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 correct answer is A, B, and C only

Concept:

• The cardiac activities of the heart are tightly regulated by intrinsic and extrinsic mechanisms.
• The intrinsic mechanism includes the nodal tissue, which generates and propagates electrical impulses within the heart, while the extrinsic mechanism involves the nervous system and hormones that modulate the heart's activity.
  • Normal activities of the heart are regulated intrinsically, i.e., autoregulated by specialised muscles (nodal tissue), hence the heart is called myogenic.
  • A special neural centre in the medulla oblangata can moderate the cardiac function through autonomic nervous system (ANS).
  • Neural signals through the sympathetic nerves (part of ANS) can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output.
  • On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.
  • Adrenal medullary hormones can also increase the cardiac output.

Explanation:

• A. Nodal tissue: The heart has specialized nodal tissues, such as the sinoatrial (SA) node and atrioventricular (AV) node, which generate and conduct electrical impulses. The SA node is known as the natural pacemaker of the heart, initiating rhythmic contractions. This is a critical intrinsic mechanism for regulating heart activity.
• B. A special neural center in the medulla oblongata: The medulla oblongata in the brainstem contains the cardiovascular center that regulates heart rate and blood pressure. This center has two components: the cardiac accelerator center (sympathetic stimulation increases heart rate) and the cardiac inhibitory center (parasympathetic stimulation decreases heart rate). This represents the extrinsic neural regulation of the heart.
• C. Adrenal medullary hormones: Hormones such as adrenaline and noradrenaline secreted by the adrenal medulla play a vital role in increasing heart rate and the force of cardiac contractions during stress or emergencies, part of the "fight or flight" response.

Other options:

• D. Adrenal cortical hormones: These hormones, such as cortisol and aldosterone, are involved in long-term stress responses and electrolyte balance, but they do not play a direct role in the immediate regulation of cardiac activities. Therefore, this option is incorrect.