We hear a lot about hormones these days. Estrogen is good for women; estrogen is bad for women. Growth hormone will help you stay young; growth hormone will give you cancer. Hormones make cows get big and tasty; hormones that we give cows are bad for our kids when they drink milk. But what IS a hormone? Why are they important? How do they work?
To start with, there are three major types of hormones – peptides, catecholamines, and steroids. Each one is different. But all three are released in response to a signal from the brain (or another hormone), and travel throughout your body in your blood, affecting cells and tissues along the way. Hormones are important before you are born, and until you die. They control how your body develops, and influence your behavior.
Peptides are proteins – they are produced within cells, and are represented by one gene. Insulin is a well-known example of a peptide hormone. Peptide hormones bind to receptors on the outside of cells, which results in complex signalling cascades (like a waterfall of biology inside the cell). These cascades eventually influence how DNA is turned into new proteins that will have different effects.
Catecholamines are kind of like amino acids, and function a little like peptides – binding to the outside of a cell. Epinephrine and dopamine are examples of catecholamines. Catecholamines can also be important in the brain.
Steroid hormones are the third major type of hormone, and perhaps the best known. Testosterone and estrogen are both examples of steroid hormones. Steroid hormones are similar in structure to cholesterol molecules, and in fact cholesterol is a kind of non-hormone steroid. Steroids differ from catecholamines and peptides in that they are able to enter cells. Instead of binding at cell surfaces, steroids can actually go straight to the DNA and have direct effects.
There are several more generally important things to recognize. First, the systems within cells that respond to hormones are very complex. Second, individuals vary genetically in how we produce hormones – your genes DO affect your life in many ways. Nevertheless, production of hormones from genes occurs in response to the environment – for example, insulin is produced in response to eating sugar. So what you do in life, what you think, and what you experience influences your hormones, which then influences your physical body. Hormonal systems are complicated and can affect each other. If you have a disorder that is characterized by low levels of a hormone, it can be difficult to figure out exactly what’s wrong – do you produce too little, does your body break it down extra fast, or is something else going on? Finally, there are other types of signals in our bodies – for example, ‘neurotransmitters’ work somewhat like hormones, but are in our brains. ‘Cytokines’ are another important signaling molecule that is especially common in immune function.
How hormones influence our outward traits, or ‘phenotypes’ is a complicated question, but hopefully this is enough of a background allowing readers without a background in biology to understand mention of hormones in future posts.