Adrenergic Receptors Lecture Notes

Introduction

• Adrenergic Receptors: Also known as adrenal receptors, these are protein receptors that mediate the effects of epinephrine (adrenaline) and norepinephrine (noradrenaline).
• Function: These receptors are found on the surface of cells and are activated by epinephrine or norepinephrine.

Classification

• Types: Adrenergic receptors are classified into alpha and beta receptors, each with multiple subtypes.

Alpha Receptors

Alpha 1 Receptors

• Activation: Activated by norepinephrine and epinephrine.
• Location: Primarily in smooth muscle cells of blood vessels and the urinary tract.
• Effect: Induces constriction of blood vessels.

Alpha 2 Receptors

• Activation: Also activated by norepinephrine and epinephrine.
• Location: Found in the central nervous system, pancreas, veins, adipose tissue, gastrointestinal sphincters, salivary glands.
• Effect: Inhibits the release of norepinephrine in the central nervous system, potentially decreasing arterial blood pressure.

Beta Receptors

Beta 1 Receptors

• Activation: Activated by norepinephrine and epinephrine.
• Location: Primarily in the heart.
• Effects:
  • Chronotropic: Increases heart rate.
  • Inotropic: Increases force of heart contraction.

Beta 2 Receptors

• Activation: Activated only by epinephrine.
• Location: Found throughout the body, especially in lungs and bronchial smooth muscle cells.
• Effects:
  • Dilates blood vessels and bronchioles.
  • Relaxes muscles in uterus, bladder, and gastrointestinal tract.
  • Decreases platelet aggregation (blood clotting).
  • Increases glycogenolysis (breakdown of glycogen into glucose).

Beta 3 Receptors

• Activation: Activated only by epinephrine.
• Location: Found in white and brown adipose tissue.
• Effects:
  • Increases fat oxidation and energy expenditure.
  • Enhances insulin-mediated glucose uptake.

Summary

• Mnemonic: B1 receptors (1 heart), B2 receptors (2 lungs).
• Overall Function: Mobilize energy resources to support the fight or flight response.

Conclusion

• The receptors are crucial in regulating various physiological responses and maintaining homeostasis during stress or emergency situations.

Note: The effects and locations mentioned are primary functions, but these receptors may also be located in other areas of the body with additional roles.

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