Lecture on the Endocrine System

Importance of the Endocrine System

• Internal regulatory system, similar to the nervous system
• Helps maintain homeostasis
• Regulates:
  • Metabolism
  • Growth and development
  • Sexual function and reproduction
  • Sleep via circadian rhythm
  • Mood

Hormones

• Chemical messengers secreted by cells into the bloodstream
• Travel to distant body cells to elicit specific physiological responses
• Enable the endocrine system to control and integrate other body systems

Primary vs. Secondary Endocrine Organs

• Primary Endocrine Organs: Main function is hormone secretion
  • Examples: Pituitary gland, thyroid gland, adrenal glands
• Secondary Endocrine Organs: Have primary functions but also secrete hormones
  • Examples: Kidneys (produce erythropoietin), skin (synthesizes vitamin D)

Hormone Characteristics

• Water-soluble hormones: Amino acid-based (amines, peptides, proteins), act on cell surface receptors
• Lipid-soluble hormones: Steroid-based hormones, act on intracellular receptors

Pituitary Gland

• Known as the "master gland"
• Two major lobes: Anterior and Posterior
• Anterior Pituitary
  • Interacts with the hypothalamus via the hypophyseal portal system
  • Major hormones: TSH, GH, FSH, LH, ACTH, Prolactin
  • Mnemonic: FLAT PEG (except endorphins)
• Posterior Pituitary
  • Hormones (oxytocin, ADH) synthesized in the hypothalamus, stored in posterior pituitary

Pineal Gland

• Secretes melatonin
• Regulates circadian rhythm
• Influenced by light exposure (e.g., blue light)

Thyroid Gland

• Butterfly-shaped, located on the anterior trachea
• Produces thyroxine (T4) and triiodothyronine (T3)
• Affects metabolic rate and temperature regulation
• Calcitonin lowers blood calcium levels

Parathyroid Glands

• Located posterior to the thyroid
• Secretes parathyroid hormone (PTH)
• Regulates blood calcium levels by:
  • Stimulating osteoclasts
  • Enhancing calcium reabsorption in the kidneys
  • Activating vitamin D for calcium absorption in intestines

Adrenal Glands

• Located on top of the kidneys
• Adrenal Medulla: Part of the sympathetic nervous system
  • Secretes epinephrine and norepinephrine
• Adrenal Cortex
  • Zones:
    • Zona glomerulosa (mineralocorticoids like aldosterone)
    • Zona fasciculata (glucocorticoids like cortisol)
    • Zona reticularis (gonadocorticoids)

Pancreas

• Has both endocrine and exocrine functions
• Endocrine role: Regulates blood sugar
  • Alpha cells secrete glucagon (raises blood sugar)
  • Beta cells secrete insulin (lowers blood sugar)

Diabetes

• Type 1 Diabetes: Autoimmune destruction of beta cells; treated with insulin
• Type 2 Diabetes: Insulin resistance often due to diet and lifestyle
  • Preventable and sometimes reversible with lifestyle changes
  • Pharmaceuticals like Metformin often used, but lifestyle changes are more effective

• Emphasized a holistic approach to understanding the interconnectedness of body systems
• Encouraged lifestyle changes to prevent and treat diseases like diabetes

Note: This is a broad overview and these points may be elaborated upon in a complete lecture series or textbook review.