Human Physiology

Lesson 31 : Heart

Heart Structure, Special Properties and Functions.

Heart: is a muscular pump which consists of two pumps arranges in series through blood vessels. Left pump (comprising of left atrium and left ventricle) is meant for distribution of blood to all parts of body through systemic arteries. The right pump (comprising of right atrium and ventricle) is meant for distribution of blood into the pulmonary arteries and subsequently into lungs (Fig 9a). Right atrium and ventricles are thin walled chambers. Right atrium receives blood from superior, inferior venacavae and coronary veins. Blood from right atrium is pushed into right ventricle through tricuspid valves which prevents back flow of blood (Fig 31a). Right ventricle pushes blood into pulmonary arteries (right and left) subsequently to two lungs through semi lunar valves (half moon shaped valves) preventing back flow of blood into ventricle. Left atrium receives oxygenated blood from lungs through pulmonary veins (left & right) and pushes into left ventricle through mitral valve (bicuspid valve, cup shaped) which prevents back flow of blood into atrium. Left ventricle is a thick walled structure for generating much greater force of pumping required to push blood into whole of the body. Oxygenated blood from left ventricle is pushed into aorta through semilunar valves.

Special properties of heart: Heart is a vital organ of body that works uninterruptedly from fetal life till death of individual for continued pumping of blood. This specialized non-stop functioning could be achieved through a specialized muscle present in heart called myocardium. Some important physiological features are listed below:

1. Ability to work without glucose: The myocardium can utilize amino acids, ketone bodies, lactic acid and fatty acids as energy substrate, so it can work even under energy deprived states.
2. Evades development of tetanus: Typical skeletal muscles can develop tetanus if works at faster speed but myocardium do not develop tetanus even if contracts more than 300 times per minute.
3. All myofibrils contracts simultaneously: myocardium fibers possesses structural and functional syncytium due to which all fibers contracts simultaneously to pump blood effectively into arterial system.
4. Automacity of myocardium: The heart muscle has its own pace-maker called sino-atrial node (SA node) which keeps heart energized with out requiring nervous stimulation. There is also a reserve pacemaker called atrio-ventricular node (AV node).

Owing to these properties the heart is able to adapt itself in extreme conditions like extreme stress, exhaustion of energy substrate, brain injuries etc. in an un-interrupted and effective manner.