The heart is an organ responsible for pumping blood through the blood vessels using rhythmic contractions of cardiac muscle.
The pericardium is a thick, membranous, fluid-filled sac which encloses, protects, and nourishes the heart.
The heart wall is comprised of three layers: the outer epicardium, the middle myocardium, and the inner endocardium.
The heart has four chambers. The two atria receive blood into the heart and the two ventricles pump blood into circulation.
Great vessels are the major vessels which directly carry blood into or out of the heart.
The myocardium (cardiac muscle) is the thickest section of the heart wall and contains cardiomyocytes, the contractile cells of the heart.
The cardiac skeleton, also known the heart's fibrous skeleton, consists of dense connective tissue in the heart that separates the atria from the ventricles.
Coronary circulation is the circulation of blood in the blood vessels of the heart.
The atrioventricular valves separate the atria from the ventricles and prevent backflow from the ventricles into the atria during systole.
The semilunar valves allow blood to be pumped into the major arteries while preventing backflow of blood from the arteries into the ventricles.
The cardiovascular system has two distinct circulatory paths, pulmonary circulation and systemic circulation.
Cardiac muscle appears striated due to the presence of sarcomeres, the highly-organized basic functional unit of muscle tissue.
Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release conducted through the intercalated discs.
Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of adenosine triphosphate (ATP) for cardiac function.
Cardiac contraction is initiated in the excitable cells of the sinoatrial (SA) node by both spontaneous depolarization and sympathetic activity.
An electrocardiogram, or ECG, is a recording of the heart's electrical activity as a graph over a period of time.
The two major heart sounds are "lub" (from the closure of AV valves) and "dub: (from the closure of aortic and pulmonary valves).
The cardiac cycle describes the heart's phases of contraction and relaxation that drive blood flow throughout the body.
Cardiac output (Q or CO) is the volume of blood pumped by the heart, in particular by the left or right ventricle, in one minute.
Aerobic exercise promotes cardiovascular health, while physical inactivity is associated with increased morbidity and mortality.
Vasculogenesis is the development of new blood vessels.
As a person ages, the walls of the heart thicken, the heart becomes heavier, valves stiffen and leak, and the aorta becomes larger.
Heart failure is defined as the inability of the heart to supply blood to the organs of the body.
Cardiopulmonary resuscitation is an emergency procedure that maintains blood flow to the heart until the return of spontaneous circulation.
Pericarditis is a swelling of the pericardium, the protective, fibrous sac surrounding the heart.
Endocarditis and myocarditis are driven by inflammation of the heart.
Valve disorders involve stenosis, insufficiency, or regurgitation.
Ischemic heart disease is caused by reduced blood flow to the heart muscle, usually due to atherosclerosis, and can lead to a heart attack.
A artificial pacemaker is a medical device that delivers electrical impulses to the heart muscles to regulate the beating of the heart.
Heart murmurs are pathologic heart sounds indicative of valve and blood flow abnormalities.
Congestive cardiac failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the body's needs.
Coronary artery disease (CAD) describes the accumulation of atheromatous or fatty plaques within the walls of the coronary arteries.
A congenital heart defect is a defect in the structure of the heart and great vessels that is present at birth.
Cardiac arrhythmia (irregular heartbeat) are a heterogeneous group of conditions involving abnormal electrical activity in the heart.
Blood vessels are flexible tubes that carry blood, associated oxygen, nutrients, water, and hormones throughout the body.
Blood vessels carry nutrients and oxygen throughout the body and aid in gas exchange.
Arteries are high-pressure blood vessels that carry oxygenated blood away from the heart to all other tissues and organs.
An elastic or conducting artery has a large number of collagen and elastin filaments in the tunica media.
Distributing arteries are medium-sized arteries that draw blood from an elastic artery and branch into resistance vessels.
A circulatory anastomosis is a connection or looped interaction between two blood vessels.
An arteriole is a small diameter blood vessel in the microcirculation system that branches out from an artery and leads to capillaries.
Capillaries, the smallest blood vessels in the body, are part of the microcirculation.
Venules are small blood vessels in the microcirculation that connect capillary beds to veins.
Veins are blood vessels that carry blood from tissues and organs back to the heart; they have thin walls and one-way valves.
The circulatory system is the continuous system of tubes that pumps blood to tissues and organs throughout the body.
Humans have a closed cardiovascular system, meaning that blood never leaves the network of arteries, veins, and capillaries.
