Tag: cardiac cycle

'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.

Heart has two ventricles and two atria, left and right respectively. Deoxygenated blood enters the left atrium through superior & inferior vena cava, when the atria relaxes, blood enters into it, whereas impulse from SA node causes contraction of atria which leads to the flow of blood into ventricles.

The pulmonary trunk is a significant human blood vessel from the right ventricle. It branches into the pulmonary arteries of the right and left that lead to the lungs.