Circulation in Animals Chapter 42. Circulation in Animals 2008-2009

2008-2009

What are the issues Animal cells exchange material across the cell membrane nutrients fuels for energy oxygen waste (urea, CO2) If you are a 1-cell organism that’s easy! If you are many-celled that’s harder 2008-2009

What are the issues? Diffusion is not adequate for moving material across more than 1 cell barrier NH3 CH CO2 O2 aa CO2 NH3 NH3 CO2 O2 CHO NH3 CH CO2 CO2 aa CO2 NH3 NH3 NH3 O2 CO2 CO2 CHO CO2 aa NH3 CH NH3 NH3 CHO O2 CO2 CO2 aa O2 aa 2008-2009

Simple diffusion Cnidarians Hydra Body cavity 2-cell layers think all cells within easy reach of fluid use gastrovascular cavity for exchange Cnidarians 2008-2009 Hydra

What are the solutions? Circulatory system solves this problem carries fluids & dissolved material throughout body cells are never far from body fluid only a few cells away from blood overcoming the limitations of diffusion 2008-2009

In circulation… What needs to be transported nutritive respiratory nutrients fuels from digestive system respiratory O2 & CO2 from & to gas exchange systems: lungs, gills excretory waste products from cells water, salts, nitrogenous wastes (urea) protection blood clotting immune defenses white blood cells & others patrolling body regulation hormones 2008-2009

Circulatory systems All animals have: circulatory fluid = blood tubes = blood vessels muscular pump = heart open closed 2008-2009

Open circulatory system Taxonomy invertebrates insects, arthropods, mollusks Structure no distinction between blood & extracellular (interstitial) fluid hemolymph The fact that open and closed circulatory systems are each widespread among animals suggests that both offer advantages. For example, the lower hydrostatic pressures associated with open circulatory systems make them less costly than closed systems in terms of energy expenditure. Furthermore, because they lack an extensive system of blood vessels, open systems require less energy to build and maintain. And in some invertebrates, open circulatory systems serve a variety of other functions. For example, in molluscs and freshly molted aquatic arthropods, the open circulatory system functions as a hydrostatic skeleton in supporting the body. 2008-2009

Closed circulatory system Taxonomy invertebrates earthworms, squid, octopuses vertebrates Structure blood confined to vessels & separate from interstitial fluid 1 or more hearts large vessels to smaller vessels material diffuses between vessels & interstitial fluid What advantages might be associated with closed circulatory systems? Closed systems, with their higher blood pressure, are more effective at transporting circulatory fluids to meet the high metabolic demands of the tissues and cells of larger and more active animals. For instance, among the molluscs, only the large and active squids and octopuses have closed circulatory systems. And although all arthropods have open circulatory systems, the larger crustaceans, such as the lobsters and crabs, have a more developed system of arteries and veins as well as an accessory pumping organ that helps maintain blood pressure. Closed circulatory systems are most highly developed in the vertebrates. 2008-2009

Vertebrate circulatory system Closed system number of heart chambers differs What’s the adaptive value of a 4 chamber heart? 4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood 2008-2009

Evolution of vertebrate circulatory system heart structure & increasing body size fish amphibian reptiles birds & mammals 2 chamber 3 chamber 3 chamber 4 chamber A powerful four–chambered heart was an essential adaptation in support of the endothermic way of life characteristic of mammals and birds. Endotherms use about ten times as much energy as equal–sized ectotherms; therefore, their circulatory systems need to deliver about ten times as much fuel and O2 to their tissues (and remove ten times as much CO2 and other wastes). This large traffic of substances is made possible by separate and independent systemic and pulmonary circulations and by large, powerful hearts that pump the necessary volume of blood. Mammals and birds descended from different reptilian ancestors, and their four–chambered hearts evolved independently—an example of convergent evolution. Why is it an advantage to get big? Herbivore: can eat more with bigger gut. lowers predation (but will push predators to get bigger as well, although no one east elephant s.) V A A A A A A A V V V V V 2008-2009

Driving evolution of CV systems Metabolic rate endothermy = higher metabolic rate greater need for energy, fuels, O2, waste removal more complex circulatory system more powerful hearts 2008-2009

Evolution of 4 chambered heart Double circulation increase pressure to systemic (body) circuit prevents mixing of oxygen-rich & oxygen-poor blood Powerful 4-chambered heart essential adaptation to support endothermy (warm-blooded) endothermic animals need 10x energy need to deliver 10x fuel & O2 convergent evolution in birds & mammals 2008-2009

