Lecture 14 BIO 311D 1st EditionOutline of Last Lecture I. Dental AdaptationsII. Stomach, Intestinal, and Mutualistic AdaptationsIII. Regulation of DigestionIV. Regulation of Appetite and ConsumptionV. Obesity and EvolutionOutline of Current Lecture I. Circulatory SystemII. Gastrovascular CavitiesIII. Evolutionary Variation in Circulatory SystemsIV. Open and Closed Circulatory SystemsV. Organization of Vertebrae Circulatory SystemsVI. The HeartCurrent LectureCirculatory 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 systemGastrovascular 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 ratioCompared to other organisms with closed circulatory systems, the open circulatory system of insects:A. Expands more energy to pump exchange materialsB. Exchanges carbon dioxide and oxygen directly with the environmentC. Independently regulates the distribution of exchange material to each organ in the bodyD. Is possible only in organisms with rigid exoskeletonsE. Allows fluids to move freely in and out of the vessels*open circulatory systems do not have vesselsEvolutionary 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 bodyOpen 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 systemsOrganization 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 returningDouble 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 heartOrganization 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 circulationThe 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 ventricleo 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 arteryA 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