Francais | English | Espanõl

From Wikipedia, the free encyclopedia

In the kidney, the macula densa is an area of closely packed specialized cells lining the region of the distal convoluted tubule lying next to the glomerular vascular pole. The cells of the macula densa are sensitive to the ionic content and water volume of the fluid in the DCT, producing molecular signals that promote renin secretion by other cells of the juxtaglomerular apparatus.<ref>Junqueira, Luiz C., Jose Carneiro (2003). Basic Histology. McGraw-Hill. ISBN 0-07-141365.</ref> The release of renin is an essential component of the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and volume.

The cells of the macula densa cells are taller and have more prominent nuclei than surrounding of the distal convoluted tubule. The close proximity and prominence of the nuclei cause this segment of the DCT's wall to appear darker in microscopic preparations, hence the name macula densa.

[edit] Function

A decrease in blood pressure results in a decreased concentration of sodium ions in the distal convoluted tubule. (This is due to reduced filtration by the glomerulus: less filtrate is expelled into Bowman's space and the proximal convoluted tubule; the resulting fluid reaching the distal convoluted tubule will have a lower sodium concentration after the water is removed.) In response, the macula densa cells release prostaglandins, which triggers granular juxtaglomerular cells lining the afferent arterioles to release renin into the bloodstream. (The juxtoglomerular cells can also release renin independently of the macula densa, as they are also triggered by baroreceptors lining the arterioles, and release renin if a fall in blood pressure in the arterioles is detected.)

[edit] External links

• Histology at BU 16010loa
• Organology at UC Davis Urinary/mammal/cortex1/cortex5 - "Mammal, kidney cortex (LM, Medium)"
• Physiology at MCG 7/7ch03/7ch03p17 - "The Nephron: Juxtaglomerular Apparatus"

[edit] References

<references/>

Urinary system - Kidney - edit
Renal capsule | Renal cortex | Renal medulla (Renal sinus, Renal pyramids) | Renal calyx | Renal pelvis
Nephron - Renal corpuscle (Glomerulus, Bowman's capsule) → Proximal tubule → Loop of Henle → Distal convoluted tubule → Collecting ducts Juxtaglomerular apparatus (Macula densa, Juxtaglomerular cells, Extraglomerular mesangial cells) Renal circulation - Renal artery → Interlobar arteries → Arcuate arteries → Cortical radial arteries → Afferent arterioles → Glomerulus → Efferent arterioles → Vasa recta → Arcuate vein→ Renal vein
Renal physiology
Filtration - Ultrafiltration | Countercurrent exchange Hormones effecting filtration - Antidiuretic hormone (ADH) | Aldosterone | Atrial natriuretic peptide Endocrine - Renin | Erythropoietin (EPO) | Calcitriol (Active vitamin D) | Prostaglandins
Assessing Renal function / Measures of dialysis
Glomerular filtration rate | Creatinine clearance | Renal clearance ratio | Urea reduction ratio | Kt/V | Standardized Kt/V | Hemodialysis product