Tag: human heart

Purkinje system is mainly present in the ventricle myocardium. They spread impulse in ventricles generated by the AV node.

Systole is defined as the ventricular contraction of heart which occurs between the first and second heart sounds of the cardiac cycle. There is pumping of blood into the aorta and pulmonary trunk and lasts for 0.3-0.4 second. During systole arterial blood pressure is maximum. 

The cardiac cycle refers to a complete heartbeat from its generation to the beginning of the next beat. The frequency of the cardiac cycle or the heart rate is expressed as heart beats per minute.

During each cardiac cycle two prominent sounds are produced, which can be easily heard through a stethoscope. The first heart sound (lubb) is associated with the closure of the tricuspid and bicuspid valves, whereas the second heart sound (dupp / dubb) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance.

The cardiac cycle is regulated by specialized areas in the heart wall, that forms the conduction system of the heart. Two of these areas are tissue mass, called as nodes; the third is a group of fibers called as the atrioventricular bundle. 

'Bundle of His' is a network of muscle fibres, found in the walls of ventricles. They originate from AV node and further give rise to Purkinje fibres. This helps in maintaining the rhythmic contraction of the ventricles. 

The cardiac impulse is initiated in the sino-atrial node also known as natural pacemaker. It then travels to the atrio-ventricular node. From there through the Purkinje fibres to the ventricles. The atrio-ventricular node regulates the rhythm of the heart rate mainly. The delay in conduction of impulse in this node changes the duration of contraction between the atria and the ventricles. Hence AV node is called as the pace-setter.

A normal heart rate is 60 to 80 beats per minute. However, in certain conditions, the heart beat is accelerated. The major system involved in acceleration of heartbeat is sympathetic nervous system. It releases hormones like adrenaline and noradrenaline during stress or excitement. Exercise also stimulates sympathetic nervous system to accelerate the heartbeat. Apart from heartbeat, sympathetic nervous system and noradrenaline constricts blood vessels, goose bumps, sweating, increased blood pressure, dilation of pupil.

A) Bundle of His is a muscular tissue.