Chapter 42: Circulatory Systems and Gas Exchange Take a look at a skeleton and see how well a heart is protected — open heart surgery takes breaking a body to get to the heart.

Exchange of materials Animal cells exchange material across their cell membrane fuels for energy nutrients oxygen waste (urea, CO2) If you are a 1-cell organism that’s easy! diffusion If you are many-celled that’s harder

Overcoming limitations of diffusion Diffusion is not adequate for moving material across more than 1-cell barrier aa CO2 NH3 O2 CH CHO aa O2 CH CHO CO2 aa NH3 CHO CH O2 aa

In circulation… What needs to be transported nutrients & fuels from digestive system respiratory gases O2 & CO2 from & to gas exchange systems: lungs, gills intracellular waste waste products from cells water, salts, nitrogenous wastes (urea) protective agents immune defenses white blood cells & antibodies blood clotting agents regulatory molecules hormones

Circulatory systems All animals have: circulatory fluid = “blood” tubes = blood vessels muscular pump = heart open closed hemolymph blood

Open circulatory system Taxonomy invertebrates insects, arthropods, mollusks Structure no separation between blood & 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.

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 blood vessels & interstitial fluid closed system = higher pressures 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.

Vertebrate circulatory system Adaptations in closed system number of heart chambers differs 2 3 4 high pressure & high O2 to body low pressure to body low O2 to body What’s the adaptive value of a 4 chamber heart? 4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood; maintains high pressure

Evolution of vertebrate circulatory system fish amphibian reptiles birds & mammals 2 chamber 3 chamber 3 chamber 4 chamber Birds AND mammals! Wassssup?! 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

Evolution of 4-chambered heart Selective forces increase body size protection from predation bigger body = bigger stomach for herbivores endothermy can colonize more habitats flight decrease predation & increase prey capture Effect of higher metabolic rate greater need for energy, fuels, O2, waste removal endothermic animals need 10x energy need to deliver 10x fuel & O2 to cells convergent evolution

Vertebrate cardiovascular system Chambered heart atrium = receive blood ventricle = pump blood out Blood vessels arteries = carry blood away from heart arterioles veins = return blood to heart venules capillaries = thin wall, exchange / diffusion 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.

Blood vessels arteries arterioles capillaries venules veins veins artery arterioles venules arterioles capillaries venules veins

Arteries: Built for high pressure pump thicker walls provide strength for high pressure pumping of blood narrower diameter elasticity elastic recoil helps maintain blood pressure even when heart relaxes

Veins: Built for low pressure flow Blood flows toward heart Veins thinner-walled wider diameter blood travels back to heart at low velocity & pressure lower pressure distant from heart blood must flow by skeletal muscle contractions when we move squeeze blood through veins valves in larger veins one-way valves allow blood to flow only toward heart Open valve Closed valve

Capillaries: Built for exchange very thin walls lack 2 outer wall layers only endothelium enhances exchange across capillary diffusion exchange between blood & cells

Controlling blood flow to tissues Blood flow in capillaries controlled by pre-capillary sphincters supply varies 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 capillaries in brain, heart, kidneys & liver usually filled to capacity Why? sphincters open sphincters closed

Exchange across capillary walls Lymphatic capillary Fluid & solutes flows out of capillaries to tissues due to blood pressure “bulk flow” Interstitial fluid flows back into capillaries due to osmosis plasma proteins  osmotic pressure in capillary BP > OP BP < OP Interstitial fluid What about edema? 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. Blood flow 85% fluid returns to capillaries Capillary 15% fluid returns via lymph Arteriole Venule

Lymphatic system Parallel circulatory system transports white blood cells defending against infection collects interstitial fluid & returns to blood maintains volume & protein concentration of blood drains into circulatory system near junction of vena cava & right atrium

Lymph system Production & transport of WBCs Traps foreign invaders lymph vessels (intertwined amongst blood vessels) lymph node

Mammalian circulation systemic Mammalian circulation pulmonary systemic What do blue vs. red areas represent?

Mammalian heart to neck & head & arms Coronary arteries

Coronary arteries bypass surgery

Heart valves 4 valves in the heart Atrioventricular (AV) valve SL Heart valves 4 valves in the heart flaps of connective tissue prevent backflow Atrioventricular (AV) valve between atrium & ventricle keeps blood from flowing back into atria when ventricles contract “lub” Semilunar valves between ventricle & arteries prevent backflow from arteries into ventricles while they are relaxing “dub” 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.

