Ultrafiltration (renal)
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In biological terms, Ultrafiltration occurs at the barrier between the blood and the filtrate in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent arteriole and leaves through a narrower efferent arteriole. The blood pressure inside these capillaries is high because:
- The renal artery contains blood at very high pressure which enters the glomerulus via the short afferent arteriole.
- The efferent arteriole has a smaller diameter than the afferent arteriole.
The high pressure forces small molecules such as water, glucose, amino acids, sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule and into the nephron. This type of high pressure filtration is ultrafiltration. The fluid formed in this way is called glomerular filtrate. Large molecules such as plasma proteins and blood cells do not pass through the filter because they are too big.
Glomerular pressure is about 75 millimeters of mercury (10 kPa). It is opposed by osmotic pressure(30 mmHg, 4.0 kPa) and hydrostatic pressure (20 mmHg, 2.7 kPa) of solutes present in capsular space. This difference in pressure is called effective pressure(25 mmHg)(3.3 kPa).
It is also used in hemodialysis to clean whole blood while keeping its composition intact.
Filtration: Ultrafiltration - Countercurrent exchange
Hormones affecting filtration:Antidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide
Endocrine: Renin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins
Assessing Renal function / Measures of dialysis: Glomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product
Fluid balance - Darrow Yannet diagram - Body water - Interstitial fluid - Extracellular fluid - Intracellular fluid/Cytosol - Plasma - Transcellular fluid - Base excess - Davenport diagram - Anion gap
Bicarbonate buffering system - Respiratory compensation - Renal compensation
