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Circulation and Gas Exchange
• Cells exchange material with external environment.
• Respiration - aerobic organisms take in O2, release CO2.
• Cells produce waste (nitrogenous) needs to be removed; need to obtain nutrients.
http://home.earthlink.net/~dayvdanls/FormingATP.GIF
• Simple organisms (protozoans, cnidarians, sponges) - small body size, close proximity of cells to external environment allows direct exchange of materials.
• True for roundworms, flatworms.
• Large multicellular organisms no passive diffusion between cells and environment - circulatory system to move fluids in body to carry nutrients to tissues, wastes away.
• Circulatory system - blood, heart, vessels that carry blood throughout body.
http://www.bodyandmind.co.za/healthweb/gifs/circulatory%20system%20copy.gif
• Circulatory systems can be closed (blood always contained within blood vessels) or open (blood in at least part of body mixes directly with tissues in open sinuses).
Invertebrate Circulatory Systems
• Most cells in earthworms (annelids) not in direct contact with external environment.
• Internal closed circulatory system indirectly brings materials from external environment to cells.
• Blood travels toward anterior heart through dorsal blood vessels.
http://biology.unm.edu/ccouncil/Biology_203/Summaries/Protostomes.htm
• 5 aortic arches (like hearts) force blood to ventral vessel, carries blood to posterior, up to complete circuit.
• Blood carries O2, CO2 between cells and skin of earthworm where gas exchange occurs.
• Circulates nutrients from digestive tract to rest of body.
http://www.nrwmg.vic.gov.au/images/ana1.gif
• Arthropods, mollusks utilize open circulatory system - blood flows through dorsal vessel, out into spaces called sinuses.
• In sinuses, blood not enclosed in blood vessels but directly bathes cells.
http://biology.unm.edu/ccouncil/Biology_203/Images/Protostomes/clam_labeled_1.jpg
• Air exchange in arthropods is accomplished through tracheal system of air tubes; heart is simple beating tube.
• Closed system more efficient than open.
http://www.emc.maricopa.edu/faculty/farabee/biobk/insectexch.gif
Vertebrate Circulatory Systems
• Vertebrate system closed - chambered heart that pumps blood through arteries that lead away from heart to capillaries.
• Capillaries - extremely small vessels in tissues where exchange of material between circulation, tissues occurs.
http://bio.rutgers.edu/~gb102/lab_10/circuits_du.jpg
• From capillaries, blood carried back to heart through veins.
• Valves in heart, veins help to prevent blood from flowing backward through system.
• Atria in heart receive blood from body; ventricles - muscular chambers that pump blood out through arteries to body.
http://www.starsandseas.com/SAS_Images/SAS_Physiol_Images/SAS%20cardiopics/heart_valves.jpg
• Fish heart - 2 main chambers, 1 atrium, 1 ventricle.
• Blood pumped from ventricle to gills (gill circulation) where it picks up O2, disposes of CO2 across capillary walls.
• Frogs - 3-chambered heart with 2 atria, 1 ventricle.
• Blood pumped through 2 systems.
• Ventricle pumps blood to lungs + rest of body at same time through 2 major arteries.
http://academic.emporia.edu/sievertl/verstruc/frogin.JPG
• Allows oxygenated blood from lungs + deoxygenated blood from body to mix in ventricle before delivered back to body.
• Allows higher arterial pressure in blood pumped to tissue.
• Reptiles - double circulation with pulmonary (lung) and systemic circuits.
• Crocodilians, birds, mammals, - ventricle completely divided into separate right and left chambers.
• Left side receives, pumps only oxygen-rich blood; right side handles only oxygen-poor blood.
http://kvhs.nbed.nb.ca/gallant/biology/reptile_heart.jpg
• Pumping blood through capillary bed with large number of small vessels creates resistance.
• Heart creates pressure in circulatory system when it contracts to force blood through system.
