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Lecture 5

BGYA02 - Lec5 (text+lec combined notes)

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

491 Why Do Animals Need a Circulatory SystemA circulatory system consists of a muscular pump the heart a fluid the blood and a series of conduits the blood vessels through which the fluid can be pumped around the body Heart blood and vessels are also known collectively as a cardiovascular system The function of circulatory systems is to transport things around the body Some animals do not have circulatory systemsoSingle celled organisms serve all of needs through direct exchanges with environment mostly found in aquatic environments or very moist terrestrial environments oUnnecessary bc all its cells are close enough to external environment that nutrients respiratory gases and wastes can diffuse easilyoSmall aquatic invertebrates have structures and body shapes that permit direct exchanges between cells and environment Many are flattened with thin body shapes that maximize the amount of surface area that is in contact with its external environment and minimize the diffusion path length Cells of other aquatic invertebrates are highly branched central cavities calledsystem bring the environment gastrovascularinto the animal eg sponges Very small maintain high metabolism and activity The larger forms are more inactive slow or even sedentaryoLarger and more active animals must support metabolism of cells by delivering nutrients to them and taking wastes away from them with circulatory systems The cells environment is in the ECM In many animals the extracellular fluid is continuous with fluid in the circulatory system The vessels of these animals empty their fluid directly into the tissues At other locations the fluid flows back into the circulatory system to be pumped back out again These types of systems are open In closed systems they completely contain the circulating fluid blood in a continuous system of vesselsoWe refer to the fluid in the circulatory systems as blood plasma and the fluid around the cells as interstitial fluidoCirculatory systems carry materials to and from all regions of the body to maintain the optimum composition of the interstitial fluids which in turn serve the needs of the cellsOpen circulatory systems move extracellular fluidoFluid squeezes through intercellular spaces as animal moves Muscle pump assists distribution of fluid in these systems Contractions of heart propel extracellular fluid through vessels to different regions of the body Fluid leaves vessels to trickle through tissues and eventually return to the heart These systems found in arthropods mollusks and some other invertebrate groupsClosed circulatory systems circulate blood through a system of blood vesselsoA system of vessels keeps circulating blood separate from the interstitial fluid Blood pumped through vascular system by one or more muscular hearts and some components of the blood never leave the vessels These are in vertebrates annelids and some other invertebrate groupsoExample is earthworm A large ventral blood vessel carries blood from anterior end to posterior end Smaller vessels branch off and transport blood to even smaller vessels In smallest vessel respiratory gases nutrients and metabolic wasters diffuse between blood and interstitial fluid Blood flows from these vessels into large vessels which lead into one large dorsal vessel which flows from posterior to anterioroClosed circulatory systems have several advantages over open systemsFluid can flow more rapidly through vessels than through intercellular spaces and can transport nutrients and wastes to and from tissues more rapidlyBy changing resistance in the vessels closed systems can be selective in directing blood to specific tissuesSpecialized 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 needed492 How Have Vertebrate Circulatory Systems EvolvedAs circulatory systems become more complex e blood that flows to the gas exchange organs becomes more completely separated from the blood that flows to the rest of the bodyIn fish the phylogenetically older vertebrates blood is pumped from the heart to the gills and then to the tissues of the body and back to the heartIn birds and mammals the phylogenetically youngest vertebrates 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 systematic circuitThe closed vascular system of vertebrates begins with arteries that carry blood away from the heart Arteries give rise to arteriolesfeed blood into capillary beds Capillaries are tiny thinwalled vessels where materials are exchanged between the blood and tissue fluid Small vessels called venules drain capillary beds The venules join together to form veins which deliver blood back to the heartFish have two chambered heartsoAtrium receives blood from the body and pumps it into a more muscular chamber the ventricle Ventricle pumps blood to gills where gases exchange Blood leaving gills collect in a large dorsal artery aorta which distributes blood to smaller arteries and arterioles leading to all the organs and tissues of the bodyoMost of the pressure imparted to the blood by the contraction of the ventricle is dissipated by the high resistance of the narrow spaces in the gill lamellae through which blood flows As a result blood leaving the gills and entering the aorta is under low pressure limiting the maximum capacity of the fish circulatory system to supply the tissues with oxygen and nutrientsoRead example on lungfishAmphibians have threechambered hearts
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