Cardiovascular and blood system

Background


The cardiovascular system, primarily a transport and exchange system for oxygen, carbon dioxide, nutrients and metabolic by-products, comprises the heart and the pulmonary and systemic circulations. It is a complex mechanical, chemical, neural and hemodynamic system in which the variables are interconnected through a variety of direct or feedback mechanisms. Important systemic circulatory variables include heart rate, stroke volume, cardiac output, peripheral resistance, and venous pressure. A most important factor is systemic arterial pressure (SAP), which maintains blood perfusion to the brain and other vital organs.

Cardiovascular Disease Risk Factors

Based on this, the cardiovascular system is a key component in the human body and health. But multiple reasons in our environment can cause cardiovascular disorders and/or conditions, including race, age, lipids (low density lipoprotein, triglycerides, high density lipoprotein) physical inactivity, obesity, hypertension, diabetes, the metabolic syndrome, smoking, and a family history of cardiovascular disease. Cardiovascular disorders/conditions are associated with health problems, family heritage and environment. In the human journey to treat cardiovascular disorders multiple drugs of different mechanisms were developed. Targeted therapy is now new kind of treatment. Some targets such as cyclooxygenase (COX), the epidermal growth factor receptor (EGFR), and muscarinic acetylcholine receptor (mAChR ) are choice for research.

Cardiovascular disease refers to diseases of the circulatory system affecting the anatomy and physiology of the heart and blood vessels. The most common types of cardiovascular disease include hypertension, ischemic heart disease, cerebrovascular disease (stroke), peripheral vascular disease, heart failure, rheumatic heart disease, valvular heart disease and congenital heart disease.

Blood is partly made up of cells as well as liquid. The liquid part of blood is known as plasma and is made up of organic and inorganic substances in aqueous solution. The plasma solution is itself mostly protein by weight. Plasma proteins are classified as albumins, globulins, or fibrinogens. The non-liquid portion of blood is composed of cells. Over ninety-nine per cent of blood cells are erythrocytes, also known as red blood cells. Other cells in the blood are leukocytes that protect against pathogens and cancer, and finally platelets which are more like cell fragments than actual cells. Blood vessels have three layers. The inner layer, called the intima, is mainly composed of endothelial cells that have the ability to change the vessel’s diameter. The middle layer, called the media, is made of elastin, collagen, and smooth muscle whose composition determines the elastic properties of the vessel. The adventitia is the outer layer of the vessel that is mostly connective tissue.

The transport of blood is accomplished through two circuits within the cardiovascular system: the systemic and pulmonary circuit. Each circuit begins and ends at the heart, and the heart itself is divided longitudinally. The left and right sides of the heart are each divided into two chambers, the atrium and ventricle. The atrium is the upper chamber of the heart and it empties blood into the ventricle, the lower chamber. When blood is pumped through the pulmonary circuit, it is pumped from the right ventricle to the lungs and eventually to the left atrium. The pulmonary circuit allows red blood cells to expel carbon dioxide and replenish oxygen which is carried into the systemic circuit. In systemic circulation, blood travels from the heart’s left ventricle to the organs of the body and back to the right atrium. Blood transport through the systemic circuit begins when the blood leaves the left ventricle via the aorta. Vessels branch from the aorta into arteries, arteries divide into arterioles, and arterioles branch into capillaries which are estimated to number in the range of ten billion. Capillaries regroup into larger sized venules that unite to form veins. Veins unite to form the inferior and superior vena cava that return blood from the upper and lower regions of the body and return the blood to the right atrium.

Each cycle of the heart consists of two phases: systole and diastole. Systole is the period of ventricular contraction and blood ejection, while diastole is the period of ventricular relaxation and blood filling. Systole can be divided into two parts. The first part of systole is known as isovolumetric contraction. Isovolumetric contraction occurs when the ventricles of the heart are contracting, but no blood is ejected because all the valves of the heart, semilunar and atrioventricular valves are closed. Eventually, the contraction of the ventricles create a high enough pressure to open the semilunar valves and eject blood. The semilunar valves open when the pressure inside the ventricles is greater than the pressure within the aorta and pulmonary trunk. Isovolumetric contraction acts so rapidly within the ventricles that pressure increases to a point that almost instantaneously ventricle pressure exceeds aortic pressure. Once the semilunar valves open, there is very little resistance to flow across the annuli leading to a very insignificant pressure gradient value. Ejection of blood from the ventricles is very rapid at first and gradually decreases. The decrease in the strength of ejection of blood is directly correlated to the reduction in the strength of ventricular contraction near the end of systole. As the ejection weakens, the rate of blood leaving the ventricles leaving the heart is less than the rate of blood leaving the aorta and pressure in the aorta decreases. Diastole can also be divided into two parts. The first part of diastole begins at the time when the ventricles relax, returning the ventricles to a lower pressure than the aortic and pulmonary trunk that they empty into and closing the semilunar valves. The atrioventricular valves are closed at the beginning of the relaxation phase of diastole, meaning that this phase is a period of isovolumetric relaxation since no blood is allowed to enter the heart’s chambers. The atrioventricular valves re-open once the pressures of the ventricles are lower than the pressure exerted by the blood flowing into the atria commencing the start of the second phase of diastole. Diastole ends when the atria contract to assist in the timely filling of the ventricles.

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