Endocrine System Lecture Notes

Overview

• Function: Communicates signals throughout the body, maintaining homeostasis (constant internal conditions).
• Endocrine Glands: Ductless organs, secrete hormones into interstitial fluid, not directly into the bloodstream.
  • Exocrine vs. Endocrine:
    • Exocrine: Have ducts, secrete locally.
    • Endocrine: Ductless, secrete hormones into interstitial fluid, then into bloodstream.

Communication Systems

• Nervous System:
  • Fast, precise communication.
  • Neurons act directly on target cells.
• Endocrine System:
  • Slower, more prolonged response.
  • Hormones act on distant target cells via bloodstream.
  • Example: Stress response with epinephrine and norepinephrine.

Endocrine Organs

• Exclusive Endocrine Glands: Secrete hormones exclusively.
• Organs with Endocrine Tissues: Have other functions besides hormone secretion.
• Examples:
  • Pancreatic islets, testes, ovaries.

Hormones

• Chemical messengers produced by endocrine glands.
• Affect only target cells/organs with specific receptors.
• Travel through bloodstream to reach tissues.

Hypothalamus and Pituitary Gland

Hypothalamus

• Role: Control center of endocrine system.
• Produces regulatory hormones affecting the anterior pituitary.
• Produces hormones stored in posterior pituitary (Oxytocin, Antidiuretic hormone).
• Oversees autonomic nervous system and adrenal medulla activity.

Pituitary Gland

• Location: Inferior to hypothalamus, protected by sella turcica of sphenoid bone.
• Divisions: Anterior and posterior lobes, with intermediate pituitary (pars intermedia).
• Posterior Pituitary:
  • Neural tissue, stores/secretes hypothalamus-produced hormones (Oxytocin, ADH).
  • Neural connection to hypothalamus via unmyelinated axons.
• Anterior Pituitary:
  • Epithelial origin, controlled by hypothalamic hormones via blood vessel network.
  • Releases secondary hormones that affect the body.
  • Portal system: Capillary beds in hypothalamus and anterior pituitary.

Important Hormones

• Oxytocin: Affects reproductive systems, plays role in social bonding, childbirth, breastfeeding.
• Antidiuretic Hormone (ADH/Vasopressin): Targets kidneys, causes water reabsorption; inhibited by alcohol.

Anterior Pituitary Hormones

• Tropic Hormones:
  • Stimulate other glands to secrete their own hormones.
  • Examples:
    • Thyroid Stimulating Hormone (TSH): Stimulates thyroid gland.
    • Prolactin: Stimulates milk production in mammary glands.
    • Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH): Affect gonad function, gamete development.
    • Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex, releases corticosteroids.
    • Growth Hormone (GH): Stimulates growth in liver, muscles, bones, adipose tissues.
    • Melanocyte Stimulating Hormone (MSH): Stimulates melanin synthesis in skin.