circulation and gas exchange chapter 42. overview: trading with the environment every organism must...
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Circulation and Gas Exchange
Chapter 42
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Overview: Trading with the Environment• Every organism must exchange materials &
energy with environment• Exchanges ultimately occur at the cellular
level
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• In unicellular organisms, exchanges occur directly with environment
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In multicellular organisms, direct exchange with environment not possible with all internal cells
Diffusion always at cellular level BUT diffusion over long dist (lung to internal cells) too slow
Therefore developed physiological systems specialized for transport (circulatory) & exchange (respiration)
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Concept 42.1: Circulatory systems reflect phylogeny
• Diffusion alone not adequate for transporting substances over long distances within animals
• Therefore complex animals have internal transport systems (circulatory systems) that circulate fluid & connect the organs of exchange with the body cells for exchg
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Invertebrate Circulation
• The wide range of invertebrate body size & form plus differences in environmental pressures = diversity in circulatory systems
Gastrovascular cavities
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Open and Closed Circulatory Systems
Complex animals with many cell layers have: - open circulatory system- closed circulatory system
Both have 3 components in common:1. circulatory fluid (blood or hemolymph2. set of tubes (blood vessels)3. muscular pump (heart provides pressure
to move fluid)
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In insects, other arthropods, & molluscs bloodbathes organs directly in open circ system
no distinction between blood & interstitial fluid; general body fluid = hemolymph
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Closed circulatory system = blood confined to vessels & distinct from interstitial fluid
Closed systems more efficient at transporting circ fluids to tissues & cells (worm is an example)
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Vertebrate Circulation
Humans & other vertebrates blood flows in closed circulatory system (blood vessels & 2- 4-
chambered heart) = cardiovascular system
- arteries: carry blood to capillaries, sites of
chemical & gas exchange between blood & interstitial fluid (single cell layer that
gas exchanges)
- veins: return blood from capillaries to heart
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Fishes• 2 main chambers: ventricle & atrium• Blood pumped from the ventricle travels to the
gills, where it picks up O2 and disposes of CO2
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Amphibians• Frogs and other amphibians have a three-
chambered heart: 2 atria & 1 ventricle
R atrium L atrium
Ventricle
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Reptiles
One can say that the reptile heart has 3 chambers, 2 atria & 1, partially divided, ventricle. Or one may argue that reptiles have 4-chambered hearts with 2 atria & 2 ventricles, but the wall between the ventricles is incomplete.
Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit
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Mammals and Birds In all mammals & birds, ventricle divided into
separate R & L chambers
L side : pumps & receives only O2-rich blood R side: receives & pumps only O2-poor blood
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A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds
Endotherms need 10x energy as equal-sized ectotherm so mustdeliver more via blood
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Concept 42.2: Double circulation in mammals depends on anatomy & pumping cycle of heart
The human circulatory system serves as a model for exploring mammalian circulation
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Mammalian Circulation: The Pathway• Heart valves dictate a one-way flow of blood
through the heart• Blood begins its flow with R ventricle pumping
blood to lungs• In lungs, blood loads O2 & unloads CO2
• O2-rich blood from lungs enters heart at L atrium & into L ventricle where then pumped to body tissues
• Blood returns to heart at R atrium
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The Mammalian Heart: A Closer Look provides a better understanding of dbl circ
Valves
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Cardiac cycle
- contraction, or pumping, phase = systole
- relaxation, or filling, phase = diastole
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Heart sounds, heard with stethoscope, caused by closing of valves.
