Endocrine Regulation of Physiological Function - Lecture Notes

  • Introduction to Endocrine Regulation:

    • Focuses on how hormones regulate physiological functions.
    • Integrates nervous and endocrine systems in their functions.

  • Types of Signaling:

    • Endocrine Signaling: Hormones released into circulatory system targeting distant cells.
    • Synaptic Signaling: Neurons transmit signals through synapses.
    • Paracrine Signaling: Local signaling where cells target nearby cells.
    • Autocrine Signaling: Cells respond to substances they secrete.
    • Neuroendocrine Signaling: Combination of neural and endocrine responses.

  • Classes of Hormones:

    • Divided into three classes:
    • Polypeptides: Water-soluble, e.g., insulin.
    • Steroids: Lipid-soluble, e.g., cortisol.
    • Amines: Include both types, e.g., epinephrine.
    • Water-soluble Hormones:
    • Secreted via exocytosis, travel freely, bind to surface receptors.
    • Lipid-soluble Hormones:
    • Diffuse across cell membranes, carried by transport proteins, bind to intracellular receptors.

  • Hormone Action Mechanism:

    • Different effects on cells based on receptor type and signal transduction pathways.
    • Example: Adrenaline effects on different cell types leading to “fight-or-flight” response.
    • Liver Cells: Increase glucose production.
    • Smooth Muscle Cells: Varying responses in skeletal muscle versus intestinal blood vessels.

  • Endocrine Tissues and Glands:

    • Endocrine glands: Ductless, e.g., thyroid, adrenal glands.
    • Exocrine glands: Ducts to surface, e.g., salivary glands.
    • Organs like the kidneys can have both endocrine and exocrine functions.

  • Feedback Mechanisms:

    • Negative Feedback: Returns variable to normal range (e.g., temperature regulation).
    • Positive Feedback: Amplifies stimulus, minimal functions (e.g., childbirth).
    • Feedforward Responses: Anticipatory (e.g., increase heart rate before exercise).

  • Hormonal Pathways:

    • Simple Endocrine Pathway:
    • Example: Secretin release due to low pH in the duodenum.
    • Simple Neuroendocrine Pathway:
    • Example: Oxytocin release during suckling (positive feedback).

  • Hypothalamus and Pituitary Gland:

    • Central role in coordinating endocrine signals.
    • Contains neurosecretory cells producing neurohormones.
    • Anterior pituitary releases tropic hormones, regulated by hypothalamic hormones.
    • Adrenal glands: medulla releases adrenaline, cortex releases corticosteroids (glucocorticoids and mineralocorticoids).

  • Thyroid Regulation:

    • Low thyroid levels trigger hypothalamus to release TRH -> Anterior pituitary secretes TSH -> Stimulates thyroid hormone release.
    • Negative feedback loop to maintain homeostasis.
    • Disorders include goiter due to iodine deficiency leading to TSH overproduction.

  • Diabetes Mellitus:

    • Most common endocrine disorder, characterized by high blood glucose.
    • Type I: Insulin deficiency.
    • Type II: Insulin resistance despite normal secretion.

  • Effects of Diabetes:

    • Insulin deficiency leads to complications: hyperglycemia, dehydration, and potential metabolic acidosis.

  • Comparison of Nervous and Endocrine Systems:

    • Nervous: Rapid, specific responses via neurotransmitters.
    • Endocrine: Slower, broader actions via hormones.