Chemical Messengers: Hormones (Nursing)

00:00 There are several different types of chemical messengers that our bodies use in order to get signals to certain cells. The endocrine system uses hormones, which are long distance chemical signals that travel from one place to another place by way of the blood or lymph tissue. We also have autocrines in our body. These are chemicals that are released by a cell and exert effects on the same cell that secreted them. Also we have chemicals known as paracrines.

00:39 Paracrines are locally-acting chemicals that affect cells that are nearby. Autocrines and paracrines, because of their local chemical messaging, are not considered a part of the endocrine system. So when we're talking about the endocrine system, we're usually specifically talking about hormones. So there are 2 main classes of hormones. There are amino acid based hormones which are amino acid derivatives, peptides, and proteins. A second class of hormones are steroid hormones. These are going to be synthesized from cholesterol and are going to make up our gonadal and adrenocortical hormones. We'll talk a lot more in detail about this shortly. Some scientists also consider a third class of hormones known as our eicosanoids, but most others really classify these as paracrines so we won't focus on those in this lecture. So how do hormones actually act to perform their function? Though hormones are able to circulate all throughout the body, only cells with receptors for that hormone are able to be affected by those hormones. These cells are referred to as our target cells and these are tissues that have receptors for specific hormone and hormones will then alter the activity of this target cell. How do hormones act on target cells? It can stimulate synthesis of enzymes or other proteins. It can alter the plasma membrane permeability and/or the membrane potential by opening and closing certain ions in our target cells. It can also activate or deactivate enzymes in the target cell. It can induce secretory activity so that the target cell is going to release certain substances. And it can also signal the target cell to undergo mitosis. Hormones act usually in one of 2 ways depending on the chemical nature of the hormone as well as the location of the receptors on the target cell. Water soluble hormones such as our amino acid-based hormones except for the thyroid hormone are going to act on receptors on the plasma membrane of the target cell. Usually these are going to activate a G protein-coupled 2nd messenger and because they are water soluble, these types of hormones are not able to readily enter the cell. Lipid-soluble hormones, however, such as our steroids and our thyroid hormone are going to act on intracellular receptors and these receptors are going to allow for the activation of specific genes inside of the cell. Because these lipid-soluble hormones are made up of lipids, they have the ability to enter the cell on their own without any help.