Lub-dub, lub-dub Heart sounds Heart murmur closing of valves “Lub” recoil of blood against closed AV valves “Dub” 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

fill (minimum pressure) 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 systolic ________ diastolic pump (peak pressure) _________________ fill (minimum pressure) 110 ____ 70

Measurement of blood pressure High Blood Pressure (hypertension) if top number (systolic pumping) > 150 if bottom number (diastolic filling) > 90

Gas Exchange Respiratory Systems alveoli Gas Exchange Respiratory Systems elephant seals gills 2008-2009

Why do we need a respiratory system? respiration for respiration Why do we need a respiratory system? Need O2 in for aerobic cellular respiration make ATP Need CO2 out waste product from Krebs cycle food ATP O2 CO2

Gas exchange O2 & CO2 exchange between environment & cells need moist membrane need high surface area

Optimizing gas exchange Why high surface area? maximizing rate of gas exchange CO2 & O2 move across cell membrane by diffusion rate of diffusion proportional to surface area Why moist membranes? moisture maintains cell membrane structure gases diffuse only dissolved in water small intestines large intestines capillaries mitochondria High surface area? High surface area! Where have we heard that before?

Gas exchange in many forms… one-celled amphibians echinoderms cilia insects fish mammals size • water vs. land • endotherm vs. ectotherm

Evolution of gas exchange structures Aquatic organisms external systems with lots of surface area exposed to aquatic environment Terrestrial Constantly passing water across gills Crayfish & lobsters paddle-like appendages that drive a current of water over their gills Fish creates current by taking water in through mouth, passes it through slits in pharynx, flows over the gills & exits the body moist internal respiratory tissues with lots of surface area

Gas Exchange in Water: Gills In fish, blood must pass through two capillary beds, the gill capillaries & systemic capillaries. When blood flows through a capillary bed, blood pressure — the motive force for circulation — drops substantially. Therefore, oxygen-rich blood leaving the gills flows to the systemic circulation quite slowly (although the process is aided by body movements during swimming). This constrains the delivery of oxygen to body tissues, and hence the maximum aerobic metabolic rate of fishes.

Counter current exchange system Water carrying gas flows in one direction, blood flows in opposite direction Living in water has both advantages & disadvantages as respiratory medium keep surface moist O2 concentrations in water are low, especially in warmer & saltier environments gills have to be very efficient ventilation counter current exchange Why does it work counter current? Adaptation! just keep swimming….

How counter current exchange works front back 70% 40% 100% 15% water 60% 30% 90% counter-current 5% blood water blood 50% 70% 100% 50% 30% 5% concurrent Blood & water flow in opposite directions maintains diffusion gradient over whole length of gill capillary maximizing O2 transfer from water to blood

Why don’t land animals use gills? Gas Exchange on Land Advantages of terrestrial life air has many advantages over water higher concentration of O2 O2 & CO2 diffuse much faster through air respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills air is much lighter than water & therefore much easier to pump expend less energy moving air in & out Disadvantages keeping large respiratory surface moist causes high water loss reduce water loss by keeping lungs internal Why don’t land animals use gills?

Terrestrial adaptations Tracheae air tubes branching throughout body gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system How is this adaptive? No longer tied to living in or near water. Can support the metabolic demand of flight Can grow to larger sizes.

Why is this exchange with the environment RISKY? Exchange tissue: spongy texture, honeycombed with moist epithelium Lungs Why is this exchange with the environment RISKY? Lungs, like digestive system, are an entry point into the body lungs are not in direct contact with other parts of the body circulatory system transports gases between lungs & rest of body

Alveoli Gas exchange across thin epithelium of millions of alveoli total surface area in humans ~100 m2

Negative pressure breathing Breathing due to changing pressures in lungs air flows from higher pressure to lower pressure pulling air instead of pushing it

Mechanics of breathing Air enters nostrils filtered by hairs, warmed & humidified sampled for odors Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli) Epithelial lining covered by cilia & thin film of mucus mucus traps dust, pollen, particulates beating cilia move mucus upward to pharynx, where it is swallowed

Autonomic breathing control don’t want to have to think to breathe! Autonomic breathing control Medulla sets rhythm & pons moderates it coordinate respiratory, cardiovascular systems & metabolic demands Nerve sensors in walls of aorta & carotid arteries in neck detect O2 & CO2 in blood

Medulla monitors blood Monitors CO2 level of blood measures pH of blood & cerebrospinal fluid bathing brain CO2 + H2O  H2CO3 (carbonic acid) if pH decreases then increase depth & rate of breathing & excess CO2 is eliminated in exhaled air

