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Cardiovascular and pulmonary systems Revision for Unit 1 Tissues, organs, blood vessels, heart, lungs, exercise physiology 10.6, 10.7 and 10.8 10.7 gas exchange • Fick’s Law Rate of diffusion = surface area x concentration difference thickness of exchange surface • • • • to maximise diffusion: maximise surface area maximise concentration difference minimise thickness of exchange surface 10.7 • Human (mammalian) lung: • maximum surface area • many tiny alveoli • with an infolded shape giving a large surface area • many branched capillaries • forming a capillary network with large surface area 10.7 • Human (mammalian) lung: • maximum concentration difference • very good blood supply • bringing deoxygenated blood (from respiring cells) • taking away oxygen (to tissues) • bringing CO2 from respiring cells 10.7 • Human (mammalian) lung: • maximum concentration difference • Ventilation (= breathing) • bringing fresh atmospheric oxygen-rich air • bringing fresh atmospheric air with little CO2 • taking away CO2 10.7 • Human (mammalian) lung: • minimum thickness of gas exchange surface • capillaries close to the alveolar epithelium • distance between blood and air down to less than 1m thick 10.7 • squamous epithelium of alveolus • 1 cell thick • very thin, flat cells • squamous endothelium of capillary • 1 cell thick • very thin flat cells 10.7 a = alveoli b = bronchiole c = arteriole d = venule e = larger bronchiole 10.7 Alveoli Bronchiole 10.7 Alveolus Nucleus of epithelial cell of alveolus Capillary Nucleus of endothelial cell of capillary Macrophage containing bacteria 10.7 A = alveolus EP1 = epithelium of alveolus EN = endothelium of capillary RBC = red blood cell 10.7 • Gross anatomy of respiratory system Rib Trachea Bronchus Lung Diaphragm Larynx (voice box) Internal intercostal muscle External intercostal muscle Bronchiole 10.7 • Ventilation • Inhalation - breathing in • diaphragm muscle contracts • diaphragm moves down 10.7 • Ventilation • Inhalation - breathing in • diaphragm moves down • external intercostal muscles contract • ribs lifted • Ventilation 10.7 • Inhalation - breathing in • diaphragm moves down • external intercostal muscles contract • ribs lifted • chest volume increased • pressure in chest drops • air rushes into chest 10.7 • Exhalation • diaphragm relaxes and springs back to its normal curved shape • elastic fibres in walls of alveoli store energy during inhalation to make chest spring back during exhalation • Internal intercostal muscles contract and pull ribs down • Chest volume decreases • Pressure in chest increases • Air rushes out 10.7 • In and out tidal breathing Stretch receptors in chest Breathing control centre in medulla of brain Phrenic motor nerves 10.7 • To change from inhalation to exhalation • Stretch receptors in lung and chest wall are stretched by inhalation • Sensory nerves stimulate breathing control centre in medulla of brain • Impulses pass down phrenic nerves to internal intercostals, making you exhale 10.7 • To change from exhalation to inhalation • Stretch receptors in lung and chest wall are not stretched by exhalation • Sensory nerves reduce stimulation of breathing control centre in medulla of brain • Impulses pass down phrenic nerves to external intercostals and diaphragm, making you inhale 10.7 • Gas • • • • O2 CO2 H2O N2 % in inspired air % in expired air 21 0.04 1 78 15 4 6 75 10.7 • Oxygen % down - diffuses into blood • Carbon dioxide % up - diffuses out of blood • Water vapour % up - lost by the wet surface of the alveoli • Nitrogen % down only because of the increase in water vapour • (actual amount of nitrogen remain constant as humans cannot use nitrogen gas) 10.8 • Spirometer used to measure lung capacities • Vital capacity is total volume that can be breathed in • Tidal volume is amount that is normally breathed in • Can also measure breathing rate and rate of oxygen consumption 10.8 A spirometer trace Breathing rate Resting tidal volume Tidal volume during exercise Rate of oxygen consumption Time Exercise starts 10.8 • Pulmonary ventilation = volume of air breathed in during one minute • tidal volume = volume breathed in during one breath in dm3 • breathing rate = number of complete breaths in one minute in breaths min-1 • Pulmonary ventilation in dm3 min-1 • = tidal volume x breathing rate 10.7 circulation • General pattern of circulatory system • Blood vessels entering heart - veins (in to heart) • inferior