Juxtaglomerular Apparatus (JGA)

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Questions and Answers

What structural modification defines the Juxtaglomerular Apparatus (JGA)?

  • The structural transformation of the distal convoluted tubule as it merges with the collecting duct.
  • The modification of the thin descending limb of the Loop of Henle where it connects with the collecting duct.
  • The structural modification of the thick ascending limb of the Loop of Henle as it contacts the glomerulus. (correct)
  • The changes in the Bowman's capsule when it directly interacts with the proximal convoluted tubule.

The macula densa is composed of modified smooth muscle cells within the afferent arteriole.

False (B)

What is the primary function of the macula densa within the JGA?

The macula densa senses changes in ionic composition/flow rate of tubular fluid and sends signals to regulate GFR.

JG cells, found mainly in the tunica media of the afferent arteriole, secrete ______, which activates the renin-angiotensin system.

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

Match the cell type with its primary location:

<p>Macula Densa = Thick ascending limb of Loop of Henle Juxtaglomerular (JG) Cells = Afferent arteriole Lacis Cells = Triangular space between arterioles and macula densa</p> Signup and view all the answers

What is the primary function of renin secreted by JG cells?

<p>To activate the renin-angiotensin system for blood pressure regulation. (C)</p> Signup and view all the answers

Lacis cells are characterized by their numerous secretory granules, similar to JG cells.

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

Besides renin, what other hormone is secreted by lacis cells?

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

The feedback mechanism by which the macula densa regulates glomerular filtration rate based on the composition of tubular fluid is known as ______ feedback.

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

Match the component of the JGA with its function

<p>Macula densa = Detects changes in ionic composition and flow rate JG cells = Secrete renin Lacis cells = Secrete renin and erythropoietin</p> Signup and view all the answers

What would be the likely effect of a significant decrease in NaCl concentration detected by the macula densa?

<p>Dilation of afferent arteriole, increasing GFR. (D)</p> Signup and view all the answers

The efferent arteriole contains a higher concentration of JG cells compared to the afferent arteriole.

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

What is the collective role of the JGA components in maintaining systemic blood pressure?

<p>The JGA components regulate blood pressure by controlling GFR, renin release, and erythropoietin secretion.</p> Signup and view all the answers

The modified vascular smooth muscle cells of the afferent arteriole within the JGA are also known as ______ cells.

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

Match the following:

<p>Low NaCl in tubular fluid = Dilation of afferent arteriole High NaCl in tubular fluid = Constriction of afferent arteriole Renin secretion = Activation of angiotensinogen</p> Signup and view all the answers

How does the JGA contribute to the long-term regulation of blood volume?

<p>By modulating GFR and renin release, which affects sodium and water reabsorption. (A)</p> Signup and view all the answers

Erythropoietin secreted by lacis cells primarily targets the kidneys to increase RBC production.

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

What is the significance of the location of the macula densa at the angle between the afferent and efferent arterioles?

<p>Its location allows it to directly sense changes in the tubular fluid and quickly influence glomerular filtration.</p> Signup and view all the answers

The renin-angiotensin system, activated by renin from JG cells, ultimately leads to increased blood pressure via the action of ______.

<p>angiotensin II</p> Signup and view all the answers

Flashcards

Juxtaglomerular Apparatus (JGA)

Modified structure where the thick ascending limb of the Loop of Henle contacts the glomerulus.

Macula Densa

Modified epithelial cells of the thick ascending limb of the Loop of Henle.

Macula Densa Function

Detects changes in ionic composition and flow rate of tubular fluid.

Tubuloglomerular Feedback

Mechanism by which macula densa regulates GFR.

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Juxtaglomerular (JG) Cells

Modified vascular smooth muscle cells in the afferent arteriole.

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JG Cells Function

Secretion of renin to regulate blood volume and pressure.

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Lacis Cells

Mesangial cells located outside the glomerulus, in JGA.

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Lacis Cells Function

Secrete small amounts of renin and erythropoietin.

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Renin Secretion Function

Activates the renin-angiotensin system to regulate blood pressure/volume.

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Tubuloglomerular Feedback Function

Sensing changes in tubular fluid and adjusting GFR.

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Hormone Secretion (by Lacis Cells) Function

Renin and erythropoietin secretion for blood pressure and RBC production.

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Study Notes

  • The Juxtaglomerular Apparatus (JGA) refers to the modified structure formed when the thick ascending limb of the Loop of Henle (LOH) comes into contact with the glomerulus of the same renal corpuscle.
  • Tubular and vascular components undergo structural modification to form the JGA.

Components of JGA:

  • The JGA consists of: macula densa, juxtaglomerular (JG) cells, and lacis cells.

Macula Densa

  • The macula densa is made of modified epithelial cells from the thick ascending limb of the LOH.
  • It is located at the angle between the afferent and efferent arterioles of the same nephron.
  • It appears as a densely packed area within the tubule.
  • It acts as a sensor and detects changes in ionic composition, especially NaCl.
  • It detects changes in the rate of flow of tubular fluid.
  • It sends feedback signals to the glomerulus to regulate glomerular filtration rate (GFR).
  • It plays a key role in the tubuloglomerular feedback mechanism.

Juxtaglomerular (JG) Cells

  • JG cells are primarily found in the tunica media of the afferent arteriole, with few in the efferent arteriole.
  • They are modified vascular smooth muscle cells with an epithelioid appearance.
  • They are also known as Polkissen cells.
  • They contain numerous secretory granules and are therefore called granular cells.
  • JG cells secrete renin, which activates the renin-angiotensin system (RAS).
  • The RAS is involved in the regulation of blood volume and pressure.

Lacis Cells

  • Lacis cells are located in the triangular space between the afferent arteriole, efferent arteriole, and macula densa.
  • They are extraglomerular mesangial cells.
  • They are agranular.
  • Lacis cells secrete small amounts of renin and erythropoietin.

Functions of JGA

Renin Secretion

  • JG cells secrete renin.
  • Renin activates the renin-angiotensin system, regulating blood pressure and blood volume.

Tubuloglomerular Feedback

  • The macula densa senses changes in the rate and composition of tubular fluid.
  • It sends signals to the glomerulus to adjust GFR accordingly.

Hormone Secretion

  • Lacis Cells secrete renin and erythropoietin.
  • These secretions contribute to blood pressure regulation and RBC production.

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