Glomerulus

The nephron is the functional unit of the kidney. The nephron accomplishes:

1.	The initial filtration of the blood
2.	The selective reabsorption of the useful substances
3.	The secretion of the unwanted substances into the urine

The tubular component starts with the glomerular (Bowman's) capsule. The glomerular capsule encompasses the glomerular tuft (capillaries), like a hand wrapped round a ball. The capsule is composed of two layers of epithelium - an outer (parietal) layer of simple squamous epithelial cells and an inner (visceral) layer composed of specialised epithelial cells called podocytes, which surround the glomerular capillaries.

The glomerular filtrate has to pass through the following layers

1.	Endothelium of the glomerulus containing tiny pores or fenestrae.
2.	The basement membrane of the glomerulus.
3.	Visceral layer of the glomerulus. These cells are large nucleated cells with several cell processes. These processes or pedicels, cover the basement membrane. The small regions between the pedicels where basement membrane is exposed are called filtration slits.

Thus by the combination of the fenestrae and the filtration slits, on small molecules (not larger than the albumin molecule) are able to pass through. This membrane acts as a filtration barrier. In this way the initial glomerular filtrate resembles the plasma in composition without the plasma proteins.