Wednesday, June 25, 2025

The endocrine system

The endocrine system is a network of glands and organs that produce and release hormones—chemical messengers that regulate major body functions like growth, metabolism, reproduction, mood, and homeostasis (balance of internal systems).


🧠 Main Components of the Endocrine System

🧬 1. Hypothalamus (in the brain)

  • Master regulator that links the nervous system to the endocrine system.
  • Controls the pituitary gland via releasing and inhibiting hormones.
  • Regulates body temperature, hunger, thirst, circadian rhythms.

📍 2. Pituitary Gland ("Master Gland") – base of the brain

  • Controlled by the hypothalamus.
  • Releases growth hormone, thyroid-stimulating hormone (TSH), ACTH, prolactin, FSH, LH, and oxytocin (via posterior pituitary).
  • Controls many downstream glands.

🧠 3. Pineal Gland – deep in the brain

  • Secretes melatonin, which regulates sleep-wake cycles.

🦋 4. Thyroid Gland – in the neck, front of trachea

  • Produces T3 and T4 (thyroid hormones), regulating metabolism, temperature, and energy.

🧫 5. Parathyroid Glands – 4 small glands behind the thyroid

  • Produce parathyroid hormone (PTH), which controls calcium and phosphate levels in blood and bone.

⚖️ 6. Adrenal Glands – on top of each kidney

  • Adrenal cortex: Produces cortisol, aldosterone, and androgens (stress, salt balance, sex hormones).
  • Adrenal medulla: Produces epinephrine (adrenaline) and norepinephrine (fight-or-flight).

🩸 7. Pancreas (Endocrine and Exocrine)

  • Endocrine portion (Islets of Langerhans):
    • Beta cells: Insulin
    • Alpha cells: Glucagon
    • Regulates blood sugar
  • Exocrine portion: Digestive enzymes (not part of endocrine system)

🧬 8. Gonads (Sex glands)

  • Testes (in males): Produce testosterone, regulate sperm production.
  • Ovaries (in females): Produce estrogen and progesterone, regulate menstrual cycle and pregnancy.

🫀 9. Thymus (behind sternum, in childhood)

  • Produces thymosin, important for T-cell (immune) development.
  • Active in childhood, shrinks after puberty.

📜 Summary Table

Gland/Organ Hormones Secreted Primary Function
Hypothalamus Releasing/inhibiting hormones Controls pituitary, homeostasis
Pituitary (Ant./Post.) GH, TSH, ACTH, LH, FSH, prolactin, oxytocin Controls other glands, growth, lactation
Pineal Melatonin Regulates sleep cycle
Thyroid T3, T4 Metabolism, energy, development
Parathyroids PTH Calcium/phosphate balance
Adrenals Cortisol, aldosterone, epinephrine Stress, fluid balance, metabolism
Pancreas (Islets) Insulin, glucagon Blood sugar regulation
Gonads (Ovaries/Testes) Estrogen, progesterone, testosterone Sexual development, reproduction
Thymus (childhood) Thymosin Immune system maturation


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