and superior vena cava - deoxygenated blood from tissues - into right atrium • pulmonary veins - oxygenated blood from lungs into left atrium • Blood vessels leaving heart - arteries (away from heart) • aorta - oxygenated blood to tissues - out of left ventricle • pulmonary artery - deoxygenated blood to lungs out of right ventricle 10.7 circulation • Blood vessels of lung • pulmonary arteries - deoxygenated blood from heart - into lungs • pulmonary veins - oxygenated blood from lungs - into heart • Blood vessels of kidney • renal arteries - oxygenated blood with urea into kidneys - from heart • renal veins - filtered, deoxygenated blood away from kidney - to heart 10.7 circulation • Blood vessels of liver • hepatic artery - oxygenated blood into liver, away from heart • hepatic portal vein - blood direct from alimentary canal (intestine) so that nutrients and toxins can be dealt with by the liver • hepatic artery - deoxygenated blood from liver towards the heart 10.7 circulation Carotid artery head Aorta Pulmonary artery Superior vena cava lungs Hepatic vein heart liver Hepatic portal vein Renal vein kidney Pulmonary vein Hepatic artery gut Renal artery Aorta Inferior vena cava 10.7 circulation • Capillaries • 5-10 m diameter • very many • very large surface area for exchange • • • • single cell thick endothelium very thin squamous (flat) cells small thickness of exchange surface Ref. Fick’s Law 10.7 circulation Low hydrostatic pressure High hydrostatic pressure artery High protein - low water potential capillary Low protein - high water potential vein Lymph system drains excess tissue fluid Osmosis due to difference in water potential Movement of small molecules due to hydrostatic pressure differences 10.7 circulation • Key features of the formation of tissue fluid • The net hydrostatic pressure (hp) acting outwards is the difference between the hp in the capillary and the hp in the tissue fluid • net hp = hp in – hp out • The net water potential () acting outwards is the difference between the in the capillary and the in the tissue fluid • net = in – out • filtration pressure (fp) = water potential () + hydrostatic pressure (hp) 10.7 circulation = -1kPa = -1kPa hp = +1kPa hp = +1kPa = -3kPa hp = +6kPa artery capillary vein = -3kPa hp = +2kPa in = -3 - -1 = -2kPa in = -3 - -1 = -2kPa hp out = +6 - +1 = +5kPa hp out = +2 - +1 = +1kPa fp = +5 + -2 = +3kPa out fp = +1 + -2 = -1kPa in 10.8 heart Pulmonary artery Aorta Semilunar valves Vena cava Right atrium Tricuspid valve Right ventricle Pulmonary vein Left atrium Bicuspid valve (mitral valve) Left ventricle 10.8 heart Pulmonary artery Superior vena cava Aorta Semilunar valves Pulmonary vein Inferior vena cava Right atrium Tricuspid valve Right ventricle Left atrium Bicuspid valve (mitral valve) Left ventricle 10.8 heart Deoxygenated blood from upper body tissues Oxygenated blood to body tissues Deoxygenated blood to lungs Oxygenated blood from lungs Deoxygenated blood from lower body tissues 10.8 Diastole - myocardium relaxed Deoxygenated blood from upper body tissues Heart muscle relaxed Oxygenated blood from Heart fills with blood lungs Lasts 0.3 seconds Deoxygenated blood from lower body tissues Bicuspid and tricuspid valves open Semilunar valves shut 10.8 Atrial systole Artria contract ventricles remain relaxed Topping up the ventricles with blood Lasts 0.1 seconds Bicuspid and tricuspid valves remain open Semilunar valves remain shut 10.8 Ventricular systole Ventricles contract, atria relax Empties ventricles into arteries, atria refill Lasts 0.2 seconds bicuspid and tricuspid valves slammed shut Semilunar valves open 10.8 Initiation of heart beat • Muscle cells contract when depolarised • calcium ion channels open • calcium ions rush in • and the muscle cells contract • Muscle cell are polarised at rest • calcium ions (Ca2+) actively transported out • calcium ion gates closed so no diffusion in 10.8 Initiation of heart beat • The sinoatrial node depolarises myogenically • an impulse (wave of depolarisation) spreads rapidly across the atria • causing atrial systole (contraction) • the impulse can’t reach the ventricles due to a ring of fibrous tissue • except through the atrioventricular node and bundle of His 10.8 Initiation of heart beat • The impulse passes slowly through the atrioventricular node • to give the atria time to empty into the ventricles • the impulse passes swiftly to the bottom of the heart in the bundle of His (Purkinje tissue) • where it