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PSLY 4210/5210 !Comparative Animal Physiology !Circulation! !Spring 2010! Figure 24.1 The human heart Figure 24.2 The heart as a pump: The dynamics of the left side of the human heart Figure 24.3 Four systems evolved by animals to supply O2 to the myocardium (Part 1) Figure 24.3 Four systems evolved by animals to supply O2 to the myocardium (Part 2) Figure 24.4 The conducting system and the process of conduction in the mammalian heart Figure 24.5 The neurogenic heart of a lobster and the cardiac ganglion that initiates and controls its contractions Topic 14 - 1! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! !Spring 2010! Figure 24.6 Electrocardiography Figure 24.7 Fluid-column effects on blood pressure in the arterial vascular system Figure 24.8 Total fluid energy: The true driving force for blood flow Figure 24.9 The physics of flow through tubes Figure 24.10 The circulatory plan in mammals and birds Figure 24.11 A microcirculatory bed Topic 14 - 2! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! !Spring 2010! Human Blood/Tissue Composition! Figure 24.12 Blood flow in the human systemic vasculature (Part 1) Figure 24.12 Blood flow in the human systemic vasculature (Part 2) Figure 24.13 Fluid exchange across mammalian systemic capillary walls: The Starling-Landis hypothesis Figure 24.14 The circulatory plan in gill-breathing fish Topic 14 - 3! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! !Spring 2010! Dipnoi (lungfishes)! Figure 24.15 The circulatory plans of some air-breathing fish Six living species! Early forms also had lungs as well as gills! South American and African lungfishes can live out of water for extended periods, and even move overland! • Aestivate in mud balls on land during dry periods! • Inside of ball is lined with slime, which drys to a parchment-like consistency and resists evaporation! Australian lungfish relies on gills for breathing (can t remain out of water)! Figure 24.16 The branchial vascular arches of a lungfish and their relation to heart, lungs, and systemic tissues Figure 24.18 The typical circulatory plans of the major vertebrate groups, plotted on a phylogenetic tree of the groups (Part 1) Figure 24.18 The typical circulatory plans of the major vertebrate groups, plotted on a phylogenetic tree of the groups (Part 2) Figure 24.19 Blood flow in the heart ventricles and the systemic and pulmonary arteries of crocodilian reptiles Topic 14 - 4! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! Annelid Circulation !Spring 2010! Figure 24.20 The circulatory plan of squids and octopuses !Blood circulates in a closed" system:! • Five main trunks run lengthwise" through the body! • The dorsal vessel above the alimentary canal has valves and functions as a true heart! • The dorsal vessel pumps blood anteriorly in to five pairs of aortic arches! • The aortic arches maintain steady pressure into the ventral vessels! • A ventral vessel serves as an aorta, delivering blood to body walls, nephridia and digestive tract! Figure 24.22 The heart of a decapod crustacean Figure 24.23 Circulation through the body of a crayfish or lobster Box 24.3 Blood flow through the tissues of an insect is principally through lacunae and sinuses Figure 24.24 The microanatomy of blood flow in a lacunar system: Blood flows most vigorously where it is needed most Topic 14 - 5! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! Life at High Altitudes! Effects of High Altitude on Humans! Atmospheric pressure decreases by 50% with each 1.61 km increase in altitude! At top of Mount Whitney (4350 m, highest point in continental US), Patm = 400 mm Hg, PO2 ≈ 75 mm Hg! At ≈ 5000 m (Patm ≈ 375 mm Hg, PO ≈ 68 mm Hg), most unacclimatized 2 persons lose consciousness from lack of oxygen! At ≈ 5500 m (Patm ≈ 350 mm Hg, PO ≈ 63 mm Hg is the highest 2 permanent human habitation (Andes)! At ≈ 8500 m (Patm ≈ 240 mm Hg, PO ≈ 43 mm Hg), human can survive on 2 atmospheric air for a few hours to couple of days! At top of Mount Everest (8882 m, highest point on Earth), Patm ≈ 220 mm Hg, PO2 ≈ 33 mm Hg! At ≈ 13,500 m (Patm ≈ 125 mm Hg) is the highest point where humans can live on pure oxygen! Migratory paths of some birds take them over the Himalayas! Ballooning juvenile spiders go even higher! Andes residents-live at very high altitudes ( highlanders vs. lowlanders , with some transient sojourners from low to high)! 1° adaptation: increase in number of red blood cells (polycythemia)! Result of chronic hypoxia: very long time before this response is elicited! Acute hypoxia (sojourners): response is reflex hyperventilation! Stimulation of peripheral chemoreceptors (carotid and aortic body) by ↑[CO2] in blood and ↓[O2] (not important at sea level at rest, but becomes more important than ↑[CO2] for lowlanders! Stimulation of medulla oblongata chemoreceptors by [HCO3–] (≈ ΔpH) in CSF and CO2•H+ (combined effects of CO2 and bicarbonate)! Blunting of hypoxic response in highlanders! CO2 response remains normal, but O2 response lost! Diving! Effects of High Altitude on Humans! !Takes long term exposure to achieve maximum acclimatization to high altitude. In addition to more RBCs, highlanders possess several adaptations for high altitudes:! Increase in capillary density ! Many air-breathing vertebrates can remain submerged for long periods! Some can actually respire underwater at a low rate! Decreases the distance from capillary to O2 source! Smaller O2 gradient from alveolar surface to capillaries due to less O2 consumption by intervening tissues! Cascade of from inspired atmospheric O2 to venous O2! Less precipitous for highlanders! Both