Specialized tissue on the wall between the atria. Electrical impulses pass from the pacemaker (SA node) through the _______ and the atrioventricular bundle (bundle of His) toward the ventricles.atrium (pl. atria)One of two upper chambers of the heart.capillary<span>Smallest blood vessel. Materials pass to and from the bloodstream through the thin walls. They have walls that are only one endothelial cell in thickness. This delicate, microscopic vessel carries nutrient-rich, oxygenated blood from the arteries and arterioles to the body cells. There, the nutrients are burned in the presence of oxygen (catabolism) to release energy.
At the same time, waste products such as carbon dioxide and water pass out of the cells and into these blood vessels. Waste-filled blood then flows back to the heart in small venues, which combine to form larger vessels called veins.</span>carbon dioxideGas (waste) released by body cells, transported via veins to the heart, and then to the lungs for exhalation.coronary arteriesBlood vessels that branch from the aorta and carry oxygen-rich blood to the heart muscle.deoxygenated bloodBlood that is oxygen-poor.diastole<span>Relaxation phase of the heartbeat.</span>
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Proteins are broken down by the enzymes pepsin and peptidase, and by hydrochloric acid. Lipids are broken down by lipases.
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Aquatic ecosystems include oceans, lakes, rivers, streams, estuaries, and wetlands. Within these aquatic ecosystems are living things that depend on the water for survival, such as fish, plants, and microorganisms. These ecosystems are very fragile and can be easily disturbed by pollution.
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