Cardiovascular

• Pulmonary circuit is the route of blood from the heart to the lungs and back to the heart.

  Systemic circuit is the route of blood from the heart to the body and back to the heart.
• Sino atrial node

  Initiates cardiac cycle, it generates an electrical impulse which is fired through the atria walls causing atrial systole and forcing remaining blood into ventricles, sends impulse to AV node
• Atrioventricular node


  Receives impulse from SA node, it delays the impulse for 0.1 seconds to allow atria to finish contracting, sends impulse to bundle of his
• Bundles of his

  Receives impulse from AV node and carries the impulse down the septum of the heart
• Bundle branches

  The left and right branches distribute the impulse to the base of each ventricle
• Purkinje fibres

  Distribute the impulse through ventricle walls causing ventricular systole and forcing blood into the aorta and pulmonary artery
• No impulse


  Causes diastole as cardiac muscle in atria and ventricle walls relax and blood enters
• Conduction system

  1. Sino atrial node initiates

  2. Atrioventricular node receives and delays

  3. Bundles of his receive and carry

  4. Bundle branches distribute

  5. Purkinje fibres distribute
• Cardiac cycle

  One complete cycle takes 0.8 seconds and has 2 phases
• Diastole

  1. Relaxation of cardiac muscle

  2. Atria/ventricles relax and expand drawing blood into the atria

  3. Pressure in atria increases opening AV valves

  4. Blood passively enters ventricles

  5. SL valves close to stop blood leaving the heart
• Systole

  1. Contraction of cardiac muscle

  2. Atrial systole - atria contract forcing remaining blood into ventricles

  3. Ventricular systole - ventricles contract forcing blood from the ventricles into the aorta/pulmonary artery due to a pressure build up

  4. AV valves close to stop back flow

  5. SL valves are forced open to let blood through
• Conduction system control the cardiac cycle:

  SA node initiates an electrical impulse and sends it through the atrial walls to the AV node causing atrial systole where the atria contract forcing blood from the atria into the ventricles. The impulse travels down the bundles of his to the purkinje fibres causing ventricular systole where the ventricles contract and blood is forced from the ventricles to the lungs and body. No impulse causes diastole.
• Heart rate is the number of times the heart beats in a minute (bpm). Count number of heart beats per minute.

  Rest:

  Untrained - 70bpm

  Trained - 50bpm

  Submaximal:

  Untrained - 120bpm

  Trained - 120bpm (can be lower)

  Maximal:

  Untrained - 220-age

  Trained -220-age
• Stroke volume is the volume of blood ejected from the left ventricle per beat (ml/l). Calculated using CO/HR.

  Rest:

  Untrained - 70ml

  Trained - 100ml

  Submaximal:

  Untrained - 120ml

  Trained - 200ml

  Maximal:

  Untrained - 120ml

  Trained - 200ml
• Cardiac output is the volume of blood ejected from the heart in a minute (L/min). Calculated using SV*HR.

  Rest:

  Untrained - 5L/min

  Trained - 5L/min

  Submaximal:

  Untrained - 10L/min

  Trained - 20L/min

  Maximal:

  Untrained - 20L/min

  Trained - 40L/min
• Heart rate response to submaximal exercise:

  Before exercise -

  At rest, low resting heart rate of 60bpm.

  Anticipatory, caused by release of adrenaline.

  During exercise -

  Heart rate rapidly increases to 150bpm because of increased oxygen demand and venous return.

  Plateau, steady state as oxygen supply equals oxygen demand.

  After exercise -

  Heart rate rapidly decreases.

  Gradual return to resting heart rate.
• Heart rate response:

  Submaximal - lower heart rate reached, plateau and oxygen supply equals oxygen demand.

  Maximal - higher heart rate reached, no plateau and works at a higher intensity.
• Stroke volume response to exercise:

  Maximum SV values are reached during submaximal exercise as ventricles are at full stretch and can’t hold any more blood so they cant pump anymore out. During intense maximal exercise SV may reduce slightly as the heart is beating so quickly it doesn’t have to fill completely.
• Stroke volume is dependant on:

  Venous return - volume of blood returning to the heart and the greater venous return the greater volume of blood available in ventricles to eject. Starlings law states the higher venous return the higher stroke volume.

  Ventricular elasticity and contractibility - degree of stretch in cardiac muscle, an increased atria/ventricular stretch the increased force of contraction and it raises SV as more blood can be forced out per beat.
• Cardiac output response to exercise:

  Venous return increases as more blood returns to the right atrium, more blood can be ejected from ventricles increasing SV, SA node fires quicker increasing HR and if SV and HR increases so does CO.
• Regulation of heart rate: Neural control

  Chemoreceptors - detect chemical changes, located in muscles/aorta/carotid arteries.

  Proprioceptors - detect changes in movement, located in muscles/tendons/joints.