• Highest pressure in blood vessels found in arteries leading away from heart to capillaries.
http://www.brianmac.demon.co.uk/heartsec.gif
• Birds, mammals (endotherms) require more energy more efficient circulation.
• Needs to be complete separation of blood flow to lungs and other tissues of body.
• Birds, mammals evolved hearts with 4 chambers: 2 atria, 2 ventricles.
http://library.thinkquest.org/19347/media/Heart.jpg
• Mammal hearts -2 pumps in one.• 1 atrium, 1 ventricle involved in
pumping blood to lungs pulmonary circulation.
• Other atrium and ventricle involved with pumping blood to rest of body through systemic circulation.
• Avoids mixing of oxygenated and deoxygenated blood; allows high arterial pressure needed for fast delivery of material to tissue.
http://www.baa.duke.edu/companat/Heart/bat/tinybat.jpg
The heart
• Human heart - 4-chambered pump with 2 collecting chambers (atria and ventricles).
• R ventricle pumps deoxygenated blood to lungs through pulmonary artery.
• Oxygenated blood returns to heart through pulmonary vein to L atrium.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 42.5
• From there it passes to L ventricle, pumped through aorta and arteries to rest of body.
• 4 valves that help prevent backflow into each chamber.
• Between each atrium and ventricle - atrioventricular (AV) valve which keeps blood from flowing back into atria when ventricles contract.
http://webanatomy.net/histology/cardiac/av_valve.jpg
• 2 sets of semilunar valves, 1 between L ventricle and aorta, other between R ventricle and pulmonary artery, prevent backflow from vessels into ventricles while they are relaxing.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 42.6
• Heart formed from 2 weaker atria, 2 stronger ventricles.
• Cardiac cycle - 1 complete sequence of pumping, as heart contracts, and filling, as it relaxes and chambers fill with blood.
• Contraction = systole• Relaxation = diastole
http://www.bhf.org.uk/appg/furniture/heart.jpg
• Heart sounds made from opening and closing of valves.
• 1st sound made from recoil of blood against closed AV valves (“lub”)
• 2nd sound made from recoil of blood against semilunar valves. (“dup”)
• Heart murmurs result of incomplete valve closure resulting in swishing noise.
http://www.nhlbi.nih.gov/health/dci/images/heart_murmur.jpg
• Heart made of cardiac skeletal muscle.
• Striated, involuntary.• Cytoplasm of each cell connected
to next to allow electrical impulses (action potentials) to pass through and cause contraction of atria and ventricles in unison.
http://cellbio.utmb.edu/microanatomy/muscle/muscle12.jpg
• Allows them to not need signal from nervous system.
• Cells synchronized by sinoatrial (SA) node (located in R atrium), or pacemaker, which sets rate and timing at which all cardiac muscle cells contract.
http://www.sjm.com/assets/popups/electsys.gif
• Cells maintain negative membrane potential across plasma membrane - resting potential.
• Wave of depolarization by action potential triggers muscle contraction.
• In SA node, pacemaker cells spontaneously depolarize membrane potential at steady rate on their own, causing voltage-gated channels in pacemaker to open.
• When action potential initiated in pacemaker cells, spreads rapidly throughout both atria to cause atria to contract together.
• Action potential cannot pass to ventricular cells - no direct path between atria and ventricles (no cell to cell connections).
http://www.lib.mcg.edu/edu/eshuphysio/program/section3/3ch2/3ch2img/page10.jpg
• Impulse carried through atrioventricular (AV) node from atria to ventricles, then through bundle of His and Purkinje fibers - all carry action potential to ventricles where it will spread throughout cardiac muscle rapidly from cell to cell.
http://www.owensboro.kctcs.edu/gcaplan/anat2/notes/Image345.gif
• Passage of impulse through AV node delays impulse so that timing of contraction by ventricles coincides with completion of atrial contraction.
http://images.med.cornell.edu/body/greystone/em_0018.jpg
• Heart rate regulated by sympathetic and parasympathetic nervous systems (both part of autonomic nervous system).
