Circulation the Cardiovascular System Biology 1107 Lecture 18 Lecture 18 Overview 2 41 cid 30 Overview diffusive surfaces 3 cid 30 Basic circulatory systems 4 16 cid 30 Open circulatory systems 5 7 cid 30 Closed circulatory systems 8 16 cid 30 Vessel types 9 14 cid 30 Capillary exchange 15 cid 30 Lymphatic system function 16 cid 30 Basic heart structures 17 26 cid 30 Evolutionary trends in vertebrate heart structure and function 18 21 cid 30 Mammalian heart structures 22 26 cid 30 Mammalian cardiac cycle and blood pressure 27 30 cid 30 Autorhythmic heart beat and pacemaker 31 34 cid 30 Blood pressure and flow patterns 35 37 cid 30 Homeostatic control of blood pressure 36 37 3 41 Maximizing Surface Area For Diffusion Animals maximize the surface area available for diffusion of gases nutrients and other key solutes in a variety of ways Single celled organisms and tiny animals have a small enough volume that diffusion over their body surface is adequate to keep them alive Jellyfish and corals have a large highly folded gastrovascular cavity that offers a large surface area for molecular exchange The flattened bodies of flatworms and tapeworms give them a high surface area volume ratio molecular exchange thus occurs over the entire body surface The Circulatory System 4 41 In larger animals however the problem of providing a large surface area for diffusion is solved by interstitial fluid and a circulatory system The function of a circulatory system is to carry blood or hemolymph into close contact with every cell in the body delivering nutrients and allowing gas exchange to occur All circulatory systems have three basic components A circulatory fluid A heart a muscular pump A set of interconnecting vessels Circulatory systems can be open or closed and rely on pumps that differ in structure 5 41 What Is an Open Circulatory System Open circulatory systems are found in arthropods e g crayfish insects and most molluscs e g snails clams Hemolymph is the circulatory fluid in these system it bathes organs directly and is not always confined to vessels thus it is the circulatory fluid and also the interstitial fluid Hemolymph transports wastes and nutrients and may also contain oxygen carrying pigments some cells and clotting agents Hemolymph is pumped by a heart into blood vessels that empty into an open fluid filled space and hemolymph is returned to the heart when the heart relaxes and internal pressure is lower 6 41 Limitations of Open Circulatory Systems Limitation 1 hemolymph is under relatively low pressure and as a result hemolymph flow rates may also be low The low pressure of open circulatory systems is most suitable for relatively sedentary organisms that do not have high oxygen demands Insects are an exception to this rule they overcome the limitations imposed by low hemolymph pressure via their tracheal respiratory system which delivers oxygen directly to the tissues 7 41 Limitations of Open Circulatory Systems Limitation 2 without discrete continuous vessels the flow of hemolymph cannot be directed toward tissues that have a high oxygen demand and CO2 buildup Crustaceans e g crayfish lobster are an exception to this rule they have a network of small vessels that can preferentially send hemolymph to tissues with high oxygen demands e g the muscular tail What Is a Closed Circulatory System Closed circulatory systems are found in annelids e g earthworms cephalopods e g octopi and squid and all vertebrates 8 41 Blood flows in a continuous circuit in which blood is under pressure generated by a heart confined to vessels A closed system can generate enough pressure to maintain a high flow rate Allows for effective delivery of O2 to tissues in relatively large and active organisms Blood flow can also be directed in a precise way in a closed circulatory system Types of Blood Vessels 9 41 Blood vessels are classified as Arteries Capillaries Veins The structure of arteries capillaries and veins correlates closely with their function in a closed circulatory system Party Fact The total length of blood vessels in an average human adult is 2xs the earth s equatorial circumference 10 41 Astrophysicist Neil deGrasse Tyson http theoatmeal com blog quotations Arteries 11 41 Arteries are tough thick walled vessels that take blood away from the heart under high pressure Small arteries are called arterioles The heart ejects blood into a large artery usually called the aorta which has elastic walls allowing it to expand when blood enters it under high pressure from the heart Arteries and arterioles have smooth muscle fibers called sphincters wrapped around their circumference The sphincters allow the diameter of the vessel to be carefully regulated in response to signals from the nervous system Veins 12 41 Veins are vessels that return blood to the heart under low pressure Small veins are called venules Veins have much thinner walls and much larger interior diameters than arteries do and contain valves thin flaps of tissue that prevent any backflow of blood All veins contain some muscle fibers which contract in response to signals from the nervous system Veins 13 41 Veins are compressed by muscle activity in the extremities which helps speed the return of blood to the heart Capillaries 14 41 Capillaries are the smallest vessels Their walls are just one cell thick They form an extremely dense network throughout the body passing within a few diameters of every cell within the body capillary beds They are where gases nutrients and wastes are exchanged between the blood and the interstitial fluid surrounding cells Capillary Exchange 15 41 Blood plasma is 90 water and 10 ions and proteins Two opposing forces control the movement of fluid between the capillaries and the surrounding interstitial fluid 1 Blood pressure tends to drive fluid out of the capillaries and into the interstitial fluid 2 The presence of blood proteins that are too large to leave the capillaries tend to pull fluid back into the capillaries Blood proteins are responsible for blood s osmotic pressure pressure produced by the difference in solute concentration across a membrane the high concentration of dissolved solutes in the blood means there is less water present in the blood than in the interstitial fluid thus water tends to flow back to the blood in the capillaries 16 41 The Role of the Lymphatic System Each day an adult human loses 4 8 L of fluid from capillaries to the surrounding tissue Any fluid that is not reclaimed in the