Tag: biology

Cardiac output is the blood volume pumped in a minute by the core. It is equivalent to the rate of heart multiplied by the quantity of the stroke. So if there are 70 beats per minute and with each heart beat 70 ml of blood is drawn, the power production is 4900 ml / minute. This value is typical of an average resting adult, although during intense practice, cardiac output can reach  upto 30 liters / minute.

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 (adrenaline, noradrenaline) can also increase the cardiac output.

Normal activities of the heart are regulated intrinsically, i.e., auto regulated 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. Epinephrine / adrenaline increases the heart rate.

Sino-atrial node (SAN) generates the maximum number of action potentials per minute (70-75/min) and therefore, it sets the pace of the activities of the heart. Hence, it is called as the cardiac pacemaker.

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 (dubb/dupp) is associated with the closure of the semilunar valves. 

The sino-atrial node (SAN) can generate the maximum number of action potentials, i.e., 70-75 /min. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called as the natural cardiac pacemaker. 

The cardiac cycle starts with atrial systole. It represents the contraction of the myocardium of the left and right atria by which blood is forced into the ventricles. It progresses to ventricular systole, in which the ventricles contract and blood forced  into the aorta and pulmonary artery. After that atrial diastole occurs which means the relaxation of atria.The cardiac cycle ends with ventricular diastole in which ventricles are relaxing and also filling with blood in preparation of the next cycle.

In the human heart, the sino-atrial node (SAN) can generate 70-75 beats/min and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker. Our heart normally beats 70-75 times in a minute (average 72 beats/min).

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 atrio-ventricular bundle.