Physiology

• Resting Membrane Potential (RMP)


  The separation of opposite charge that exists across the cell membrane
• Resting Membrane Potential (RMP)


  • Intracellular fluid (ICF) is negative compared to extracellular fluid (ECF)
• Membrane potential


  The separation of positive and negative charges across the cell membrane
• Determination of membrane potential


  1. No potential as [+] and [-] balanced

  2. Different in charge across membrane = has potential

  3. Unbalanced charges tend to accumulate along opposite sides of cell membrane

  4. The greater the number of separated charges across the membrane, the larger the potential
• Resting Membrane Potential (RMP)


  Concentration and permeability of ions responsible for RMP
• Cardiovascular system


  Consists of the heart and circulatory system
• Role of the cardiovascular system


  To supply every cell in the body with oxygen and nutrients
• Heart works as a double pump


  1. Deoxygenated blood enters the right atrium

  2. Deoxygenated blood passes through the right AV valve and enters the right ventricle

  3. Deoxygenated blood is pumped into the pulmonary arteries through the pulmonary valve

  4. Oxygenated blood returns from the lungs to the left atrium

  5. Oxygenated blood enters the left ventricle through the left AV valve

  6. Oxygenated blood is pumped by the left ventricle through the aortic valve into the systemic circulation
• Components of the cardiovascular system


  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
• Functions of the cardiovascular system


  • Collect and transport oxygen from lungs and nutrients from GI tract to all cells in the body
  • Collect and transport Carbon dioxide (cell's main metabolic by product) and other waste products
• Normal cells in tissues are rarely more than 100micrometers away from capillaries. If cells are further away they would die due to low levels of oxygen- hypoxia
• Cardiac muscle


  Excitation-contraction in cardiac muscle
• Autorhythmic cells


  These cells have an unstable resting membrane potential and continuous depolarisation produces pacemaker potentials that initiate action potentials
• In skeletal muscle, each muscle fibre is attached to a motor nerve and will only contract when that motor nerve is stimulated (Motor unit)
• Absolute refractory period


  1. 2ms in cardiac muscle
• Cardiac muscle


  The heart either contracts as a unit or doesn't at all. It acts as a functional syncytium, as electrical activity can spread from one cell to the next
• Cardiac absolute refractory period

  250ms, nearly as long as the contraction
• Action potentials in cardiac cells


  • Non-contractile cells: autorhythmic cells comprise 1% of cardiac muscle fibres
  • Contractile cells; cardiac muscle cells comprise 99% of cardiac muscle fibres
• Electrical events in cardiac contractile muscle cells


  1. Depolarisation

  2. Voltage gated sodium channels cause rapid depolarisation (sodium channels inactivation ends this phase)

  3. Plateau phase of AP

  4. Slow Calcium channels (slow channels) open

  5. Repolarisation

  6. Slow calcium channels inactivate and potassium channels open
• Calcium induced calcium release (CICR)


  1. type Calcium channels in cell membrane open in response to depolarisation caused by the opening of fast sodium ion channels. 10-20% of Calcium enters here. These local influxes of Calcium triggers ryanodine receptors causing opening of calcium sensitive channels in the SR called calcium induced calcium release. Sensitive to caffeine
• Cardiac intrinsic conduction system and action potential succession during one heartbeat


  1. The SA node is activated and the atria contract (P)

  2. The AV node is activated

  3. The ventricles contract (QRS)

  4. The ventricles repolarise and relax (T)
• Autonomic innervation of the heart


  • Sympathetic stimulation speeds up heart rate and force of contraction
  • Parasympathetic stimulation slows down heart rate
• Electrocardiograms show the sequence of electrical events during one heartbeat
• Atrioventricular valves


  1. Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are forced open

  2. As ventricles fill, atrioventricular valve flaps hang limply into ventricles

  3. Atria contract, forcing additional blood into the ventricles

  4. Ventricles contract, forcing blood against atrioventricular valve cusps

  5. Atrioventricular valves close

  6. Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria
• Semilunar valves


  As ventricles contract and intraventricular pressure rises, blood is pushed up against the semilunar valves forcing them to open
• Heart sounds


  • Lub- atrioventricular valve closes (louder, longer, ventricular pressure> atrial pressure, beginning of ventricular systole)
  • Dub- semilunar valves close (short, sharp, beginning of ventricular relaxation, diastole)
• Heart murmurs


  • Result from turbulent blood flow due to valve malfunction
  • Stenotic valve: stiff, narrowed valves which do not open completely, blood forced through a high pressure, produces whistling sound
  • Insufficient/ incompetent valve: cannot close fully, backflow of blood causes turbulence, creates a swishing/ gurgling sound
• Cardiac cycle


  Rhythmic changes in cardiac electrical activity result in a cycle of contraction and relaxation. Resulting pressure changes control blood flow through the heart. Blood flows down a pressure gradient through any available opening
• Systole


  Period of the cardiac cycle when either the ventricles or atria are contracting
• Diastole


  Period of the cardiac cycle when either the ventricles or atria are relaxing
• Cardiac output


  The amount of blood pumped out by each ventricle in 1 minute. Cardiac output= heart rate x stroke volume
• Stroke volume


  The volume of blood pumped out by one ventricle with each beat. This indicates the force of ventricular contraction. Stroke volume represents the difference between end diastolic volume and end systolic volume
• Factors affecting stroke volume


  • Preload- degree of stretch of heart muscle
  • Contractility- contractile strength achieved at a given muscle length
  • Afterload- back pressure exerted by arterial blood
• Preload


  Degree of stretch of the heart muscle. Increased preload (increased end diastolic volume) means increased stroke volume
• Contractility


  Contractile length achieved at a given muscle length. Increased contractility (decreased end systolic volume) means increased stroke volume
• Afterload


  Back pressure exerted by arterial blood. Increased afterload (increased systolic volume) means decreased stroke volume
• Regulation of heart rate


  • Autonomic nervous system (Sympathetic stimulation increases heart rate, Parasympathetic stimulation decreases heart rate)
  • Chemical regulation (Hormones like Adr, cortisol, thyroxine increase heart rate, Ions like decreased Calcium and increased Potassium decrease heart rate)
  • Other factors (age, gender, exercise, body temperature)
• Coronary arteries


  Branch from aorta just beyond aortic valve, most arteriole flow occurs during diastole, blood flow normally adjusted to meet oxygen requirements
• Cardiovascular heart disease


  Most common cause of death in the UK, includes diseases of the heart and circulation like coronary heart disease (angina and heart attack) and stroke, occurs due to atherosclerosis: coronary arteries become narrowed by a gradual buildup of fatty material within their walls (atheroma)
• Angina


  The pain resulting when coronary arteries cannot deliver enough oxygen containing blood to the heart muscle, particularly at times when there is more demand