  Baroreceptors - detect changes to blood pressure, located in blood vessel walls.

  These detect changes and inform CCC located in the medulla oblongata.
• Neural control during exercise:

  Chemoreceptors detect a decrease in oxygen and increase in carbon dioxide, proprioceptors detect an increase in movement and baroreceptors detect an increase in blood pressure. This is sent to the CCC and stimulates the sympathetic nervous system, impulses are sent down the accelerator nerve which stimulates the SA node to increase heart rate.
• Neural control during recovery:

  Chemoreceptors detect an increase in oxygen and a decrease in carbon dioxide, proprioceptors detect a decrease in movement and baroreceptors detect a decrease in blood pressure. This is sent to the CCC via the parasympathetic nervous system, impulses are sent down the vagus nerve which inhibits the SA node to decrease heart rate.
• Intrinsic control during exercise:

  Body temperature - the higher the temperature the faster nerve transmission so the SA node fires quicker, thinner blood travels faster causing a faster HR.

  Venous return - increased VR increases ventricle stretch/increases force and speed of contraction/increases SV which directly stimulates SA node to increase HR.
• Intrinsic control during recovery:

  Body temperature - the lower the temperature the slower nerve transmission so SA node fires slower causing a slower HR.

  Venous return - decreased VR decreases ventricle stretch/force and speed of contraction/SV and HR.
• Hormonal control during exercise:

  Adrenaline is released from adrenal glands which directly stimulates the SA node increasing the speed of electrical activity through the heart (increasing HR)/force of ventricular contraction (increasing SV), sympathetic nervous system is stimulated.
• Hormonal control during recovery:

  Release of adrenaline is inhibited by parasympathetic nervous system, SA node is stimulated less causing the HR to lower.
• Arteries and arterioles

  • Transport blood away from the heart
  • Arterioles have a large layer of smooth muscle meaning both vessels can vasodilate/constrict to regulate blood flow and control blood pressure
  • Arterioles have a ring of smooth muscle surrounding the entry of a capillary bed (pre capillary sphincter) which dilate and constrict to control the Blood flow through the capillary bed
• Capillaries

  • Bring blood directly in contact with tissues where oxygen and carbon dioxide are exchanged
  • One cell thick and have a large surface area
• Veins and venules

  • Transport blood back towards the heart
  • Have a small layer of smooth muscle that venodilates/constricts to maintain the slow flow of blood towards the heart
• Pocket valves

  • One way valves located in the veins which prevent back flow of blood
  • Used all the time and during exercise
• Muscle pump

  • Skeletal muscles contract compressing the veins located between them squeezing the blood back to the heart
  • Used during exercise
• Respiratory pump

  • During inspiration/expiration a pressure difference between the thoracic and abdominal cavity is created squeezing and sucking blood back to the heart
  • Used during exercise
• Smooth muscle

  • Layer of smooth muscle in vein walls that venoconstricts to create venomotor tone and aid movement of blood
  • Used all the time and during exercise
• Gravity

  • Blood from the upper body (above the heart) is aided to return by gravity
  • Used all the time and during exercise
• Mechanisms of venous return:

  Pocket valves

  Muscle pump

  Respiratory pump

  Smooth muscle

  Gravity
• Active cool down is important for venous return as it maintains the action of the muscle and respiratory pump, it maintains venous return, removes carbon dioxide/lactic acid from the body and takes oxygen rich blood to muscles, and it prevents blood pooling (where blood sits int he pocket valves causing dizziness).
• Redistribution of CO during exercise:

  Rest -

  CO is 5L/min, muscles get 20% (1L/min) and organs get 80% (4L/min).

  Submaximal -

  CO is 20L/min, muscles get 80% (16L/min) and organs get 20% (4L/min)

  Maximal -

  CO is 40L/min, muscles get 88% (35.2L/min) and organs get 12% (4.8L/min)
• Role of vascular shunt, pre capillary sphincters and arterioles in the distribution of CO:

  At rest -

  Organs are vasodilated allowing 80% of the blood flow to them and muscles are vasoconstricted allowing 20% of the blood flow to them.

  During exercise -

  Organs are vasoconstricted allowing 20% of the blood flow to them and muscles are vasodilaed allowing 80% of the blood flow to them.
• Vasomotor control centre during exercise

  1. Chemoreceptors detect decrease in oxygen and increase in carbon dioxide

  2. Proprioceptors detect increase in movement

  3. Baroreceptors detect increase in blood pressure against arterial walls

  4. VCC increases sympathetic stimulation

  5. Arterioles and pre capillary sphincters vasoconstrict, decreasing blood flow to organs (20%)

  6. VCC decreases sympathetic stimulation

  7. Arterioles and pre capillary sphincters vasodilate, increasing blood flow to muscles (80%)