chapter 1 anat + phys

• the heart

  divided into left and right by the septum into 4 chambers, the atria are smaller and have thinner walls as the blood they carry does not have much force, and the left side of the heart is larger as it needs to pump blood around the body

  
• blood vessels of the heart

  vena cava brings deoxygenated blood back to the right atrium and the pulmonary vein delivers oxygenated blood back to the left atrium, the pulmonary artery leaves the right ventricle with deoxygenated blood to go to the lungs and the aorta leaves the left ventricle to lead to all of body
• valves of the heart

  4 main valves that move in one direction and open to allow blood to pass through then close to prevent back flow, the tricuspid valve is between the right atrium and ventricle, the bicsupid valve is located between the left atrium and ventricle, the semi-lunar valves are found between the left and right ventricles and the pulmonary artery and aorta
• cardiac conduction system

  group of specialised cells located in the heart calls which send electrical impulses to the cardiac muscle, causing it to contract and the heart is myogenic

  
• myogenic

  the capacity of the heart to generate its own impulse
• cardiac conduction system order of cells

  electrical impulse is started

  1. sinoatrial node (SAN) and this spreads through the heart in a wave
  2. this impulse causes the atria to contract and force blood to ventricles
  3. atrioventricular node (AVN) delays the transmission to let atria empty
  4. ventricular systole occurs and electrical impulse send to bundle of His
  5. bundle located between septum separating 2 ventricles
  6. branches out into 2 branches then into the purkinje fibres which spread through ventricles
• how does the conduction system affect heart rate during exercise

  it ensures that heart rate increases during exercise to allow the work muscles to receive more oxygen, the electrical impulse in the SAN is generated alone, but they can be controlled by 3 mechanisms
• neural control mechanism

  involve the sympathetic and parasympathetic system which return the heart to its resting level, the CNS and the peripheral nervous system are coordinated in the medulla oblongata in the brain, sympathetic nerve impulses are sent to the SAN and there is a decrease in parasympathetic nerve impulses so heart rate increases
• sympathetic nervous system

  part of the autonomic nervous system that speeds up heart rate
• parasympathetic

  part of the autonomic nervous system that decreases heart rate
• 3 stimuli for the cardiac control centre

  chemoreceptors, baroreceptors and proprioceptors
• chemoreceptors

  tiny structures in the carotid arteries and aortic arch that detect changes in blood acidity caused by an increase or decrease in the concentration of carbon dioxide, and this stimulates the sympathetic system to increase HR
• baroreceptors

  special sensors in tissues in the aortic arch, carotid sinus, heart and pulmonary vessels that respond to changes in blood pressure to either increase or decrease heart rate, establish a set point for blood pressure
• how are baroreceptors stimulated

  an increase in arterial pressure causes and increase in the stretch of the baroreceptor sensors and results in a decrease in heart rate, but a decrease in arterial pressure causes a decrease in the stretch so heart rate increases
• proprioceptors

  sensory nerve endings in the muscles, tendons and joints that detect changes in muscle movement
• proprioceptors in exercise

  at the start, they detect an increase in muscle movement and they send an impulse to the medulla, which sends an impulse through the sympathetic nervous system to the SAN to increase heart rate, when the parasympathetic system stimulates the SAN, heart rate decreases
• adrenaline


  stress hormone that is released by the parasympathetic nerve and cardiac nerve during exercise which causes an increase in heart rate
• adrenaline stimulated the SAN which results in an increase in the speed and force of the contraction, increasing cardiac output, and this results in more blood being pumped to the working muscles so they can receive more oxygen for the energy they need
• stroke volume


  volume of blood pumped out by the heart ventricles in each contraction
• stroke volume depends on the:

  1. venous return - if VR increases then SV also increases
  2. elasticity of cardiac fibres - the more stretch the greater the contraction
• a greater force of contraction can increase the ejection fraction in the heart = Starling's Law
• ejection fraction


  percentage of blood pumped out by the left ventricle per beat
• Starling's law

  1. increased venous return
  2. greater diastolic filling of the heart
  3. cardiac muscle stretched
  4. more force of contraction
  5. increased ejection fraction
• ejection fraction


  E.F = stroke volume / end diastolic volume

  
• the greater the contractility of cardiac tissue, the greater the force of contraction, increases stroke volume
• heart rate


  number of times the heart beats per minute, on average the resting heart rate is approximately 72 bpm
• cardiac output


  volume of blood pumped out by the heart ventricles per minute
• cardiac output (Q) = stroke volume (SV) x heart rate (HR)


  Q = 70 ml x 72 bpm

  Q = 5.04 litres
• maximum heart rate


  220 - age = max heart rate
• a trained performer has a greater heart range because their resting heart rate is lower and their maximum heart rate increases
• regular aerobic training leads to cardiac hypertrophy, a bigger and stronger heart increases stroke volume, and the ventricles can contract more and push out more blood causing bradycardia, and this improves oxygen delivery to muscles as there is less oxygen needed for contractions of the heart
• cardiac hypertrophy


  thickening of the muscular wall of the heart so it becomes bigger and stronger, also means a larger ventricular activity
• bradycardia


  decrease in resting heart rate to below 60 bpm
• during exercise there is a large increase in cardiac output, but will increase until a maximum intensity is reached then it plateaus

  
• at rest cardiac output for both the trained and untrained performer stays the same, during exercise the maximum cardiac output for the trained performer is higher as they can carry more oxygen
• stroke volume increases as exercise intensity increases up to 40-60% of maximum effort, and then plateaus because increased heart rate near maximum efforts result in a shorter diastolic phase as ventricles do not have as much time to fill up with blood so cannot pump out as much
• coronary heart disease (CHD)


  occurs when coronary arteries that supply heart muscle with oxygenated blood become blocked or start to narrow due to a gradual build up of fatty deposits (atheroma), high blood pressure, high cholesterol, lack of exercise and smoking can cause atherosclerosis
• atherosclerosis


  occurs when arteries harden and narrow as they become clogged up by fatty deposits
• atheroma


  fatty deposit found in the inner lining of an artery
• angina


  chest pain that occurs when the blood supply through the coronary arteries to the muscles of the heart is restricted