Bowman's capsule

Bowman's capsule
Glomerulus. (Bowman's capsule not labeled, but visible at top.)
Glomerulus is red; Bowman's capsule is green.
Latin	capsula glomeruli
Gray's	subject #253 1222
Precursor	Metanephric blastema
MeSH	Bowman+Capsule

The Bowman's capsule (other names: capsula glomeruli, glomerular capsule) is a cup-like 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. This process is known as ultrafiltration.

Anatomy

Outside the capsule, there are two "poles":

• The vascular pole is the side with the afferent arteriole and efferent arteriole.
• the urinary pole is the side with the proximal convoluted tubule.

Inside the capsule, the layers are as follows, from outside to inside:

See glomerulus for more details.

A - Renal corpuscle B - Proximal tubule C - Distal convoluted tubule D - Juxtaglomerular apparatus 1. Basement membrane (Basal lamina) 2. Bowman's capsule - parietal layer 3. Bowman's capsule - visceral layer 3a. Pedicels (podocyte's) 3b. Podocyte 4. Bowman's space (urinary space) 5a. Mesangium - Intraglomerular cell 5b. Mesangium - Extraglomerular cell 6. Granular cells (Juxtaglomerular cells) 7. Macula densa 8. Miocytes (smooth muscle) 9. Afferent arteriole 10. Glomerulus Capillaries 11. Efferent arteriole

Physiology

The process of filtration of the blood in the Bowman's capsule is ultrafiltration (or glomerular filtration), and the normal rate of filtration is 125 ml/min, equivalent to ten times the blood volume daily.

Any proteins under roughly 30 kilodaltons 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 Bowman's space, but cells, platelets and large proteins do not.

As a result, the filtrate leaving the Bowman's capsule is very similar to blood plasma in composition as it passes into the proximal convoluted tubule.

Clinical significance

Measuring the glomerular filtration rate (GFR) is a diagnostic test of kidney function.

A decreased GFR may be a sign of renal failure.

A number of diseases can result in various problems within the glomerulus. Examples include acute proliferative (endocapillary) glomerulonephritis, mesangioproliferative glomerulonephritis, mesangiocapillary (membranoproliferative) glomerulonephritis, acute crescentic glomerulonephritis, focal segmental glomerulonephritis, and diabetic glomerulosclerosis. Bowmans capsule.

Eponym

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.

See also

• mesangium

Additional images

Distribution of blood vessels in cortex of kidney.

Glomerulus.

References

1. ^ Histology at BU 22401lba

External links

• Histology at BU 16006loa
• Diagram at ircc.edu