In my Blog-1 on CVDs, we talked about the basic functionality of the heart and how it is placed well-protected inside the human body. We used the simile of a pump for the heart that is responsible for circulating the blood throughout our body at the required pressure running through major vessels viz., arteries and veins. The blood running in arteries carries not only oxygenated blood but also the nutrients to reach every cell of the human body for its functioning, growth, and biochemical responsibility assigned to it for the organ, whose part the cell is, performs in a normal manner.
In addition to that, the blood also brings back through veins the deoxygenated blood to the heart, which then pumps it to the lungs for getting reoxygenated and finally returns it to the heart for its circulation back into the body. In this way, the blood keeps getting circulated 24x7x365 in a human being’s lifetime.
The key lesson we learn from here is the heart must pump blood at the required pressure. To understand this one must first look at the macro components of the heart.
The heart is made of 4 chambers, 4 valves, and major vessels as shown in Fig 1 below.
The blue color used here shows the deoxygenated blood coming back from the human body through the veins (Inferior and Superior Vena Cava), into the Right Atrium (RA). It then moves to Right Ventricle (RV) passing through the Tricuspid Valve (TV), when the Pulmonic Valve (PV) is closed. After the TV closes, the RV muscles on contraction pump the deoxygenated blood to the Lungs through Pulmonic Artery (PA), making it pass through the PV and get oxygenated in the lungs.
Once the blood has been oxygenated, it returns to the Left Atrium (LA) through the Pulmonic Veins (PuV), four in number. The oxygenated blood then moves to Left Ventricle (LV) passing through the Mitral Valve (MV) as it opens when the Aortic Valve (AV) is closed. Once the MV closes, the blood is pushed by LV muscles into Aorta (Ao) with the opening of the AV. All arteries — large or small in a human body get the oxygenated blood as they are all linked ultimately with Aorta in one manner or another because it is the primary source to provide oxygenated blood to the human body.
How does all this happen?
It is certainly a very intriguing question for every human being: a child, an adult, a male, or a female. Imagine it keeps happening 24x7x365 throughout the life of a human being from conception to death. Well, a very simple answer is through the contraction and relaxation of the muscles of the Right and Left sides of the heart.
This leads to the change in pressure across chambers of the heart due to relaxation and contraction of RA, LA, and RV, LV respectively in an alternate manner, by the flow of “electric charge” in the muscles of those four chambers. We will talk about it in the Blog on ECG and in what manner the malfunctioning of electric charging and discharging taking place alternatively, can cause problems in the heart. It is here one can register the role Physics plays to stimulate Biophysical actions.
So, together Physics and Biochemistry play the role in changing the pressure across the valves. The point is how this motion gets triggered periodically throughout one’s life is the first question. We will account for this in another blog for arising pathologies in an exclusive manner. For the moment let us recall what Newton’s First Law says, “A body continues in a state of rest or uniform motion unless acted upon by an external force”! So, due to the change in pressure the movement of the muscles of RA, RV. LA, and LV, ensure the circulation of blood. This physical action of pushing out of the blood by contraction of muscles is termed in medicine as Systole and filling up of the RV and LV by their physical relaxation, is termed as Diastole.
Muscle Movement of the Heart
The heart muscles have a very intriguing characteristic unlike anywhere else in the human body’s other muscles. It can be understood by looking at Fig 2 below shows the 6 degrees of freedom in which movements can take place of the heart’s muscles.
Here the top where the cross-section of the valves can be seen is called the “Base” of the heart. While the pointed lower part forming a tip is called the “Apex” of the heart. So, during the Systole, the LV and RV muscles simultaneously move from Apex towards the Base (upward), also come inward or by closing in, and even have a torsional motion. Fig 3 below depicts this.
Cardiac Arteries and Veins
Till this point we only talked about how the oxygenated blood reaches across the entire human body’s muscles, but what about the heart muscles themselves? From where, how, and when do these muscles get the oxygenated blood and the process of getting back on becoming deoxygenated into the RA?
For the heart’s muscles in specific, it is the Coronary Arteries that supply oxygenated blood to the muscles of RA, RV, LA, and LV. They originate at the “Root of the Aorta” just after the AV at the beginning of the Aorta. So, they get the oxygenated blood in them only when the AV closes as during the Systole the cusps of AV block the openings of the Left Coronary Artery (LCA) and Right Coronary Artery (RCA), by the existence of the Left Coronary Cusp (LCC) and Right Coronary Cusp (RCC) respectively of the heart. Only during diastole, AV closes, the Aorta contracts, and pushes the blood toward the Aortic Arch and then towards the descending Aorta. This contraction of the Aortic muscles also simultaneously pushes the oxygenated blood into the LCA and RCA as now there is no blocking by the LCC and RCC of the coronary arteries anymore. While it is the Coronary Sinus that collects the deoxygenated blood from the RA, RV, LA, and LV and drops it in the Superior Vena Cava, thereby making that blood reach RA for circulation. In a separate Blog on Coronary Arteries, we will discuss it in more detail.
When the valves do not function normally viz., opening and closing, or the muscles of RA, RV, LA, and LV malfunction, it is an immediate indication of the existence of pathologies linked to that specific part or structure of the heart. When it is valves malfunction, we call it valvular pathologies such as Prolapse, Regurgitation, Stenosis, Endocarditis, etc. We will deal with them in a separate Blog exclusively on valvular pathologies.
On the other hand, when it is the malfunctioning of the muscles of RV, LV falls broadly under “Cardiomyopathies”. This too will be dealt with in an independent blog.
The separation between RV and LV is by the Intraventricular Septum (IVS). While the RA and LA have a separation between them called Interatrial Septum (IAS). Another Blog will discuss the pathologies of the IAS and IVS.
We all have seen how blood clots on drying. Since blood is running in arteries as well as veins, because of internal bleeding or injury, or accident it can clot up or there can be plaque formation within the blood vessels. That will result in a hindrance to the normal flow of the blood. Fig 4a and Fig 4b below depict how blood flow can get affected in arteries.
Hence any restriction on the flow of blood to the heart’s muscles when takes place immediately results in the muscles getting deprived of both oxygen and nutrients for their healthy normal performance. The heart muscle getting blood from the specific blood vessels is then investigated and such pathology is removed by various methodologies. We will talk about them too in another blog.
The last group we classified into had “Genetic” issues in the formation of the heart, its structure, and that affecting its functioning as the pump after the child is born. It is an independent section and needs an exclusive blog.
We have so far seen the broad structure of the heart and its functioning at the macro level. However, each component’s malfunction can cause serious effects on the circulation of blood in general in the human body. Unless that is controlled and removed this would result in the body’s different parts malfunctioning, ultimately affecting various organs viz., brain, kidney, liver, spleen, bones, skin, etc. So, blood’s normal circulation by the heart can broadly be called a de facto guarantee of the normal functioning of the human body!