• Sympathetic system causes heart rate to increase by acting on sinoatrial node pacemaker through epinephrine.
http://www.becomehealthynow.com/images/organs/nervous/sympathetic.jpg
• Parasympathetic nervous system more important in regulation of heart rate with vagus nerve of system directly innervating SA node and slowing heart rate.
http://www.becomehealthynow.com/images/organs/nervous/parasympathetic.jpg
Heart Disease• More than ½ of all deaths in US
due to heart disease.• Heart attack - death of cardiac
tissue due to prolonged blockage.• Stroke - death of nervous tissue.• Both usually occur because of
thrombus that gets caught in coronary artery or an artery in brain.
http://nonstandardized.com/pao2/images/heart_attack.jpg
• Heart damage can interrupt electrical conduction of heart causing individual to stop breathing, heart stops beating.
• Most heart attacks result of atherosclerosis (narrowing of arteries) mostly from increased levels of LDL in blood.
• Plaque begins to build in artery and artery begins to thicken as deposits of cholesterol are added.
• Can lead to arteriosclerosis - hardening of arteries.
• Arteries more likely to capture a thrombus - turns into embolus.
Blood vessels • Capillaries lack 2 outer walls, only
have endothelium and basement membrane.
• Arteries - thicker middle and outer layers than veins - under higher pressure than veins.
• Veins thinner - passive blood flow.• Also have flaps - act as valves to
prevent backflow.
http://www.livescience.com/images/060619_artery_anatomy_02.jpg
• Arteries carry blood away from heart, branch into smaller arteries called arterioles.
• Arterial blood oxygenated except for pulmonary artery - carries deoxygenated blood from tissues to lungs.
• Veins carry blood from capillaries to heart.
• No pulse, carry dark red deoxygenated blood, except for pulmonary vein -carries oxygenated blood from lungs.
• Capillaries permit exchange of materials between blood and body’s cells.
• Fluid seeps from thin-walled capillaries by osmosis.
Regulation of blood flow
• Needs for blood flow increase and decrease; flow of blood regulated locally in tissues to match supply of blood to metabolic needs.
• Smooth muscle in walls of arterioles constrict to reduce blood flow to capillaries in tissue.
• Smooth muscle relaxes when blood leaving capillaries low in O2.
http://www2.uerj.br/micron/atlas/atlasenglish/Muscle/Liso1.jpg
• Allows more blood to flow through arteriole and through capillaries increasing oxygen supply to tissue.
• Levels of carbon dioxide can also cause relaxation of arteriole smooth muscle to increase blood flow.
• Nervous system regulates blood flow by autonomic nervous system.
http://cti.itc.virginia.edu/~psyc220/kalat/JK365.fig12.5.nervous_syste.jpg
• Sympathetic nervous system causes constriction of arteries in many tissues (i.e. digestive tract) causes dilation in skeletal muscle.
• Control of blood flow occurs in medulla of brain - receives information from sensors in aorta about stretching, from oxygen sensors in other arteries.
http://www.brainexplorer.org/brain-images/medulla_oblongata2.jpg
• If aorta stretched, arterial blood pressure is high - causes control center in medulla to inhibit sympathetic nervous system.
• Relaxes arteries in periphery, slows heart rate.
• If blood is lost, decreasing arterial pressure, stretch sensors trigger response from sympathetic nervous system.
http://www.med.umich.edu/1libr/aha/dilation.gif
• Causes vessels to constrict, increases heart rate.
• Also occurs if decrease in oxygen levels by oxygen sensors.
• Epinephrine increases heart rate, constricts arteries - increases arterial pressure.
• When blood pressure in arteries fall, kidney secretes enzyme (renin) - activates angiotensin.
• Acts on smooth muscle in arterioles, causes constriction to increase central pressure.
