Lecture on the Endocrine System by Dr. Mike

Overview of the Endocrine System

• A collection of cells and glands that produce and release hormones
• Hormones: Chemicals that travel in the bloodstream to affect distant parts of the body
• Comparison with Nervous System:
  • Nervous System: Fast, direct, short-acting
  • Endocrine System: Slow, indirect (via bloodstream), long-lasting (effects lasting hours to weeks)

Structure and Function

• Top to toe approach starting with the brain

Hypothalamus

• Located at the base of the brain, below the thalamus
• Produces and releases hormones regulating other endocrine tissues
• Known as the master regulator or control center of the endocrine system
• Key Hormones:
  • Thyrotropin-releasing hormone (TRH)
  • Corticotropin-releasing hormone (CRH)
  • Growth hormone-releasing hormone (GHRH)
  • Prolactin-releasing hormone (PRH)
  • Gonadotropin-releasing hormone (GnRH)

Pituitary Gland

• Anterior Pituitary:
  • Connected to the hypothalamus via blood supply
  • Hormones released:
    • Thyroid-stimulating hormone (TSH)
    • Adrenocorticotropic hormone (ACTH)
    • Growth hormone (GH)
    • Prolactin
    • Gonadotropins (Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH))
• Posterior Pituitary:
  • Connected to the hypothalamus via nerves
  • Hormones released:
    • Oxytocin
    • Antidiuretic hormone (ADH) or Vasopressin

Hormone Pathways and Effects

Thyrotropin-Releasing Hormone (TRH)

• Stimulates release of Thyroid-Stimulating Hormone (TSH)
• TSH targets the thyroid gland
• Thyroid Hormones:
  • T3 (Triiodothyronine)
  • T4 (Thyroxine) – mainly converted to T3
• Functions: Metabolism, development, catecholamine (adrenaline, noradrenaline) release
• Calcitonin: Reduces calcium levels in the bloodstream by promoting storage in bones

Corticotropin-Releasing Hormone (CRH)

• Stimulates release of Adrenocorticotropic Hormone (ACTH)
• ACTH targets the adrenal cortex
• Adrenal Cortex Hormones:
  • Cortisol: Increases blood glucose, suppresses immune response, stimulates fight or flight response
  • Aldosterone: Increases salt reabsorption in the kidneys → increases blood volume and pressure
  • Androgens: Male sex hormones (limited discussion)
• Adrenal Medulla Hormones (less influenced by ACTH):
  • Noradrenaline (Norepinephrine)
  • Adrenaline (Epinephrine)

Other Hormones

• Growth Hormone (GH): Stimulates growth, protein synthesis, metabolic processes
• Prolactin: Stimulates milk production (not ejection)
• Oxytocin: Uterine contractions, milk ejection, relationship bonding
• Antidiuretic Hormone (ADH)/Vasopressin: Maintains hydration by reducing urine output
• Gonadotropins (LH and FSH):
  • In Females: LH stimulates progesterone and ovulation; FSH stimulates follicle maturation and estrogen production
  • In Males: LH stimulates testosterone production (Leydig cells); FSH stimulates androgen-binding protein and supports sperm production (Sertoli cells)

Additional Endocrine Glands

Parathyroid Gland

• Behind the thyroid
• Hormone: Parathyroid hormone (PTH) – Increases blood calcium levels (opposes Calcitonin)

Kidneys

• Hormones:
  • Renin: Works with Aldosterone to increase blood pressure and volume
  • Erythropoietin: Increases red blood cell production to ensure adequate oxygenation

Pancreas

• Both endocrine (hormones) and exocrine (digestive enzymes) functions
• Key Hormones:
  • Insulin: Lowers blood glucose levels after meals
  • Glucagon: Raises blood glucose levels during fasting periods

Summary

• The endocrine system maintains homeostasis and regulates processes critical for survival and reproduction through hormone release and interaction.