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Chapter 49

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Biological Sciences
Mary Olaveson

[Type the company name] 1 BIOA02H3 Chapter 11 Chapter 49: Circulatory systems 49.1 Why do animalsneed a circulatory system? Circulatory system consists of muscular pump (heart), a fluid (blood) and series of blood vessels; collectively known as cardiovascular system Function: to transport things around body o Heat o Hormones o Respiratory gases o Blood cells o Platelets and elements of immune system Single-celled organisms do not have circulatory system; their exchange of substances occurs in a direct manner. For some multicellular organisms a circulatory system is not necessary if the cells are in direct contact with the external environment. o Small aquatic invertebrates have structures and body shapes that permit direct exchanges between cells and environment o They have flattened, thin body shapes that allow for a greater surface area and minimizes the diffusion path length o The cells of some aquatic invertebrates have highly branched central cavities called gastrovascular systems that is need to bring the external environment into the animals. o Large animals need circulatory systems; those that dont tend to be inactive, slow or even sedentary (i.e sponges and flatworms) Larger animals need to be able to support the metabolism of the cells by delivering the nutrients to them and taking wastes from them with the circulatory systems. Extracellular fluid surrounds each cell and provides the oxygen, fuel and essential molecules that the cells need; the waste products also go into the extracellular fluid Two types of systems: o Open circulatory system: Extracellular fluid continuous with the fluid in blood vessels Vessels of these animals empty their fluid directly into the tissues o Closed circulatory system: The circulating blood and fluid are contained in continuous systems of vessels Extracellular fluid refers to both the fluid surrounding the cell and the fluid in the circulatory system: o Fluid in circulatory system: blood plasma o Fluid around cell: interstitial fluid o A 70kg person has about 14L of extracellular fluid and about 3 L is blood plasma and the rest are interstitial fluid Open circulatory systems move extracellular fluid o Extracellular fluid squeezes through the intercellular spaces as the animal moves o The heart helps the distribution of the fluid in these systems o When heart contracts the extracellular fluid is propelled through the vessels into different regions of the body; the fluid goes through the tissue and eventually makes it back to the heat o Found in arthropods, mollusks and other invertebrates Closed circulatory systems circulate blood through a system of blood vessels: o System of vessels keeps the circulating blood separated from the interstitial fluid o Blood is pumped through the vascular system by heart and some components of the blood never leave the vessels o In earthworms there is one large ventral blood vessel that carries blood from one end (anterior) to the other (posterior) and smaller vessels branch off and transports the blood to even smaller vessels that take the blood to tissues. In the small vessels respiratory gases, nutrients and metabolic wastes diffuse between the blood and interstitial fluid. The blood then flows from these vessels into a larger vessel and leads to one large dorsal vessel which carries the blood from the posterior to the anterior Five pairs of vessels connect the dorsal and ventral vessels in the anterior end and the circuit is complete Advantages of closed CS over open CS: o Fluid flows faster through vessels that through intercellular spaces and therefore can transport nutrients faster o Changing resistance in vessels allows closes system to be selective in directing blood to specific tissues o Specialized cells and large molecules that help in the transport of hormones and nutrients can be kept in the vessels but can drop their cargo in tissues where it is needed. 2 49.2 How have vertebrate circulatory systems evolved? Vertebrates have closed systems with a heart that has two or more chambers When heart contracts, it squeezes blood, putting pressure on it o Blood flows out of heart and into vessels where pressure is lower o Valves prevent blood to backflow between contraction and relaxation As C becomes more complex the blood that flows to the gas exchange organs is more separated from the blood that flows to the rest of the body (evolution) In birds and mammals (youngest vertebrates) blood is pumped from heart to blood and then back to heart (pulmonary circuit) and then from the heart to the rest of the body (systemic circuit) Closed vascular system begins with arteries o Arteriesarteriolescapillary bedsvenulesveins o Capillaries are tiny, thin-walled vessels where materials re exchanged between the blood and tissue fluid o Venules are small capillaries that drain the capillaries o Venules join to form larger vessels called veins which takes the blood back to the heart Fish have two chambered hearts: o Atrium: receives blood from body and pumps it into the ventricle (a more muscular chamber) o Ventricle: pumps blood to gills where gas exchange occurs o Blood that leaves gills collects in a large dorsal artery called aorta: distributes blood to smaller arteries and arterioles o The pressure imposed on blood by the contraction of the heart is dissipated by the high resistance of the narrow spaces in the gill lamellae through which the blood flows. Blood leaving the gills and entering the aorta is under low pressure, limiting the max capacity of the fish circulatory system to supply the tissues with oxygen and nutrient Limitation does not hamper the performance of may rapidly swimming species (i.e. tuna or marlin) There has been an evolutionary transition from water breathing to air breathing. This can be seen in African Lungfish o Lungfish are exposed to water that have low oxygen content and situations in which their aquatic environment are dried up. To deal with the lack of oxygen in water, lungfish have an out-pocketing from the gut that serves as a lung. The lung contains many thin-walled blood vessels so blood flowing through these vessels can pick up oxygen from the air that they breath in o The gill arteries in the posterior of the fish have been modified such that it can carry blood to the lung and a new vessel carries oxygenated blood back to the heart from the lungs o Few gill arches lost their gils and their blood vessel delivers blood from heart directly to the dorsal aorta o Unlike other fish, the lungfish had a partly divided atrium: the left side receives oxygenated blood from the lungs while the right side receives deoxygenated blood from other tissues; the two bloodstreams are separated. o Oxygenated blood goes to the anterior gill arteries deoxygenated blood goes to other gill arches that have functional gills and to gill arteries that go to the lungs Amphibians have three chambered hearts: o Pulmonary and systemic circulation is partly divided in adult amphibians o Single ventricle pumps blood to the lungs and to the rest of the body o Both atria receive blood returning to heart; one oxygenated blood from lungs and the other deoxygenated blood from the body o Both atria deliver blood to same ventricle; blood could mix; blood going to tissue would not carry full load of oxygen However the mixing is limited because the anatomical features of the ventricle direct the flow of deoxygenated blood from right atrium to the pulmonary circuit and the flow of oxygenated blood from the left atrium to the aorta. Partial separation of the pulmonary and systemic circulation allows blood destined for the tissue to overcome the high flow resistance of the gas exchange organ. Blood leaving amphibian heart moves directly to aorta at a higher pressure that if it had first flowed through the lungs (???)3 Reptiles have exquisite control of pulmonary and systemic circulation: o Turtle, lizards, snakes have three chambered hearts because their ventricles are not separated from left and right atrium o Crocodiles and alligators have four chambered hearts because their left and right ventricles are completely separated o Many reptiles and crocodilians are very active and powerful in bursts and then there are periods where their metabolic rates are much lower than that of a resting animal.
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