The Bowman’s capsule is a part of the nephron which forms the basic unit of the excretory system. It is also known as the glomerular capsule or the capsula glomeruli. It acts as a filter that functions to process the blood and fluids that pass through the nephron to form urine that is further eliminated from the body.
The Bowman’s capsule is a sac structure shaped like a cup. It houses the glomerulus. Fluids flowing through the glomerulus are removed of larger particles and are further sent to the Bowman’s capsule for removal of fine material. This is a process of ultrafiltration.
The supply of fluids to and from the Bowman’s capsule is by the afferent and efferent arterioles both of which communicate with the glomerulus. The Bowman’s capsule continues on the other end into the proximal convoluted tubule, the next part of the nephron.
The Bowman’s capsule has an outer covering of simple squamous epithelium. This is followed by the visceral layer that is composed of cells called podocytes. These are elongated and comprise foot processes that are extended and wrapped around capillaries to form slits for filtration. These help in reducing the size of molecules that get passed into urine.
Above the visceral layer and beneath the epithelium is the Bowman’s space or the urinary space where the filtrate from the glomerulus enters. Below the visceral layer is the filtration barrier where actual filtration happens. This barrier is composed of the endothelium from the basement membrane of the glomerulus and the podocytes. This barrier is selectively permeable to small molecules like water and ions but restricts charged and larger molecules like proteins.
The filtrate that passes out of the Bowman’s capsule is similar in composition to blood plasma. The glomerular filtration rate is taken to be a measure of kidney function and health.