Describe the role of adrenaline in the control of metabolic activity, limited to: (a) increasing the blood glucose concentration (b) increasing heart rate

Adrenaline, also known as epinephrine, plays a crucial role in the control of metabolic activity, particularly during stressful situations characterized by the “fight or flight” response. Here’s how it affects metabolic processes, specifically focusing on increasing blood glucose concentration and increasing heart rate.

(a) Increasing Blood Glucose Concentration

• Mechanism of Action: Adrenaline increases blood glucose levels primarily through two mechanisms:
  • Glycogenolysis: Adrenaline stimulates the liver and muscle cells to break down glycogen (the stored form of glucose) into glucose, which is then released into the bloodstream. This process provides a rapid source of energy.
  • Gluconeogenesis: In addition to glycogenolysis, adrenaline promotes gluconeogenesis, the synthesis of glucose from non-carbohydrate sources (like amino acids and glycerol), further increasing blood glucose levels.
• Physiological Effect: The increase in blood glucose concentration ensures that sufficient energy is available for immediate use by muscles and other vital organs during stressful situations. This rapid mobilization of energy is essential for physical responses such as fighting or fleeing from danger.

(b) Increasing Heart Rate

• Mechanism of Action: Adrenaline exerts its effects on the heart by binding to beta-adrenergic receptors located in cardiac tissue. This binding triggers several physiological changes:
  • Increased Heart Rate: Adrenaline accelerates the firing rate of the sinoatrial (SA) node, which is the natural pacemaker of the heart. This leads to an increase in heart rate (tachycardia).
  • Enhanced Cardiac Output: The hormone also increases the force of heart contractions, leading to greater stroke volume (the amount of blood pumped with each heartbeat). This combination results in a significant increase in cardiac output, ensuring that more blood—and therefore more oxygen and nutrients—are delivered to muscles and organs during stress .
• Physiological Effect: The increase in heart rate prepares the body for intense physical activity by ensuring that oxygen-rich blood reaches tissues quickly. This response is critical for optimizing performance during emergencies or high-stress situations