Cardiovascular system

Cardiovascular system

1. heart

   • 4 chambers
     • right atrium
       • receives blood from systemic circuit
     • right ventricle
       • pumps blood into pulmonary circuit
     • left atrium
       • receives blood from pulmonary circuit
     • left ventricle
       • pumps blood into systemic circuit
   • base
     • superior
     • where great vessels connect
   • apex
     • inferior
     • pointed tip
   • sits between 2 pleural cavities in mediastinum
     • mediastinum: space between both lungs inside the chest cavity
   • valves
     • atrioventricular
       • tricuspid
       • mitral
       • folds of fibrous tissue that extends into opening between atria and ventricles
       • permit blood flow in one direction: atrium->ventricle
     • semilunar
       • pulmonary
       • aortic
       • prevents backflow of blood into ventricles
   • conducting system
     • heartbeat
       • a single cardiac contraction
       • cardiac cycle
         • from start of one heartbeat to beginning of next
           • including alternating periods of contraction and relaxation
         • phases within chambers
           • systole
             • 1.atrial
               • 1)atrial contraction begins
                 • 2)right and left AV valves open
                   • 3)atria eject blood into ventricles
                     • 4)ends
             • 2.ventricular
               • 4)ventricle contracts and builds pressure
                 • 5)AV valves close
                   • producing isovolumetric contraction
                   • ventricular pressure exceeds arterial pressure
                     • 6)opens semilunar valves
                       • 7)ventricular ejection
                         • amount of blood ejected = stroke volume (SV)
                         • ventricular pressure falls, ventricles contain end-systolic volume (ESV) (40% of end-diastolic volume)
                           • 8)Seminlunar valves close
             • blood pressure rises
           • diastole
             • 2.atrial
               • 4)begins
                 • ventricles contain maximum blood volume (EDV)
             • 3.ventricular
               • isovlumetric relaxation
                 • all heart valves are closed
                 • ventricular pressure is higher than atrial pressure
                   • blood cannot flow into ventricles
                 • 9)AV valves open
                   • ventricles fill passively
                   • atrial pressure is higher than ventricular pressure
             • blood pressure falls
         • 75 heart beats per minute (bpm)
         • a cycle lasts 800 ms
         • blood flows from an area of higher pressure to one of lower pressure
           • controlled by timing of contractions and directed by one-way valves
         • when heart rate increases all phases of cycle shorten, particularly diastole
     • cardiac muscle cells
       • autorhythmic
         • control and coordinate heartbeat
       • contractile
         • produce contraction that propel blood (99%)
           • role of calcium ions
             • extracellular Ca2+ crosses plasma membrane during plateau phase
               • provides 20% of Ca2+ required for contraction
             • entr
             • entry of extracellular Ca2+ from sarcoplasmic reticulum
               • SR is a specialized type of smooth ER that regulates the calcium ion conc. in the cytoplasm of muscle cells
             • cardiac muscle tissues are very sensitive to extracellular Ca2+ conc.
               • as slow calcium channels close, intracellular Ca2+ is pumped back into SR or out of cell
         • form bulk of atrial and ventricular walls
         • receive stimulus from Pukinje fibres
         • resting membrane potential
           • ventricular cell
             • -90mV
           • atrial cell
             • -80mV
         • action potential
           • 1.rapid depolatization
             • massive influx of Na+ through fast sodium channels
             • 2.plateau
               • extracellular Ca2+ enters cytosol through slow calcium channel
               • 3.repolarization
                 • K+ rushes out of cells through slow potassium channels
           • refractory
             • absolute (200ms)
               • cardiac contractile cells cannot respond
             • relative (50ms)
               • cells respond only to strong stimuli
     • pacemaker cells
       • establishes normal cardiac rhythm
       • found in
         • Sinoatrial (SA) node
           • in wall of right atrium
         • atrioventricular (AV) node
           • at junction between atria and ventricles
       • potential
         • gradual depolarization
           • do not have a stable resting membrane potential
         • rate of spontaneous depolarization
           • SA node faster than AV node
         • SA node depolarizes first
           • establishing sinus rhythm
         • parasympathetic stimulation slows heart rate
     • conducting cells
       • found in
         • internodal pathways of atria
         • atrioventricular bundle, bundle branches, Purkinje fibres of ventricles
     • impulse conduction
       • 1.SA node activity and atrial activation begins
         • 2.stimulus spreads across atria and reaches AV node
           • 3.impulse is delayed for 100ms at AV node
             • atrial contraction begins
             • 4.impulse travels in AV bundle to left and right bundle branches in interventricular septum
               • to Purkinje fibres and to papillary muscles via moderator band
               • 5.Purkinje fibres distribute impulse to ventricular myocardium
                 • atrial contraction is completed; ventricular contraction begins
     • electrocardiogram (ECG)
       • a recording of electrical events in the heart
         • obtained by placing electrodes at specific locations on body surface
       • abnormal patterns are used to diagnose damage
       • P wave
         • depolarization of atria
       • QRS complex
         • depolarization of ventricles; ventricles begin contracting shortly after P wave
       • T wave
         • repolarization of ventricles
       • P-R interval
         • from start to atrial depolarization; to start of QRS complex
       • Q-T interval
         • time required for ventricles to undergo a single cycle of depolarization and repolarization
     • intercalated discs
       • unique structural formations found between the myocardial cells of the heart
       • bond cardiac muscle cells together
       • membranes of adjacent cells are held together by desmosomes; linked by gap junctions
       • transfer force of contraction from cell to cell
       • propagate action potentials
   • heart sounds
     • detected withh a stethoscope
     • S1
       • loud sounds as AV valves are closed
     • S2
       • loud sounds as semilunar valves close
     • S3, S4
       • soft sounds - blood flowing into ventricles and atrial contraction