highlanders and lowlanders have same venous O2 levels! Some amphibians can respire through the skin! Some turtles can perform buccal-pharyngeal and/or cloacal respiration! However, the majority of diving vertebrates (reptiles, birds, and mammals):! Stop breathing (apnea)! Rely on oxygen stores in blood! Regulate cardiovascular system to provide oxygen to body parts (brain, heart, and some endocrine glands) that can least withstand anoxia! Highlanders have easier dissociation of O2 from Hb! Highlanders have higher DPG levels! !Spring 2010! Decreases Hb affinity slightly! Increases O2 loading, decreases O2 unloading! Diving Patterns! Figure 25.6 A comparison of the total O2 stores of five species of marine mammals and humans Extremely variable! Some species (e.g., Weddell seal) dive deeply and repetitively, others (e.g., fur seal) dive less deeply and more variably! Some dive aerobically, others anaerobically! Some animals hyperventilate before diving! Animals may dive on inspiration, expiration or both! When varying diving time, animals know what they are going to do, and adjust their physiology accordingly! Change their store of O2 that they take down with them! O2 stores in blood depend on affinity, blood volume, initial quantity of dissolved O2 ! Some animals show a big increase in blood O2, others stay about the same! Topic 14 - 6! In seals, there is a large increase in myoglobin-stored O2! Also, more O2 stored in lungs, but may not be available during dive! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! !Spring 2010! Some Physiological Characteristics of Divers! Figure 25.1 Durations of dives by wild Weddell seals High resting tidal volumes! Restore O2 to tissues after surfacing, rather than acting as a reservoir of O2 during the dive! This allows a decrease in the interval between dives! Low resting ventilation rate! Lower chemoreceptor sensitivity to CO2 ! Lungs collapse and alveoli close during dives! Restriction of peripheral blood flow via vasoconstriction! No gas exchange means no gas pressure increase in lungs: decreases possibility of the bends! Decreases O2 consumption in tissues by isolating muscle mass from perfused blood! Bradycardia (slower heart rate)! May be stress response or experimental artifact! Weddell seals have very variable bradycardia: heart rate slows as length of dive increases! Figure 25.5 The thorax is highly compressible in marine mammals Figure 25.14 The hypothesis of preferential collapse of the alveoli and alveolar sacs at depth Figure 25.10 Metabolic subdivision of the body in seals during forced submergence Figure 25.9 Diving heart rate varies with dive duration in a graded manner in freely diving seals Topic 14 - 7! PSLY 4210/5210 !Comparative Animal Physiology !Circulation! Physiological Responses Accompanying Resumption of Breathing! Physiological Responses During Diving! In mammals (but not other vertebrates) stimulation of the facial receptors that inhibit breathing induces bradycardia.! As animal undergoes apnea and the lungs are compressed during the dive, lung stretch-receptor activity decreases.! Initial pressurization of the lungs can produce a transient increase in blood O2 and CO2. Continued diving reduces O2 and increases CO2. Lactic acid washout occurs only on long dives (little buildup during short dives because no bradycardia and hence on anoxia in tissues).! Decreased O2 stimulates arterial chemoreceptors and, in the absence of lung stretch-receptor activity, causes increase in sympathetic nerve output and consequent peripheral vasoconstriction and reduction in heart rate and cardiac output. Blood flow to major organs such as the kidneys is greatly reduced. In some cases, blood flow to muscles is also reduced (depending on exercise during the dive).! In some animals, increase in arterial pressure is sensed by baroreceptors and bradycardia is maintained by a rise in both chemoreceptor and baroreceptor discharge frequency. Bradycardia is caused by an increase in parasympathetic activity and decrease in sympathetic activity of nerve fibers innervating the heart. In birds, decreased O2, increased CO2, and ΔpH stimulate chemoreceptors in carotid body, inducing bradycardia.! Diving in a Seal! !Spring 2010! In absence of breathing, lung inflation tends to suppress reflex cardiac inhibition and peripheral vasoconstriction caused by stimulation of arterial chemoreceptors. As animal rises in the water column, the lung becomes inflated, possibly activating lung stretch-receptors and causing cardiac acceleration! Once animal resumes breathing, stimulation of arterial chemoreceptors results in a marked increase in lung ventilation! Low blood O2 and/or high blood CO2 levels cause peripheral vasodilation! Leads to increased cardiac output to maintain blood pressure in the face of this increased peripheral blood flow! Thus, hypoxia caused by a cessation in breathing during diving is associated with a decrease in heart rate and cardiac output. In contrast, hypoxia that occurs during breathing (e.g., at high altitudes) is associated with an increase in heart rate and cardiac output.! Figure 25.11 The aftermath of a prolonged dive: Lactic acid in muscles and blood When a seal dives, heart rate, cardiac output, and blood O2 content decrease, and blood CO2 increases. During the post-dive recovery period, blood lactate increases greatly, while the other parameters first overshoot and then return to their predive levels. ! Figure 25.12 Peak concentration of lactic acid in arterial blood of freely diving, adult Weddell seals following dives of various durations Figure 25.13 Energy-sparing behaviors of freely diving Weddell seals Topic 14 - 8!