NEET 2025 Botany Question 112 Solution

Normal activities of the human heart are regulated intrinsically, i.e., auto-regulated by specialized cardiac muscle tissues called nodal tissue (Sinoatrial node, Atrioventricular node, bundle of His, Purkinje fibers). Hence, human heart is termed myogenic. Thus, Statement A is correct.

A special neural center in the medulla oblongata moderates cardiac function through the autonomic nervous system (ANS):

• • Sympathetic neural signals increase the rate of heartbeat, the strength of ventricular contraction, and thereby the cardiac output.
• • Parasympathetic neural signals (via vagus nerve) decrease the rate of heartbeat, speed of action potential conduction, and cardiac output.
• • Thus, Statement B is correct.

Hormonal regulation of heart rate:

• • Adrenal medullary hormones (epinephrine and norepinephrine / catecholamines) act during emergency / fight-or-flight states to significantly increase the rate of heartbeat, stroke volume, and cardiac output. Thus, Statement C is correct.
• • Adrenal cortical hormones (glucocorticoids like cortisol and mineralocorticoids like aldosterone) are involved in carbohydrate metabolism, anti-inflammatory responses, and electrolyte balance (Na⁺/water retention in renal tubules), not direct cardiac pacing. Thus, Statement D is incorrect.

Only A, B, and C are true regulators of cardiac activities according to the canonical NCERT text.