Glomerulus (kidney)

Glomerulus
Glomerular Physiology.png
Looped capillaries of glomerulus between the arterioles
Details
Precursor Metanephric blastema
Identifiers
Latin glomerulus renalis
MeSH A05.810.453.324.359
Dorlands
/Elsevier
g_07/12394744
FMA 15624
Anatomical terminology

The glomerulus ( RP s/, US: s/), plural glomeruli, is a network of capillaries known as a tuft, located at the beginning of a nephron in the kidney. The tuft is structurally supported by intraglomerular mesangial cells. The blood is filtered across the capillary walls of this tuft through the glomerular filtration barrier, which yields its filtrate of water and soluble substances to a cup-like sac known as Bowman's capsule. The filtrate then enters the renal tubule, of the nephron.

The glomerulus receives its blood supply from an afferent arteriole of the renal arterial circulation. Unlike most capillary beds, the glomerular capillaries exit into efferent arterioles rather than venules. The resistance of the efferent arterioles causes sufficient hydrostatic pressure within the glomerulus to provide the force for ultrafiltration.

The glomerulus and its surrounding Bowman's capsule constitute a renal corpuscle, the basic filtration unit of the kidney. [1] The rate at which blood is filtered through all of the glomeruli, and thus the measure of the overall renal function, is the glomerular filtration rate (GFR).

Structure

The glomerulus is a tuft of small blood vessels called capillaries located within Bowman's capsule within the kidney. [1] Glomerular mesangial cells structurally support the tufts. Blood enters the capillaries of the glomerulus by a single arteriole called an afferent arteriole and leaves by an efferent arteriole. [2] The capillaries consist of a tube lined by endothelial cells with a central lumen. The walls have a unique structure: there are pores between the cells that allow water and soluble substances to exit, and after passing through the glomerular basement membrane, and between podocyte foot processes, enter the capsule as ultrafiltrate.

Blood supply

Figure 2: (a) Diagram of the juxtaglomerular apparatus: it has specialized cells working as a unit which monitor the sodiujuxtaglomerular apparatus: it has three types of specm content of the fluid in the distal convoluted tubule (not labelled - it's the tubule on the left) and adjust the glomerular filtration rate and the rate of renin release. (b) Micrograph showing the glomerulus and surrounding structures.

Lining

Scanning electron microscope view of the inner surface of an opened (broken) capillary with fenestrae visible.(100,000x magnification)

Capillaries of the glomerulus are lined by endothelial cells. These contain numerous pores - also called fenestrae) - 50–100 nm in diameter. [3] Unlike those of other capillaries with fenestrations, these fenestrations are not spanned by diaphragms. [3] They allow for the filtration of fluid, blood plasma solutes and protein, at the same time preventing the filtration of red blood cells, white blood cells, and platelets.

The glomerulus has a glomerular basement membrane (GBM) consisting mainly of laminins, type IV collagen, agrin and nidogen, which are synthesized and secreted by both endothelial cells and podocytes: thus the GBM is sandwiched between the glomerular capillaries and the podocytes. The GBM is 250–400  nm in thickness, which is thicker than basement membranes of other tissue. It is a barrier to blood proteins such as albumin and globulin. [4]

The part of the podocyte in contact with the GBM is called a podocyte foot process or pedicle (Fig. 3): there are gaps between the foot processes through which the filtrate flows into Bowman's space of the capsule. [3] . The space between adjacent podocyte foot processes is spanned by slit diaphragms consisting of a mat of proteins, including podocin and nephrin. In addition, foot processes have a negatively charged coat ( glycocalyx) that repels negatively charged molecules such as serum albumin.

Other Languages
العربية: كبيبة (كلية)
български: Гломерула
čeština: Glomerulus
فارسی: گلومرول
한국어: 사구체
italiano: Glomerulo
עברית: פקעית
Кыргызча: Гломерула
Nederlands: Glomerulus
日本語: 糸球体
norsk: Glomerulus
português: Glomérulo
slovenščina: Ledvični glomerul
svenska: Glomerulus
粵語: 腎小球
中文: 腎小球