Trombley Final Exam Study Guide CHAPTERS 42 48 49 50 7 30 9 30AM Wednesday 04 25 12 102 HCB Chapter 42 Circulation and Gas Exchange Exchange between an animal and their surroundings takes place at the cellular level Nutrients and oxygen enter the cytoplasm by crossing the plasma membrane metabolic by products such as carbon dioxide exit the cell by crossing the plasma membrane also Circulatory systems link exchange surfaces with cells throughout the body Diffusion is rapid only over very small distances Each cell of an animal participates in exchange this is made possible in two ways o 1 Body shape and size keep many or all cells in direct contact with the environment This type of body plan is found only in certain invertebrates including cnidarians and flatworms o 2 In all other animals the circulatory system moves fluid between each cell s immediate surroundings and the tissues where exchange with the environment occurs A flat body optimizes diffusional exchange by increasing surface area and minimizing diffusion distances A circulatory system has three basic components o A circulatory fluid o A set of interconnecting vessels o A muscular pump Heart powers circulation by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid which then flows through the vessels and back to the heart By transporting fluid throughout the body the circulatory system functionally connects the aqueous environment of the body cells to the organs Circulatory systems are either open or closed vary with regard to the number of circuits in the body and rely on pumps that differ in structure and organization Arthropods and most molluscs have an open circulatory system in which the circulatory fluid bathes the organs directly In these animals the circulatory fluid called hemolymph is also the interstitial fluid that bathes body cells Contractions of the heart pump the hemolymph through the circulatory vessels into interconnected sinuses spaces surrounding the organs Within the sinuses chemical exchange occurs between the hemolymph and body cells Body movements help circulate the hemolymph by periodically squeezing the sinuses In a closed circulatory system a circulatory fluid called blood is confined to vessels and is distinct from the interstitial fluid The heart pumps blood into large vessels that branch into smaller ones that infiltrate the organs Chemical exchange occurs between the blood and the interstitial fluid as well as between the interstitial fluid and the body cells Annelids including earthworms cephalopods including squids and octopuses and all vertebrates have closed circulatory systems Closed systems are more efficient at transporting circulatory fluids to tissues and cells The lower hydrostatic pressures associated with open circulatory systems make them less costly than closed systems in terms of energy expenditure The closed circulatory system of humans and other vertebrates is often called the cardiovascular system The total length of blood vessels in an average human adult is twice the earth circumference at the equator Three main types of blood vessels o Arteries carry blood away from the heart to organs throughout the body Within organs arteries branch into arterioles small vessels that convey blood to the capillaries o Capillaries microscopic vessels with very thin porous walls Networks of these vessels called capillary beds infiltrate every tissue passing within a few cell diameters of every cell in the body Across the thin wall of the capillaries chemicals including dissolved gases are exchanged by diffusion between the blood and the interstitial fluid around the tissue cells At their downstream end capillaries converge into venules and venules converge into veins o Veins The vessels that carry blood back to the heart Arteries and veins are distinguished by the direction of blood flow not by O2 content The hearts of all vertebrates contain two or more muscular chambers The chambers that receive blood entering the heart are called atria singular atrium The chambers responsible for pumping blood out of the heart are called ventricles In bony fishes rays and sharks the heart consists of two chambers an atrium and a ventricle The blood passes through the heart once in each complete circuit an arrangement called single circulation In single circulation blood that leaves the heart passes through two capillary beds before returning to the heart The circulatory systems of amphibians mammals and reptiles have two circuits an arrangement called double circulation The pumps for the two circuits are combined into a single organ the heart Having both pumps within a single heart simplifies coordination of the pumping cycles In reptiles and mammals oxygen poor blood flows through the pulmonary circuit to pick up oxygen through the lungs Oxygen rich blood delivers oxygen through the systemic circuit Double circulation provides a vigorous flow of blood to the brain muscles and other organs because the heart re pressurizes the blood destined for these tissues after it passes through the capillary beds of the lungs or skin Blood pressure is often much higher in the systematic circuit than in the gas exchange circuit Mammals and birds have a four chambered heart with two atria and two ventricles Ventricles have thicker walls and contract much more forcefully than the atria especially the left ventricle which pumps blood to all body organs through the systematic circuit However the left ventricle still pumps the same volume of blood as the right ventricle during each contraction The left side of the heart pumps and receives only oxygen rich blood while the right side receives and pumps only oxygen poor blood Oxygen rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle The aorta provides blood to the heart through the coronary arteries When a heart contracts it pumps blood when it relaxes its chambers fill with blood One complete sequence of pumping and filling is referred to as the cardiac cycle The contraction phase of the cycle is called systole and the relaxation phase is called diastole The volume of blood each ventricle pumps per minute is the cardiac output Two factors determine cardiac output o The rate of contraction or heart rate number of beats per minute o Stroke volume the amount of blood pumped by a ventricle in a single contraction Four valves in the heart prevent backflow and
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