Vertebrate cardiovascular system Chambered heart atria (atrium) = receive blood ventricles = pump blood out Blood vessels arteries = carry blood away from heart arterioles veins = return blood to heart venules capillaries = point of exchange, thin wall capillary beds = networks of capillaries Arteries, veins, and capillaries are the three main kinds of blood vessels, which in the human body have a total length of about 100,000 km. Notice that arteries and veins are distinguished by the direction in which they carry blood, not by the characteristics of the blood they contain. All arteries carry blood from the heart toward capillaries, and veins return blood to the heart from capillaries. A significant exception is the hepatic portal vein that carries blood from capillary beds in the digestive system to capillary beds in the liver. Blood flowing from the liver passes into the hepatic vein, which conducts blood to the heart. 2008-2009

Blood vessels arteries arterioles capillaries venules veins 2008-2009

Mammalian circulation Pulmonary circuit vs. Systemic circuit 2008-2009

Mammalian circulation 2 circulations pulmonary = lungs systemic = body operate simultaneously 4 chambered heart 2 atria = thin-walled collection chambers 2 ventricles = thick-walled pumps ventricles pump almost in unison Vessels veins carry blood to heart arteries carry blood away from heart 2008-2009

Mammalian heart to neck & head & arms Coronary arteries 2008-2009

Heart valves 4 valves in the heart Atrioventricular (AV) valve flaps of connective tissue prevent backflow & keep blood moving in the correct direction Atrioventricular (AV) valve between atrium & ventricle keeps blood from flowing back into atria when ventricles contract Semilunar valves between ventricle & arteries prevent backflow from vessels into ventricles while they are relaxing SL AV AV The heart sounds heard with a stethoscope are caused by the closing of the valves. (Even without a stethoscope, you can hear these sounds by pressing your ear tightly against the chest of a friend—a close friend.) The sound pattern is “lub–dup, lub–dup, lub–dup.” The first heart sound (“lub”) is created by the recoil of blood against the closed AV valves. The second sound (“dup”) is the recoil of blood against the semilunar valves. 2008-2009

Cardiac cycle 1 complete sequence of pumping heart contracts & pumps heart relaxes & chambers fill contraction phase systole ventricles pumps blood out relaxation phase diastole atria refill with blood 2008-2009

Cardiac Cycle How is this reflected in blood pressure measurements? ventricles fill How is this reflected in blood pressure measurements? systolic ________ diastolic The cardiac cycle. For an adult human at rest with a pulse of about 75 beats per minute, one complete cardiac cycle takes about 0.8 second. During a relaxation phase (atria and ventricles in diastole), blood returning from the large veins flows into the atria and ventricles. A brief period of atrial systole then forces all remaining blood out of the atria into the ventricles. During the remainder of the cycle, ventricular systole pumps blood into the large arteries. Note that 7/8 of the time—all but 0.1 second of the cardiac cycle—the atria are relaxed and are filling with blood returning via the veins. chambers fill pump ________ fill 2008-2009 ventricles pump

Measurement of blood pressure 2008-2009

Lub-dup, lub-dup Heart sounds Heart murmur closing of valves “Lub” recoil of blood against closed AV valves “Dup” recoil of blood against semilunar valves Heart murmur defect in valves causes hissing sound when stream of blood squirts backward through valve SL AV AV 2008-2009

Form follows function Arteries thicker middle & outer layers thicker walls provide strength for high pressure pumping of blood elasticity (elastic recoil) helps maintain blood pressure even when heart relaxes 2008-2009

Form follows function Veins thinner-walled blood travels back to heart at low velocity & pressure blood flows due to skeletal muscle contractions when we move squeeze blood in veins in larger veins one-way valves allow blood to flow only toward heart 2008-2009

