What is the name for chemical signals that are released into the blood stream and travel to the body part they are designed to activate?

• Endocrine Disrupting Chemicals
• The Hormones
  • Androgens
  • Corticoids
  • Estrogens
  • Progestins
  • Thyroid
• Actions
  • Docking: Receptor Binding
  • Delivery: Transport Proteins
  • Disposal: Metabolic Changes
  • Dynamics: Interactions
• Wildlife Effects
• Human Effects
• Sources
• Phytoestrogens
• Gathering Evidence
• What Does ED Mean?
• Endocrine System
  • Hormone Glands
  • Target Cells
  • Types of Hormones
  • Feedback Loops
• Glossary

1. Signaling Near and Far
2. Chemical Structures
3. Water vs Fat Solulable

Hormones are classified (separated into groups) according to how they travel in the body and their chemical structure.

Paracrine, autocrine and synaptic are three types of local hormone signaling. In paracrine signaling, hormones are released into the fluid between cells (the interstitial fluid) and diffuse to nearby target cells. Hormones that influence secretions or other processes on the same cells that released them are said to be autocrine signalers. The more specialized synaptic signaling occurs between neurons (the nerve cells that make up the nervous system) and between neurons and muscle cells, allowing nerve cells to talk to each other and to muscles.

Chemical Structures
Hormones are also grouped according to chemical structure. Structures dictate if the hormone prefers to be surrounded by water or fat (water or fat soluble), which determines:

• if the hormone travels in the blood alone or attached to a protein
• if the hormone will bind to receptor sites outside or inside of the target cell (fat soluble can bind both whereas water soluble hormones usually bind on the outside) and
• how the hormone is broken down (metabolized).

1. Steroid hormones are fat-soluble molecules made from cholesterol. Among these are the three major sex hormones groups: estrogens, androgens and progesterones. Males and females make all three, just in different amounts. Steroids pass into a cell's nucleus, bind to specific receptors and genes and trigger the cell to make proteins.
2. Amino acid derivatives, such as epinephrine, are water-soluble molecules derived from amino acids (the building blocks of protein). These hormones are stored in endocrine cells until needed. They act by binding to protein receptors on the outside surface of the cell. The binding alerts a second messenger molecule inside the cell that activates enzymes and other cellular proteins or influences gene expression.
3. Insulin, growth hormone, prolactin and other water-soluble polypeptide hormones consist of long chains of amino acids, from several to 200 amino acids long. They are stored in endocrine cells until needed to regulate such processes as metabolism, lactation, growth and reproduction.