Lecture Notes: The Endocrine System

Introduction

• Endocrine System: A network of cells and glands that produce and release hormones into the bloodstream.
  • Functions as a communication network similar to the nervous system.
  • Slower and longer-lasting effects compared to the nervous system.

Key Components of the Endocrine System

Hypothalamus

• Location: Base of the brain, below the thalamus.
• Function: Master regulator of the endocrine system.
• Hormones Produced:
  • Thyrotropin-releasing hormone (TRH)
  • Corticotropin-releasing hormone (CRH)
  • Growth hormone-releasing hormone (GHRH)
  • Prolactin-releasing hormone (PRH)
  • Gonadotropin-releasing hormone (GnRH)

Pituitary Gland

• Divisions: Anterior and Posterior

Anterior Pituitary

• Connection: Via blood supply from hypothalamus.
• Hormones Released:
  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotropic Hormone (ACTH)
  • Growth Hormone (GH)
  • Prolactin
  • Gonadotropins (Luteinizing Hormone - LH, Follicle-Stimulating Hormone - FSH)

Posterior Pituitary

• Connection: Via nerves from hypothalamus.
• Hormones Stored/Released:
  • Oxytocin
  • Anti-diuretic hormone (ADH, also known as vasopressin)

Specific Glands and Their Hormones

Thyroid Gland

• Location: Around the trachea.
• Hormones Produced:
  • T3 (Triiodothyronine) and T4 (Thyroxine)
    • Important for metabolism and catecholamine release (e.g., adrenaline).
  • Calcitonin
    • Lowers blood calcium levels.

Adrenal Gland

• Cortex Hormones:
  • Cortisol
    • Increases blood glucose, suppresses the immune system, and stimulates fight or flight response.
  • Aldosterone
    • Increases salt reabsorption, blood volume, and blood pressure.
• Medulla Hormones:
  • Adrenaline (Epinephrine), Noradrenaline (Norepinephrine)

Gonads

Female (Ovaries)

• Hormones:
  • Luteinizing Hormone (LH)
    • Stimulates progesterone production and ovulation.
  • Follicle Stimulating Hormone (FSH)
    • Stimulates follicle maturation and estrogen production.

Male (Testes)

• Hormones:
  • Luteinizing Hormone (LH)
    • Stimulates testosterone production in Leydig cells.
  • Follicle Stimulating Hormone (FSH)
    • Stimulates androgen binding protein production in Sertoli cells, promoting sperm production.

Parathyroid Gland

• Hormone: Parathyroid hormone (PTH)
  • Increases blood calcium levels, opposing calcitonin activity.

Kidneys

• Hormones:
  • Renin
    • Works with aldosterone to increase blood pressure and volume.
  • Erythropoietin
    • Increases red blood cell production.

Pancreas

• Dual Function:
  • Exocrine: Releases digestive enzymes into ducts.
  • Endocrine:
    • Insulin
      • Lowers blood glucose levels.
    • Glucagon
      • Raises blood glucose levels.

Summary

• The endocrine system plays a crucial role in maintaining homeostasis and regulating numerous physiological processes through hormone release. The coordination between different glands and hormones ensures the body's proper function and adaptation to changes.