2-20 circulatory systems I

2-20 circulatory systems I - CIRCULATORY SYSTEMS, PART I...

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CIRCULATORY SYSTEMS, PART I LIFE 49 – 49.3 49.1 Why do animals need a circulatory system? - circulatory system consists of a muscular pump (the heart ), a fluid ( blood ), and a series of conduits ( blood vessels ) through which the fluid can be pumped around the body. Heart, blood, and vessels are also known collectively as a cardiovascular system -circulatory systems transport: heat, hormones , respiratory gases, blood cells, platelets , and elements of the immune system , nutrients, and waste products 49.1.1 Some animals do not have circulatory systems -Single-celled organisms serve all of their needs through direct exchanges with the environment -The cells of some other aquatic invertebrates are served by highly branched central cavities called gastrovascular systems that essentially bring the external environment into the animal (i.e. sponge) -Larger and more active animals must support the metabolism of their cells by delivering nutrients to them and taking wastes away from them with circulatory systems. The critical environment for each cell is the extracellular fluid that surrounds it. All of the cell’s nutrients—oxygen, fuel, essential molecules— comes from that fluid, and the waste products of the cell go into that fluid 49.1.2 Open circulatory systems move extracellular fluid -In open circulatory systems extracellular fluid squeezes through intercellular spaces as the animal moves. A muscular pump usually assists the distribution of the fluid in these systems. Open circulatory systems are found in arthropods, mollusks, and some other invertebrate groups 49.1.3 Closed circulatory systems circulate blood through a system of blood vessels -In a closed circulatory system , a system of vessels keeps circulating blood separate from the interstitial fluid. Blood is pumped through this vascular system by one or more muscular hearts. Closed circulatory systems characterize vertebrates, annelids, and some other invertebrate groups -Closed circulatory systems have several advantages over open systems: Fluid can flow more rapidly through vessels than through intercellular spaces, and can therefore transport nutrients and wastes to and from tissues more rapidly. By changing resistance in the vessels, closed systems can be selective in directing blood to specific tissues . Specialized cells and large molecules that aid in the transport of hormones and nutrients can be kept within the vessels, but can drop their cargo in the tissues where it is needed. 49.2 How have vertebrate circulatory systems evolved? -Vertebrates have closed circulatory systems and hearts with two or more chambers. When a heart chamber contracts, it squeezes the blood, putting it under pressure. Blood then flows out of the heart and into vessels where pressure is lower. Valves prevent the backflow of blood as the heart cycles between contraction and relaxation -as circulatory systems become more complex, the blood that flows to the gas exchange organs
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2-20 circulatory systems I - CIRCULATORY SYSTEMS, PART I...

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