Tag: transportation in plants and circulation in animals

One heartbeat in an average man lasts  0.8 second.

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 number of heart beats per minute in resting person is called as normal heart rate. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the contractions of the heart cause an increase in blood pressure in arteries that leads to noticeable pulse.

The human circulatory system consists of a muscular four-chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated. Circulation was discovered by William Harvey. He was the first to recognize the full circulation of blood in the human body and to provide experiments and arguments to support this idea.

The human heart is an example of myogenic heart, it possesses cardiac muscle helping the heart to automatically contract spontaneously; which do not need any stimuli as in neurogenic heart. A myogenic heart is capable of generating a cardiac contraction independent of nervous input. In a myogenic heart, contraction is initiated by the cells called myocyte  (Pacemakers)itself instead of an outside occurrence or stimulus such as nerve innervation.

Smaller animals have much higher metabolism; proportionate to body size, smaller animals tend to have a much smaller heart than larger animals. This means that in order to circulate blood at the same rate, the hearts of smaller animals need to pump more times within a specified time because the volume they can pump each time is smaller.

• Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. 
  
• Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. 
• The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.
  

The sinoatrial node (SAN) is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava.