Stock and flow model is a practical method to predict and calculate chemical or substance concentration in a building with a simple model. However, more sophisticate approach has to be done to measure chemical concentration in human tissue, how it move and concentrated in the living thing organs, the body. Therefore physiologically based pharmacokinetic may be applied for this case.

I will try to give the picture by giving the example. Let us consider we are in a lab, and we have animal objects such as mice. We feed them 0.1 mg/day a chemical substance A for a long period of time. After, say, 3 weeks, measure the level of A, and assume we obtain information that the level of A has reached equilibirum with 20% going through digestive system without being absorbed and the rest are bound by the blood, metabolized by kidneys and carried out by urine. Total amound of A in mice’s tissue is 1 mg. The concentration of A in the kidneys is four times that in the blood. Assume that mice has 400 mL of blood and each mice kidney weighs about 4 gram. Try to draw a diagram showing the stocks and flows model of A.

So I basically the diagram will speak about this scheme:

ingestion—>stomach (in,out trough excretion) –> absorption by blood –> transported to kidneys –> excreted through urine.

Let us try to calculate the amount absorbed by the blood. If 20% of A through digestive system without being absorbed, so the 80%, which is 0.08 mg/day is absorbed in the digestive system, with 0.02 mg/day A passes trough. At equilibrium, the amount entering the body will be equal to that leaving, thus the concentration of A in urine is 0.02 mg/day. We will discuss further about this example.

Bookmark to:

This entry was posted on Friday, May 25th, 2007 at 9:32 pm and is filed under Modelling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Related Posts

Physiologically based pharmacokinetics example part 3

Last post we have already talked about physiologically based pharmacokinetics example part 1 and part 2. These two posts give example on how to calculate the concentration of a suspected toxic che...

Bio Transfer Factor

Bio Transfer Factor (BTF) is a constant to describe the relationship between chemical substance in a tissue and the rate of ingestion to body of particular toxic agent (chemical substance). Often,...

Physiologically based pharmacokinetics example part 2

After simple calculation on previous post physiologicaly based pharmacokinetics part 1, we now try to compute the concentration of a chemical substance A in blood and in the kidney. Assume that 0....

Physiogically based pharmacokinetic (PBPK)

Physiologically based pharmacokinetic (PBPK) models are stock and flow models used to think about how chemicals move and concentrate within the body. While many dose-response experiments look only at ...

Physiologically based pharmacokinetics example part 4

This post relates to previous post about biotransfer factor in previous post. If you haven't visited that post yet, I suggest you do so. I would like to provide an example on how to calculate the conc...