Kidney Essay

Each kidney contains over one million microscopic filtering units called nephrons. Urea, along with salt, water and glucose is extracted from the blood in the kidney by a process called ultrafiltration. Blood that passes the top of the nephron is under high pressure, so fluid is forced through the sieve-like capillaries and into the capsule. This fluid is called the filtrate. It does not contain any blood cells or larger proteins, as they are too big to pass out of the capillaries and into the capsule. Much of what has been filtered out needs to be returned to the blood. They are too precious to lose and so the next process is called selective reabsorption.
Each nephron is divided into a number of distinct regions which are renal capsule, first

Ultrafiltration is a process that takes place in the renal capsule. Water soluble substances pass from the blood in to the lumen of the renal capsule. The filtrate, which is now in the nephron, contains excretory products but also substances useful to the body. A renal capsule is a double walled cup shape structure surrounding a knot of capillaries called glomerulus. The space inside the renal capsule is called the lumen. The capillary walls of the glomerulus are composed of a single layer of endothelial cells with spaces between the cells of between 50-100 nm. These cells sit on a basement membrane which is the filtration membrane. It’s the only continuous structure separating the blood in the capillary from the lumen of the renal capsule. The cells of the inner layer in the renal capsule do not fit tightly together. These cells called podocytes, have many projections in contact with the basement membrane. Between the projections are gaps through which the filtrate can flow. The only barrier between the lumen of the capillary and the lumen of the renal capsule is the basement membrane. This is the filter which is preventing the passage of cells and large molecules, but mainly proteins from the