An essential component of the human body
The heart continuously circulates nutrient-rich, oxygenated blood throughout the body. Additionally, the heart transports immunological components, waste products like carbon dioxide out from the tissues, and other functioning cells that help maintain hemostasis. Five to six liters of blood are pumped out of the body in a single heartbeat as the heart contracts and expands to form a heartbeat. The circulatory system, a network of blood vessels, is the system through which the heart pumps blood. The cardiovascular system, which regulates blood flow, includes the heart and its complex network of capillaries, veins, and arteries. The heart's cardiovascular system helps in maintaining the life of a person.
Systemic and Pulmonary Circuits
The blood from the heart flows through the peripheral circulatory system providing the body organs with nutrients including oxygen and removes waste products like carbon dioxide. The blood vessels of the heart are structured into circulatory routes which transport the blood to various tissues and organs of the body. The pulmonary circuit consists of the right ventricle. This is the route that pumps blood to the lungs. The systemic circuit comprises of the left ventricle and pumps blood to tissues and organs. "Systemic circuit output is the input to the pulmonary circuit and vice versa" (Fitzpatrick 7). The pulmonary circuit carries blood to the lungs' alveoli for gases exchange to occur. The pulmonary circuit flow is in line to ventilation in order to make the oxygen move from the alveoli to the bloodstream (Fitzpatrick 9). This is also to facilitate the movement of carbon dioxide from the bloodstream to the alveoli. At the right ventricle, the pulmonary circuit starts and pumps deoxygenated blood to the big pulmonary trunk which divides forming the right pulmonary artery that pumps blood to the right lung. The left pulmonary artery pumps blood to the left lung. The pulmonary arteries further divide into two lobar arteries that enter the left lung and three in the right lung. Every lobar artery supplies a lung lobe, and more divisions occur resulting in the formation of capillaries around the alveoli. Carbon dioxide is exhaled, and oxygen is inhaled into the lungs and transferred to the blood. Venules form pulmonary capillaries and later unite creating the two vessels known as pulmonary veins that leave the lungs.
The blood which is now rich in oxygen enters the systemic circulation
to distribute the oxygenated and nutrient-rich blood to the entire body parts. This blood is pumped into the aorta from the left ventricle, and it flows to the small systemic arteries. The aim is to distribute the blood to tissues and organs. There is also branching of the Systemic arteries which occur to create smaller arterioles leading to a widespread network of systemic capillaries. Here, gases and nutrients are exchanged between the systemic tissues and the blood in the walls of capillaries. This blood then travels in the capillary vessels and to the systemic venule which carries the deoxygenated blood to systemic veins. The blood from the veins eventually gets into the right atrium through "the superior vena cava, inferior vena cava, and coronary sinus" and is transported back to the heart (Harvey 17).
Heart rate, Stroke Volume and Cardiac Output
Heart rate refers to the number of heartbeats of the heart per unit time and is expressed as beats per minute (BPM). A normal heartbeat is between 70-90 beats in a minute, and this is measured by the body pulse. The pulse rate can also be measured with the use of heart rate monitors or electrocardiographs. Stroke volume is the blood amount that is pumped from the left ventricle in every heartbeat. It is found by using measurements of ventricle volumes by getting the difference between the end-systolic volume and end-diastolic volume. Cardiac output is the amount of blood that is pumped by the heart in every heartbeat. The stroke volume is significant in determining the cardiac output. Cardiac output is the product of the heart rate and the stroke volume. Hence, the relationship between the cardiac output, the stroke volume, and the heartbeat is given as: Cardiac output = Heart Rate X Stroke Volume and it is expressed in liters per minute (Fitzpatrick 28).
Factors Affecting Heart Rate
Emotional stress is one of the key factors that affect the heartbeat. Human response to psychological stress is explained by an increase in the heart rate. Fear, anxiety, and depression cause the release of hormones which make the heart pump harder and faster in providing the muscles with the essential energy. Physical stress resulting from hard work also leads to an increase in the rate at which the heart pumps blood. This is done in order to make the body meet the demand for more oxygen required. Vagal stimulation involving special sensors in the body which cause a change in the blood pressure also increase the heart rate. For example, when a person lifts a heavy material or delivers a baby, the body pressure increases and this increases the heart rate. Additionally, some medications alter the heart rate causing an increase or a slower heartbeat. More importantly, illness tends to affect the heart rate of a person. For instance, fever places a metabolic demand increase on the body, and thus the heart will increase the heartbeat to meet the increased demand for the oxygen. Other illnesses like anemia and thyroid disease as well as trauma affect the heart rate. Some diseases will make the heart rate increase, and some will slow it down. Heart disease also affects the heartbeat and can make it faster or slower or even cause heart failure. The body position affects the heartbeat to either increase or decrease. When a person moves from standing to sitting or lays down the heartbeat decreases. The environment and the sex of a person affect the heart rate. When it is hot, the heart rate tends to increase (Sutton and Fagan 18). This is also the reason why the heartbeat increases when one exercises because the body temperature increases. Women also tend to have a small cardiovascular system compared to men, and this makes women have a low stroke volume. Hence women have a higher heart rate compared to men.
Layers of Walls of the Blood Vessels
The blood vessels have well-structured blood vessels which enable it to endure the pressure that comes from the circulation of blood. The walls of the blood vessels, that is the capillaries, the arteries, and the veins, are structured having three layers called tunic. The tunic surrounds the lumen, and the three layers are called the tunica intima, tunica media, and tunica externa. Tunica intima is the innermost part of the blood vessel. It has an endothelium substance which is an epithelial lining of the vessels. Also, it contains the sub-endothelial layer which contains a thin layer of areolar connecting the tissues. The middle part is called tunica media and comprises smooth muscle cells that are circularly arranged in layers. The smooth muscles undergo contraction leading to vasoconstriction. This is the narrowing of the blood vessels when the blood is pumped and when the vessel relaxes; it causes vasodilation. Vasodilation refers to the widening of the blood vessels (Sutton and Fagan 15). The tunica externa forms the outer layer of the blood vessel. It has areolar connecting tissues that contain collagen and elastic fibers. This layer assists in anchoring the vessel to the other structures.
Structure and Function of Blood Vessels
The arteries are the blood vessels that carry blood away from the heart to the other parts of the body while veins carry the blood back to the heart. On the other hand, the capillaries transport the blood to the body tissue cells and denote to be the exchanging sites of the gases, nutrients, and wastes. When the blood leaves the heart, it enters the arteries which are the vessels involved in transporting blood away from the heart. The arteries then branch into arterioles and branch more to create capillaries. These vessels are located on every organ and are the site of nutrient and gaseous exchange. The capillaries, which are smaller, coalesce forming large vessels called venules that later combine to form veins. The veins carry blood back to the heart.
Works Cited
Fitzpatrick, Anne. The Heart. North Mankato, Minn. Smart Apple Media, 2004.
Harvey, William. The Circulation Of The Blood. New York, Cosimo Classics, 2006.
Sutton, Paul, and Toby Fagan. Cardiovascular System. Edinburgh, Mosby, 2008.
