Scheme of renal tubule and its vascular supply. (Loop of Henle visible center-left.)
Details
Precursor
Metanphrogenic blastema
Identifiers
Latin
Ansa nephroni
MeSH
D008138
FMA
17698
Anatomical terminology
[edit on Wikidata]
In the kidney, the loop of Henle (English: /ˈhɛnli/) (or Henle's loop, Henle loop,[1]nephron loop[2] or its Latin counterpart ansa nephroni) is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer, the German anatomist Friedrich Gustav Jakob Henle, the loop of Henle's main function is to create a concentration gradient in the medulla of the kidney.[3]
By means of a countercurrent multiplier system, which uses electrolyte pumps, the loop of Henle creates an area of high urea concentration deep in the medulla, near the papillary duct in the collecting duct system. Water present in the filtrate in the papillary duct flows through aquaporin channels out of the duct, moving passively down its concentration gradient. This process reabsorbs water and creates a concentrated urine for excretion.[3]
Contents
1Structure
1.1Blood supply
2Physiology
3Additional images
4References
5Further reading
6External links
Structure
The loop of Henle can be divided into four parts:
Thin descending limb of loop of Henle
The thin descending limb has low permeability to ions and urea, while being highly permeable to water. The loop has a sharp bend in the renal medulla going from descending to ascending thin limb.
Thin ascending limb of loop of Henle
The thin ascending limb is impermeable to water, but it is permeable to ions.
Ascending limb of loop of Henle
Sodium (Na+), potassium (K+) and chloride (Cl−) ions are reabsorbed from the urine by secondary active transport by a Na-K-Cl cotransporter (NKCC2). The electrical and concentration gradient drives more reabsorption of Na+, as well as other cations such as magnesium (Mg2+) and calcium (Ca2+).
Cortical thick ascending limb
The cortical thick ascending limb drains urine into the distal convoluted tubule.[3]
The tissue type of the loop is simple squamous epithelium. The "thick" and "thin" terminology does not refer to the size of the lumen, but to the size of the epithelial cells.[4] The loop is also sometimes called the Nephron loop.
Blood supply
Counter current multiplier diagram
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 multiplier 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 capillaries. 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.[citation needed]
As well, blood in the vasa recta still has large proteins and ions which were not filtered through the glomerulus. This provides an oncotic pressure for ions to enter the vasa recta from the interstitium.[citation needed]
The main function of the loop of Henle is to set up a concentration gradient.[citation needed]
Physiology
The descending loop of Henle receives isotonic (300 mOsm/L) fluid from the proximal convoluted tubule (PCT). The fluid is isotonic because as ions are reabsorbed by the gradient time system, water is also reabsorbed maintaining the osmolarity of the fluid in the PCT. Substances reabsorbed in the PCT include urea, water, potassium, sodium, chloride, glucose, amino acids, lactate, phosphate, and bicarbonate. Since water is also reabsorbed the volume of fluid in the loop of Henle is less than the PCT, approximately one-third of the original volume.