spreads over the ventricles • causing ventricular systole from the bottom up • so the ventricles empty into the arteries at the top of the heart 10.8 Initiation of heartbeat Sinoatrial node Atrioventricular node Ring of fibrous tissue Bundle of His 10.8 Initiation of heartbeat Sinoatrial node Atrioventricular node Fibrous tissue Bicuspid valve Bundle of His Semilunar valves 10.8 Control of heart output • Hormones e.g adrenaline speeds up heart rate and makes stroke volume bigger • Nerves - autonomic nervous system • sympathetic nerve speeds heart rate up • parasympathetic (vagus) nerve slows it down • Stretched cardiac muscle has bigger contractions - increases stroke volume 10.8 Nervous control of heart rate • During exercise pressure in vena cava rises • stretch receptors in the vena cava are stimulated • more impulses pass along sensory nerves • to the cardiac accelerator centre in the medulla of the brain • that sends out more impulses in sympathetic nerves to the sinoatrial node • speeding up the heart rate 10.8 Nervous control of heart rate Cardiac accelerator centre in medulla stimulated, causing more impulses in sympathetic nerve to sinoatrial node More impulses in sympathetic nerve to sinoatrial node speeds up heart rate Sensory nerves to medulla in brain carry more impulses Stretch receptors in vena cava are stimulated More active muscles squeeze harder and more often on veins One-way valves in veins ensure that blood can only flow back to heart 10.8 Nervous control of heart rate • ‘Blood pressure’ is pressure in the arteries • It rises and falls depending on • heart rate • vasoconstriction of arteries • It can rise too high if: • • • • Peak pressure during systole ‘systolic bp’ 120 80 exercise has finished Minimum pressure you lie down during diastole ‘diastolic’ bp) many arteries vasoconstrict many arteries lose their elasticity (causes hypertension = high blood pressure) 10.8 Nervous control of heart rate • • • • If pressure in aorta rises dangerously stretch receptors in the aorta are stimulated more impulses pass along sensory nerves to the cardiac decelerator centre in the medulla of the brain • that sends out more impulses in parasympathetic (vagus) nerves to the sinoatrial node • slowing down the heart rate 10.8 Nervous control of heart rate Cardiac decelerator centre in medulla stimulated, causing more impulses in parasympathetic nerve to sinoatrial node More impulses in parasympathetic (vagus) nerve to sinoatrial node slows down heart rate Sensory nerves to medulla in brain carry more impulses Stretch receptors in aorta and carotid arteries stimulated by high arterial blood pressure 10.8 Pressure and volume in the heart • During diastole • pressure is low in atria and ventricles • volume of ventricles increase • During atrial systole • pressure is a bit higher in the atria • volume of the ventricles continues to increase • During ventricular systole • pressure is very high in the ventricles • ventricular volume drops rapidly 10.8 Pressure and volume in the heart Semilunar valves open Semilunar valves shut Pressure Bi & tri - cuspid valves shut 0 Bi & tri - cuspid valves open 0.2 0.4 0.6 0.8 1.0 Aorta Volume Ventricles Atria 0 0.2 0.4 0.6 0.8 1.0 10.8 Exercise & pulmonary ventilation • • • • exercise - muscle works harder muscle respires more produces more carbon dioxide lowers blood pH • lower blood pH • increases pulmonary ventilation 10.8 Exercise & cardiac output • exercise - muscle works harder • muscle squeezes harder / more often on veins, pushing blood back to heart faster • increases venous return of blood to heart • stretches vena cava and cardiac muscle • stretched vena cava and cardiac muscle • increases cardiac output 10.8 Control of cardiac output • Hormonal • e.g adrenaline speeds up heart rate and makes stroke volume bigger increasing cardiac output • Nervous - autonomic nervous system • sympathetic nerve speeds heart rate up • parasympathetic (vagus) nerve slows it down • Stretching of cardiac muscle • gives bigger contractions - increases stroke volume 10.8 Nervous control of heart rate • During exercise pressure in vena cava rises • stretch receptors in the vena cava are stimulated • more impulses pass along sensory nerves • to the cardiac accelerator centre in the medulla of the brain • that sends out more impulses in sympathetic nerves to the sinoatrial node • speeding up the heart rate 10.8 Nervous control of heart rate Cardiac decelerator centre in medulla stimulated, causing