Endocrine System Overview

Importance

• Facilitates long-distance communication within the body.
• Essential for maintaining homeostasis.

Hormones

• Chemicals secreted from glands.
• Enter bloodstream to affect target cells.

Types of Hormones

1. Amino Acid Derivatives

   • Small molecules derived from amino acids (e.g., tyrosine, tryptophan).
   • Example: Melatonin (involved in sleep-wake cycles).
   • Sources: Turkey, chocolate, milk.

2. Peptide Hormones

   • Composed of multiple amino acids.
   • Examples: Thyroid-stimulating hormone, oxytocin, prolactin.

3. Lipid Derivatives (Steroid Hormones)

   • Lipophilic (affinity for lipid structures).
   • Circulate bound to carrier proteins, lasting longer in circulation.

Mechanisms of Hormone Action

Non-Steroid Action

• Utilized by amino acid and peptide hormones.
• Cannot freely cross cell membrane.
• Process:
  1. Hormone binds to a cell surface receptor.
  2. Triggers an intracellular signaling cascade.
  3. Involves G proteins and conversion of ATP to cyclic AMP (cAMP).
  4. cAMP acts as a second messenger to initiate cell response.
• Examples of Hormones: ACTH, calcitonin, epinephrine, glucagon, parathyroid hormone, ADH.

Steroid Action

• Utilized by lipid derivative or steroid hormones.
• Freely cross cell membrane into the cell.
• Process:
  1. Hormone binds to an internal receptor or directly enters nucleus.
  2. Alters gene activity, increasing transcription and mRNA production.
  3. Leads to increased protein production.
• Examples of Hormones: Testosterone, estrogen, progesterone, aldosterone, calcitriol.

Summary

• Two main mechanisms determine how hormones interact with target cells: non-steroid action and steroid action.
• Understanding these mechanisms is crucial for comprehending hormonal regulation in the body.