Kidney Structure and Function

Each nephron is an independent entity until the point at which its collecting ducts merge with other collecting ducts. The nephron consists of a glomerulus bowmans capsule arteriole( glomerulus, bowmans capsule, arteriole ) and tubule. The glomerulus is a cluster of blood vessels from which the plasma filtrate originates. The tubule is an epithelial structure consisting of many subdivisions including the PCT, thin descending limb, thick ascending limb and the DCT.

The control of blood flow in the kidney occurs by:
1. Myogenic Response Neurogenic Response Vascular Response( Myogenic Response, Neurogenic Response, Vascular Response )- Afferent arterioles have an ability to respond to changes in vessel circumference by contracting or relaxing Mechanism in response to opening of stretch-activated voltage gated( stretch-activated, voltage gated ) non-selective cation channels, depolarising the cell and leading to an influx of calcium. sodium potassium( calcium., sodium, potassium )
2. Tubuloglomerular Feedback Juxtamedullary feedback( Tubuloglomerular Feedback, Juxtamedullary feedback )
The filtrate is detected by the Juxtaglomerular apparatus (macula densa cells) and in response to an increase in GFR, translate this into contraction of the afferent efferent( afferent, efferent ) arteriole. The JGA Na-K-ATPase pump( JGA, Na-K-ATPase pump ) mediates this response.

Factors that increase sensitivity of TGF are: volume contraction, adenosine cAMP Endothlelin( adenosine, cAMP, Endothlelin ), PGE2, TXA2, Ang 2.
Factors that decrease the sensitivity of TGF are: volume expansion, ANP Adenosine Endothelin( ANP, Adenosine, Endothelin ), NO, cAMP, PGI2,

The descending limb of the LOH is highly permeable impermeable( permeable, impermeable ) to water but does not extrude sodium potassium( sodium, potassium ) for reabsorption. The thick ascending limb of the LOH actively passively( actively, passively ) transports sodium and other ions out of the tubular lumen into the interstitium, thus creating a counter-current gradient. Na+ and Cl- reabsorption in the ascending limb is both passive and active (Na/K/Cl-) cotransporter. The filtrate is 100m 200m 300m( 100m, 200m, 300m ) OSM at the DCT. Urea recycling contributes to the medually osmotic gradient. The urea is unable to leave ascending limb of LOH but is transported by facilitated diffusion in the collecting tubule descending limb( collecting tubule, descending limb ), into the interstitium.
The vasa-recta nephron( vasa-recta, nephron ) shape and slow blood flow protects this gradient.