2. blood

   • flow
     • 1.superior and inferior vena cava
       • 2.right atrium
         • 3.right ventricle
           • 4.left pulmonary arteries
             • 5.pulmonary circuit (lungs)
               • gas exchange occurs in the pulmonary capillaries: oxygen into blood, carbon dioxide out)
               • 6.left pulmonary veins
                 • 7.left atrium
                   • 8.left ventricle
                     • 9.aorta
                       • 10.systemic circuit
                         • exchange in systemic capillaries: oxygen and nutrients out, carbon dioxide and wastes in
                         • back to 1. = cycle is repeated
                 • blood high in oxygen and low in carbon dioxide
             • blood is low in oxygen but relatively high in carbon dioxide
   • specialized connective tissue
     • contain cell suspended in a fluid matrix
   • function
     • 1.transporting dissolved gases, nutrients, hormones and metabolic water
     • 2.regulating pH, ion composition of interstitial fluids
     • 3.restricting fluid losses at injury sites
     • 4.defending against toxins and pathogens
     • 5.stabilizing body temperature
   • components
     • whole blood
       • plasma
         • fluid
         • 55% of blood volume
         • >90% is water
           • rest contains dissolved plasma proteins and other solutes
       • similar in composition to interstitial fluids because water, ions and small solutes are exchanged across capillary walls
     • fractionation
       • process of separating whole blood into plasma and formed elements
         • plasma proteins
           • 10% of plasma
           • Albumins (60%)
             • plasma osmolarity
             • transport insolubles (fatty acids, thyroid hormones, steroid hormones)
           • Globulins (35%)
             • immunoglobulins
               • antibodies
             • transport globulins
               • hormone-binding proteins, metalloproteins, apoliopoproteins (lipoproteins), steroid-binding proteins
           • Fibrinogen (4%)
             • soluble protein that functions in clotting
             • converted to insoluble fibrin during injury
               • leave serum (fluid) in blood sample
           • Other (1%)
             • varying concentrations of enzymes and hormones
         • haemopoiesis
           • process of producing formed elements
         • formed elements
           • red blood cells (erythrocytes
             • haemoglobin (Hb) (280 billion)
               • red pigment that gives blood its color (iron)
               • protein that transports respiratory gases
               • 12-18 g/dL whole blood
               • complex quaternary structure
                 • 4 globular protein subunits
                   • 2 alpha chains
                   • 2 beta chains
                   • each with 1 molecule of haem
                     • each haem contains 1 iron ion
                       • iron interacts with oxygen to form oxyhaemoglobin, HbO2
                         • dissociate easily to form deoxyhaemoglobin
               • in peripheral capillaries (low O2)
                 • releases O2
                 • binds CO2
                   • carbaminohhaemoglobin
               • at lungs (high O2)
                 • binds O2
                 • releases CO2
             • 99.9% of formed elements
               • 4.2-6.3 million per mcL of whole blood
             • small, highly specialized cells
             • large SA:V
               • quickly absorb and release oxygen
             • biconcave discs
               • thin central region and thicker outer margin
             • form stacks called rouleaux
               • smooth blood flow through narrow blood vessels
             • binds and transports oxygen and carbon dioxide
             • bend and flex when entering small capillaries
             • mature RBCs - anucleate
               • lack nuclei, mitochondria, ribosomes
               • unable to divide, synthesize proteins or repair damage
               • live 120 days
           • white blood cells (leukocytes)
             • have nuclei and other organelles
             • lack Hb
             • functions
               • defending body against pathogens
               • removing toxins and waste
               • attacking abnormal or damaged cells
             • most are in connective tissue proper and organs of lymphatic system
