We have discussed two mechanisms for regulating physiological responses to hormones: controlling the amount of hormone released, and controlling the availability of receptors. A technique for measuring hormone and receptor concentrations is therefore necessary for studying hormonal mechanisms. The most common means of quantifying hormones and receptors is an immunoassay.
This technique is based on competition for protein-binding sites on antibody. A typical immunoassay begins with a known quantity of an antibody to a specific hormone. A saturating concentration of the hormone is labeled in some manner (often radioactively) and mixed with the antibody until all of the antibody's binding sites are labeled (Figure 42.15). An unlabeled sample of a known concentration of the same hormone is then added to the mixture. This unlabeled hormone will displace some of the labeled hormone from the antibody. The ratio of labeled to unlabeled antibody is a measure of the amount of unlabeled hormone added to the mixture. The process is repeated with different, known concentrations of unlabeled hormone until a standard curve is generated. By comparing a sample of unknown concentra-
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.