Types of Hormones

There are many types of hormones in the human body. However, they all can be divided into three classes. This categorization based on their chemical structure.

  • Amino Acid-derived Hormones
    • Amino acid- derived hormones are relatively small molecules
    • Commonly derived from tyrosine and tryptophan
    • Amino acid-derived hormones will have a chemical name that ends in –ine.
    • Water-soluble and insoluble in lipids.
    • These hormones cannot pass through plasma membranes of cells.
  • Lipid-Derived Steroid Hormones
    • Most lipid hormones are derived from cholesterol
    • The main class of lipid hormones is the steroid hormones.
    • Chemically, these hormones are either ketones or alcohols with their chemical names ending in “-ol” for alcohols or “-one” for ketones.
    • Insoluble in water
    • Lipid-derived hormones can diffuse across plasma membranes whereas the amino acid-derived and peptide hormones cannot.
    • Transported by designated transport proteins in the blood.
    • These remain in circulation for a longer duration than peptide hormones.
    • Lipid Derived Steroid hormones regulate water balance, sexual development and the stress response.
  • Peptide Hormones (which includes peptides and proteins).
    • Peptide hormones derived from peptides.
    • Includes molecules that are short polypeptide chains (chain of amino acids)
    • Includes small proteins such as GH that is produced in the pituitary gland of the brain.
    • Secreted peptides are stored within the vesicles in the cells.
    • Secreted peptides are released in response to stimuli.
    • Water-soluble and insoluble in lipids.
    • The receptors for peptide hormones are located in the plasma membrane.
    • Peptide hormones cannot pass through plasma membranes of cells.
    • Peptide hormones must bind to receptors on the cell’s surface.
    • This passage causes changes within the cell by affecting enzymes within the cell’s cytoplasm.
    • The binding of the peptide hormone to the cell membrane receptor initiates development of a second messenger molecule inside the cell, that carries the chemical signal within the cell.

Exocrine hormones are secreted through a duct into the bloodstream. They will usually effect a distant organ or tissue.

Endocrine hormones are secreted from the tissue instead of through a duct. They enter the bloodstream via capillaries.

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