Bowman's capsule
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Bowman's capsule is a blind sac at the beginning of the tubular component of a nephron in the mammalian kidney. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine.
Bowman's capsule is named after Sir William Bowman (1816-1892), a British surgeon and anatomist.
Together with the glomerulus it is known as a renal corpuscle, or a Malpighian corpuscle, named after Marcello Malpighi (1628-1694), an Italian physician and biologist. This name is not used widely anymore, probably to avoid confusion with a Malpighian corpuscle in the spleen.
Physiology
The barrier between the blood and the lumen of the nephron here is formed of three layers: the squamous endothelium of the capillaries; the basement membrane; and the endothelial podocytes forming the nephron. The barriers are 'leaky' in the sense that some large molecules can pass through unfiltered.The process of filtration of the blood in the Bowman's capsule is ultra-filtration or glomerular filtration, the normal rate of glomerular filtration is 125 ml/min, equivalent to 10x the blood volume daily. Any proteins under ~30,000 daltons in size can pass freely through the membrane, although there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes. Any small molecules such as water, glucose, salt (NaCl), amino acids and urea pass freely into the nephron but cells, platelets and large proteins do not.
The filtrate leaving the Bowman's capsule is very similar to plasma fluid in composition and passes on into the distal convoluted tubule.
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