# Hormones --- **Hormones** are [[signaling molecule|signaling molecules]] of the [[endocrine system]] that are released into plant and animals' [[cardiovascular system|circulatory systems]] that act on specific target cells. When a hormone binds with the [[receptor proteins]], the receptor undergoes a conformational change, which kicks off the desired response. Although they flow through the whole system, only certain receptors are even able to recognize them, so they can have **large results despite not being densely distributed**. Some hormone receptors are even present on different cell types in the same person, but produce different reactions depending on what the cell is. For example, testosterone might cause a hair follicle to produce a hair, while it causes growth hormone to be produced elsewhere. **Many hormones have a similar structure**, sometimes only differing by one or two atoms. Despite this, their specific receptors are highly sensitive to their shape, and can "see the difference" quite effectively. ## Types of Hormones There are two major types of hormones, depending on their makeup (or more specifically, their solubility). A **steriod hormone** is synthesized from [[cholesterol]]—this makes them lipid-solubule, so they a cell directly. These hormones tend to elicit a very specific, targeted response. [[glucocorticoids]] are a class of steroid hormones. A **nonsteroidal** hormone is any hormone that is not synthesized with cholesterol. They can be either [[protein|proteins]] (which is much more common) or **biogenic amines** (which are [[amino acids]] with the carboxyl group removed). These are largely lipid insoluble[^1] and as such *cannot* enter the cell. These types of hormones must undergo [[receptor proteins|signal transduction]] of some kind. [^1]: The exception is [[thyroid hormone]] is a biogenic amine but it is lipid soluble. **Tropic hormones** are another class of homone that do not directly effect a cell, but simply triggers an effecor to release of another, *different* hormone. ## Types of Signaling Hormones can do **systemic signaling** (which is sort of what we might think of naturally for what hormones are), that reaches all parts of the body; **paracrine signaling** which only reaches the very local area of the particular cell; and **autocrine signaling**, which is actually when the signals that the cell can send *itself*. %%this line intentionally left blank%%