Chapter 42 Circulation and Gas Exchange Concept 42 1 Circulatory Systems link exchange surfaces with cells throughout the body 2 Adaptations that permit effective gas exchange o A body plan that places many or all cells in direct contact with the environment Only found in certain invertebrates such as cnidarians and flatworms o Circulatory System Found in all other animals Moves fluids between each cells immediate surroundings and the body tissues where exchanges with the immediate environment occurs Gastrovascular Cavities o Functions Distribution of substances Digestion waste o Cnidarians o Fluid in the inner and outer tissue layers facilitating the exchange of gases and cellular Gastrovascular cavity with a branching pattern o Planarians Flatworms Flat body optimizes exchange by increasing surface area and minimizing diffusion distances Open and closed circulatory systems o 3 Basic components Circulatory Fluid Interconnecting tissues A muscular pump usually a heart o 2 Types Open Circulatory fluid called hemolymph is also the interstitial fluid that bathes cell walls Common in arthropods grasshoppers and some mollusks clams Heart contraction pumps hemolymph through circulatory vessels into interconnected sinuses Sinuses are the spaces surrounding the organs Chemical exchange between the hemolymph and body cells occurs in the sinuses Closed Circulatory fluid is called blood o Confined to vessels and distinct from the interstitial fluid One or more hearts pumps blood into large vessels that branch into smaller ones Chemical exchange occurs between the blood and the interstitial fluid Both types are evolutionary advantages Open circulatory system o Lower hydrostatic pressure makes open circulatory systems less costly than closed circulatory systems in terms of energy expenditure o Also have other advantages ex spiders use the hydrostatic pressure generated to extend their legs Closed circulatory system o High blood pressure enables effective delivery of oxygen and nutrients to cells of larger and more active animals o Closed systems are well suited to regulating the distribution of blood to different organs Organization of Vertebrate Circulatory Systems o Closed circulatory system of humans and other vertebrates is often called the cardiovascular system o 3 Main Types of Blood Vessels Arteries Arterioles Capillaries o Capillary Beds Carry blood away from the heart to organs throughout the body Small vessels within organs that convey blood to capillaries Microscopic vessels with very thin porous walls Networks of capillaries that infiltrate tissues passing within a few cell diameters of every cell in the body o Gas exchange occurs across the thin walls of capillaries by diffusion between the blood and interstitial fluid around the tissue cells o Veins Carry blood back to the heart oxygen content o The Hearts of Vertebrates o Arteries and veins are distinguished by the direction in which they carry blood not their Contain two or more muscular chambers Atria Ventricles Chambers that receive blood entering the heart Chambers responsible for pumping blood out of the heart The number of chambers in a heart differs among groups of vertebrates Single and Double Circulation o Single Circulation When blood passes through the heart once in each complete circuit through the body The heart pumps blood to the gills to be re oxygenates gill circulation after which the blood flows to the rest of the body and back to the heart o Double Circulation Contains two circuits Pumps for the two circuits are combined into a single organ the heart Provides a vigorous flow of blood to the brain muscles and other organs because the heart repressurizes the blood destined for these tissues after it passes through the capillary beds of the lungs or skin Having both pumps within a single heart simplifies coordination of the pumping cycles Pulmonary Pulmocutaneous Circuit Right side of the heart The right side of the heart delivers oxygen poor blood to the capillary beds of the gas exchange tissues Ex the lungs o Net movement of Oxygen into the blood and carbon dioxide out of the blood Called the pulmonary circuit when o The capillary beds are all in the lungs o Reptiles and mammals Call the pulmocutaneous circuit when o Capillary beds are in the lungs and skin o Many amphibians Systemic Circuit Capillary Beds After oxygen enriched blood leaves the gas exchange it enters the left side of the heart Contraction of the heart propels this blood to capillary beds in organs and tissues throughout the body Following the exchange of Oxygen and Carbon Dioxide as well as nutrients and waste products the now oxygen poor blood returns to the heart which completes the systemic circuit Networks of capillaries that infiltrate tissues and pass within a few cell diameters of every cell in the body Across the thin walls of capillaries chemicals and dissolved gases are exchanged by diffusion into blood and the interstitial fluid around the tissue cells At the end of capillaries are venules that converge into veins o This is how oxygen diffuses from the lungs into the blood stream The Heart Arteries o Carry blood away from the heart toward capillaries o Return blood toward the heart from the capillaries o Chambers that receive blood that flows into the heart Veins Atria Ventricles o Chambers responsible for pumping blood out of the heart Pulmonary Circuit One pump the right side of the heart delivers blood to the capillary beds of the gas exchange tissues where O2 comes in and CO2 goes out Only called the pulmonary circuit if all the capillary beds are located in the lungs Pulmocutaneous Circuit Includes capillaries in both the lungs and skin Ex amphibians Concept 42 2 Coordinated cycles of heart contractions drive double circulation in mammals Mammalian Circulation o Steps of the cardiovascular system beginning with the pulmonary circuit Contraction of the right ventricle pumps blood to the lungs via the pulmonary arteries As the blood flows through capillary beds in the lungs Oxygen is taken inhalation in and Carbon Dioxide is released exhalation Oxygen diffuses into the pulmonary veins and travels into the left atrium of the heart The oxygen rich blood then flows into the hearts left ventricle The left ventricle pumps the oxygen rich blood out towards the body tissues through the systemic circuit o Steps of the cardiovascular system involving the pulmonary circuit Blood leaves the left ventricle through the aorta which conveys