The interstitium of the kidney increases in osmolarity outside as the loop of Henle descends from 600 mOsm/L in the outer medulla of the kidney to 1200 mOsm/L in the inner medulla. The descending portion of the loop of Henle is extremely permeable to water and is less permeable to ions, therefore water is easily reabsorbed here and solutes are not readily reabsorbed. The 300 mOsm/L fluid from the loop loses water to the higher concentration outside the loop and increases in tonicity until it reaches its maximum at the bottom of the loop. This area represents the highest concentration in the nephron, but the collecting duct can reach this same tonicity with maximum ADH effect.[3]
The ascending limb of the loop of Henle receives an even lower volume of fluid and has different characteristics compared to the descending limb. In the ascending portion, the loop becomes impermeable to water and the cells of the loop actively reabsorb solutes from the luminal fluid; therefore water is not reabsorbed and ions are readily reabsorbed. As ions leave the lumen via the Na-K-2Cl symporter and the Na-H antiporter, the concentration becomes more and more hypotonic until it reaches approximately 100-150 mOsm/L. The ascending limb is also called the diluting segment of the nephron because of its ability to dilute the fluid in the loop from 1200 mOsm/L to 100 mOsm/L.[3]
Flow of the fluid through the entire loop of Henle is considered slow. As flow increases, the ability of the loop to maintain its osmolar gradient is reduced. The vasa recta (capillary loops) also have a slow flow as well. Increases in vasa recta flow wash away metabolites and cause the medulla to lose osmolarity as well. Increases in flow will disrupt the kidney's ability to form concentrated urine.[3]
Overall the loop of Henle reabsorbs around 25% of filtered ions and 20% of the filtered water in a normal kidney. These ions are mostly Na+, Cl−, K+, Ca2+and HCO3−. The powering force is the Na/K ATPase on the basolateral membrane which maintains the ion concentrations inside the cells. On the luminal membrane, Na enters the cells passively; using the Na-K-2Cl symporter. Then the Na/K ATPase will pump 3 Na out into the peritubular fluid and 2 K into the cell on the non-lumen side of the cell. This gives the lumen of the fluid in the loop a positive charge in comparison and creates a Na concentration gradient, which both push more Na into the cell via the Na-H antiporter. The hydrogen ion for the antiporter comes from the enzyme carbonic anhydrase, which takes water and carbon dioxide and forms bicarbonate and a hydrogen ion. The hydrogen ion is exchanged for the Na in the tubular fluid of the loop of Henle.[3]
Additional images
Transverse section of pyramidal substance of kidney of pig, the bloodvessels of which are injected.
Diagram of physiological functions of nephron, including the loop of Henle.
References
^Elsevier, Dorland's illustrated Medical Dictionary, Elsevier.
^"THh306".
^ abcdefgDunn R. B.; Kudrath W.; Passo S.S.; Wilson L.B. (2011). "8". Kaplan USMLE Step 1 Physiology Lecture Notes. pp. 209–223.
^Human Anatomy 7th edition (p.705)
Further reading
Douglas C. Eaton; John Pooler (2004). Vander's Renal Physiology (6th ed.). McGraw-Hill Medical. ISBN 0-07-135728-9.
Lote, Christopher J. (2000). "The loop of Henle, distal tubing and collecting duct". Principles of Renal Physiology. Springer. p. 70. ISBN 978-0-7923-6178-7.
External links
Loop of Henle physiology
v
t
e
Anatomy of the urinary system
Kidneys
Layers
Fascia
Capsule
Cortex
column
Medulla
sinus
pyramids
medullary interstitium
Lobe
Cortical lobule
Medullary ray
Nephron
Circulation
Arteries
Renal artery
segmental
interlobar
arcuate
interlobular
afferent
Veins
Renal vein
Peritubular capillaries
Vasa recta
arcuate
interlobar
efferent
Nephron
Renal corpuscle
Glomerulus
Bowman's capsule
Glomerular basement membrane
Podocyte
Filtration slits
Mesangium
Intraglomerular mesangial cell
Renal tubule
Proximal convoluted tubule
Loop of Henle
Descending
Thin ascending
Thick ascending
Distal convoluted tubule
Collecting duct system
Connecting tubule
Papillary duct
Tubular fluid
Renal papilla
Minor calyx
Major calyx
Renal pelvis
Juxtaglomerular apparatus
Macula densa
Juxtaglomerular cells
Mesangium
Extraglomerular mesangial cell
Ureters
Ureteropelvic junction
Bladder
Circulation
Vesical arteries
Vesical veins
Vaginal artery (female)
Detrusor muscle
Median umbilical ligament
Mucosa
Submucosa
Trigone
Urethra
Internal urethral orifice
Urethral sphincters
External
male
female
Internal
Male urethra
pre-prostatic
prostatic
intermediate
spongy
navicular fossa
Lacunae of Morgagni
urethral gland
Urinary meatus
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…process involves two basic steps: (1) calcium is reabsorbed passively in the proximal tubule and loop of Henle down the favorable electrochemical gradients created by sodium and water reabsorption; and (2) …
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loop of Henle n. See nephronic loop. loop of Henle [hen′lē] Etymology: ME, loupe; [Friedrich Gustave Henle, German anatomist, 1809-1885 the U-shaped part of a renal tubule, consisting of a thin descending limb and a thick ...
