1. antibody
    Protein produced in response to the presence of an antigen; each antibody combines with a specific antigen.
  2. antigen
    Foreign substance, usually a protein or a polysaccharide, that stimulates the immune system to react, such as to produce antibodies.
  3. aorta
    In humans, the major systemic artery that takes blood from the heart to the tissues.
  4. arteriole
    Vessel that takes blood from an artery to capillaries.
  5. artery
    Blood vessel that transports blood away from the heart.
  6. atrioventricular valve
    Heart valve located between an atrium and a ventricle.
  7. atrium (pl., atria)
    Chamber; particularly an upper chamber of the heart lying above a ventricle.
  8. AV (atrioventricular) node
    Small region of neuromuscular tissue that transmits impulses received from the SA node to the ventricular walls.
  9. blood
    Fluid circulated by the heart through a closed system of vessels.
  10. blood pressure
    Force of blood pushing against the inside wall of blood vessels.
  11. capillary
    Microscopic blood vessel; gases and other substances are exchanged across the walls of a capillary between blood and tissue fluid.
  12. cardiac cycle
    One complete cycle of systole and diastole for all heart chambers.
  13. cardiovascular system
    Organ system in which blood vessels distribute blood under the pumping action of the heart.
  14. closed circulatory system
    Cardiovascular system in all vertebrates and some invertebrates that is composed of a muscular heart and blood vessels.
  15. diastole
    Relaxation period of a heart chamber during the cardiac cycle.
  16. electrocardiogram (ECG)
    Recording of the electrical activity associated with the heartbeat.
  17. formed elements
    Constituents of blood that are either cellular (red blood cells and white blood cells) or at least cellular in origin (platelets).
  18. heart
    Muscular organ whose contraction causes blood to circulate in the body of an animal.
  19. heart attack
    Damage to the myocardium due to blocked circulation in the coronary arteries; myocardial infarction.
  20. heart murmur
    Clicking or swishy sounds, often due to leaky valves.
  21. hemocoel
    Body cavity in arthropods where exchange between hemolymph and tissues occurs.
  22. hemoglobin
    Iron-containing respiratory pigment occurring in vertebrate red blood cells and in the blood plasma of some invertebrates.
  23. hypertension
    Elevated blood pressure, particularly the diastolic pressure.
  24. lymph
    Fluid, derived from tissue fluid, that is carried in lymphatic vessels.
  25. lymphatic system
    Organ system consisting of lymphatic vessels and lymphatic organs; transports lymph and lipids, and aids the immune system.
  26. lymphatic vessel
    Vessel that carries lymph.
  27. lymphocyte
    Specialized white blood cell that functions in specific defense; occurs in two forms�T lymphocytes and B lymphocytes.
  28. macrophage
    In vertebrates, large phagocytic cell derived from a monocyte that ingests microbes and debris.
  29. monocyte
    Type of a granular leukocyte that functions as a phagocyte, particularly after it becomes a macrophage.
  30. neutrophil
    Granular leukocyte that is the most abundant of the white blood cells; first to respond to infection.
  31. open circulatory system
    Circulatory system, such as that found in a grasshopper, where a tubular heart pumps hemolymph through channels and body cavities.
  32. ostium (pl., ostia)
    Opening in the heart of an animal with an open circulatory system, which allows blood to fill the relaxed heart.
  33. plaque
    Accumulation of soft masses of fatty material, particularly cholesterol, beneath the inner linings of the arteries.
  34. plasma
    In vertebrates, the liquid portion of blood; contains nutrients, wastes, salts, and proteins.
  35. platelet
    Formed element in blood that is necessary to blood clotting.
  36. portal system
    Pathway of blood flow that begins and ends in capillaries, such as the portal system located between the small intestine and liver.
  37. pulmonary artery
    Blood vessel that takes blood away from the heart to the lungs.
  38. pulmonary circuit
    Circulatory pathway between the lungs and the heart.
  39. pulmonary trunk
    Large blood vessel that divides into the pulmonary arteries; takes blood away from the heart to the lungs.
  40. pulmonary vein
    Blood vessel that takes blood to the heart from the lungs.
  41. pulse
    Vibration felt in arterial walls due to expansion of the aorta following ventricle contraction.
  42. red blood cell
    Erythrocyte; contains hemoglobin and carries oxygen from the lungs or gills to the tissues in vertebrates.
  43. SA (sinoatrial) node
    Small region of neuromuscular tissue that initiates the heartbeat; also called the pacemaker.
  44. semilunar valve
    Valve resembling a half-moon located between the ventricles and their attached vessels.
  45. septum
    Partition or wall that divides two areas; the septum in the heart separates the right half from the left half.
  46. sinus
    Cavity into which hemolymph flows and baths the organs in an open circulatory system. Also, air-filled spaces in nasal cavities.
  47. stroke
    Condition resulting when an arteriole in the brain bursts or becomes blocked by an embolism; cerebrovascular accident.
  48. systemic circuit
    Circulatory pathway of blood flow between the tissues and the heart.
  49. systole
    Contraction period of the heart during the cardiac cycle.
  50. thrombin
    Enzyme that converts fibrinogen to fibrin threads during blood clotting.
  51. vein
    Blood vessel that arises from venules and transports blood toward the heart.
  52. 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.
  53. ventricle
    Cavity in an organ, such as a lower chamber of the heart or the ventricles of the brain.
  54. venule
    Vessel that takes blood from capillaries to a vein.
  55. 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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