Loop of Henle
Scheme of renal tubule and its vascular supply. (Loop of Henle visible center-left.)
Latin	ansa nephroni
Gray's	subject #253 1223
Precursor	Metanephric blastema
MeSH	loop+of+henle

In the kidney, the loop of Henle (or Henle's loop or ansa nephroni) is the portion of the nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. The loop has a hairpin bend in the renal medulla. The main function of this structure is to create a concentration gradient in the medulla of the kidney. By means of a countercurrent multiplier system, which utilizes sodium pumps, it creates an area of high sodium concentration deep in the medulla, near the collecting duct. Water present in the filtrate in the collecting duct flows through aquaporin channels out of the collecting duct, moving passively down its concentration gradient. This process reabsorbs water and creates a concentrated urine for excretion. It is named after its discovery by F. G. J. Henle.

Contents 1 Components 2 Blood supply 3 Additional images 4 References 5 External links

[edit] Components

It can be divided into five parts:

thick descending limb of loop of Henle	The descending limb has low permeability to ions and urea, while being highly permeable to water.
thin descending limb of loop of Henle	The descending limb has low permeability to ions and urea, while being highly permeable to water.
thin ascending limb of loop of Henle	The thin ascending limb is not permeable to water, but it is permeable to ions.
medullary thick ascending limb of loop of Henle	Sodium (Na+), potassium (K+) and chloride (Cl-) ions are reabsorbed from the urine by active transport. K+ is passively transported along its concentration gradient through a K+ channel in the apical aspect of the cells, back into the lumen of the ascending limb. This K+ "leak" generates a positive electrochemical potential difference in the lumen. The electrical gradient drives more reabsorption of Na+, as well as other cations such as magnesium (Mg2+) and importantly calcium (Ca2+).
cortical thick ascending limb	The cortical thick ascending limb drains urine into the distal convoluted tubule.

[edit] Blood supply

The loop of Henle is supplied by blood in a series of straight capillaries descending from the cortical efferent arterioles. These capillaries (called the vasa recta; recta is from the Latin for "straight") also have a countercurrent exchange mechanism that prevents washout of solutes from the medulla, thereby maintaining the medullary concentration. As water is osmotically driven from the descending limb into the interstitium, it readily enters the vasa recta. The low bloodflow through the vasa recta allows time for osmotic equilibration, and can be altered by changing the resistance of the vessels' efferent arterioles.

Also, the vasa recta still has the large proteins and ions which were not filtered through the glomerulus, which provides an oncotic pressure for ions to enter the vasa recta from the interstitium.

The main function of the Loop of Henle is to set up a concentration gradient.

[edit] Additional images

Transverse section of pyramidal substance of kidney of pig, the bloodvessels of which are injected.

[edit] References

• Douglas C. Eaton, John Pooler (2004). Vander's Renal Physiology (6th edition ed.). McGraw-Hill Medical. ISBN 0-07-135728-9. 

[edit] External links

• Loop of Henle physiology

v • d • e Anatomy: urinary system (TA A08, GA 11.1215) Abdomen Kidneys Layers Renal fascia • Renal capsule • Renal cortex  (Renal column) • Renal medulla (Renal sinus, Renal pyramids, medullary interstitium) • Renal lobe • Cortical lobule • Medullary ray • Nephron Afferent circulation Renal artery → Segmental arteries → Interlobar arteries → Arcuate arteries → Interlobular arteries → Afferent arterioles → Renal corpuscle (Glomerulus, Bowman's capsule) Renal tubule Proximal tubule → Loop of Henle (Descending, Thin ascending, Thick ascending) → Distal convoluted tubule → Connecting tubule → Collecting ducts aka Duct of Belini → Renal papilla → Minor calyx → Major calyx → Renal pelvis Efferent circulation Glomerulus → Efferent arterioles → Peritubular capillaries / Vasa recta → Arcuate vein → Interlobar veins → Renal vein Juxtaglomerular apparatus Macula densa • Juxtaglomerular cells • Mesangium/Extraglomerular mesangial cell Filtration Glomerular basement membrane • Podocyte • Filtration slits • Mesangium/Intraglomerular mesangial cell • Tubular fluid Ureters Orifice of ureter Pelvis Bladder Uvula • Trigone • Detrusor • Apex • Neck Urethra Urethral sphincters (External sphincter muscle of male urethra, External sphincter muscle of female urethra, Internal sphincter muscle of urethra) urinary system navs: anat/physio/dev, noncongen/acid+base/congen/neoplasia, symptoms+signs/eponymous, proc