“lub-dup, lub-dup”
Lub=close AV
Dub=close semilunar
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Heart murmur = defect in valve detectable as a hissing sound when blood squirts backward through it
Rheumatic fever can cause
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Heart rate = pulse = beats per minute
Cardiac OP = volume blood pumped into systemic circ per minute
Stroke vol = amt blood pumped by L ventricle per contraction________________________________________
Av stroke vol … 75 mlAv ht rate ……..70/min
Cardiac OP: 75 * 70 = (5,250 ml) 5.25 L/min
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Heart’s Rhythmic BeatCardiac muscle stims self = contract without signal from nervous syst
Pacemaker influenced by nerves, hormones, body T, & exercise
Impulses during cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)
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Concept 42.3: Physical principles govern blood circulation
Structure/function: arteries, veins, & capillariesVelocity blood flow slowest in capillary beds
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- arteries: thick wall + muscle- veins: blood flow result muscle action; valves
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Systolicpressure
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- Exchange materials & gases at capillaries- BP at capillaries pushes fluid out into tissues
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Fluid in tissues & 85% reenters at venous end Remaining 15% returned via lymphatic system
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Critical exchange between blood & interstitial fluidtakes place across thin endothelial walls capillaries
Diff between BP & π drives fluids out capillaries at arteriole end & into capillaries at venule end
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Fluid Return by the Lymphatic System
• The lymphatic system returns fluid to the body from the capillary beds
• This system role in body defense• Fluid reenters the circulation directly at the
venous end of the capillary bed & indirectly through the lymphatic system
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Concept 42.4: Blood is a connective tissue with cells suspended in plasma
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Cellular ElementsSuspended in blood plasma
- red blood cells (erythrocytes) transport O2- white blood cells (leukocytes) body defenses
- platelets = frags cells & involved in clotting
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Stem Cells & Replacement of Cellular Elementspluripotent stem cells in red marrow of bones
erythropoietin
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Blood ClottingCascade rxs (fibrinogen to fibrin) = clot
hemophiliathrombus
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Cardiovascular Disease disorders of heart & blood vessels account for > half deaths in United States
Artheroscloresis: accumulation cholesterol in arteries
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Chlosterol transported as lipid:prot particlesLDL (low density lipoprot) = “BAD” cholesterolHDL (high density lipoprot) = “GOOD” cholesterol
Satd fats = ↑ tendency artherosclerotic plaques
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• Hypertension, or high blood pressure, promotes atherosclerosis and increases the risk of heart attack and stroke
• A heart attack is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
• A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head (can be side effect of heart attack)
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Concept 42.5: Gas exchange occurs across specialized respiratory surfaces
Gas exchange = uptake O2 from environment & discharge CO2 (from cell resp) to environment
Animals require large, moist respiratory surfaces for adequate diffusion of gases between their cells & the respiratory medium…. air for terrestrial animals and water for most aquatic animals
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Respiratorymedium(air or water)
Organismallevel
Cellular level
Energy-richfuel molecules
from food
Respiratorysurface
Circulatory system
Cellular respiration
CO2O2
ATP
Structure of respiratory surface depends on size of organism & whether it lives in water or on land
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A. Water Habitat- Have gills = outfoldings of body surface suspended in water- Water [O2] low so special processes to ↑ efficiency of exchg
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B. Terrestrial HabitatTracheal system of insects consists of tinybranching tubes that penetrate the body
The tracheal tubes supply O2 directly to body cells
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LungsMost terrestrial vertebrates have internal lungs
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system of branching ducts conveys air to lungsAir inhaled through the nostrils passes throughpharynx into trachea, bronchi, bronchioles, &dead-end alveoli, where gas exchange occurs
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Mammals ventilate their lungs by neg pressure Inhale = ↑vol lung = pulls air into the lungs Exhale = musc relax & elastic fibers retract lung
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Sensors in aorta & carotid arteries monitor O2 &CO2 concentration in blood = exert 2ndary control over breathing
Main breathing control center in brain which regulates rate & depth of breathing in response to pH changes in Cerebrospinal fluid
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Gases diffuses from higher partial pressure (conc) to lower partial pressure
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Oxygen TransportHemoglobin reversibly binds O2
- loads O2 in lungs - unloads it in other parts body
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Drop in pH lowers affinity of hemoglobin for O
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Carbon Dioxide Transport (mostly as HCO3)
CO2 diffuses into Red blood cells where + H2O forms carbonic acid which dissoc into
H+ & HCO3-
H+ binds to Hemoglobin
HCO3- diffuses into
plasma & carried to lungs
In lungs, reverse occurs
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CO2 from respiring cells diffuses into
blood plasma & then into red
blood cells
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CO2 from tissues carried
as HCO3- in
plasma of blood &
released in lungs
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Baby steals O2 from mom’s blood