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bioa02 chapter 49

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Biological Sciences
Mary Olaveson

Chapter 49 49.1 Why do animals need a circulatory system? - a circulatory system consists of a muscular pump (the heart), a fluid (the blood), and a series of conduits (blood vessels) through t which the fluid can be pumped around the body - cardiovascular system where the heart, blood and vessels are also known as - circulatory systems is to transport things around the body o transports heat, hormones, reparatory gases, blood cells, platelets and elements of the immune system - single cell organisms serve all of their need through direct exchanges with the environment o mostly found in aquatic environments, or moist terrestrial environment - multicellular organisms a circulatory system is not necessary if all of their cells are close enough to the external environment that nutrients, respiratory gases, and wastes can diffuse between the cells and the environment - small aquatic invertebrates have structures and body shapes that permit direct exchanges between cells and environment o have flattened, thin body shapes that maximize the amount of surface area that is in contact with the environment o some other aquatic invertebrates are served by highly branched central cavities called gastrovasular systems bring the external environment into the animal - very small animals without circulatory systems can maintain high levels of metabolism and activity, but bigger animals without circulatory systems such as sponges, coelenterates, and flatworms tend to be inactive, slow, or even sedentary - 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 - extracellular fluid contains oxygen, fuel, essential molecules o it is continuous with the fluid in the circulatory system o the vessels of these animals empty their fluid directly into the tissues o open where the extracellular fluid flows back into the circulatory system to be pumped back out again o close completely contain the circulating fluid, blood, in a continuous system of vessels liquids and low-molecular weight solutes are exchanged between the blood and the extracellular fluid even though its closed - extracellular fluid refers to both the fluid in the circulatory system (blood plasma) and the fluid between the cells of the body (interstitial fluid) - a normal 70 kg human contains 14 L of extracellular fluid, and 3 L is blood plasma - open circulatory systems extracellular fluid squeezes through intercellular spaces as the animal moves o the contraction of this simple heart propel the extracellular fluid through cessels leading to different regions of the body, but the fluid leaves those vessels to trickle through the tissues and eventually return to the heart o are found in arthropods, mollusks, and some invertebrates groups in arthropods, fluid returns to the heart through valved opening called ostia in mollusks, open vessels aid in the return of extracellular fluid to the heart - closed circulatory system a system vessels keeps circulating blood separate from the interstitial fluid o blood is pumped through this vascular system by one or more muscular hearts, and some components of the blood never have the vessels o are characterize vertebrates, annelids, and some other invertebrates groups o in earthworms, one large ventral blood vessel carries blood from its anterior end to its posterior end smaller vessels branch off and transport the blood to even smaller vessels in the smaller vessels, respiratory gases, nutrients, and metabolic wastes diffuse between the blood and the interstitial fluid the blood then flows from these vessels into larger vessels that lead into one large dorsal vessel, which carries the blood from the posterior to the anterior end of the body five paris of muscular vessels connect the large dorsal and ventral vessels in the anterior end, thus completing the circuit the doral vessel and the five connection vessels serve as hearts for the earthworm - closed circulatory systems have several advantages over open systems o fluid can flow more rapidly through vessels than through intercellular spaces, and can therefore transport nutrients and wastes to and from tissues more rapidly o by changing resistance in the vessels, closed systems can be selective in directing blood to specific tissues o 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 - closed circulatory systems can support higher levels of metabolic activity than open systems can 49.2 How have vertebrate circulatory systems evolved? - vertebrates have closed circulatory systems and hearts with two or more chambers - when the heart chamber contracts, it squeezes the blood, putting it under pressure o then the blood flows out of the heart and into vessels where pressure is lower o valves prevent 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 becomes more completely separated from the blood that flows to the rest of the body o in fish, blood is pumped from the heart to the gills and then to the tissues of the body and back to the heart o in birds and mammals, blood is pumped from the heart to the lungs and back to the heart in a pulmonary circuit and then from the heart to the rest of the body and back to the heart in a systemic circuit - the closed vascular system of vertebrates begins with vessels called arteries - arteries give rise to smaller vessels called arterioles, which feed blood into capillary beds - capillaries are the tiny, thin-walled vessels where materials are exchanged between the blood and the tissue fluid - small vessels called venules drain capillary beds o join together to form larger vessels called veins, which deliver blood back to the heart - the fish heart has two chambers o an atrium receives blood from the body and pumps it into a more muscular chamber the ventricle o the ventricle pumps the blood to the gills, where gases are exchanged o blood leaving the gills collects in a large dorsal artery the aorta, which distributes blood to smaller arteries and arterioles leading to all the organs and tissues of the body o in the tissues, blood flows through beds of tiny capillaries, collects in venules and veins, and eventually returns to the atrium of the heart o since there are only narrow spaces in the gill lamellae through which blood flows, therefore blood leaving the gills and entering the aorta is under low pressure, limiting the maximum capacity of the fish circulatory system - the lungfish heart has two atria, one receiving oxygenated blood from the lung and one receiving deoxygenated blood from the body o the lung contains many thin-walled blood vessels, so blood flowing through those vessels can pick up oxygen from air gulped into the lung o the posterior pair of gill arteries has been modified to carry blood to the lung, and a new vessel carries oxygenated blood from the lung back to the heart o two anterior gill arches have lost their gills, and their blood vessels deliver blood from the heart directly to the dorsal aorta o has adaptations that partially separate the flow of its blood into pulmonary and systemic circuits o has a partly divided atrium the left side receives oxygenated blood form the lungs, and the right side receives deoxygenated blood from the other tissues o oxygenated blood mostly goes to the anterior gill arteries leading to the dorsal aorta, and the deoxygenated blood mostly goes to the other gill arches that have functional gills as well as to the gill arties that serve the lung - In adult amphibians, the pulmonary and systemic circuits are partially separated. The heart has three chambers o A single ventricle pumps blood to the lungs and to the rest of the body o Two atria receive blood returning to the heart One receives oxygenated blood from the lungs and the other receives deoxygenated blood form the body o Since both atria deliver blood to the same ventricle, the oxygenated and deoxyge
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