cardio system

• septa keep the two circulations seperate
• pulmonary circulation is supplied by:

  right atrium is a weak pump and receives blood from the periphery via the vena cava, priming the right ventricle, the right ventricle is a stronger pump and pumps blood out of the heart and to the pulmonary artery
• systemic circulation is supplied by

  left atrium is a weak pump and receives blood from pulmonary circulation, priming left ventricle, the left ventricle is the strongest pump and pumps blood through the aorta to the systemic circulation at a very high pressure
• diastole

  atrioventricular valves are open, semilunar valves are closed, atria and ventricles are both relaxed and are passively filling with blood
• atrial systole/ ventricular diastole

  atrioventricular valves are open, semilunar valves are closed, atria contract and empty the last bit of blood into the ventricles, both ventricles are still relaxed
• systole

  atrioventricular valves are closed, semilunar valves are open, atria relax, both ventricles contract and eject blood out of the heart
• the left ventricle pumps into the aorta
• the right ventricle pumps to the pulmonary artery
• stroke volume

  volume of blood ejected from the heart per beat
• determinants of stroke volume

  preload (increased means increased SV), afterload (increased means decreased SV), contractility (increased means increased stroke volume)
• preload

  the amount of blood that fills the heart before it contracts
• afterload

  the pressure that the heart works against during ejection
• contractility

  the performance of the ventricle at a given preload and afterload
• PNS reduces heart rate and the SNS increases heart rate
• below 60bpm: bradycardia
• above 100bpm: tachycardia
• pulse pressure

  difference between systolic and diastolic
• systolic pressure

  pressure in aorta and large arteries during peak systole
• mean arterial blood pressure

  determined by heart rate, stroke volume, and total peripheral resistance
• if pressure drops, baroreceptor reflex leads to:

  heart rate and contractility increase, vasoconstriction
• the kidney senses reduced blood pressure and activates the RAS
• angiotension stimuates vasoconstriction, aldosterone and AH release
• cardiac conduction sequence

  SA node, AV node, bundle of his, left and right bundle branches, purkinje fibres
• SA node

  in right atrium, and is the physiological pacemaker
• AV node

  the second pacemaker
• bundle of his

  wire of myocytes, going into bundle branches
• an action potential initiated in one part of the atria or ventricles will propagate throughout the chanmber
• the signal must pass through the AV node to get into the ventricles
• depolarisation happens when action potential from sinoatrial enters cardiomyocytes, opening sodium channels
• repolarisation happens when calcium channels close, and potassium moves out of the cell
• excitation contraction coupling

  depolarisation and contraction, prolonged increase of calcium, leading to a long and strong contraction
• refractory period

  avoids multiple action potentials summating
• aorta

  pulse dampening and distribution
• large arteries

  distribution of arterial blood
• small arteries

  distribution and resistance
• arterioles

  resistance, controls blood to capillaries
• venules

  exchange, collection, capacitance
• veins

  capacitance
• vena cava

  collection of venous blood
• resistance is directly proportional to vessel length and blood viscosity, and inversely proportional to the radius