Description A - Renal corpuscle
B - Proximal tubule
C - Distal convoluted tubule
D - Juxtaglomerular apparatus
1. Basement membrane (Basal lamina)
2. Bowman's capsule - parietal layer 3. Bowman's capsule - visceral layer
3a. Pedicels (podocytes)
3b. Podocyte
4. Bowman's space (urinary space)
5a. Mesangium - Intraglomerular cell
5b. Mesangium - Extraglomerular cell 6. Granular cells (Juxtaglomerular cells)
7. Macula densa
8. Myocytes (smooth muscle)
9. Afferent arteriole
10. Glomerulus Capillaries 11. Efferent arteriole Distribution of bloodvessels in cortex of kidney. Latin corpusculum renis Gray's subject #253 1221 In the kidney, a renal corpuscle is the initial blood-filtering component of a nephron. It consists of two structures: a glomerulus and a Bowman's capsule. The glomerulus is a small tuft of capillaries
containing two cell types. Endothelial cells,
which have large fenestrae, are not
covered by diaphragms. Mesangial cells are
modified smooth muscle cells that lie
between the capillaries and the glomerulus. They regulate blood flow by
their contractile activity and secrete
extracellular matrix, prostaglandins, and
cytokines. Mesangial cells also have
phagocytic activity, removing proteins and
other molecules trapped in the glomerular basement membrane or filtration barrier.
The Bowman's capsule has an outer
parietal layer composed of simple
squamous epithelium. The visceral layer,
composed of modified simple squamous
epithelium, is lined by podocytes. Podocytes have foot processes, pedicels,
that wrap around glomerular capillaries.
These pedicels interdigitate with pedicels
of adjacent podocytes forming filtration
slits. The renal corpuscle filtration barrier is
composed of: the fenestrated endothelium
of glomerular capillaries, the fused basal
lamina of endothelial cells and podocytes,
and the filtration slits of the podocytes.
This barrier permits passage of water, ions, and small molecules from the bloodstream
into Bowman's space (the space between
the visceral and parietal layers). Large
and/or negatively charged proteins are
prevented from passing into Bowman's
space, thus retaining these proteins in the circulation. The basal lamina is composed
of 3 layers: lamina rara externa, lamina
densa, and lamina rara interna. The lamina
rara externa is adjacent to the podocyte
processes. The lamina densa is the central
layer consisting of type IV collagen and laminin. This layer acts as a selective
macromolecular filter, preventing the
passage of large protein molecules into
Bowman's space. The lamina rara interna is
adjacent to endothelial cells. This layer
contains heparan sulfate, a negatively charged glycosaminoglycan that
contributes to the electrostatic barrier of
the glomerular filter. There are two poles in the renal corpuscle,
a vascular pole, and a urinary pole. The
vascular pole is where the afferent and
efferent arterioles communicate with the
glomerulus. The urinary pole is where the
corpuscle opens into the lumen of the proximal convoluted tubule. Fluid from blood in the glomerulus is
collected in the Bowman's capsule to form
"glomerular filtrate", which is then further
processed along the nephron to form urine. Eponym A renal corpuscle is also known as a Malpighian corpuscle, named after Marcello Malpighi (1628–1694), an Italian physician and biologist. This name is not used widely anymore, probably to avoid confusion with
a Malpighian corpuscle in the spleen.
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