Circulation and Gas Exchange. Cells exchange material with external environment. Respiration -...

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

http://www.baa.duke.edu/companat/Heart/mammalian%20heart.htm

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.

• 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.

• 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.


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.


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.


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.


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.


Fig. 42.29


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

Circulation and Gas Exchange. Cells exchange material with external environment. Respiration -...

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