Form follows function Capillaries lack 2 outer wall layers very thin walls = only endothelium enhancing exchange 2008-2009

pre-capillary sphincters regulate flow into capillary beds Blood flow at any given time, only ~5-10% of body’s capillaries have blood flowing through them capillaries in brain, heart, kidneys & liver usually filled to capacity for other sites, blood supply varies over times as blood is needed after a meal blood supply to digestive tract increases during strenuous exercise, blood is diverted from digestive tract to skeletal muscles At any given time, only about 5–10% of the body’s capillaries have blood flowing through them. However, each tissue has many capillaries, so every part of the body is supplied with blood at all times. Capillaries in the brain, heart, kidneys, and liver are usually filled to capacity, but in many other sites, the blood supply varies over time as blood is diverted from one destination to another. After a meal, for instance, blood supply to the digestive tract increases. During strenuous exercise, blood is diverted from the digestive tract and supplied more generously to skeletal muscles and skin. This is one reason that exercising heavily immediately after eating a big meal may cause indigestion. pre-capillary sphincters regulate flow into capillary beds 2008-2009

Exchange across capillary walls arteriole side venule side BP > OP BP < OP 85% fluid return 15% from lymph About 85% of the fluid that leaves the blood at the arterial end of a capillary bed reenters from the interstitial fluid at the venous end, and the remaining 15% is eventually returned to the blood by the vessels of the lymphatic system. Direction of movement of fluid between blood & interstitial fluids depends on blood pressure & osmotic pressure 2008-2009

Exchange across capillary walls Diffusion bulk flow transport due to fluid pressure blood pressure within capillary pushes fluid – water & small solutes – through capillary wall causes net loss of fluid at upstream end of capillary Endocytosis & exocytosis larger molecules Left behind blood cells & most proteins in blood are too large to pass through, so remain in capillaries The exchange of substances between the blood and the interstitial fluid that bathes the cells takes place across the thin endothelial walls of the capillaries. Some substances are carried across endothelial cells in vesicles that form by endocytosis on one side and then release their contents by exocytosis on the other side. Others simply diffuse between the blood and the interstitial fluid across cells or through the clefts between adjoining cells. At any given time, only ~5-10% of body’s capillaries have blood flowing through them capillaries in brain, heart, kidneys & liver are usually filled to capacity, for other sites, blood supply varies over times as blood is needed after a meal blood supply to digestive tract increases during strenuous exercise, blood is diverted from digestive tract to skeletal muscles 2008-2009

Lymphatic system Parallel circulatory system transports WBC defending against infection collects interstitial fluid & returns to blood maintains volume & protein concentration of blood drains into circulatory system near junction of venae cavae with right atrium transports fats from digestive to circulatory system 2008-2009

Lymph System 2008-2009

Control of heart Timely delivery of O2 to body’s organs is critical mechanisms evolved to assure continuity & control of heartbeat cells of cardiac muscle are “self-excitable” contract without any signal from nervous system each cell has its own contraction rhythm cells are synchronized by the sinoatrial (SA) node, or pacemaker sets rate & timing of cardiac muscle cell contraction located in wall of right atrium 2008-2009

Electrical signals Cardiac cycle regulated by electrical impulses that radiate across heart transmitted to skin = EKG 2008-2009

Coordinated contraction SA node generates electrical impulses coordinates atrial contraction impulse delayed by 0.1 sec at AV node relay point to ventricle allows atria to empty completely before ventricles contract specialized muscle fibers conduct signals to apex of heart & throughout ventricular walls stimulates ventricles to contract from apex toward atria, driving blood into arteries The impulses generated during the heart cycle produce electrical currents that are conducted through body fluids to the skin. Here, the currents can be detected by electrodes and recorded as an electrocardiogram (ECG or EKG). 2008-2009

Effects on heart rate Physiological cues affect heart rate nervous system speed up pacemaker slow down pacemaker heart rate is compromise regulated by opposing actions of these 2 sets of nerves hormones epinephrine from adrenal glands increases heart rate body temperature activity exercise, etc. In large land animals, blood pressure is also affected by gravity. In addition to the peripheral resistance, additional pressure is necessary to push blood to the level of the heart. In a standing human, it takes an extra 27 mm of Hg pressure to move blood from the heart to the brain. In an organism like a giraffe, this extra force is about 190 mm Hg (for a total of 250 mm Hg). Special check valves & sinuses, as well as feedback mechanisms that reduce cardiac output, prevent this high pressure from damaging the giraffe’s brain when it puts its head down. 2008-2009

Blood & blood cells Blood is a mixture of fluid & cells plasma = fluid (55% of volume) ions (electrolytes), plasma proteins, nutrients, waste products, gases, hormones cells (45% of volume) RBC = erythrocytes transport gases WBC = leukocytes defense platelets blood clotting Dissolved in the plasma are a variety of ions, sometimes referred to as blood electrolytes, These are important in maintaining osmotic balance of the blood and help buffer the blood. Also, proper functioning of muscles and nerves depends on the concentrations of key ions in the interstitial fluid, which reflects concentrations in the plasma. 2008-2009

