Hormones and Their Classifications

Hormone Functions

• Hormones can be classified by:
  • Where they function: Autocrine, paracrine, endocrine.
  • Structure, which determines their function.

Types of Hormones

1. Proteins and Polypeptides

• Composition: Made up of amino acids linked by peptide bonds.
• Size Range: Can vary from small (3 amino acids) to large (>100 amino acids).
• Production: Synthesized in the rough endoplasmic reticulum (RER), processed in the Golgi apparatus, and excreted from the cell in vesicles.
• Properties:
  • Water-soluble due to charged amino acids.
  • Difficulty crossing cell membranes.
• Receptors: Located on the cell surface.
• Mechanism: Trigger a cascade of secondary messengers within the cell (e.g., insulin).

2. Steroids

• Origin: Derived from lipids, primarily cholesterol.
• Structure: Characteristic four-ring carbon backbone (three cyclohexane rings, one cyclopentane ring).
• Properties:
  • Lipid-soluble, allowing easy passage through cell membranes.
• Receptors: Located inside the cell (cytoplasm or nucleus).
• Mechanism: Act as primary messengers, influencing transcription and translation of proteins.
• Examples: Cortisol, aldosterone, testosterone, estrogen, and progesterone.

3. Tyrosine Derivatives

• Origin: Derived from the amino acid tyrosine.
• Unique Traits:
  • Derived from a single amino acid.
  • Can act like proteins/polypeptides or like steroids.
• Examples:
  • Thyroid Hormones: T3 (triiodothyronine) and T4 (thyroxine) stimulate metabolism, act like steroids.
  • Catecholamines: Epinephrine and norepinephrine, involved in the fight or flight response, act like proteins/polypeptides.

Key Takeaways

• The structure of hormones dictates their function and mode of action.
• Hormones are crucial in regulating various biological processes and responses.
• Understanding hormone structure is vital to comprehending their roles in the body.