The heart is a muscular organ composed of specialized muscles called cardiac muscles. The main function of the human heart is to pump blood to various parts of the body. There are several internal factors which enable the human heart to regulate its activities on its own, but there are some external influences as well which regulate cardiac activity. These factors include an autonomic nervous system, chemicals like hormones, ions etc. Let us start our discussion with the cardiac cycle.
Cardiac Cycle
The cardiac cycle helps in the circulation of blood. It includes systole (contraction of cardiac muscles) and diastole (relaxation of cardiac muscles). The cardiac cycle is a normal activity of the human heart and is regulated automatically by the nodal tissues- the sinoatrial node (SA node) and atrioventricular node (AV node). The variation in the cardiac cycle results in an increase or decrease in cardiac output.
The occurrence of a cardiac cycle is illustrated by the heartbeat rate, which is the number of beats per minute. Our heart beats 72 times per minute and is stated as 72 cardiac cycles per minute.
Autonomic regulation-Sympathetic and Parasympathetic Nerves
Cardiac output variation and rhythmic control can also be achieved by the autonomic nervous system (ANS) impulse generation. Medulla oblongata in the brain is responsible for this ANS activity. ANS consists of two nerves- sympathetic nerves and parasympathetic nerves, which contradict each other. Stimulation of sympathetic nerves leads to stronger ventricular and atrial contraction which increases the cardiac output. It also increases heart rate. In contrast to sympathetic action, parasympathetic stimulation reduces the contraction of the atria and ventricles. This results in less cardiac output and heart rate.
Chemical Regulation-Hormones and Ions
Apart from autonomic regulation, there are certain chemicals which can affect the regulation of cardiac activity. These chemicals include hormones like epinephrine, norepinephrine, thyroxine etc. They can increase the contraction and heart rate. Ions are the other chemicals that have an impact on the heart.
The regulation of cardiac activity is influenced not only by these factors. Even the gender of an individual can influence it.
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