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a little re fresher emedicine at cambridgeready for tuesdaandthursdays 7pm-8pmphysics concepts capacitance - can store electrical charge - two parallel conductors with an insulator in between - what might be a biological example? - C=Q/V - dependent on: - The area - The distance between the plates - The material between themequations - V=IR - Q=It - C=Q/V - R=ρA/Lnerve impulses the resting potential - Imbalance of sodium and potassium ions - Polarisatiocauses voltage across membrane - -70mV - Maintained by imbalance of ions, selective permeability (and in part the sodium potassium pump) - Electrochemical gradient - High Kon inside, low Na - Outside positive relative to insideaction potentials action potentials 1. depolarisatio: influx of Na+ due to opening of voltage gated sodium channels 2. repolarisatio: efflux of K+ ions due to opening of voltage gated potassium channels 3. hyperpolarisati:n ore K+ exits than Na+ entered 4. returning to resting potential: returning to electrochemical equilibirum remember electrochemical gradients! speed of action potentials 1. presence or absence of myelin sheath: saltatory conduction 2. diameter of the axon: greater diameter 3. temperature synaptic transmission 1. voltage gated calcium channels open 2. fusion of synaptic vesicles filled with ACh 3. released into synaptic cleft 4. binds to receptors on the post synaptic membrane allowing sodium ions to enter 5. causesdepolarisationf the-pos synaptic membranemusclesmuscle vocabulary - sarcolemma - sarcoplasmic reticulumstructure of musclestructure of musclestructure of muscle structure of muscle - myofibrils made from thick and thin filaments - actin and myosin - two actin molecules twist together - myosin has heads that bind to actin during contraction excitation contraction coupling - depolarisationauses the sarcoplasmic reticulum to release calcium ions - they bind to troponin - if calcium remains available the cycle continuesmuscle contractionHaemoglobin Haemoglobin • Large quaternary structure • 4 polypeptide chains • 4 Haemgroups • Each containing iron • 4 oxygen moleculesOxygen dissociation curve AFFINITY VARIES DEPENDING ON THE PARTIAL PRESSURE OF OXYGEN >> Conformational change Low partial High partial oxygenre of pressure of oxygen Bohr Shift qRespiring tissue produce CO2 qCO2 + H2O carbonic acH+ +HCO- qCarbonic anhydrase catalyses qLowers pH qDecreases oxygen affinity Bohr Shift qRespiring tissue produce CO2 qCO2 + H2O carbonic acH+ +HCO- qLowers pH qDecreases oxygen affinity qFacilitates O2 unloading at actively respiring tissues qFacilitates CO2 uptake and removal from these tissues Fetal Haemoglobin q Left shift q Oxygen slowertion in placenta q SofHbmust have higher affinity for O2 q To ensuoxygenatedlood is sufficientlyThe heartThe heart - Notice the difference in thickness of the walls - Valves prevent backflow - CO = HR x SVCardiac cycle text - Ventricles relax, atria contract - Ventricles contract, atria relax - Ventricles relax, atria relaxCardiac cycle Nodes • SA Node– wall of RA • R and L atria contract at same time • Non-conducting collagen • AV Node • Slight delay • Bundle of His • Purkinjfibres • Ventricles contact ECG qP wave =depolarisation f atria qQRS complex = ventricular depolarization qT wave = repolarization of ventricles qBigger wave = stronger contractionSome clinical applications… - Bradycardia - Tachycardia - Atrial fibrillation Problem Solving… o ‘Hole in the heart’ (ventricular septal defect or other) o Which way will the blood flow?te Left to right shunt - Left ventricular wall thicker than the right - As it pumps blood through systemic circulation - So blood at a higher pressure in left ventricle - Blood flows from left to right ventricleProblem solving… - Right ventricle coping with higher volume of blood - Wall thickens - Pressure builds up - When P Right > P Left, shunt reverses Right to left shunt …. Eisenmenger syndrome 1-6% of adults born with a heart defect (GARD) – an NCATS Program (nih.gov) Rare Diseases InformationCenterEisenmenger Syndrome - What symptoms do you think these patients will have?Eisenmenger Syndrome - Breathlessness - Cyanosis - Pulmonary hypertension - Chest pain - Dizziness and fatigue - Clubbing of fingers and toesRespiratory physiology Breathing • Pressure difference for air to flow • Inspiration = active • Expiration = passive • Pleural space Inspiration 1. Muscles contract 2. Volume of pleural space increase 3. Pressure of pleural space decreases 4. Lungs expand 5. Lung pressure decreases 6. Air flows into the lungs Expiration 1.Muscles relax 2.Volume of pleural space decreases 3.Pressure in pleural space increases 4.Lung volume decreases 5.Lung pressure increase 6.Air moves out of the lungs Lungs Trachea - Bronchi - Bronchioles - Alveoli • Warm • Humidify • Filter Gas exchange Atmosphere Blood TissuesPulmonary circulation • Too large for diffusion • Right ventricle to left atriumAlveoli • Large surface area • Thin diffusion barrier • Air and blood in close proximity Oxygen PO2 atmosphere> PO2 blood > PO2 tissues Carbon Dioxide PCO2 tissues> PCO2 blood > PCO2 atmosphereRenal physiologyKidneys • Regulate body fluids • Volume, osmolality and composition • Produce urineNephron • Glomerulus • Proximal convoluted tubule • Loop of henle • Distal convoluted tubule • Collecting ductFiltration • Glomerulus • Filtered into bowmans capsule • Water and solutesGFR • Afferent and efferent arterioles • Afferent dilates + efferent constricts to increase filtration pressureReabsorption • Transport of solutes and water into blood • Avoid excess losses • Passive • Active • 65% of wate, Na, Cl and K in PCT • 100% of glucose and amino acids in PCTSecretion • Transport from capillaries • Acids and bases • Drugs and toxinsfeedback form