Intracellular space

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In pharmacology, the intracellular space (IZR) is the distribution space within the human organism , which is formed from the entirety of all cell components enclosed by cell membranes and therefore mainly consists of the cell organelles , the cell fluid and various inclusions. The IZR is neither a coherent nor - due to constant exchange and remodeling processes - a clearly delimited space, but a model conception that is of practical importance in pharmacokinetics .

Since the pharmacological definition of a distribution space ( compartment calls), a substance that is dispersed homogeneously therein and biokinetic laws same subject, the ICR is divided into compartments again in the specific case - according to the physico - chemical properties of the drug .

Definition

The adjective intracellular is not completely synonymous with in the intracellular space :

  • On the one hand, in cell biology , individual cells or cell types are often described as examples with regard to their content, which is bounded by the cell membrane, or its relationship to the environment, without establishing a direct reference to the (entire) ICR.
  • On the other hand, findings on the IZR compartment do not necessarily say anything about the condition of individual cells.

However, by definition, all intracellular components of the organism are also located in the IZR.

Dimensions

Proportion of body weight

The structures and substances in the IZR make up around 75% of the body weight of humans. As a result, the extracellular body components ( extracellular matrix such as in the bones and the fluid in the blood vessels ) account for around a quarter of the total body weight. (The total water is about 60% by weight, in men it is about 10% higher than in women.)

Share of the liquid volume

The IZR has a share of almost two thirds of the total volume of body water in adults.

Volume determination

The volume of the IZR can be determined by administering an indicator whose distribution behavior is well known. The IZR volume can then be approximately calculated from its concentration in a certain volume (e.g. in a blood sample ; the erythrocytes are components of the ICR , but the plasma is part of the ECR). Radionuclides or dyes , for example, are used as indicators .

meaning

From the point of view of pharmacology, the intracellular space is the second essential distribution space of the organism next to the extracellular space (ECR).

While the ECR is seldom the goal of a drug effect and is predominantly important for the transport of substances, the desired sites of action of drugs are often in the ICR. After ingestion or administration, most active ingredients initially distribute themselves extensively in the vascular system - i.e. in the ECR - before they reach intracellular sites of action.

Typically, the distribution of an administered drug dose between EZR and IZR changes significantly over time, the elimination mechanisms being effective from the time the substance is taken and, in the case of a single dose, mostly no effective concentrations are reached at the target sites.

With repeated administration, on the other hand, a (dynamic) equilibrium develops between the substance concentrations in the IZR and EZR. Then z. B. inferences from measurements of the substance level in the plasma on the concentration at the site of action.

literature

  • physio lexicon: Therapy A to Z . Lexicon, Georg Thieme Verlag, Stuttgart 2010, p. 425 ( online )
  • Wolfgang von Engelhardt: Physiology of domestic animals . Georg Thieme Verlag, Stuttgart 2005, p. 11 ( online )
  • Wilfried Kraft, Ulrich M. Dürr: Clinical laboratory diagnostics in veterinary medicine . Schattauer Verlag, Stuttgart 2014, p. 336 ( online )
  • Hamid Abdolvahab-Emminger: Physikum exactly: The entire test knowledge for the 1st ÄP . Georg Thieme Verlag, Stuttgart 2005, p. 555 ( online )
  • Anatomy, physiology: I care . Lexicon, Georg Thieme Verlag, Stuttgart 2015, p. 252 ( online )

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