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| 9083593868 | diffusion | the random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated |  | 0 |
| 9083593869 | gastrovascular cavity | a central cavity with a single opening in the body of certain animals, including cnidarians and flatworms, that functions in both the digestion and distribution of nutrients |  | 1 |
| 9083593870 | heart | a muscular pump that uses metabolic energy to elevate the hydrostatic pressure of the circulatory fluid (blood or hemolymph). The fluid then flows down a pressure gradient through the body and eventually returns to the heart |  | 2 |
| 9083593871 | open circulatory system | a circulatory system in which fluid called hemolymph bathes the tissues and organs directly and there is no distinction between the circulating fluid and the interstitial fluid |  | 3 |
| 9083593872 | hemolymph | in invertebrates with an open circulatory system, the body fluid that bathes tissues |  | 4 |
| 9083593873 | closed circulatory system | a circulatory system in which blood is confined to vessels and is kept separate from the interstitial fluid |  | 5 |
| 9083593874 | blood | a connective tissue with a fluid matrix called plasma in which red blood cells, white blood cells, and cell fragments called platelets are suspended |  | 6 |
| 9083593875 | cardiovascular system | a closed circulatory system with a heart and branching network of arteries, capillaries, ad veins. The system is characteristic of vertebrates |  | 7 |
| 9083593876 | artery | a vessel that carries blood away from the heart to organs throughout the body | 8 | |
| 9083593877 | capillary | a microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid |  | 9 |
| 9083593878 | capillary bed | a network of capillaries in a tissue or organ |  | 10 |
| 9083593879 | atrium (plural, atria) | a chamber of the vertebrate heart that receives blood from the veins and transfers blood to a ventricle |  | 11 |
| 9083593880 | ventricle | a heart chamber that pumps blood out of the heart |  | 12 |
| 9083593881 | single circulation | a circulatory system consisting of a single pump and circuit, in which blood passes from the sites of gas exchange to the rest of the body before returning to the heart |  | 13 |
| 9083593882 | double circulation | a circulatory system consisting of separate pulmonary and systemic circuits in which blood passes through the heart after completing each circuit |  | 14 |
| 9083593883 | gas exchange circuit | the branch of the circulatory system that supplies the organs where gases are exchanged with the environment; in many amphibians, it supplies the lungs and skin and is called a pulmocutaneous circuit, whereas in birds and mammals, it supplies only the lungs and is called a pulmonary circuit. | 15 | |
| 9083593884 | systemic circuit | the branch of the circulatory system that supplies oxygenated blood to and carries deoxygenated blood away from organs and tissues throughout the body |  | 16 |
| 9083593885 | cardiac cycle | the alternating contractions and relaxations of the heart |  | 17 |
| 9083593886 | systole | the stage of the cardiac cycle in which a heart chamber contracts and pumps blood |  | 18 |
| 9083593887 | diastole | the state of the cardiac cycle in which a heart chamber is relaxed and fills with blood | | 19 |
| 9083593888 | atrioventricular (AV) valve | a hart valve located between each atrium and ventricle that prevents a backflow of blood when the ventricle contracts |  | 20 |
| 9083593889 | semilunar valve | a valve located at each exit of the heart, where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle |  | 21 |
| 9083593890 | sinoatrial (SA) node | a region in the right atrium of the heart that sets the rate and timing at which all cardiac muscle cells contract; the pacemaker |  | 22 |
| 9083593891 | electrocardiogram (ECG or EKG) | a record of the electrical impulses that travel through heart muscle during the cardiac cycle |  | 23 |
| 9083593892 | atrioventricular (AV) node | a region of specialized heart muscle tissue between the left and right atria where electrical impulses are delayed for about 0.1 second before spreading to both ventricles and causing them to contract |  | 24 |
| 9083593893 | endothelium | the simple squamous layer of cells lining the lumen of blood vessels |  | 25 |
| 9083593894 | pulse | the rhythmic bulging of the artery walls with each heartbeat |  | 26 |
| 9083593895 | vasoconstriction | a decrease in the diameter of blood vessels caused by contraction of smooth muscles in the vessel walls |  | 27 |
| 9083593896 | vasodilation | an increase in the diameter of blood vessels caused by relaxation of smooth muscles in the vessel walls |  | 28 |
| 9083593897 | lymphatic system | a system of vessels and nodes separate from the circulatory system, that returns fluid, proteins, and cells to the blood | 29 | |
| 9083593898 | lymph | thee colorless fluid, derived from interstitial fluid, in the lymphatic system of vertebrates | 30 | |
