Cardiac activities of the heart are regulated by:

A .  Nodal tissue

B.  A special neural centre in the medulla oblongata

C.  Adrenal medullary hormones

D.   Adrenal cortical hormones

Choose the correct answer from the options given below :

The regulation of cardiac activity involves several physiological mechanisms that act together to maintain heart rate and contractility.

1. Nodal tissue (Option A) – The sino‑atrial (SA) node and atrioventricular (AV) node are intrinsic pacemakers located in the heart. They generate and conduct electrical impulses that initiate each heartbeat, thereby directly regulating the timing of cardiac contractions.

2. A special neural centre in the medulla oblongata (Option B) – The cardiovascular centre in the medulla, comprising the cardiac accelerator and depressor areas, receives input from baroreceptors and chemoreceptors. It modulates autonomic (sympathetic and parasympathetic) outflow to the heart, adjusting heart rate and force of contraction in response to physiological demands.

3. Adrenal medullary hormones (Option C) – The adrenal medulla secretes catecholamines (epinephrine and norepinephrine) into the bloodstream during stress or exercise. These hormones bind to β‑adrenergic receptors in the heart, increasing heart rate (positive chronotropic effect) and contractile strength (positive inotropic effect).

Adrenal cortical hormones (Option D) primarily influence electrolyte balance and water retention; they do not have a direct, acute role in regulating heart rhythm or contractility. Therefore, they are not considered part of the immediate regulation of cardiac activity.

Combining the above points, the correct set of regulators is A, B and C Only.