• Vasopressin secreted by posterior pituitary in response to stretch sensors (increases central pressure)
http://content.answers.com/main/content/wp/en-commons/thumb/8/8a/600px-Renin-angiotensin-aldosterone_system.png
• Inflammation of local tissues cause arterioles to expand, increasing flow of fluid into capillaries and tissues causing swelling.
• Histamine released in allergic reaction, causes increased blood flow and permeability of capillaries.
• Generalized swelling (edema) occurs if osmotic balance of plasma is low.
http://www.uth.tmc.edu/courses/dental/pulpalmicro/pics/fig5large.jpg
Blood
• Blood - liquid component - plasma - contains dissolved nutrients, wastes, proteins, hormones, fibrinogen.
• Fraction of blood without cells left after clotting – serum; contains glucose, lipids, salts, hormones, albumin.
http://www.ndsu.nodak.edu/instruct/tcolvill/435/plasma.gif
• Materials suspended in plasma - red blood cells, white blood cells, platelets.
http://ucdavismagazine.ucdavis.edu/issues/fall04/graphics/BloodParts.jpg
• Blood placed in centrifuge cells can separate out; volume of cells measured.
• Percent of blood occupied by cells - hematocrit - about 40% of total blood volume.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.14
• Red blood cells (erythrocytes) - most numerous.
• Main function - oxygen transport -depends on rapid diffusion of oxygen across red cell’s plasma membranes.
• Formed in bone marrow, lose nuclei and become disk like.
http://nmhm.washingtondc.museum/news/imgs/red_blood_cells_lg.jpg
• Red blood cell production stimulated by erythropoietin - produced by kidneys.
• Wear out after 4 months - destroyed in spleen and liver.
• Contain hemoglobin - unites with oxygen to form oxyhemoglobin.
http://sickle.bwh.harvard.edu/hctchart.gif
• Tissues - partial pressure of oxygen low; hemoglobin releases oxygen.
• Lactic acid buildup also stimulates oxygen release by hemoglobin.
• Carbon monoxide binds to hemoglobin permanently, preventing it from binding to oxygen + delivering to tissues.
http://www.beliefnet.com/healthandhealing/images/si55551241_ma.jpg
• When RBCs mature - lose mitochondria - can’t perform aerobic respiration.
• Prevents them from using oxygen to perform respiration themselves.
• Manufacture 2 major types of antigens: A + B.
• In any individual, one, both, or neither can be present.
http://www.ncbi.nlm.nih.gov/projects/mhc/images/otherimages/rbc_antigens.jpg
• Plasma of every individual contains antibodies for antigens not present on individual’s red blood cells.
• Type A have anti-B antibodies - if they come into contact with it, blood will clump.
http://medicalimages.allrefer.com/large/antibodies.jpg
• 5 major types of white blood cells, or leukocytes: monocytes, neutrophils, basophils, eosinophils, lymphocytes.
• Function to fight infection. • Monocytes, neutrophils -
phagocytes, engulf and digest bacteria and debris from our cells.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.13
• Platelets not really cells - cell fragments produced in marrow as pieces of megakaryocyte cells.
• At site of bleeding injury, activation of thrombin cleaves fibrinogen protein in blood to make fibrin that forms net across wound, trapping more cells and blocking flow of blood.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.16
The lymph system
• Fluids, some blood proteins leak from capillaries into interstitial fluid returned to blood via lymphatic system.
• Fluid (lymph) diffuses into lymph capillaries.
• Drains into circulatory system.
http://www.acm.uiuc.edu/sigbio/project/updated-lymphatic/thymus_p.gif
• Along lymph vessels - organs called lymph nodes.
• Lymph nodes filter lymph, attack viruses and bacteria through cells specialized for fighting infection.
• When body is fighting, lymph nodes will become swollen and painful.
• Lymph system transports fats from digestive system to circulatory system.
Respiration• Vital function of organisms is
ability to exchange gases with environment (respiration).
