Hormones
Over 50 hormones have been discovered, with more added to the list every year. Hormones are generally classified into categories based on structure and mechanism of action.
Steroid hormones are built from cholesterol and can travel across cell membranes, as they are lipid soluble. They usually enter the cell, bind to a steroid receptor in or near the nucleus, and activate gene transcription to create new protein. They tend to be slower than non-steroid hormones.
<<PIC OF A STEROID HORMONE AT WORK>>
Nonsteroid hormones are built from amino acids, often forming polypeptide structures. They generally bind to receptors on the cell surface to open or close ion channels or activate signaling pathways inside the cell. These often activate second messengers within the cell. This is kind of like flipping a light switch outside the cell. They tend to work faster because the protein enzymes and signaling components are sitting, waiting to be act, in the cell.
<<PIC OF A NONSTEROID HORMONE AT WORK>>
In order for steroid and thyroid hormones to be soluble in blood, they require carrier proteins, ie binding globulins. Most protein hormones have binding globulins as well.
Specific Hormones are as follows:
Hypothalamus
Anterior PituitaryPosterior Pituitary |
Adrenal glandThyroid
Sex Hormones
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