Bowman's Capsule and the glomerulus of the kidney (600X)
The renal corpuscle consists of two main parts:
- Bowman's Capsule (Glomerular Capsule): This is a double-walled, cup-shaped structure that surrounds and encases the glomerulus. The inner layer of Bowman's capsule is composed of specialized cells called podocytes, which have foot-like extensions (pedicels) that wrap around the capillaries of the glomerulus. The outer layer of Bowman's capsule is formed by simple squamous epithelial cells.
- Glomerulus: The glomerulus is a network of tiny, fenestrated (porous) capillaries that arise from the afferent arteriole and drain into the efferent arteriole. The glomerulus is responsible for filtering blood to initiate the formation of urine. The high pressure in the glomerulus, along with its fenestrated capillaries, allows small molecules and solutes to be forced out of the blood and into Bowman's capsule. This process is known as glomerular filtration.
The layers of cells which the filtrate from the blood must pass through in order to enter the urinary space is called the urine barrier. It consists of endothelial cells belonging to capillaries in the glomerulus, a well-developed basal membrane and protuberances of podocytes/membranes.
The inner layer (visceral layer) from Bowman's capsule consists of very special epithelial cells with a complicated structure. These cells are called podocytes.
Mesangial cells are a special star-shaped cell type found in the glomerulus. Their function has not been fully established, but they are thought to function as an intraglomular skeleton and provide support. In addition, they can also phagocyte foreign bodies.