Heart disease and cardiovascular disorders
Heart disease is any affliction that impairs the structure or function of the heart, such as atherosclerotic and hypertensive diseases, congenital heart disease, rheumatic heart disease, and other conditions. Heart disease is primarily a disease of lifestyle, and is largely preventable through risk factor awareness and modification. Major modifiable risk factors include high blood cholesterol, high blood pressure (hypertension), type 2 diabetes, and overweight or obesity. The most common type of heart disease, coronary artery disease, occurs when the arteries that supply blood to the heart become hardened and narrowed from fatty plaque buildup on the artery walls, a process called atherosclerosis. Plaque buildup can cause blood clots to form that block the arteries, can narrow the arteries so that less blood can flow to the heart (experienced as chest pain or angina), or can completely block the arteries and the flow of blood to the heart, causing a heart attack (myocardial infarction) and possible death. Lack of blood flow to the heart is referred to as ischemia (localized tissue anemia due to obstruction of the inflow of arterial blood). Over time, coronary artery disease can also weaken the heart muscle and contribute to heart failure (inability of the heart to pump blood to the rest of the body the way that it should), or to arrhythmias (changes in the normal rhythm of the heartbeats). In the literature, coronary artery disease, coronary heart disease, ischemic heart disease, and heart disease are often used interchangeably.
The main job of the heart is to pump blood to the rest of the body. The primary concern with most heart conditions is how much they affect the heart's ability to pump blood. When people use the term heart disease, they are often referring to atherosclerosis, or clogged arteries. Located in the left side of the chest cavity, the heart is a muscular, fist-sized organ that continuously pumps blood, beating as many as 100,000 times a day. The blood that the heart moves carries oxygen and nutrients throughout the body and transports carbon dioxide and other wastes away. The heart ensures its own oxygen supply through a set of coronary arteries and veins. The heart is also an endocrine organ that produces the hormones atrial natriuretic hormone (ANP) and B-type natriuretic peptide (BNP), which coordinate heart function with blood vessels and the kidneys. Internally, the heart is essentially hollow. It is divided vertically into two halves by a septum, and each side of the heart has two internal chambers – an atrium on top and a ventricle on the bottom. Venous blood enters the right side of the heart through the right atrium and is pumped by the right ventricle to the lungs. Oxygenated blood from the lungs enters the left atrium and is pumped by the left ventricle into arteries that carry it throughout the body. Four heart valves regulate the direction and flow of blood through the heart. It is their opening and shutting that gives the heart its characteristic “lub-dub” beat. The heart muscle itself is called the myocardium. Lining the chambers of the heart and the valves is a membrane called the endocardium. Encasing the outside of the heart is the pericardium – a layered membrane that is fibrous on the outside and serous (fluid-secreting) on the inside. The pericardium forms a protective barrier around the heart and allows it to beat in a virtually friction free environment.
Among the most common causes of heart disease are degenerative changes in the coronary blood vessels, infectious diseases, and congenital heart disease. Congenital defects result from abnormal development of the fetal heart, commonly in the valves or septa. Such defects can be precipitated by environmental conditions in the uterus, such as the presence of the rubella virus, or they can be inherited. Infectious diseases acquired after birth, such as rheumatic fever, syphilis, and endocarditis, can also damage the valves of the heart. In addition, the heart muscle itself can be affected: hypertensive heart disease (see hypertension) can cause it to enlarge, and it can become inflamed by rheumatic fever. Arteriosclerotic depositions in the coronary arteries result in the narrowing of these vessels, causing insufficient blood flow and oxygen to the heart muscle, a condition known as coronary artery disease. The characteristic radiating chest pain, angina pectoris, is the most prominent symptom of this condition. Coronary arteries already narrowed by arteriosclerosis are made susceptible to blockage by a clot (coronary thrombosis), causing the death of the heart muscle supplied by the affected artery, a life-threatening event called a myocardial infarction, or heart attack. Hypertensive, coronary, congenital, and other forms of cardiovascular disease, either singly or in combination, can lead to a state in which the heart is unable to expel sufficient blood for the metabolic demands of the body, ultimately resulting in congestive heart failure. Disturbances in the normal heartbeat, called arrhythmias, can occur by themselves or in conjunction with other heart problems, for example infarction affecting the area of the heart that controls the heartbeat. Diseases affecting the heart may be structural or functional. Anything that damages the heart, makes it less efficient, reduces its ability to fill and pump, or decreases the heart’s supply of oxygen will disrupt the coordinated relationship between the heart, kidneys, and blood vessels and will harm not only the heart but the rest of the body as well.
Cardiovascular diseases are those affecting the heart and/or associated blood vessels. Widely known cardiovascular conditions include coronary heart disease, heart failure, rheumatic heart disease, stroke, and peripheral vascular disease. Except for rheumatic heart disease, the diseases are caused by a damaged blood supply to the heart, brain or limbs.The World Health Organization (WHO) has classified diseases of the circulatory system in the International Classification of Diseases (ICD), a compilation of all known conditions according to the system of the body that is affected. In the ICD, diseases of the circulatory system are categorised according to whether they are blood vessel disorders, hypertensive diseases, heart disorders, blood/brain disorders, or rheumatic disorders.
Cardiovascular diseases are often caused by atherosclerosis, a form of arteriosclerosis (hardening of the arteries) affecting large and medium-sized arteries. Cardiovascular disease (CVD) refers to a variety of conditions affecting the circulatory system including hypertension, coronary heart disease, and stroke. The circulatory system is a group of organs that transport blood and the substances it carries to and from all parts of the body. The circulatory system can be considered as composed of two parts: the systemic circulation, which serves the body as a whole except for the lungs, and the pulmonary circulation, which carries the blood to and from the lungs. The organs of circulatory system consist of vessels that carry the blood and a muscular pump, the heart, that drives the blood. The parts of the circulatory system include the heart, along with all the arteries, veins, and capillaries. The organs of the lymphatic system are also considered to be part of the circulatory system. Nutrients, oxygen, and other vital substances are carried throughout the body by the blood, which is pumped by rhythmic contractions of the heart. Blood is pumped from the heart to the arteries, which branch into smaller and smaller vessels as they move away from the heart. The blood passes oxygen and nutrients to the cells and picks up waste in the capillaries, then returns to the heart via a system of veins.
Cardiovascular diseases affect the organs of the circulatory system. The circulatory system is situated in the chest in front of the respiratory system. It is made up of the heart, arteries, capillaries and veins. The heart is the control-centre for the circulatory system, and is responsible for circulating blood throughout the body. The heart receives deoxygenated blood (blood depleted of oxygen) from the veins and replaces it with oxygenated blood (blood rich with oxygen) it receives from the lungs and subsequently pumps out to the rest of the body. The oxygenated blood is transported from the heart throughout the body via the arteries. The arteries always carry blood away from the heart. The blood in the arteries (arterial blood) usually looks bright red because the haemoglobin (oxygen-carrying protein) in the red blood cells is full of oxygen. The blood is supplied to the rest of the body through the capillaries. The capillaries are tiny blood vessels that form a fine network throughout many parts of the body, and connect the smallest arteries (arterioles) and the smallest veins (venules). The walls of the capillaries are very permeable and allow for the exchange of fluids and gases (such as oxygen and carbon dioxide). They distribute oxygenated blood from the arteries to the tissues of the body and feed deoxygenated blood from the tissues back into the veins. The veins transport deoxygenated blood to the heart so that the oxygen levels can be replenished. The blood in the veins usually looks dark red and occasionally purple because the haemoglobin in the red blood cells is depleted of oxygen.