Endocrine System Overview

Thyroid Gland

• Bilobed gland, shaped like a shield of cartilage
• Produces thyroid hormones
  • Calcitonin: Decreases blood calcium levels (triggers osteoblasts to store calcium in bones)
  • Thyroxine (T4): Essential for normal energy production, growth, and development in children
  • Triiodothyronine (T3)
• Two thyroid hormones regulate metabolic rate of all tissues and help develop the nervous system

Parathyroid Glands

• Four glands, usually two pairs
• Secrete parathyroid hormone (PTH)
  • Increases blood calcium levels (activates osteoclasts to break down bone and release calcium into the bloodstream)
  • Calcium is vital for muscle contraction

Adrenal Glands

• Located on top of the kidneys
• Adrenal medulla (inner part)
  • Secretes epinephrine (adrenaline) and norepinephrine (a vasoconstrictor)
  • These peptide hormones are released during stress and exercise, affecting the entire body
• Adrenal cortex (outer part)
  • Secretes steroid hormones
    • Mineralocorticoids (e.g., aldosterone): Regulate water and electrolyte balance
      • Aldosterone acts on the kidney to retain sodium, thus water, increasing blood volume
    • Glucocorticoids (e.g., cortisol, hydrocortisone): Increase blood sugar levels
      • Essential for brain function, but excessive release can reduce immune function and affect cerebral cortex structure
    • Gonadocorticoids: Converted to testosterone and estrogen in peripheral tissues

Pineal Gland

• Regulates circadian rhythm
• Secretes melatonin

Pancreas

• Has both endocrine and exocrine functions
• Endocrine portion: Islets of Langerhans
  • Alpha cells: Secrete glucagon (increases blood sugar by breaking down glycogen in the liver)
  • Beta cells: Secrete insulin (decreases blood sugar by promoting glycogen storage)

Thymus

• Part of the immune system
• Secretes thymic hormones (e.g., thymosin, thymopoietin) that initiate lymphocyte development

Gonads

• Testes: Produce sperm and androgens (primarily testosterone)
• Ovaries: Produce ova (eggs) and hormones
  • Estrogen: Feminizing hormone (counterpart to testosterone)
  • Progesterone: Prepares the uterus for pregnancy, stimulating endometrial lining growth

Test your knowledge on the endocrine system, focusing on the thyroid, parathyroid, and adrenal glands. This quiz covers the hormones they produce and their functions in regulating metabolism and calcium levels. Perfect for biology students studying human physiology!