• Most organisms rely on oxidation of glucose through aerobic respiration to generate energy.
• Oxygen final electron acceptor in ETC of aerobic respiration to produce ATP.
http://www.stanford.edu/group/hopes/treatmts/ebuffer/f_j13electtrans.jpg
• CO2 produced as waste product from burning glucose in Krebs cycle.
• Diffuse easily across plasma membranes - molecules move into and out of cells by simple diffusion across concentration gradient.
• Prokaryotes, protists, sponges, etc. have cells exposed to external environment, respiratory gases easily exchanged through cell membranes.
http://www.findhealer.com/glossary/images/krebs.gifs
• Complex multicellular organisms need more complex ways of exchanging gases with environment.
• Annelid (earthworm) secretes mucus on external surface of body which provides moist surface for gas exchange from air to blood through diffusion.
• Circulatory system brings O2 to cells and CO2 to skin to be excreted.
http://www1.istockphoto.com/file_thumbview_approve/527708/2/istockphoto_527708_earth_worm_macro_against_a_white_background.jpg
• Arthropods - series of respiratory tubules (trachae)
• Tubules open to outside in orifices (spiracles).
• Inside body, trachae subdivide into smaller and smaller branches so they can maintain close contact with most cells.
http://www.esu.edu/~milewski/intro_biol_two/lab__12_annel_arthro/images/romalea_abdomen.jpg
• System allows for direct intake, distribution, removal of respiratory gases between air and body.
• No specialized cells for transporting oxygen.
• No blood system intervenes with transport of gases to body’s tissues, so system is very efficient and fast.
• Arthropods can produce large amounts of energy, limits their size because of system.
Respiration in fish
• Water contains less oxygen, more difficult to breathe in water.
• Oxygen limiting resource in water, not on land.
• Aquatic organisms require large surface area to gas exchange.
http://www.kwic.com/~pagodavista/schoolhouse/species/fish/pics/fishgill.jpg
• Gills of fish divided into numerous thin-walled, threadlike filaments well fed by capillaries.
• Walls of gills thin to maximize diffusion of gases between blood and water; also to minimize distance these substances must travel.
• Gills protected from outside by opercular flap so other organisms won’t eat them.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.20
• As water passes over filaments, O2 diffuses into blood, CO2 leaves blood enters water.
• Arteries transport oxygenated blood throughout body.
• Water passes out of body through openings of sides of head, takes CO2 with it.
http://www.agriteach.com/lessonfiles/aquaculture/basic_fish_anatomy.jpg
• Countercurrent exchange maximizes exchange of gases between blood in gills and water flowing over gills.
• Blood flowing through gills moves in opposite direction as water moving across gills outside.
• Maximizes concentration gradient of gases in blood and water, which maximizes gas exchange.
Respiration in humans
• Amphibians evolved lungs - moved to land - consist of simple air sacs with very little surface area.
• Decreased surface area requires exchange of gases across moist skin.
• Mammals cannot exchange gases across skin - respiratory system evolved to meet demands.
http://www.ama-assn.org/ama1/pub/upload/images/446/respiratorydetail.gif
• Humans - complex system of respiration to transport oxygen to cells, get rid of CO2.
• Air passages involved - nose, pharynx, larynx, trachea (windpipe), bronchi (lead into each lung), bronchioles that branch throughout lungs, end in tiny sacs (alveoli) - site of gas exchange.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.23
• Amount of alveoli create large surface area for gas exchange.
• Lungs must move air in and out - bring external air in contact with alveoli.
• Found in chest (pleural cavity) bound by ribs, separated from abdomen by diaphragm.
http://www.aduk.org.uk/gfx/lungs.jpg
• Negative pressure in pleural cavity keeps pleural membrane drawn tightly outward against walls of chest cavity.
• Keeps lungs inflated.• If pleural cavity punctured, lungs
can collapse.• Diaphragm curved upward when
relaxed, flattens when contracted.
