(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)
Out of the numerous organs found in the human body, the heart is perhaps the most well-known. This is probably because since the dawn of time, man has put his hand on his chest and felt the rhythmic pounding of his heart – a reminder that he is alive. The function of the heart is to pump oxygenated blood from the lungs to the rest of the body via the circuit of blood vessels (vascular system).
The heart relies on electricity to pump blood in a rhythmic, autonomous way. Because of this property, a heart will beat on its own even if you took it out of the human body. Every muscle in the human body requires an electrical impulse for it to contract. This is also the case in the heart, but unlike the skeletal muscle in other parts of the body which receive their impulses from the brain and spinal cord, the heart has its own source of electricity.
The heart has a small group of pacemaker cells in the right atrium called the sinoatrial node, which always fires electrical impulses at a set rate and rhythm (sinus rhythm). The SA node will do this without any instruction from the brain. The impulse from the SA node spreads throughout the atria of the heart, causing the atrial muscles to contract simultaneously to squeeze blood into the ventricles. The impulses then reach the atrioventricular node, which filters the signals and sends a stream of electricity through a wiring system known as the Purkinje fibres. These fibres act like a high-speed internet cables running down the centre of the heart, sending rapid signals through out the ventricles to induce a strong, cooridnated contraction in both ventricles. This causes blood to be forcefully squeezed out through the two outlet vessels of the heart: the pulmonary artery (to the lungs) and the aorta (to the rest of the body).
Although the SA node is completely autonomous, it can be controlled using hormones, nerve signals and medications. For example, adrenaline will speed up the rate the heart beats at while massaging the carotid arteries in the neck will slow the heart down.
One thing people wonder about is what the doctors listen to when they put a stethoscope to a patient’s chest. Everyone knows the heart makes a rhythmic “lub dub” sound as it beats away, but what information could that give away? A doctor can gain much information about the heart from a cardiac examination by taking the pulse and blood pressure, but listening to the heart (auscultation) may reveal a medical sign known as a murmur. A murmur is any added sound other than the normal “lub dub” sound of the heart. For example, a heart with aortic stenosis may give the sound “shhhhhhh” as if it was giving off static. This sound is produced when blood flow in the heart is turbulent and not smooth. This may be for a number of reasons but the most common reason is because the valves of the heart are not functioning properly. For example, the valve between the left atrium and left ventricle may be leaky (mitral regurgitation) or the valve at the start of the aorta may be stiff and narrowed (aortic stenosis).
By carefully listening to the sound the heart makes, an experienced doctor may pick up on such structural abnormalities even without the use of fancy medical imaging technologies.