Endocrinology
In endocrinology, target cells can refer to the cells where hormones have their effect. Target cells are capable of responding to hormones because they bear receptors to which the hormone can bind. Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone. Hormone receptors are found either exposed on the surface of the cell or within the cell, depending on the type of hormone. A hormone may bind target cells in three general ways:
- Endocrine action: the hormone is distributed in blood and binds to distant target cells.
- Paracrine action: the hormone acts locally by diffusing from its source to target cells in the neighborhood.
- Autocrine action: the hormone acts on the same cell that produced it.
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