Extraction ratio is a measure in
renal physiology
Renal physiology (Latin language, Latin ''renes'', "kidneys") is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodiu ...
, primarily used to calculate
renal plasma flow in order to evaluate
renal function
Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging.
Functions of a healthy kidney include maintaining a person's flu ...
. It measures the percentage of the compound entering the kidney that was excreted into the final urine.
Renal Mathematics
Texas Tech University Health Sciences Center
Measured in concentration in blood plasma
Blood plasma is a light Amber (color), amber-colored liquid component of blood in which blood cells are absent, but which contains Blood protein, proteins and other constituents of whole blood in Suspension (chemistry), suspension. It makes up ...
, it may thus be expressed as:
:
, where Pa is the concentration in renal artery
The renal arteries are paired arteries that supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle.
The renal arteries carry a large portion of total blood flow to the kidneys. Up to ...
, and Pv is the concentration in the renal vein
The renal veins in the renal circulation, are large-calibre veins that drain blood filtered by the kidneys into the inferior vena cava. There is one renal vein draining each kidney. Each renal vein is formed by the convergence of the interlobar v ...
.
For instance, para aminohippuric acid (PAH) is almost completely excreted in the final urine, and thus almost none is found in the venous return (Pv ~0). Therefore, the extraction ratio of PAH ~1. This is why PAH is used in PAH clearance
Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function.
PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtr ...
to estimate renal plasma flow.
Hepatic extraction ratio
The "Hepatic Extraction Ratio" is a similar measurement for clearance of a substance (usually a pharmacological drug) by the liver. It is defined as the fraction of drug removed from blood by the liver, and depends on 3 factors— the hepatic blood flow, the uptake into the hepatocytes
A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass.
These cells are involved in:
* Protein synthesis
* Protein storage
* Transformation of carbohydrates
* Synthesis of cholesterol, bile ...
, and the enzyme metabolic capacity. Examples of drugs with a high hepatic extraction ratio include propranolol
Propranolol is a medication of the beta blocker class. It is used to treat hypertension, high blood pressure, some types of cardiac dysrhythmia, irregular heart rate, thyrotoxicosis, capillary hemangiomas, akathisia, performance anxiety, and ...
, opiates
An opiate is an alkaloid substance derived from opium (or poppy straw). It differs from the similar term ''opioid'' in that the latter is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain ( ...
, and lignocaine
Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia and ventricular fibrillation. When used for local anaesth ...
.
References
{{DEFAULTSORT:Extraction Ratio
Renal physiology