3.12.2. Structure of kidney
Structure of kidney
1 million nephrons
3 types of nephrones
- Superficial cortical nephrons
* Short loop of Henle
- Midcortical nephrons
- Juxtamedullary nephrons
* All have long loops of Henle, extending into the inner medulla
* Difference in loop lengths are all due to variabilities in thin descending and ascending limbs
* All ascending limbs change from thin to thick at the junction of inner and outer medulla [AV6:p91]
- Before distal convoluted tubules, the cells in any given segments are homogenous.
- Beginning from DCT, 2 cell types are found in most of the remaining segments
* Principle cells
* Intercalated cells (A and B)
- Later portion of medullary collecting duct contains neither type and has a distinct cell type called inner medullary collecting duct cells.
- Nephrons remain separate until cortical collecting duct, where tubules from several nephrons merge
- Medullary - outer and inner
- Beginning of the thick ascending limb mark the border of outer and inner medulla.
- i.e. No thick ascending limb in the inner medulla
- Granular cells (i.e. JG cells)
* Secretes renin
* Located in the media of the afferent arterioles as they enter glomeruli
- Macula densa
* Monitors tubular content
* Marks the end of the thick ascending limb and the beginning of distal convoluted tubule.
* Essentially modified tubular epithelium
- Extraglomerular mesangial cells
* [WG21:p461] aka lacis cells
- Endothelial cells of renal capillary have large fenestrae
- Epithelial cells - podocytes, with foot processes (pedicels)
- Pedicels interdigitate with other pedicels from adjacent podocytes
- Slit diaphragm covers the space between pedicels
- Glomerular mesangial cells act as phagocytes
- Glomeruli, and interlobar, arcuate, and interlobular arteries, are found only in the cortex.
- Vasa recta are found only in medulla
- Descending vasa recta has smooth muscles at the beginning
- Ascending vasa recta has fenestrated endothelium like in glomerular capillaries.
- Most of glomerular blood flow continue on in peritubular capillaries after leaving efferent arterioles
- Rich sympathetic innervation
- No significant parasympathetic innervation
- Distributed to
* Afferent arteriole
* Efferent arteriole
* JG apparatus
- From sympathetic celiac plexus