Constituents of blood 2008-2009

Plasma proteins Synthesized in liver & lymph system fibrinogen clotting factor blood plasma with clotting factors removed = serum albumins buffer against pH changes, help maintain osmotic balance & blood’s viscosity globulins immune response immunoglobins = antibodies help combat foreign invaders 2008-2009

Cell production Development from stem cells ribs, vertebrae, breastbone & pelvis Development from stem cells Differentiation of blood cells in bone marrow & lymph tisssues Recently, researchers succeeded in isolating pluripotent stem cells and growing these cells in laboratory cultures. Purified pluripotent stem cells may soon provide an effective treatment for a number of human diseases, including leukemia. A person with leukemia has a cancerous line of the stem cells that produce leukocytes. The cancerous stem cells crowd out cells that make erythrocytes and produce an unusually high number of leukocytes, many of which are abnormal. One experimental treatment for leukemia involves removing pluripotent stem cells from a patient, destroying the bone marrow, and restocking it with noncancerous stem cells. As few as 30 of these cells can completely repopulate the bone marrow. 2008-2009

Red blood cells O2 transport Small biconcave disks large surface area produced in marrow of long bones lack nuclei & mitochondria more space for hemoglobin iron-containing protein that transports O2 generate ATP by anaerobic respiration last 3-4 months (120 days) ingested by phagocytic cells in liver & spleen ~3 million RBC destroyed each second Enucleated RBC The nucleus is squeezed out of the cell and is ingested by the macrophage. Cellular Life Expectancy Red blood cells usually circulate for only about 3 to 4 months and are then destroyed by phagocytic cells in liver & spleen. Enzymes digest the old cell’s macromolecules, and the monomers are recycled. Many of the iron atoms derived from hemoglobin in old red blood cells are built into new hemoglobin molecules. But some are reused in digestive bile. As adults, we make more than 2 million red blood cells in our bone marrow every second to replace those lost through normal attrition. 2008-2009

Red blood cell production 5-6 million RBC in 1µL of human blood 5 L of blood in body = 25 trillion RBC produce ~3 million RBC every second in bone marrow to replace cells lost through attrition each RBC 250,000 molecules hemoglobin each Hb molecule carries 4 O2 each RBC carries 1 million O2 A negative–feedback mechanism, sensitive to the amount of O2 reaching the body’s tissues via the blood, controls erythrocyte production. If the tissues do not receive enough O2, the kidney synthesizes and secretes a hormone called erythropoietin (EPO), which stimulates production of erythrocytes. If blood is delivering more O2 than the tissues can use, the level of EPO falls and erythrocyte production slows. Physicians use synthetic erythropoietin to treat people with health problems such as anemia, a condition of lower–than–normal hemoglobin levels. However, some athletes abuse EPO by injecting themselves with the drug to increase their erythrocyte levels. This practice, known as blood doping, is banned by the International Olympic Committee and other sports federations. In 2002, several athletes competing in the winter Olympics in Salt Lake City tested positive for EPO–like chemicals and as a result were stripped of some of their medals. 2008-2009

Hemoglobin Protein with 4° structure O2 carrier molecule 2008-2009

Blood clotting Cascade reaction self-sealing material Powerful evolutionary adaptation emergency repair of circulatory system prevent excessive blood loss Inherited defect in any step of the clotting process causes hemophilia, characterized by excessive bleeding from even minor cuts & bruises 2008-2009

Cardiovascular disease Leading cause of death in U.S. plaques develop in inner wall of arteries, narrowing channel stroke, heart attack, atherosclerosis, arteriosclerosis, hypertension tendency inherited, but other risk factors: smoking, lack of exercise, diet rich in fat 2008-2009

Cardiovascular health (U.S. 2001) Heart Disease 696,947 Cancer 557,271 Stroke 162,672 Chronic lower respiratory diseases 124,816 Accidents (unintentional injuries) 106,742 Diabetes 73,249 Influenza/Pneumonia 65,681 Alzheimer's disease 58,866 Nephritis, nephrotic syndrome & nephrosis 40,974 Septicemia 33,865 2008-2009

Stroke Fact Sheet 2008-2009