Blood pressure is a vital sign reflecting the pressure exerted on blood vessels when blood is forced out of the heart during contraction.
The measurement of blood pressure without further specification usually refers to systemic arterial pressure measured at the upper arm.
Venous pressure is the vascular pressure in a vein or the atria of the heart, and is much lower than arterial pressure.
The cardiovascular system plays a role in body maintenance by transporting hormones and nutrients and removing waste products.
Neural regulation of blood pressure is achieved through the role of cardiovascular centers and baroreceptor stimulation.
Blood pressure is controlled chemically through dilation or constriction of the blood vessels by vasodilators and vasocontrictors.
Consistent and long-term control of blood pressure is determined by the renin-angiotensin system.
Checking circulation involves measurement of blood pressure and pulse through a variety of invasive and noninvasive methods.
Pulse is a measurement of heart rate by touching and counting beats at several body locations, typically at the wrist radial artery.
Measurement of blood pressure includes systolic pressure during cardiac contraction and diastolic pressure during cardiac relaxation.
Chronically elevated blood pressure is called hypertension, while chronically low blood pressure is called hypotension.
Blood flow is a pulse wave that moves out from the aorta and through the arterial branches, then is reflected back to the heart.
Blood flow is regulated locally in the arterioles and capillaries using smooth muscle contraction, hormones, oxygen, and changes in pH.
Blood flow to an active muscle changes depending on exercise intensity and contraction frequency and rate.
Cerebral circulation is the movement of blood through the network of blood vessels supplying the brain, providing oxygen and nutrients.
Blood flow to the skin provides nutrition to skin and regulates body heat through the constriction and dilation of blood vessels.
Pulmonary circulation in the lungs is responsible for removing carbon dioxide from and replacing oxygen in deoxygenated blood.
The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs.
The hepatic portal system is responsible for directing blood from parts of the gastrointestinal tract to the liver.
Hydrostatic and osmotic pressure are opposing factors that drive capillary dynamics.
Transcytosis is a process by which molecules are transported into the capillaries.
Capillary fluid movement occurs as a result of diffusion (colloid osmotic pressure), transcytosis, and filtration.
Circulatory shock is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration.
An organism responds with numerous reactions during each of the four stages of shock in an attempt to maintain cellular homeostasis.
The clinical manifestation of shock varies depending on the type of shock and the individual, but there are some general symptoms.
New blood vessels are formed from endothelial stem cells, which give rise to the endothelial cells that line the vessels.
Fetal circulation includes the blood vessels within the placenta and the umbilical cord that carry fetal blood.
The health of the myocardium can become impaired with age as the arteries narrow or become clogged due to atherosclerosis.
The aorta is the largest artery in the body and is divided into 3 parts: the ascending aorta, arch of the aorta, and descending aorta.
The ascending aorta is the first portion of the aorta; it includes the aortic sinuses, the bulb of the aorta, and the sinotubular junction.
The arch of the aorta follows the ascending aorta and begins at the level of the second sternocostal articulation of the right side.
The thoracic aorta is the section of the aorta that travels through the thoracic cavity to carry blood to the head, neck, thorax and arms.
The abdominal aorta is the largest artery in the abdominal cavity and supplies blood to most of the abdominal organs.
The abdominal aorta divides into the major arteries of the leg: the femoral, popliteal, tibial, dorsal foot, plantar, and fibular arteries.
Veins are blood vessels that carry blood towards the heart, have thin, inelastic walls, and contain numerous valves.
In the head and neck, blood circulates from the upper systemic loop, which originates at the aortic arch.
The veins of the upper extremity are divided into superficial and deep veins, indicating their relative depths from the skin.
The veins of the thorax drain deoxygenated blood from the thorax region for return to the heart.
The major veins of the abdomen and pelvis return deoxygenated blood from the abdomen and pelvis to the heart.
The deep veins of the lower extremity have valves for unidirectional flow and accompany the arteries and their branches.
Angiogenesis, the growth of new blood vessels from existing vessels, contributes to both normal tissue growth and tumorigenesis in cancer.
Varicose veins, typically found in the legs, are those that have become enlarged and tortuous due to malfunctioning valves.
Edema is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling.
Syncope, the medical term for fainting, is a transient loss of consciousness.
The carotid sinus is a dilation of the internal carotid artery at its origin, where the homeostatic controls of blood pressure are located.
Hypertension is elevated blood pressure, clinically defined as at or greater than 140/90 (systolic/diastolic) mm/Hg.