  in the kidney, a tubular structure called the nephron filters blood to form urine. at the beginning of the nephron, the renal glomerulus is a network (tuft) of capillaries that performs the first step of filtering blood. the glomerulus is surrounded by bowman's capsule. the blood plasma is filtered through the capillaries of the glomerulus into the bowman's capsule. the bowman's capsule empties the filtrate into a tubule that is also part of the nephron. a glomerulus receives its blood supply from an afferent arteriole of the renal circulation. unlike most other capillary beds, the glomerulus drains into an efferent arteriole rather than a venule. the resistance of these arterioles results in high pressure within the glomerulus, aiding the process of ultrafiltration, where fluids and soluble materials in the blood are forced out of the capillaries and into bowman's capsule. a 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 renal function, is the glomerular filtration rate (gfr). ==afferent circulation== thumb|600px|right|the juxtaglomerular apparatus allows specialized cells to monitor the composition of the fluid in the distal convoluted tubule and adjust the glomerular filtration rate. (b) this micrograph shows the glomerulus and surrounding structures. the afferent arteriole that supplies the capillaries of a glomerulus branches off an interlobular artery in the renal cortex. glomerular capillary pressure, and thus glomerular filtration rate, can be influenced by constriction or relaxation of the afferent arteriole, resulting in decreases or increases in pressure. as an example, one study involving rats found that having narrowed afferent arterioles contributed to the development of increased blood pressure.{{cite journal |last1=norrelund |fir
Kidney_anatomy