Lecture 14 BIO 311D 1st Edition Outline of Last Lecture I Dental Adaptations II Stomach Intestinal and Mutualistic Adaptations III Regulation of Digestion IV Regulation of Appetite and Consumption V Obesity and Evolution Outline of Current Lecture I Circulatory System II Gastrovascular Cavities III Evolutionary Variation in Circulatory Systems IV Open and Closed Circulatory Systems V Organization of Vertebrae Circulatory Systems VI The Heart Current Lecture Circulatory systems link exchange surfaces with cells throughout the body Function of circulatory system To allow oxygen to enter cells and to transport carbon dioxide to be removed Diffusion time is proportional to the square of the distance Diffusion is only efficient over small distances In small and or thin animals cells can exchange materials directly with the surrounding medium In most animals cells exchange materials with the environment via a fluid filled circulatory system Gastrovascular Cavities Some animals lack a circulatory system Some cnidarians such as jellies have elaborate gastrovascular cavities A gastrovascular cavity functions in both digestion and distribution of substances throughout the body The body wall that encloses the gastrovascular cavity is only two cells thick Flatworms have a gastrovascular cavity and a large surface area to volume ratio Compared to other organisms with closed circulatory systems the open circulatory system of insects A Expands more energy to pump exchange materials B Exchanges carbon dioxide and oxygen directly with the environment C Independently regulates the distribution of exchange material to each organ in the body D Is possible only in organisms with rigid exoskeletons E Allows fluids to move freely in and out of the vessels open circulatory systems do not have vessels Evolutionary Variation in Circulatory Systems A circulatory system minimizes the diffusion distance in animals with many cell layers A circulatory system has three main components A circulatory fluid A set of interconnecting vessels A muscular pump the heart The circulatory system connects the fluid that surrounds cells with the organs that exchange gases absorb nutrients and dispose of wastes Circulatory systems can be open or closed and vary in the number of circuits in the body Open and Closed Circulatory Systems In insects other arthropods and most molluscs blood bathes the organs directly in an open circulatory system In an open circulatory system there is no distinction between blood and interstitial fluid and this general body fluid is called hemolymph In a closed circulatory system blood is confined to vessels and is distinct from the interstitial fluid Closed systems are more efficient at transporting circulatory fluids to tissues and cells Annelids cephalopods and vertebrates have closed circulatory systems Organization of Vertebrate Circulatory Systems Humans and other vertebrates have a closed circulatory system called the cardiovascular system The three main types of blood vessels are arteries veins and capillaries Blood flow is one way in these vessels Arteries branch into arterioles and carry blood away from the heart to capillaries Arteries are taking blood away from the heart Veins are taking blood to the heart Veins and arteries are distinguished by the direction not by the type of blood it carries Capillaries is where gases exchange Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid Venules converge into veins and return blood from capillaries to the heart Arteries and veins are distinguished by the direction of blood flow not by O2 content Heart is divided into four chambers Vertebrate hearts contain two or more chambers Blood enters through an atrium is the top and is pumped out through a ventricle is the bottom compartment The right and left parts of the heart are opposite from the way it is perceived Right side of the heart brings blood to the lungs to pick up oxygen Left side brings oxygenated blood to the rest of the body Single Circulation Bony fishes rays and sharks have single circulation with a two chambered heart In single circulation blood leaving the heart passes through two capillary beds before returning Double Circulation Amphibian reptiles and mammals have double circulation Oxygen poor and oxygen rich blood are pumped separately from the right and left sides of the heart Organization of Vertebrate Circulatory Systems In reptiles and mammals oxygen poor blood flows through the pulmonary circuit to pick up oxygen through the lungs In amphibians oxygen poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin Oxygen rich blood delivers oxygen through the systemic circuit Double circulation maintains higher blood pressure in the organs than does single circulation The Heart Blood flow goes in this direction o Blood in the right atrium causes atrioventricular valve to open so blood can move to the right ventricle o Right ventricle contracts causing blood to flow out to arteries to pulmonary circulation o Blood returns back to the left atrium then to left ventricle then to the aorta The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle The contraction or pumping phase is called systole The relaxation or filling phase is called diastole The heart rate also called the pulse is the number of beats per minute The stroke volume is the amount of blood pumped in a single contraction The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume Four valves prevent backflow of blood in the heart The atrioventricular AV valves separate each atrium and ventricle The semilunar valves control blood flow to the aorta and the pulmonary artery A Heartbeat Comes From The lub dup sound of a heart beat is caused by the recoil of blood against the AV valves lub then against the semilunar dup valves Backflow of blood through a defective valve causes a heart murmur Some cardiac muscle cells are self excitable meaning they contract without any signal from the nervous system The sinoatrial SA node or pacemaker sets the rate and timing at which cardiac muscle cells contract Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram ECG or EKG Impulses from the SA node travel to the atrioventricular AV node At the AV node the impulses are delayed and then travel to