             • constitute small fraction of whole blood - 5000-10000 per mcL
             • all
               • can migrate out of the bloodstream
               • are capable of amoeboid movement
               • are attracted to specific chemical stimuli (positive chemotaxis)
             • some are phagocytic
           • platelets (thrombocytes)
             • cell fragments
             • involved in clotting system
             • circulate for 9-12 days
             • removed by phagocytes
             • mainly (1/3) in spleen (vascular organs)
             • 150,000-500,000 per mcL of blood
             • mobilized in circulatory crisis
             • functions
               • release important clotting chemical
               • temporarily patch damaged vessel walls
               • reduce size of break in vessel wall
   • Haemostasis/ BLOOD CLOTTING/ cessation of bleeding
     • phases
       • 1.vascular
         • 1.a cut triggers vascular spasm: contraction of smooth muscle fibres of vessel wall (lasts about 30 mins)
           • 2.endothelial cells contract and expose basement membrane to bloodstream
             • 3.endothelial cells release chemical factors and local hormones (ADP, tissue factor and prostacyclin; endothelin (peptide hormones))
               • 4.cause smooth muscle contraction and cell division
                 • 5.endothelia plasma membranes become 'sticky', seal off tear and prevent blood flow
       • 2.platelet
         • platelet adhesion
           • 1.platelets attach to exposed surfaces = platelet aggregation
             • 2.platelets stick to each other
               • 3.forms platelet plug that closes small breaks
         • activated platelets release clotting compounds (ADP, clotting factors)
         • 15s after injury
       • 3.coagulation
         • 30s or more after injury, depends on clotting factors (procoagulants)
           • procoagulants: Ca2+, 22 other proteins, inactive proenzymes converted to active enzymes that direct reactions in clotting response
         • fibrinogen -> fibrin
         • cascade
           • chain reactions of 3 pathways
             • extrinsic
               • occurs when damaged cells release factor III
               • produces lots of thrombin
                 • thrombin cleaves fibrinogen to fibrin
             • intrinsic
               • occurs during exposure to negatively charged molecules e.g. molecules on bacteria and lipids
             • common
               • begins with the activation of factor X by factor III
                 • converts prothombin (proenzyme) to thrombin
                   • thrombin converts fibrinogen to insoluble fibrin
                     • blood clot
                   • 1)stimulates formation of factor III
                   • 2)stimulates release of PF-3 platelets
                   • =3)form positive feedback loop that accelerates clotting process
                     • feedback control of blood clotting
                       • anticoagulants: enzymes that inhibit clotting)
                         • antithrombin-III
                         • heparin
                           • accelerates activation of antithrombin-III
                         • thrombomodulin
                           • activates protein C
                             • inactivates clotting factors
                             • stimulates formation of plasmin (breaks down fibrin)
                         • prostacyclin
                           • inhibits platelet aggregation
                           • oppose factors
     • Calcium ions
       • required in all 3 pathways
     • vitamin K
       • required for synthesis of 4 clotting factors
     • clot retraction
       • pulls torn edges of vessel closer together
         • reduces residual bleeding and stabilizes injury site
         • reduces damaged area, easier for fibroblasts, smooth muscle cells and endothelial cells to complete repair
     • fibrinolysis
       • gradual process of dissolving clot
       • thrombin and tissue plasminogen activator (t-PA) activate plasminogen, producing plasmin
         • plasmin digests fibrin strands

3. blood vessels

   • arteries
     • carry blood away from heart
   • veins
     • return blood to heart
   • capillaries
     • interconnect smallest arteries and veins
     • exchange dissolved gases, nutrients and wastes between blood and surrounding tissues