Epinephrine Norepinephrine

Introduction to Epinephrine and Norepinephrine

  • Epinephrine and Norepinephrine are hormones released from the adrenal suprarenal glands.

Anatomical Overview of the Adrenal Glands

  • The adrenal glands are located above the kidneys.

  • Each adrenal gland has a pyramid-like shape.

  • A capsule surrounds each adrenal gland.

Structure of the Adrenal Gland

  • Adrenal Medulla (inner central part):

    • Contains chromaffin cells that produce hormones.

  • Adrenal Cortex (outer part):

    • Distinct from the medulla; involved in different hormonal functions.

Hormonal Function

  • Chromaffin Cells:

    • Produce and secrete the hormones epinephrine (also called adrenaline) and norepinephrine (also called noradrenaline).

Role in the Sympathetic Nervous System

  • Epinephrine and norepinephrine reinforce the impact of the sympathetic division of the nervous system.

  • Fight or Flight Response:

    • Activation occurs during stress or emergency situations, resulting in increased secretion of epinephrine and norepinephrine.

Mechanism of Action and Hormone Secretion

  • Nerves exiting the central nervous system, specifically some thoracic spinal nerves, stimulate the adrenal medulla to secrete epinephrine and norepinephrine.

  • These hormones are released into the interstitial fluid and subsequently enter the bloodstream.

  • Hormones are defined as secretions transported through the bloodstream.

Hormonal Distribution

  • There is unequal secretion of the two hormones from the adrenal medulla:

    • 80% of the secreted hormones are epinephrine.

    • 20% are norepinephrine.

Effects on Cardiovascular Function

  • Target Organ: Heart

    • Epinephrine and norepinephrine increase:

    • Heart Rate

    • Force of Muscle Contraction (specifically, the ventricles):

      • Increased forcefulness of contraction leads to greater stroke volume (amount of blood pumped out of the ventricle with each contraction).

      • This raises cardiac output (the total volume of blood pumped by the heart per minute).

  • Consequences of Increased Cardiac Output:

    • Results in increased blood pressure.

    • Essential during fight or flight to ensure blood flow to critical organs.

Blood Flow Regulation in Non-Critical Organs

  • Non-Critical Organs (e.g., skin, abdominal viscera, kidneys):

    • Blood vessels in these areas constrict to redirect blood to critical organs.

    • Constriction results in:

    • Increased systemic vascular resistance, explaining higher blood pressure.

    • Increased venous return to the heart due to venous constriction.

Mechanisms of Constriction Effects

  • Arterioles:

    • Narrowed arterioles in non-critical organs increase systemic vascular resistance, contributing to higher blood pressure.

  • Veins:

    • Constriction of veins helps push blood back to the right atrium, increasing venous return, thereby elevating cardiac output and blood pressure.

Blood Flow to Critical Organs

  • Critical Organs needing increased blood flow include:

    • Heart

    • Skeletal Muscles

    • Liver

    • Fat Tissue

  • Nutrient Release Responsibilities:

    • Liver cells: Store glycogen and triglycerides; during emergencies they break down these stores and release glucose into the bloodstream.

    • Adipocytes (fat cells): Store triglycerides; break them down for fatty acids during emergencies to fuel cells.

Summary of Impact of Epinephrine and Norepinephrine

  • Increase levels of nutrients such as glucose and fatty acids in the bloodstream during emergency situations, ensuring that cells have the necessary fuel to respond to stress.