Chapter 42 Circula/on and Gas Exchange BIOL 223 Simple animals such as cnidarians Body wall only two cells thick Flatworms Gastrovascular Cavi/es Encloses gastrovascular cavity diges/on and distribu/on gastrovascular cavity and large surface area to volume ra/o Circular canal Mouth Pharynx Mouth Radial canal (a) The moon jelly Aurelia, a cnidarian 5 cm (b) The planarian Dugesia, a flatworm 2 mm More complex animals Open and Closed Circulatory Systems either open or closed circulatory systems Both systems have three basic components: 1. circulatory fluid (blood or hemolymph) 2. set of tubes (blood vessels) 3. muscular pump (the heart) Open circulatory system insects, other arthropods, most molluscs Hemolymph bathes organs directly No dis/nc/on between blood and inters//al fluid Closed circulatory system Blood is confined to vessels Dis/nct from the inters//al fluid More efficient at transpor/ng circulatory fluids to /ssues and cells Pores Heart Tubular heart (a) An open circulatory system Hemolymph in sinuses surrounding organs Interstitial fluid Dorsal vessel (main heart) Heart Blood Small branch vessels In each organ Auxiliary hearts Ventral vessels (b) A closed circulatory system 1
Vertebrates have closed circulatory systems Arteries Branch into arterioles Capillary beds carry blood to capillaries Networks of capillaries Venules Organiza/on of Vertebrate Circulatory Systems Sites of exchange between the blood and inters//al fluid Carry blood away from capillary beds merge into veins return blood from capillaries to the heart Organiza/on of Vertebrate Circulatory Systems Vertebrate hearts Contain two or more chambers Atrium - Blood entry chamber Ventricle - Blood pumping chamber Single Circula/on Single circula<on Gill capillaries Blood leaving heart passes through two capillary beds before returning Results in very low pressure in system aver first capillary bed Bony fishes, rays, and sharks Heart Artery Ventricle Atrium Vein Gill circulation Systemic circulation Systemic capillaries 2
Double Circula/on Double circula<on Two separate s or pulmocutaneous To pick up O 2 and drop off CO 2 right side of heart Systemic To the body /ssues LeV side of heart Amphibians Lung and skin capillaries Reptiles (Except Birds) Lung capillaries Mammals and Birds Lung capillaries Pulmocutaneous systemic aorta Atrium (A) Atrium (A) A A A A Ventricle (V) Systemic V V systemic aorta V Systemic V Systemic capillaries Systemic capillaries Systemic capillaries Double Circula/on Oxygen- poor blood Flows to lungs to pick up oxygen Rep/les and mammals Pulmocutaneous Oxygen- poor blood flows through lungs and skin Systemic to pick up oxygen amphibians Delivers oxygen- rich blood to /ssues Double circula/on maintains higher blood pressure in the organs than does single circula/on amphibians three- chambered heart Two atria and one ventricle Underwater Amphibians ventricle pumps blood into forked artery Splits the ventricle s output into pulmocutaneous and systemic blood flow to the lungs is nearly shut off 3
Reptiles (Except Birds) rep/les Have a three- chambered heart Two atria and one ventricle alligators, caimans, and other crocodilians a septum divides the ventricle Creates four chambered heart Rep/les have double circula/on pulmonary (lungs) and a systemic Mammals and birds Have a four- chambered heart Mammals and Birds with two atria and two ventricles LeV side pumps and receives only oxygen- rich blood side receives and pumps only oxygen- poor blood Mammals and birds are endotherms require more O 2 than ectotherms Mammalian Circula/on ventricle Pumps blood to the lungs Loads O 2 and unloads CO 2 LeV atrium Receives oxygen- rich blood from the lungs Passes blood to lev ventricle LeV ventricle Pumps oxygen rich blood to rest of body Via aorta The aorta provides blood to the heart through the coronary arteries 4
Mammalian Circula/on Blood returns to the heart Through the superior vena cava blood from head, neck, and forelimbs And Inferior vena cava blood from trunk and hind limbs Both flow into the right atrium atrium passes blood to right ventricle Fig. 42-6 Superior vena cava 7 Capillaries of head and forelimbs artery artery Capillaries of right lung 9 Aorta Capillaries of left lung 3 2 4 3 11 vein atrium 10 1 5 vein atrium ventricle ventricle Inferior vena cava Aorta 8 Capillaries of abdominal organs and hind limbs Fig. 42-7 artery atrium Aorta artery atrium Semilunar valve Atrioventricular valve Semilunar valve Atrioventricular valve ventricle ventricle 5
