cardiovasculer

Cardiovascular disease

Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels (arteries and veins).^[1] While the term technically refers to any disease that affects the cardiovascular system (as used in MeSH C14), it is usually used to refer to those related to atherosclerosis (arterial disease). These conditions usually have similar causes, mechanisms, and treatments.

Most countries face high and increasing rates of cardiovascular disease. Each year, heart disease kills more Americans than cancer. In recent years, cardiovascular risk in women has been increasing and has killed more women than breast cancer.^[2] A large histological study (PDAY) showed vascular injury accumulates from adolescence, making primary prevention efforts necessary from childhood.^[3][4]

By the time that heart problems are detected, the underlying cause (atherosclerosis) is usually quite advanced, having progressed for decades. There is therefore increased emphasis on preventing atherosclerosis by modifying risk factors, such as healthy eating, exercise, and avoidance of smoking.

Cardiovascular system

n      The cardiovascular system has three types of blood vessels:

Arteries (and arterioles) – carry blood away from the heart

Capillaries – where nutrient and gas exchange occur

Veins (and venules) – carry blood toward the heart.

n      Arteries and arterioles take blood away from the heart.

The largest artery is the aorta.

The middle layer of an artery wall consists of smooth muscle that can constrict to regulate blood flow and blood pressure.

Arterioles can constrict or dilate, changing blood pressure.

n      Capillaries have walls only one cell thick to allow exchange of gases and nutrients with tissue fluid.

Capillary beds are present in all regions of the body but not all capillary beds are open at the same time.

Contraction of a sphincter muscle closes off a bed and blood can flow through an arteriovenous shunt that bypasses the capillary bed.

n      Venules drain blood from capillaries, then join to form veins that take blood to the heart.

Veins have much less smooth muscle and connective tissue than arteries.

Veins often have valves that prevent the backward flow of blood when closed.

Veins carry about 70% of the body’s blood and act as a reservoir during hemorrhage.

n      The heart is a cone-shaped, muscular organ located between the lungs behind the sternum.

The heart muscle forms the myocardium, with tightly interconnect cells of cardiac muscle tissue.

The pericardium is the outer membranous sac with lubricating fluid.

The heart has four chambers: two upper, thin-walled atria, and two lower, thick-walled ventricles.

The septum is a wall dividing the right and left sides.

Atrioventricular valves occur between the atria and ventricles – the tricuspid valve on the right and the bicuspid valve on the left; both valves are reenforced by chordae tendinae attached to muscular projections within the ventricles.

Passage of Blood Through the Heart

n      Blood follows this sequence through the heart: superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk and arteries to the lungs → pulmonary veins leaving the lungs → left atrium → bicuspid valve → left ventricle → aortic semilunar valve → aorta → to the body.

The pumping of the heart sends out blood under pressure to the arteries.

Blood pressure is greatest in the aorta; the wall of the left ventricle is thicker than that of the right ventricle and pumps blood to the entire body.  Blood pressure then decreases as the cross-sectional area of arteries and then arterioles increases.