Monday, November 23, 2009

Bowman's Capsule

The Bowman's capsule, or glomerular capsule, is a cup-like sac at the beginning of the renal tubule of a nephron in the kidney. The Bowman's capsule encloses and contains the glomerulus, which is the primary filtering device of the nephron. Blood is transported into the glomerulus contained in the Bowman's capsule from the afferent arteriole, which branches off of the interlobular artery. The cleaned blood exits at the vascular pole into the efferent arteriole, while the impurities flows into the renal tubule of the nephron and start working their way to the ureter.

When blood reaches the Bowman's capsule, it separates the blood into two components: a cleaned blood product, and a filtrate which is moved through the renal tubule of the nephron, another structure in the kidneys. As the filtrate travels along the renal tubule, additional impurities are removed, and the filtrate is concentrated into urine for the purpose of expressing waste products and excess water, which flow into collecting duct system.

Fom outside to inside, the Bowman's capsule is made up of the three layers: 1) parietal layer, which is a single layer of simple squamous epithelium; 2) visceral layer, which lies just beneath the thickened glomerular basement membrane and is made of podocytes (eneath the visceral layer lie the glomerular capillaries); 3) filtration Barrier, which is composed of the fenestrated endothelium of the glomerular capillaries, the fused basal lamina of the endothelial cells and podocytes, and the filtration slits of the podocytes. The barrier allows the passage of water, ions, and small molecules from the bloodstream into the Bowman's space. The barrier prevents the passage of large and/or negatively charged proteins, such as albumin.