Water-soluble hormones derived from amino acids primarily include amine hormones and peptide/protein hormones.
These hormones differ in size and complexity, but they share the characteristic of being water-soluble, which affects how they travel in the bloodstream and interact with target cells.
Types of Water-Soluble Amino Acid-Derived Hormones:
-
Amine Hormones: These are relatively small molecules derived from single amino acids like tyrosine, tryptophan, or phenylalanine. Examples include:
- Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline): Derived from tyrosine, these hormones are crucial for the "fight or flight" response.
- Thyroid Hormones (Thyroxine (T4) and Triiodothyronine (T3)): Also derived from tyrosine, these hormones regulate metabolism. Although they are amino acid-derived, they exhibit some lipid-soluble characteristics due to the presence of iodine atoms, allowing them to enter cells more easily than typical water-soluble hormones.
- Melatonin: Derived from tryptophan, melatonin regulates sleep cycles.
- Dopamine: While also functioning as a neurotransmitter, dopamine can act as a hormone, inhibiting prolactin release.
-
Peptide/Protein Hormones: These are larger molecules consisting of chains of amino acids linked by peptide bonds. They range in size from small peptides (like TRH) to large proteins (like growth hormone). Examples include:
- Insulin: Regulates blood glucose levels.
- Growth Hormone: Promotes growth and development.
- Oxytocin: Involved in social bonding, reproduction, and childbirth.
- Antidiuretic Hormone (ADH or Vasopressin): Regulates water balance.
- Releasing and Inhibiting Hormones from the Hypothalamus (e.g., TRH, GnRH): Control the release of other hormones from the pituitary gland.
Characteristics and Mechanisms of Action:
Because these hormones are water-soluble, they cannot easily diffuse through the lipid bilayer of cell membranes. Therefore:
- Transport: They travel freely in the bloodstream, unbound to carrier proteins.
- Receptors: Their receptors are located on the cell surface.
- Signal Transduction: When a hormone binds to its receptor, it triggers a cascade of intracellular events, often involving second messengers like cyclic AMP (cAMP) or calcium ions, ultimately leading to a cellular response.
Summary Table:
| Hormone Type | Derivation | Examples | Solubility | Receptor Location | Mechanism of Action |
|---|---|---|---|---|---|
| Amine Hormones | Single Amino Acid | Epinephrine, Norepinephrine, Melatonin | Water | Cell Surface | Second Messenger Systems |
| Peptide/Protein Hormones | Amino Acid Chains | Insulin, Growth Hormone, Oxytocin, ADH | Water | Cell Surface | Second Messenger Systems |
