When the normal heart of a man is injected with physiological concentration of adrenaline, it shows

Options

A. Systolic arrest
B. Decreased rate
C. Sustained increased rate
D. First increased then normal rate

Answer

**Step-by-Step Solution:**

1. **Understanding Adrenaline:** Adrenaline, also known as epinephrine, is a hormone produced by the adrenal medulla, which is the inner part of the adrenal glands located on top of the kidneys. It plays a crucial role in the body's fight-or-flight response.

2. **Effects of Adrenaline on the Heart:** When adrenaline is injected into the heart, it typically causes an increase in heart rate. This is part of the body's response to stress or emergency situations, allowing for more blood flow and energy availability.

3. **Physiological Concentration of Adrenaline:** The term "physiological concentration" refers to the normal levels of adrenaline that the body would naturally produce. At this concentration, the heart's response is expected to be regulated and not overwhelming.

4. **Expected Response:** Upon injection of adrenaline at physiological levels, the heart will initially increase its rate (tachycardia) as it responds to the hormone. After this initial increase, the heart rate may stabilize back to a normal level once the immediate effects of adrenaline subside.

5. **Conclusion:** Therefore, the correct response of a normal heart when injected with physiological concentrations of adrenaline is that it will show an initial increase in heart rate followed by a return to normal rate.

**Final Answer:** The normal heart of a man, when injected with physiological concentrations of adrenaline, shows an initial increase in heart rate followed by a return to normal rate.

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