• Chest muscles move ribs up and out as diaphragm moves - creates larger chest cavity + vacuum that draws air into respiratory passages (inhalation).
• When diaphragm and rib muscles relax, chest cavity size decreases - air forced out of lungs (exhalation).
• Exhalation passive - muscle contraction not part of it.
• During strenuous exercise, muscles activate exhalation.
• Breathing rate regulated in medulla to supply tissues with correct levels of O2 and CO2 removal.
http://www.brainexplorer.org/brain-images/medulla_oblongata2.jpg
• Excess CO2 in blood stimulates medulla to send message to diaphragm to increase frequency of respiration.
• Less sensitivity to O2 levels.
• All air, whether inhaled or exhaled, passes through trachea at same time.
http://graphics.cs.ucr.edu/projects/simulatedBreathing/images/a4.jpg
• Some air not involved in gas exchange.
• Even with strongest exhalation, still air left in lungs - residual volume.
• Air breathed in mixes with air already in lungs, diffuses to alveoli.
http://www.cptc.ctc.edu/library/Bio%20118%20Lecture%20Notes%20Rev%200105_files/image172.jpg
• Air in alveoli - different composition from air in atmosphere.
• More water vapor, more carbon dioxide, less oxygen.
http://upload.wikimedia.org/wikipedia/en/thumb/d/db/Alveoli_diagram.png/300px-Alveoli_diagram.png
Gas transport and exchange• Alveoli - thin, moist walls,
surrounded by thin-walled capillaries.
• Moist allows for gases to dissolve in thin layer of fluid then diffuse across respiratory membranes.
• O2 diffuses from alveolar air into blood through alveolar and capillary membranes.
http://library.thinkquest.org/19347/media/alveoli.jpg
• CO2, H2O diffuse out in same way.
• Gases always diffuse from high concentration to low concentration.
• In tissues, O2 diffuses into tissues, CO2 leaves.
• In lungs, O2 diffuses out of lungs, CO2
enters because of increased O2 pressure.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.29
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 42.29, continued
• Inside alveoli liquid mostly water - high surface tension - draws walls of alveoli together with liquid - gives potential to collapse, lose ability to exchange gases.
• Prevented by secretion of surfactant - reduces surface tension.
• Premature infants may not have this when born - causes difficulty in breathing.
http://www.ees.adelaide.edu.au/research/enviro/evol_physiology/Fig%201%20synthesis%20and%20secretion%20diag%20large%20&%20higher%20res.jpg
• O2 transported in blood by RBCs.
• Contain oxygen transport protein (hemoglobin).
• O2 binds to hemoglobin - allows efficient delivery of O2 to tissues.
• Under normal conditions, hemoglobin saturated with O2 in lungs.
http://www.kacr.or.kr/img/gene_expression/hemoglobin.jpg
• As blood travels to tissues, low O2 levels in tissues allows some of O2 bound to hemoglobin to be released, diffuse into tissue.
• Allows small changes in O2 needs in tissues to cause large changes in delivery of O2 to tissues.
http://www.shands.org/images/ency/fullsize/19510.jpg
• Increased pH during exercise decreases affinity of hemoglobin for O2 which allows more O2 to be delivered to muscles.
• CO2 carried in blood as dissolved carbonate ions, does not have specific protein carrier.
http://www.gly.fsu.edu/~salters/GLY1000/6_Minerals/Slide55.jpg
• When CO2 dissolves in blood in tissues, enters RBCs, converted by enzyme carbonic anhydrase into bicarbonate ions to be transported back into blood.
• Lungs - enzyme converts bicarbonate back into CO2 to be exhaled.
http://www.breathcoach.co.uk/assets/images/hh_balance02.jpg
• Bicarbonate also pH buffer in blood, regulated by kidney to maintain plasma pH within normal range.
http://www.egms.de/figures/journals/cto/2005-4/cto000007.f8.png