The circulatory system consists of the heart, blood vessels, and blood. Blood vessels encompass arteries, arterioles, veins, and capillaries. All these parts play their respective roles in the normal functioning of the circulatory or cardiovascular system. The basic structure of the circulatory system can be considered as a closed loop that begins at the heart and finishes there. For better understanding, let's have a discussion about the heart.
Heart: The human heart is divided into four chambers - left atrium, left ventricle, right atrium, and right ventricle. The ventricle walls are thicker and stronger as compared to the atria walls. After all, these chambers contract and push blood to the blood vessels. The right atrium is the upper right chamber that receives deoxygenated blood via the superior vena cava (for upper body) and inferior vena cava (for lower body). The left atrium collects the oxygenated blood from the pulmonary veins and is pumped into the aorta (biggest artery of the heart), to be distributed to arteries and arterioles.
Working of the Circulatory System
As we all are aware, the main purpose of the circulatory system is to provide nutrients and oxygen to the various parts of the body, via the blood, which is circulated through the veins and arteries. Arteries carry the oxygenated blood from the heart to the cells and tissues, whereas veins return the oxygen-depleted blood from the cells and tissues to the heart. Based on the mode of functioning, the circulatory system can be classified into the two categories - the systemic circulation and the pulmonary circulation.
The Systemic Circulation: The systemic circulation is actually a loop starting from the heart and distributing to various parts of the body, which works in contrast to the pulmonary circulation. In the systemic circulation, arteries collect the oxygen-rich blood from the heart and is transported to the body tissues. In the process, oxygen from the blood (or precisely, the red blood cells, RBCs) is diffused into the body cells; whereas carbon dioxide from the cells is diffused in the blood. This exchange of gases takes place with the help of small capillaries that surround the body cells.
The Pulmonary Circulation: The pulmonary circulation is also a loop that begins in the heart and continues to the lungs. It is that portion, where the deoxygenated blood from the heart is carried to the lungs and in turn, returns oxygenated blood to the heart. The oxygen-depleted blood leaves the heart (right ventricle) through the two pulmonary arteries and moves into the lungs. In the lungs, respiration takes place in which the red blood cells (RBCs) release carbon dioxide and absorbs oxygen. Oxygenated blood from the lungs is then carried back to the heart (left atrium) with the help of pulmonary veins. The systemic circulation distributes this oxygen-rich blood to the body parts.
Working of the circulatory system will not be complete, unless we talk about the cardiac cycle. A cardiac cycle is defined as one complete heartbeat, which comprises two phases - systole and diastole. In the former case, contraction of ventricles takes place to pump blood for pulmonary and systemic circulation; whereas, the ventricles relax and blood is filled in the atria in diastole phase. This way, blood pumps in the close loop of the circulatory system. Any disorder in the heart and blood vessels can lead to heart diseases, such as atherosclerosis, hypertension, coronary artery disease, heart attacks, and stroke.
To sum up, the circulatory system works in association with the other organ systems of the body. For example, it functions in coordination with the respiratory system and digestive system to supply oxygen and nutrients to the body. Also, blood carries the messenger chemicals - hormones, secreted by the organs of the endocrine system. Thus, the circulatory system is responsible for circulating hormones for proper communication between the body organs.