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antibody
Protein produced in response to the presence of an antigen; each antibody combines with a specific antigen.
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antigen
Foreign substance, usually a protein or a polysaccharide, that stimulates the immune system to react, such as to produce antibodies.
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aorta
In humans, the major systemic artery that takes blood from the heart to the tissues.
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arteriole
Vessel that takes blood from an artery to capillaries.
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artery
Blood vessel that transports blood away from the heart.
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atrioventricular valve
Heart valve located between an atrium and a ventricle.
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atrium (pl., atria)
Chamber; particularly an upper chamber of the heart lying above a ventricle.
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AV (atrioventricular) node
Small region of neuromuscular tissue that transmits impulses received from the SA node to the ventricular walls.
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blood
Fluid circulated by the heart through a closed system of vessels.
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blood pressure
Force of blood pushing against the inside wall of blood vessels.
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capillary
Microscopic blood vessel; gases and other substances are exchanged across the walls of a capillary between blood and tissue fluid.
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cardiac cycle
One complete cycle of systole and diastole for all heart chambers.
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cardiovascular system
Organ system in which blood vessels distribute blood under the pumping action of the heart.
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closed circulatory system
Cardiovascular system in all vertebrates and some invertebrates that is composed of a muscular heart and blood vessels.
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diastole
Relaxation period of a heart chamber during the cardiac cycle.
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electrocardiogram (ECG)
Recording of the electrical activity associated with the heartbeat.
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formed elements
Constituents of blood that are either cellular (red blood cells and white blood cells) or at least cellular in origin (platelets).
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heart
Muscular organ whose contraction causes blood to circulate in the body of an animal.
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heart attack
Damage to the myocardium due to blocked circulation in the coronary arteries; myocardial infarction.
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heart murmur
Clicking or swishy sounds, often due to leaky valves.
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hemocoel
Body cavity in arthropods where exchange between hemolymph and tissues occurs.
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hemoglobin
Iron-containing respiratory pigment occurring in vertebrate red blood cells and in the blood plasma of some invertebrates.
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hypertension
Elevated blood pressure, particularly the diastolic pressure.
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lymph
Fluid, derived from tissue fluid, that is carried in lymphatic vessels.
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lymphatic system
Organ system consisting of lymphatic vessels and lymphatic organs; transports lymph and lipids, and aids the immune system.
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lymphatic vessel
Vessel that carries lymph.
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lymphocyte
Specialized white blood cell that functions in specific defense; occurs in two forms�T lymphocytes and B lymphocytes.
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macrophage
In vertebrates, large phagocytic cell derived from a monocyte that ingests microbes and debris.
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monocyte
Type of a granular leukocyte that functions as a phagocyte, particularly after it becomes a macrophage.
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neutrophil
Granular leukocyte that is the most abundant of the white blood cells; first to respond to infection.
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open circulatory system
Circulatory system, such as that found in a grasshopper, where a tubular heart pumps hemolymph through channels and body cavities.
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ostium (pl., ostia)
Opening in the heart of an animal with an open circulatory system, which allows blood to fill the relaxed heart.
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plaque
Accumulation of soft masses of fatty material, particularly cholesterol, beneath the inner linings of the arteries.
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plasma
In vertebrates, the liquid portion of blood; contains nutrients, wastes, salts, and proteins.
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platelet
Formed element in blood that is necessary to blood clotting.
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portal system
Pathway of blood flow that begins and ends in capillaries, such as the portal system located between the small intestine and liver.
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pulmonary artery
Blood vessel that takes blood away from the heart to the lungs.
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pulmonary circuit
Circulatory pathway between the lungs and the heart.
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pulmonary trunk
Large blood vessel that divides into the pulmonary arteries; takes blood away from the heart to the lungs.
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pulmonary vein
Blood vessel that takes blood to the heart from the lungs.
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pulse
Vibration felt in arterial walls due to expansion of the aorta following ventricle contraction.
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red blood cell
Erythrocyte; contains hemoglobin and carries oxygen from the lungs or gills to the tissues in vertebrates.
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SA (sinoatrial) node
Small region of neuromuscular tissue that initiates the heartbeat; also called the pacemaker.
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semilunar valve
Valve resembling a half-moon located between the ventricles and their attached vessels.
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septum
Partition or wall that divides two areas; the septum in the heart separates the right half from the left half.
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sinus
Cavity into which hemolymph flows and baths the organs in an open circulatory system. Also, air-filled spaces in nasal cavities.
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stroke
Condition resulting when an arteriole in the brain bursts or becomes blocked by an embolism; cerebrovascular accident.
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systemic circuit
Circulatory pathway of blood flow between the tissues and the heart.
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systole
Contraction period of the heart during the cardiac cycle.
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thrombin
Enzyme that converts fibrinogen to fibrin threads during blood clotting.
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vein
Blood vessel that arises from venules and transports blood toward the heart.
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vena cava (pl., venae cavae)
Large systemic vein that returns blood to the right atrium of the heart in tetrapods; either the superior or inferior vena cava.
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ventricle
Cavity in an organ, such as a lower chamber of the heart or the ventricles of the brain.
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venule
Vessel that takes blood from capillaries to a vein.
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white blood cell
Leukocyte, of which there are several types, each having a specific function in protecting the body from invasion by foreign substances and organisms.
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