The filtered blood leaves through the renal veins. Each kidney consists of an outer renal cortex, an inner renal medulla, and a renal pelvis. Blood is filtered in the renal cortex. The renal medulla contains the renal pyramids, where urine formation takes place.
Urine passes from the renal pyramids into the renal pelvis. This funnel-shaped structure occupies the central cavity of each kidney and then narrows as it extends out to join the ureter. Urine drains from the renal pelvis into the ureter.
Each kidney contains over 1 million tiny structures called nephrons. The nephrons are located partly in the cortex and partly inside the renal pyramids, where the nephron tubules make up most of the pyramid mass. Nephrons perform the primary function of the kidneys: regulating the concentration of water and other substances in the body.
Portions of the renal cortex extend into the spaces between adjacent pyramids to form renal columns. The cortex and medulla make up the parenchyma , or functional tissue, of the kidney.
The central region of the kidney contains the renal pelvis , which is located in the renal sinus, and is continuous with the ureter. The renal pelvis is a large cavity that collects the urine as it is produced. The periphery of the renal pelvis is interrupted by cuplike projections called calyces. A minor calyx surrounds the renal papillae of each pyramid and collects urine from that pyramid.
Several minor calyces converge to form a major calyx. From the major calyces, the urine flows into the renal pelvis; and from there, it flows into the ureter. The arteries, veins, and nerves that supply the kidney enter and exit at the renal hilum. Renal blood supply starts with the branching of the aorta into the renal arteries which are each named based on the region of the kidney they pass through and ends with the exiting of the renal veins to join the inferior vena cava.
The renal arteries split into several segmental arteries upon entering the kidneys. Each segmental artery splits further into several interlobar arteries and enters the renal columns, which supply the renal lobes. The interlobar arteries split at the junction of the renal cortex and medulla to form the arcuate arteries.
Cortical radiate arteries , as the name suggests, radiate out from the arcuate arteries. The cortical radiate arteries branch into numerous afferent arterioles, and then enter the capillaries supplying the nephrons.
Veins trace the path of the arteries and have similar names, except there are no segmental veins. As mentioned previously, the functional unit of the kidney is the nephron, illustrated in Figure 3.
Each kidney is made up of over one million nephrons that dot the renal cortex, giving it a granular appearance when sectioned sagittally. There are two types of nephrons— cortical nephrons 85 percent , which are deep in the renal cortex, and juxtamedullary nephrons 15 percent , which lie in the renal cortex close to the renal medulla. A nephron consists of three parts—a renal corpuscle , a renal tubule , and the associated capillary network, which originates from the cortical radiate arteries.
Figure 3. The nephron is the functional unit of the kidney. The glomerulus and convoluted tubules are located in the kidney cortex, while collecting ducts are located in the pyramids of the medulla. The renal tubule is a long and convoluted structure that emerges from the glomerulus and can be divided into three parts based on function. The first part is called the proximal convoluted tubule PCT due to its proximity to the glomerulus; it stays in the renal cortex. The second part is called the loop of Henle , or nephritic loop, because it forms a loop with descending and ascending limbs that goes through the renal medulla.
The renal hilum is the area where the renal artery, renal vein and ureter enter the kidney. The nephrons are the millions of small tubes inside each kidney. Each nephron has 2 parts. Tubules are tiny tubes that collect the waste materials and chemicals from the blood moving through the kidney. The corpuscles contain a clump of tiny blood vessels called glomeruli that filter the blood as it moves through the kidney.
The waste products are passed through the tubules to the collecting ducts, which drain into the renal pelvis. The blood from the body enters the kidneys through the renal arteries.
Once in the kidney, the blood passes through the nephrons, where waste products and extra water are removed.
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