Cardiac cycle Mammalian Heart Semilunar valves closed 2 Atrial systole; ventricular diastole Rhythmic contrac/ons of heart Systole 0.1 sec The contrac/on phase Diastole AV valves open 0.4 sec 0.3 sec Semilunar valves open The relaxa/on phase 1 Atrial and ventricular diastole AV valves closed 3 Ventricular systole; atrial diastole Cardiac Cycle Pulse or heart rate The number of beats per minute Stroke volume Amount of blood pumped in a single contrac/on Cardiac output Volume of blood pumped into the systemic circula/on per minute and depends on both the heart rate and stroke volume Cardiac Cycle Four valves prevent backflow of blood in the heart Atrioventricular (AV) valves separate each atrium and ventricle Semilunar valves control blood flow to the aorta and the pulmonary artery 6
Cardiac Cycle The lub- dup sound of a heart beat recoil of blood against AV valves (lub) then against semilunar valves (dup) Backflow of blood through a defec/ve valve causes a heart murmur Cardiac Cycle Sinoatrial (SA) node, or pacemaker Sets rate and /ming of contrac/on Superior end of right atrium Impulses from SA node travel to the atrioventricular (AV) node At AV impulses are delayed then travel to Purkinje fibers make the ventricles contract Cardiac Cycle Electrocardiogram electrical ac/vity of heart throughout the cardiac cycle ECG or EKG 7
Fig. 42-9- 5 1 Pacemaker generates wave of signals to contract. 2 Signals are delayed at AV node. 3 Signals pass to heart apex. 4 Signals spread throughout ventricles. SA node (pacemaker) AV node Bundle branches Heart apex Purkinje fibers ECG Blood Vessel Structure Capillaries Thin, simple squamous walls Plus its basement membrane Facilitate the exchange of materials Arteries and veins Endothelium, smooth muscle, and connec/ve /ssue Arteries Thicker walls accommodate high pressure of blood pumped from heart Veins Thinner- walled Blood flows back to heart mainly as a result of muscle ac/on Fig. 42-10 Artery Vein SEM Endothelium 100 µm Basal lamina Endothelium Valve Artery Smooth muscle Connective tissue Capillary Smooth muscle Connective tissue Vein Red blood cell Arteriole Capillary Venule LM 15 µm 8
Physical laws governing movement of fluids through pipes Blood Flow Velocity Affect blood flow and blood pressure Velocity of blood flow Area (cm 2 ) 5,000 4,000 3,000 2,000 1,000 0 50 Slowest in the capillary beds Result of the large total cross- sec/onal area Necessarily slow for exchange of materials Velocity (cm/sec) Pressure (mm Hg) 40 30 20 10 0 120 100 80 60 40 20 0 Diastolic pressure Aorta Arteries Systolic pressure Arterioles Capillaries Venules Veins Venae cavae Changes in Blood Pressure During the Cardiac Cycle Systolic pressure pressure in arteries during ventricular systole highest pressure Diastolic pressure pressure in the arteries during diastole lower than systolic pressure Blood pressure Regula/on of Blood Pressure determined by cardiac output and peripheral resistance due to constric/on of arterioles Vasoconstric<on contrac/on of smooth muscle in arteriole walls Vasodila<on Increases blood pressure relaxa/on of smooth muscles in arterioles Reduces blood pressure Rubber cuff inflated with air Artery closed Pressure in cuff greater than 120 mm Hg 120 120 Sounds audible in stethoscope Blood pressure reading: 120/70 Pressure in cuff drops below 120 mm Hg Sounds stop Pressure in cuff below 70 mm Hg 70 9
Fain/ng Caused by inadequate blood flow to the brain Animals with longer necks Require a higher systolic pressure to pump blood a greater distance against gravity Blood is moved through veins by smooth muscle contrac/on skeletal muscle contrac/on expansion of the vena cava with inhala/on Blood Pressure One- way valves in veins prevent backflow of blood Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) Capillary Func/on Precapillary sphincters Thoroughfare channel Two mechanisms regulate distribu/on of blood in capillary beds: Arteriole vasoconstric/on Precapillary sphincters Arteriole (a) Sphincters relaxed Capillaries Venule Control flow of blood between arterioles and venules Arteriole Venule (b) Sphincters contracted 10