Hormones and Pheromones Lecture Notes

Introduction to the Endocrine System

  • Overview:
    • The endocrine system is composed of small glands (4-5 ounces of tissue) dispersed throughout the body.
    • These glands secrete hormones directly into the bloodstream, acting as chemical messengers.

Functions of the Endocrine System

  • Communication:
    • Facilitates communication between cells within an organism and between organisms.
  • Hormones vs. Pheromones:
    • Hormones: Chemical messengers within an organism.
    • Pheromones: Chemicals that affect other organisms.

Role of Hormones in Homeostasis

  • Key Functions:
    • Maintain homeostasis.
    • Initiate stress responses.
    • Regulate growth, development, and sexual functions.
  • Definition of Hormones:
    • Hormones are chemical substances secreted by glands into the bloodstream, targeting specific cells to regulate metabolic functions.

Target Cells and Hormone Receptors

  • Mechanism of Action:
    • Hormones act like a lock-and-key mechanism, where hormones bind specifically to receptors on target cells, initiating a physiological response.
    • Non-target cells do not respond to the hormone.

Classification of Hormones

  • Types of Hormones:
    • Steroid Hormones:
    • Derived from cholesterol; lipid-soluble; can cross the plasma membrane directly.
    • Form complexes with intracellular receptors that modify gene transcription.
    • AA-Based Hormones (Amino Acid-based):
    • Cannot penetrate the plasma membrane; bind to surface receptors and activate secondary messengers to bring about metabolic changes.

Hormone Activity

  • Characteristics:
    • Extremely potent; effective at low concentrations (ppm/ppb).
  • Hormonal Concentration is influenced by:
    1. Rate of release from endocrine cells.
    2. Speed of inactivation by the body (can vary from seconds to 30 minutes).

Regulation of Hormone Release

  • Negative Feedback Mechanism:
    1. Hormone secretion is initiated by a stimulus.
    2. Hormone reaches target cells and exerts effects.
    3. Increase in blood levels of the hormone triggers feedback shutdown of its secretion.

Endocrine Organs and Their Hormones

  • Pituitary Gland:
    • Small, pea-sized gland attached to the hypothalamus; divided into anterior and posterior lobes.
Anterior Pituitary Hormones
  • Types of Hormones:
    • Trophic Hormones (affect/ regulate other glands):
    1. Thyroid Stimulating Hormone (TSH): Stimulates thyroid activity.
    2. Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex activity.
    3. Gonadotropins: Regulate gonads (e.g., FSH, LH).
    • Follicle Stimulating Hormone (FSH):
    • Regulates gamete production (sperm in males, ova in females).
    • Luteinizing Hormone (LH):
    • Triggers ovulation in females and stimulates testosterone production in males.
    • Release controlled by Gonadotropin Releasing Hormone (GnRH).
    • Non-Trophic Hormones (do not affect other glands):
    1. Growth Hormone (GH):
      • Stimulates growth and cell division; regulated by GHRH and GHIH from the hypothalamus.
    2. Prolactin:
      • Stimulates milk production; regulated by Prolactin Releasing Hormone (PRH) and Prolactin Inhibiting Hormone (PIH).
      • PIH is identified as dopamine; PRH dominates during pregnancy.