Glomerulus (kidney)

The glomerulus (pl.: glomeruli) is a network of small blood vessels (

The glomerulus is a tuft of capillaries located within

Capillaries of the glomerulus are lined by

The glomerulus has a

The mesangium is a space which is continuous with the smooth muscles of the arterioles. It is outside the capillary lumen but surrounded by capillaries. It is in the middle (meso) between the capillaries (angis). It is contained by the basement membrane, which surrounds both the capillaries and the mesangium.

The mesangium contains mainly:

• pericytes
  that participate in the regulation of the filtration rate by contracting or expanding: they contain actin and myosin filaments to accomplish this. Some mesangial cells are in physical contact with capillaries, whereas others are in physical contact with podocytes. There is two-way chemical cross talk among the mesangial cells, the capillaries, and the podocytes to fine-tune the glomerular filtration rate.
• Mesangial matrix, an amorphous basement membrane-like material secreted by the mesangial cells.

Blood supply

The glomerulus receives its blood supply from an

Blood exits the glomerular capillaries by an

The main function of the glomerulus is to filter

If a substance has passed through the glomerular capillary endothelial cells, glomerular basement membrane, and podocytes, then it enters the lumen of the tubule and is known as glomerular filtrate. Otherwise, it exits the glomerulus through the efferent arteriole and continues circulation as discussed below and as shown on the picture.

Permeability

The structures of the layers determine their

The oncotic pressure on glomerular capillaries is one of the forces that resist filtration. Because large and negatively charged proteins have a low permeability, they cannot filtrate easily to Bowman's capsule. Therefore, the concentration of these proteins tends to increase as the glomerular capillaries filtrate plasma, increasing the oncotic pressure along the glomerular capillary.^[6]

Starling equation

The rate of filtration from the glomerulus to Bowman's capsule is determined (as in systemic capillaries) by the Starling equation:^[6]

${\displaystyle \ GFR=K_{\mathrm {f} }((P_{\mathrm {gc} }-P_{\mathrm {bc} })-(\pi _{\mathrm {gc} }-\pi _{\mathrm {bc} }))}$

• GFR is the glomerular filtration rate
• K_f is the filtration coefficient—a proportionality constant
• P_gc is the glomerular capillary
  hydrostatic pressure
• P_bc is the Bowman's capsule hydrostatic pressure
• π_gc is the glomerular capillary oncotic pressure
• π_bc is the Bowman's capsule oncotic pressure

Blood pressure regulation

The walls of the afferent arteriole contain specialized smooth muscle cells that synthesize renin. These juxtaglomerular cells play a major role in the renin–angiotensin system, which helps regulate blood volume and pressure.

Clinical significance

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Damage to the glomerulus by disease can allow passage through the glomerular filtration barrier of red blood cells, white blood cells, platelets, and blood proteins such as albumin and globulin. Underlying causes for glomerular injury can be inflammatory, toxic or metabolic.

Due to the connection between the glomerulus and the glomerular filtration rate, the glomerular filtration rate is of clinical significance when suspecting a kidney disease, or when following up a case with known kidney disease, or when risking a development of renal damage such as beginning medications with known nephrotoxicity.^[10]

History

In 1666, Italian biologist and anatomist Marcello Malpighi first described the glomeruli and demonstrated their continuity with the renal vasculature (281,282). About 175 years later, surgeon and anatomist William Bowman elucidated in detail the capillary architecture of the glomerulus and the continuity between its surrounding capsule and the proximal tubule.^[11]

See also

• Glomerulus
• Blood–brain barrier

Additional images

• 
  Scanning electron microscope image of a glomerulus in a mouse (1000x magnification)
• 
  Scanning electron microscope image of a glomerulus in a mouse (5000x magnification)
• 
  Scanning electron microscope image of a glomerulus in a mouse (10,000x magnification)
• 
  Looped capillaries of glomerulus between the arterioles

References

Sources

Wikimedia Commons has media related to Renal corpuscle.

• Hall, Arthur C. Guyton, John E. (2005). Textbook of medical physiology (11th ed.). Philadelphia: W.B. Saunders. p. Chapter 26.
  ISBN 978-0-7216-0240-0.{{cite book}}: CS1 maint: multiple names: authors list (link
  )
• Deakin, Barbara Young ... [] ; drawings by Philip J.; et al. (2006). Wheater's Functional Histology: a text and colour atlas (5th ed.). [Edinburgh?]: Churchill Livingstone/Elsevier. p. Chapter 16.
  ISBN 978-0-443068508.{{cite book}}: CS1 maint: multiple names: authors list (link
  )