In-Depth Notes on the Endocrine System

Overview of the Endocrine System

  • Functions:
    • Regulates metabolic function of cells
    • Consists of glands that secrete hormones
    • Hormones serve as chemical messengers through the circulatory system.

Types of Hormones

  • General Types:
    • Steroid Hormones:
    • Lipid-soluble, can enter cells.
    • Amino Acid-Based Hormones:
    • Bind to receptors on plasma membranes.

Hormone Functions

  • Hormones Can:
    • Activate or deactivate enzymes
    • Stimulate or inhibit protein synthesis
    • Alter membrane permeability
    • Stimulate mitosis.

Control of Hormone Release

  • Three Methods of Stimulation:
    • Humoral Stimuli:
    • Change in blood levels of ions/nutrients (e.g., low Ca2+ stimulates parathyroid glands).
    • Neural Stimuli:
    • Nervous system fibers stimulate glands (e.g., sympathetic fibers to adrenal medulla).
    • Hormonal Stimuli:
    • Hormones from one gland stimulate another gland.

Major Endocrine Glands and Functions

  • Hypothalamus:

    • Produces regulatory hormones that control the pituitary gland.

  • Pituitary Gland:

    • Anterior Pituitary:

    • Produces:

      • Growth Hormone (GH) - stimulates growth.
      • Thyroid Stimulating Hormone (TSH) - stimulates thyroid.
      • Adrenocorticotropic Hormone (ACTH) - stimulates adrenal cortex.
      • Prolactin (PRL) - stimulates milk production.
      • Follicle Stimulating Hormone (FSH) - stimulates ovary follicle development and sperm production.
      • Luteinizing Hormone (LH) - stimulates ovulation and testosterone production.
      • Melanocyte-Stimulating Hormone (MSH) - stimulates melanin production.

    • Posterior Pituitary:

    • Stores and releases antidiuretic hormone (ADH) and oxytocin.

  • Thyroid Gland:

    • Hormones:
    • Thyroxine (T4) and Triiodothyronine (T3) - control BMR, growth, and development.
    • Calcitonin - stimulates calcium storage in bones.

  • Parathyroid Glands:

    • Secretes parathyroid hormone (PTH).
    • Regulates blood calcium by stimulating absorption.

  • Adrenal Glands:

    • Cortex:
    • Secretes glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and androgens.
    • Medulla:
    • Secretes epinephrine and norepinephrine for stress response (fight or flight).

  • Pancreas:

    • Islets of Langerhans:
    • Secretes insulin (lowers blood sugar) and glucagon (raises blood sugar).

  • Gonads:

    • Ovaries:
    • Produce estrogens and progesterone.
    • Testes:
    • Produce testosterone.

Summary of Hormonal Effects and Targets

  • ADH: Affects kidneys to reabsorb water.
  • Oxytocin: Stimulates smooth muscle contraction in uterus and mammary glands.
  • PTH: Increases blood calcium levels by acting on bones and kidneys.
  • Thyroid Hormones (T3 & T4): Affect nearly every cell and regulate metabolism.
  • Cortisol: Affects glucose metabolism and stress response.