What is the mechanism of hormone action in cells?

Hormones act on cells by binding to specific receptors, triggering a series of reactions that lead to a response.

Hormones are chemical messengers produced by the endocrine glands in the body. They travel through the bloodstream to reach their target cells or tissues. The mechanism of hormone action involves a complex process that begins when a hormone binds to a specific receptor on the cell surface or inside the cell. This binding triggers a series of reactions within the cell that lead to a response.

There are two main types of hormones: steroid and non-steroid hormones. Steroid hormones, such as cortisol and oestrogen, are lipid-soluble and can easily pass through the cell membrane. Once inside the cell, they bind to specific receptors in the cytoplasm or nucleus. This hormone-receptor complex then binds to specific regions of the DNA, triggering the transcription of specific genes and leading to the production of proteins that bring about a response.

Non-steroid hormones, on the other hand, are water-soluble and cannot pass through the cell membrane. Instead, they bind to receptors on the cell surface. This binding activates a second messenger, such as cyclic AMP (cAMP), inside the cell. The second messenger then triggers a series of reactions that lead to the desired response. This process is known as signal transduction.

In both cases, the binding of the hormone to its receptor is highly specific, much like a key fitting into a lock. This ensures that each hormone only affects its target cells and brings about a specific response. The response could be anything from the stimulation of cell growth and division, to the regulation of metabolism and immune function. The precise mechanism of hormone action can vary depending on the specific hormone and target cell involved.