more impulses in parasympathetic nerve to sinoatrial node More impulses in parasympathetic (vagus) nerve to sinoatrial node slows down heart rate Sensory nerves to medulla in brain carry more impulses Stretch receptors in aorta and carotid arteries stimulated by high arterial blood pressure 10.8 Breathing and exercise • • • • • • • • Muscles respire faster during exercise more CO2 in blood lowers blood pH detected by CO2 receptors in carotid arteries stimulates respiratory centre in medulla so you breath more frequently and tidal volume increases Pulmonary ventilation increases during exercise 10.8 Breathing and exercise Breathing centres in medulla stimulated and initiate faster deeper breaths Intercostal and diaphragm muscles contract more often and more vigorously Sensory nerves carry more impulses Motor nerves carry more impulses More CO2 in blood, so pH lower (more acid) Carotid and aortic bodies detect drop in blood pH Pulmonary ventilation Pulmonary ventilation 10.8 Breathing and exercise CO2 normal O2 Drop in blood pH due to increased CO2 causes pulmonary ventilation to increase normal 10.6 Tissues • A tissue is: • a group of similar cells • carrying out a similar function • e.g. epithelium of alveolus in lung • e.g. blood 10.6 Tissues • • • • Epithelial tissues lining of organs e.g. squamous epithelium lining lungs thin flattened cells to: • minimise diffusion distance and • maximise rate of diffusion • ref. Fick’s Law 10.6 Tissues • Histology of lung Red blood cell Air inside alveolus Thin endothelium of capillary wall Thin epithelium of alveolus 10.6 Tissues • Cuboidal epithelium • lining kidney tubules Lumen - hole down middle Microvilli - to maximise surface area for diffusion and active transport Cuboidal epithelium with lots of mitochondria to release energy for active transport 10.6 Tissues • Columnar epithelium • e.g. lining trachea air Columnar cells protecting surface of trachea, with lots of mitochondria to release energy for cilia Cilia to remove mucus with trapped dust and bacteria 10.6 Tissues • Some simple epithelia are one cell thick • Other stratified epithelia have several layers of cells • e.g. skin - stratified squamous epithelium 10.6 Tissues • Histology of blood Granulocyte • ingest bacteria Erythrocyte - red blood cell Monocyte • transports oxygen • shows antigens to lymphocytes Lymphocyte • specific immunity - antibodies 10.6 Tissues • Red blood cells • large surface area:volume ratio • due to biconcave disc shape • small size so short diffusion distance to centre • no nucleus • maximises volume available for carrying oxygen • flexible • so can fit through small capillaries 10.6 Tissues • As size of a cell increases, e.g. by 2 m • its volume increases by the cube of the increase in size, e.g. by 23 m3 = 8 m3 • but its surface area increases only by the square of the increase in size, e.g. 22 m2 = 2 4 m • Small cells have larger surface area:volume ratio 10.6 Tissues • Find the surface area, volume and surface area: volume ratio of the following shapes. The first has been done for you: Side 1cm 2cm 4cm 8cm Volume =1x1x1=1cm3 surface area=1x1x6=6cm2 Surface area:volume ratio = sa/vol = 6/1 = 6 10.6 Organs • Organs • structures made of different tissues • co-operating to perform particular functions • e.g. arteries, arterioles, veins and venules 10.6 Organs • Artery lumen - hole down middle endothelium - covering tissue like squamous epithelium tough connective tissue with collagen fibres elastic connective tissue and smooth muscle tissue tough connective tissue with collagen fibres 10.6 Organs • Aterioles • small arteries • with muscle tissue so they can vasoconstrict - make lumen smaller and vasodilate - allow lumen to become larger • and elastic connective tissue - to absorb pulse • and strong collagen connective tissue to resist bursting 10.6 Organs • Veins • relatively thin walls mostly of tough connective tissue with collagen to resist bursting • valves to enhance blood flow back to heart 10.6 Organs • Veins • large lumen - slow flow - low pressure • minimises friction • smooth endothelium lining - minimises friction and blood clot formation • thin walls (compared to arteries) • collagen connective tissue - strong, resist bursting • few elastic and muscle fibres - no pulse to absorb, can’t vasoconstrict • one-way valves - assist venous return to heart by preventing backflow of blood 10.6 Organs A A A B Skeletal muscles relaxed B Skeletal muscles contract B Skeletal muscles relaxed