Endine System Revision Sheet

1. 📌 Essentials

• The endocrine system regulates physiological functions via hormone secretion into the blood.
• Endocrine tissues include glands (thyroid, hypophysis cell clusters (Leydig, Langerhans), and diffuse neuroendocrine cells.
• Hormones are classified as hydrophilic (proteins, peptides, amines) or hydrophobic (steroids, thyroid hormones).
• Peptide hormones are synthesized as preprohormones, processed in ER and Golgi, stored in granules, secreted by exocytosis.
• Steroid hormones derive from cholesterol, are not stored, diffuse freely into target cells.
• Hormone secretion is regulated by hormonal, humoral, neural stimuli, often via negative feedback.
• Hormone secretion exhibits circadian, pulsatile, or complex rhythms.
• Receptors: membrane-bound (G-protein, enzyme-linked, ion channels) or intracellular (cytoplasmic, nuclear).
• Hydrophilic hormones trigger intracellular cascades; lipophilic hormones modulate gene transcription.
• Disorders include hyposecretion and hypersecretion, primary or secondary.

2. 🧩 Key Structures & Components