma Clearance Definition

  • Volume of plasma cleared of a particular substance by the kidney per minute

Plasma Clearance Formula

  • Cx = (Ux × V) / Px
    • Ux = Urine concentration of substance x
    • V = Rate of urine flow
    • Px = Plasma concentration of substance x

PAH Acid Clearance

  • Para-aminohippuric acid (PAHA) clearance is a method for measuring renal plasma flow, an indicator of renal function
  • PAHA is completely removed from blood passing through the kidneys (glomerular filtration and tubular secretion)
  • The rate of PAHA clearance reflects total renal plasma flow

Clearance of a Substance

  • Means the volume of plasma cleared from a specific substance per minute

Effective Renal Plasma Flow (ERPF) Calculation

  • ERPF = (UPAH × V) / PPAH

Urine Formation

  • Three basic processes
    • Glomerular filtration (GFR)
    • Tubular reabsorption (TR)
    • Tubular secretion (TS)

Glomerular Filtration Rate (GFR)

  • 20% of plasma entering the glomerulus is filtered (125 ml/min)
  • 80% of plasma entering the glomerulus is not filtered and leaves through the efferent arteriole (625 ml/min)

Regulation of Renal Blood Flow (RBF)

  • Two main types of regulation
    • Autoregulation
    • Extrinsic control (Sympathetic)

Autoregulation

  • Aims to keep RBF and GFR constant despite fluctuations in mean arterial blood pressure (75-160 mmHg)
  • Mechanisms include
    • Myogenic
    • Tubuloglomerular feedback (through Juxtaglomerular apparatus)

Mechanism of Action: Myogenic

  • Increased arterial blood pressure stretches afferent arterioles
  • Inherent property of vascular smooth muscle causes it to contract, reducing blood flow into the glomerulus
  • Decreasing arterial pressure relaxes afferent arterioles, increasing blood flow back to normal.

Mechanism of Action: Tubuloglomerular feedback

  • Macula densa cells in the distal tubule detect changes in sodium chloride concentration
  • Release vasoactive chemicals that cause changes in afferent arteriolar diameter, regulating the glomerular capillary pressure.

Extrinsic Control (Sympathetic)

  • Change in GFR occurs even within the autoregulatory limit
  • Main aim is to control arterial blood pressure

Extrinsic Control (Sympathetic) Mechanisms

  • Aortic and carotid sinus baroreceptors detect arterial blood pressure changes
  • Sympathetic activity causes generalized arteriolar vasoconstriction, which decreases blood flow into the glomerulus (afferent arterioles vasoconstrict).
  • Aims to maintain blood pressure by changing GFR, overriding autoregulation

Autoregulation within ABP Ranges (75–160 mmHg)

  • GFR is relatively constant despite fluctuations in systemic arterial blood pressure within this range
  • Above or below this range, GFR changes

Points to Remember

  • Renal blood flow (RBF) is about 1/4 of cardiac output
  • RBF regulated by
    • Extrinsic regulation (sympathetic)
    • Intrinsic regulation (autoregulation)
  • Clearance of a substance defines the volume of plasma cleared per unit time (substance/min)
  • Renal plasma flow determined by para-aminohippuric acid (PAH) clearance

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