Lecture on the Endocrine System

Importance of the Endocrine System

• Essential for long-distance communication within the body.
• Major role in maintaining homeostasis.
• Utilizes hormones to communicate between glands and target cells.

Hormones Overview

• Chemicals secreted by glands, entering the bloodstream.
• Exert effects on downstream target cells.

Types of Hormones

1. Amino Acid Derivatives
   • Derived from amino acids like tyrosine and tryptophan.
   • Example: Melatonin (involved in sleep-wake cycles).
   • Sources of tryptophan: turkey, chocolate, milk.
2. Peptide Hormones
   • Composed of chains of amino acids.
   • Examples: Thyroid-stimulating hormone, oxytocin, prolactin.
3. Lipid Derivatives (Steroid Hormones)
   • Lipophilic, have affinity for lipid structures.
   • Circulate bound to carrier proteins, longer-lasting in circulation.

Hormone Mechanisms of Action

Non-Steroid Action

• Employed by amino acid and peptide hormones.
• Unable to cross cell membranes freely.
• Process:
  • Bind to cell surface receptors.
  • Initiate intracellular signaling cascade.
  • Involves G proteins next to enzymes converting ATP to cyclic AMP (cAMP).
  • cAMP acts as a second messenger, altering enzymatic activity to trigger cell response.
• Examples of Hormones Using cAMP System:
  • ACTH, Calcitonin, Epinephrine, Glucagon, Parathyroid Hormone, ADH.

Steroid Action

• Employed by lipid derivative (steroid) hormones.
• Can freely cross cell membranes.
• Process:
  • Bind to receptors within cells or move into the nucleus.
  • Alter gene activity, increasing transcription and mRNA production.
  • Lead to increased protein production in cells.
• Examples of Hormones Using Steroid Mechanisms:
  • Testosterone, Estrogen, Progesterone, Aldosterone, Calcitriol.