Glomerular capillary

The glomerulus (plural glomeruli), is a network of small blood vessels (capillaries) known as a tuft, located at the beginning of a nephron in the kidney. The tuft is structurally supported by the mesangium - the space between the blood vessels - made up of 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.Scanning electron microscope of a glomerulus in a mouse (1000x magnification)Scanning electron microscope of a glomerulus in a mouse (5000x magnification)Scanning Electron Microscope of a glomerulus in a mouse (10,000x magnification)Looped capillaries of glomerulus between the arterioles The glomerulus (plural glomeruli), is a network of small blood vessels (capillaries) known as a tuft, located at the beginning of a nephron in the kidney. The tuft is structurally supported by the mesangium - the space between the blood vessels - made up of 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. The rate at which blood is filtered through all of the glomeruli, and thus the measure of the overall kidney function, is the glomerular filtration rate (GFR). The glomerulus is a tuft of small blood vessels called capillaries located within Bowman's capsule within the kidney. 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. 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. Capillaries of the glomerulus are lined by endothelial cells. These contain numerous pores - also called fenestrae - 50–100 nm in diameter. Unlike those of other capillaries with fenestrations, these fenestrations are not spanned by diaphragms. 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. 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. . 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. The space between the capillaries of a glomerulus is the mesangium, occupied by intraglomerular mesangial cells. They are not part of the filtration barrier but are specialized pericytes that participate in the regulation of the filtration rate by contracting or expanding: they contain actin and myosin filaments to accomplish this. Some mesangial cells are in physical contact with capillaries, others are in physical contact with podocytes. There is two-way chemical cross talk among the mesangial cells, the capillaries, and the podocytes to fine-tune the GFR. 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.