| 9083593899 | lymph node | a organ located along a lymph vessel. Lymph nodes filter lymph and contain cells that attack viruses and bacteria | 31 | |
| 9083593900 | plasma | the liquid matrix of blood in which the blood cells are suspended |  | 32 |
| 9083593901 | platelet | a pinched-off cytoplasmic fragment of a specialized bone marrow cell. Platelets circulate in the blood and are important in blood clotting |  | 33 |
| 9083593902 | stem cell | any relatively unspecialized cell that can produce, during a single division, one identical daughter cell and one more specialized daughter cell that can undergo further differentiation | 34 | |
| 9083593903 | erythrocyte | a blood ell that contains hemoglobin which transports oxygen; also called a red blood cell |  | 35 |
| 9083593904 | hemoglobin | an iron-containing protein in red blood cells that reversibly binds oxygen | 36 | |
| 9083593905 | sickle-cell disease | a recessively inherited human blood disorder in which a single nucleotide change in the beta-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals | 37 | |
| 9083593906 | leukocyte | a blood cell that functions in fighting infections; also called a white blood cell |  | 38 |
| 9083593907 | thrombus | a fibrin-containing clot that forms in a blood vessel and blocks the flow of blood |  | 39 |
| 9083593908 | low-density lipoprotein (LDL) | a particle in the blood made up of thousands of cholesterol molecules and other lipids bound to a protein. LDL transports cholesterol from the liver for incorporation into cell membranes | 40 | |
| 9083593909 | high-density (HDL) | a particle in the blood made up of thousands of cholesterol molecules and other lipids bound to a protein. HDL scavenges excess cholesterol | 41 | |
| 9083593910 | atherosclerosis | a cardiovascular disease in which fatty deposits called plaques develop in the inner walls of the arteries, obstructing hte arteries and causing them to harden |  | 42 |
| 9083593911 | heart attack | the damage or death of cardiac muscle tissue resulting from prolonged blockage of one or more coronary arteries | 43 | |
| 9083593912 | stroke | the death of nervous tissue in the brain, usually resulting from the rupture or blockage of arteries in the head | 44 | |
| 9083593913 | hypertension | a disorder in which blood pressure remains abnormally high | 45 | |
| 9083593914 | gas exchange | the uptake of molecular oxygen from the environment and the discharge of carbon dioxide to the environment |  | 46 |
| 9083593915 | partial pressure | the pressure exerted by a particular gas in a mixture of gases (for instance, the pressure exerted b oxygen in air) | 47 | |
| 9083593916 | ventilation | the flow of air or water over a respiratory surface | 48 | |
| 9083593917 | countercurrent exchange | the exchange of a substance or heat between two fluids flowing in opposite directions. For example, blood in a fish gill flows in the opposite direction of water passing over the gill, maximizing diffusion of oxygen into and carbon dioxide out of the blood | 49 | |
| 9083593918 | tracheal system | in insects, a system of branched, air-filled tubes that extends throughout the body and carries oxygen directly to cells |  | 50 |
| 9083593919 | lung | an infolded respiratory surface of a terrestrial vertebrate, land snail, or spider that connects to the atmosphere by narrow tubes |  | 51 |
| 9083593920 | larynx | the portion of the respiratory tract containing the vocal cords; also called the voice box |  | 52 |
| 9083593921 | trachea | the portion of the respiratory tract that passes from the larynx to the bronchi; also called the windpipe |  | 53 |
| 9083593922 | bronchus (plural, bronchi) | one of a pair of breathing tubes that branch from the trachea into the lungs |  | 54 |
| 9083593923 | alveolus (plural, alveoli) | one of the dead-end air sacs where gas exchange occurs in a mammalian lung |  | 55 |
| 9083593924 | surfactant | a substance secreted by alveoli that decreases surface tension in the fluid that coats the alveoli | 56 | |
| 9083593925 | breathing | ventilation of the lungs through alternating inhalation and exhalation | 57 | |
| 9083593926 | positive pressure breathing | a breathing system in which air is forced into the lungs | 58 | |
| 9083593927 | negative pressure breathing | a breathing system in which air is pulled into the lungs | 59 | |
| 9083593928 | diaphragm | a sheet of muscle that forms the bottom wall of the thoracic cavity in mammals. Contraction of the diaphragm pulls air into the lungs |  | 60 |
| 9083593929 | tidal volume | the volume of air a mammal inhales and exhales with each breath | 61 | |
| 9083593930 | vital capacity | the maximum volume of air that a mammal can inhale and exhale with each breath | 62 | |
| 9083593931 | residual volume | the amount of air that remains in the lungs after forceful exhalation | 63 | |
| 9083593932 | respiratory pigment | a protein that transports oxygen in blood or hemolymph | 64 | |
| 9083593933 | myoglobin | an oxygen-storing, pigmented protein in muscle cells | 65 |
