Tag: transportation in plants and circulation in animals

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. 

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 pressure exerted on the arterial wall during left ventricular contraction pushing blood into the aorta. This is called ventricular pressure or ventricular systole. During ventricular systole closing of atrioventricular valves produces the first heart sound lubb. Thus, the correct option is B.

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. Normal adult human heart rate ranges from 60-100 bpm. So, the correct answer is option B.

The sino-atrial node (SAN) is a mass of nodal tissue found in the upper part of right auricle. It generates the nerve impulses which is responsible for starting the contraction of the heart. It controls the rhythm of the heart contraction. Hence, it is called as the natural pacemaker of the heart.

Chordae _ tending are numerous, strong inelastic thread like tendons  present in the ventricles of the  mammalian heart.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the pumping action of the heart causes an increase in blood pressure in arteries that leads to noticeable pulse. Hence pulse rate can be defined as the rate at which the blood is pumped.