Breathing and Homeostasis ATP Homeostasis keeping the internal environment of the body balanced need to balance O2 in and CO2 out need to balance energy (ATP) production Exercise breathe faster need more ATP bring in more O2 & remove more CO2 Disease poor lung or heart function = breathe faster need to work harder to bring in O2 & remove CO2 CO2 O2

Diffusion of gases Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue capillaries in lungs capillaries in muscle O2 O2 O2 O2 CO2 CO2 CO2 CO2 blood lungs blood body

Hemoglobin Why use a carrier molecule? Reversibly binds O2 O2 not soluble enough in H2O for animal needs blood alone could not provide enough O2 to animal cells hemocyanin in insects = copper (bluish/greenish) hemoglobin in vertebrates = iron (reddish) Reversibly binds O2 loading O2 at lungs or gills & unloading at cells heme group The low solubility of oxygen in water is a fundamental problem for animals that rely on the circulatory systems for oxygen delivery. For example, a person exercising consumes almost 2 L of O2 per minute, but at normal body temperature and air pressure, only 4.5 mL of O2 can dissolve in a liter of blood in the lungs. If 80% of the dissolved O2 were delivered to the tissues (an unrealistically high percentage), the heart would need to pump 500 L of blood per minute — a ton every 2 minutes. cooperativity

Cooperativity in Hemoglobin Binding O2 binding of O2 to 1st subunit causes shape change to other subunits conformational change increasing attraction to O2 Releasing O2 when 1st subunit releases O2, causes shape change to other subunits lowers attraction to O2

O2 dissociation curve for hemoglobin Effect of pH (CO2 concentration) Bohr Shift drop in pH lowers affinity of Hb for O2 active tissue (producing CO2) lowers blood pH & induces Hb to release more O2 PO2 (mm Hg) 10 20 30 40 50 60 70 80 90 100 120 140 More O2 delivered to tissues pH 7.60 pH 7.20 pH 7.40 % oxyhemoglobin saturation

O2 dissociation curve for hemoglobin Effect of Temperature Bohr Shift increase in temperature lowers affinity of Hb for O2 active muscle produces heat PO2 (mm Hg) 10 20 30 40 50 60 70 80 90 100 120 140 More O2 delivered to tissues 20°C 43°C 37°C % oxyhemoglobin saturation

Transporting CO2 in blood Dissolved in blood plasma as bicarbonate ion Tissue cells Plasma CO2 dissolves in plasma CO2 combines with Hb CO2 + H2O H2CO3 H+ + HCO3– HCO3– CO2 Carbonic anhydrase Cl– carbonic acid CO2 + H2O  H2CO3 bicarbonate H2CO3  H+ + HCO3– carbonic anhydrase

Releasing CO2 from blood at lungs Lower CO2 pressure at lungs allows CO2 to diffuse out of blood into lungs Plasma Lungs: Alveoli CO2 dissolved in plasma HCO3–Cl– CO2 H2CO3 Hemoglobin + CO2 CO2 + H2O HCO3 – + H+

Adaptations for pregnancy Mother & fetus exchange O2 & CO2 across placental tissue Why would mother’s Hb give up its O2 to baby’s Hb?

Fetal hemoglobin (HbF) HbF has greater attraction to O2 than Hb low % O2 by time blood reaches placenta fetal Hb must be able to bind O2 with greater attraction than maternal Hb Both mother and fetus share a common blood supply. In particular, the fetus's blood supply is delivered via the umbilical vein from the placenta, which is anchored to the wall of the mother's uterus. As blood courses through the mother, oxygen is delivered to capillary beds for gas exchange, and by the time blood reaches the capillaries of the placenta, its oxygen saturation has decreased considerably. In order to recover enough oxygen to sustain itself, the fetus must be able to bind oxygen with a greater affinity than the mother. Fetal hemoglobin's affinity for oxygen is substantially greater than that of adult hemoglobin. Notably, the P50 value for fetal hemoglobin (i.e., the partial pressure of oxygen at which the protein is 50% saturated; lower values indicate greater affinity) is roughly 19 mmHg, whereas adult hemoglobin has a value of approximately 26.8 mmHg. As a result, the so-called "oxygen saturation curve", which plots percent saturation vs. pO2, is left-shifted for fetal hemoglobin in comparison to the same curve in adult hemoglobin. Hydroxyurea, used also as an anti-cancer drug, is a viable treatment for sickle cell anemia, as it promotes the production of fetal hemoglobin while inhibiting sickling. What is the adaptive advantage? 2 alpha & 2 gamma units