juxta glomerular apparatus

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JUXTA GLOMERULAR APPARATUS WAN ‘AINUL YAQEEN BT WAN ZAMDAN (3207) MAS AMIRA BINTI ABD GHANI (3084) NUR AISYAH BINTI ABAS (3222) NADIAH BINTI ZAKWAN (3197) FASIHAH BINTI MAKETAR (3083)

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Page 1: Juxta Glomerular Apparatus

JUXTA GLOMERULA

R APPARATUS

WAN ‘AINUL YAQEEN BT WAN ZAMDAN

(3207)

MAS AMIRA BINTI ABD GHANI

(3084)

NUR AISYAH BINTI ABAS

(3222)

NADIAH BINTI ZAKWAN

(3197)

FASIHAH BINTI MAKETAR

(3083)

Page 2: Juxta Glomerular Apparatus

Macula densa

Microscopic appearance:

Tall columnar epithelial cells with their most prominent feature being tall and having elongated nuclei.

Appear darker in microscopic preparations, hence the name  macula densa.

No basemant membrane. Golgi apparatus is present between nucleus and base of cell.

Thickening in the wall of distal convoluted tubule of kidney, that consist of a group closely packed specialized cells of modified epithelial, where it is in contact with afferent arteriole and lies in direct opposition of juxta-glomerular cells, just before it enters the glomerulus.

Function:

Macula densa is salt sensors that generate paracrine chemical signals in the juxtaglomerular apparatus to control vital kidney functions including renal blood flow, glomerular filtration, and renin release.

Control renin release by relaying information about sodium (Na) concentration in the fluid passing through convoluted tubule to the renin-producing juxta-glomerular cells of the afferent arteriole. It is part of negative-feedback system of sodium.

Renin is the rate-limiting step in the activation of the renin-angiotensin system, a key modulator of body fluid homeostasis.

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JUXTAGLOMERULAR CELLS

The juxtaglomerular cells (JG cells, or granular cells) are cells in the kidney that synthesize, store, and secrete the enzyme renin. They are specialized smooth muscle cells in the wall of the afferent arteriole (and sometimes the efferent arteriole) that delivers blood to the glomerulus. In synthesizing renin, they play a critical role in the renin-angiotensin system and thus in renal autoregulation, the self-governance of the kidney.

In appropriately stained slides by, juxtaglomerular cells are distinguished by their granulated cytoplasm.

Similar to cardiac tissue, juxtaglomerular cells harbor β1 adrenergic receptors. When stimulated by epinephrine or norepinephrine, these receptors induce the secretion of renin. These cells also respond directly to a decrease in systemic blood pressure which is manifested as a lower renal perfusion pressure.

JG cells

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Renal corpuscle. Juxtaglomerular cells are #6.

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LACIS CELLS (ALSO KNOWN AS MESANGIAL CELLS)

Definitions:● One of the cells of the juxtaglomerular complex found at the vascular pole of the renal corpuscle.

Structure :● Flat, elongated cells with extensive fine cytoplasmic processes● Consists of the epithelioid cells (granular cells) and agranular cells. ● These agranular Lacis cells are sometimes being referred to also as :- -Goormaghtigh cells -Polkissen cells [polar cushion cells], or -Extraglomerular mesangial cells. ● Possess gap junctions, which exist between themselves and between Lacis cells and mesangial cells that have been considered as modified smooth musle cells

Site :● Found outside the kidney glomerulus near the macula● Bound laterally by afferent and efferent arterioles

Functions :● Most likely function as supportive cells, ● Transfer information about sodium chloride tubular load to the granular cells ● May be involved in tubuloglomerular feedback regulation

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Function of juxtaglomerular apparatus

Function of each cells of JGA :

1) Macula densa cells (Na+ sensors) of Distal Convoluted Tubule (DCT) which function as chemoreceptors to sense changes in the solute concentration and flow rate of filtrate.

2) Juxtaglomerular cells (modified smooth muscle cells) of afferent arteriole including renin containing (synthesizes and stores renin) and sympathetically innervated granulated cells which function as mechanoreceptors to sense blood pressure.

3) Juxtaglomerular/Extraglomerular mesangial cells (Lacis cells) forming connections via actin and microtubules which allow for selective vasoconstriction/vasodilation of the renal afferent and efferent arterioles with mesangial cell contraction.

Functions of Juxtaglomerlar Apparatus (JGA):

1. Regulation of blood pressure- Macula densa acts as chemoreceptor which is stimulated by

low sodium chloride (NaCl) level of fluid in the renal tubule- Macula densa stimulates JG cells to secrete renin hormone- Renin hormone converts angiotensinogen in the blood into

angiotensinogen I, which converted to angiotensinogen II, which is a vasoconstrictor (hypertensive) substance.

2. Secretion of erythropoietin factor- Stimulate development of erythrocytes in the bone marrow.

3. Local transmission of Tubuloglomerular Feedback (TGF) at its own nephron via angiotensin II (AT II)

- The tubuloglomerular feedback mechanism has 2 components that act together to control GFR:

i. Afferent arteriolar feedback mechanismii. Efferent arteriolar feedback mechanism

- Increased renal arterial pressure leads to an increased delivery of fluid (increased osmolality or increased flow rate) to the macula densa. The macula densa senses the

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load and causes constriction of nearby afferent arteriole, increasing the resistance. This will return osmolality and filtrate flow rate to normal.

- Decreased renal arterial pressure leads to a decreased delivery of fluid (decreased osmolality or decreased flow rate) to the macula densa. The macula densa senses this and causes:

i. Vasodilation of afferent arterioleii. Constriction of efferent arteriole as a result of renin

release by stimulated JG cells

4. Systemic production of Angiotensin II (AT II) as part of Renin-Angiotensin-Aldosterone System (RAAS)

- When systemic blood pressure decreases, there is decreased stretch of JG cells, which leads to their release of

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renin. Renin release causes the activation of renin-angiotensin mechanism, which ultimately leads to an increased blood pressure.

REFERENCE :

Macula densa :

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Text Book of Histology Part II http://jasn.asnjournals.org/content/21/7/1093.abstract http://www.merriam-webster.com/medical/macula%20densa

Juxtaglomerular Cells :

Text Book of Histology Part II http://en.wikipedia.org/wiki/Juxtaglomerular_cel l

Lacis Cells :

Text Book of Histology Part II http://www.copewithcytokines.de/cope.cgi?key=Lacis%20cells http://www.vetmed.vt.edu/education/curriculum/vm8054/labs/lab23/

lab23.htm

Function of JGA :

Text Book of Histology Part II http://medchrome.com/basic-science/physiology/function-

juxtaglomerular-apparatus-jga/

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