1.1b cardiovascular and respiratory systems

• the cardiovascular system refers to the heart (Cardiac muscle), blood vessels and the blood they contain. they form a closed system transporting oxygen, nutrients and hormones to every corner of the body and removing waste products as they are produced. at the core is the heart, a dual pump moving blood through two separate circuits
• pulmonary circuit

  circulation of blood through the pulmonary artery to the lungs and pulmonary vein back to the heart
• systemic circuit

  circulation of blood through the aorta to the body and vena cava back to the heart
• the more efficient a body's cardiovascular system the greater the capacity to transport oxygen to the muscles and the greater the capacity to remove waste products such as carbon dioxide and lactic acid. for an aerobic athlete, this is essential to maximise energy production and delay the onset of fatigue
• the structure of the heart

  the heart is divided into two sides separated by the septum, with an atrium at the top and ventricle at the bottom. this keeps oxygenated and deoxygenated blood separated
• the left side of the cardiac muscle has a thicker muscular wall, which can contract with more force to circulate oxygenated blood from the lungs through the large systemic circuit to the muscles and organs

  the right side of the cardiac muscle contracts to circulate deoxygenated blood from the body through the pulmonary circuit to the lungs
• between the atria and ventricles are the atrio-ventricular (AV) valves and between the ventricles and exiting blood vessels are the semi-lunar (SL) valves which prevent the backflow of blood
• the pathway of blood through the heart

  blood is oxygenated at the lungs and brought back to the left atria via the pulmonary vein. oxygenated blood moves from the left atrium through the bicuspid valve into the left ventricle to be forced out of the left side of the heart into the aorta, which carries the oxygenated blood to the muscles and organs.

  deoxygenated blood from the muscles and organs arrives at the right atria via the vena cava and then through the tricuspid valve into the right ventricle, where its forced out of the heart by the pulmonary artery, where it is taken to the lungs
• the conduction system

  the cardiac muscle is myogenic. it has the capacity to generate its own electrical impulses that pass through the muscular walls, forcing them to contract. the conduction system is a set of five structures which pass the electrical impulse through the cardiac muscle in a co-ordinated fashion

  SA node --> AV node --> Bundle of His --> bundle branches --> purkinje fibres
• 1. sinoatrial (SA) node. located in the right atrial wall, the SA node generates the electrical impulse and fires it through the atria walls, causing them to contract. the SA node is also known as the "pacemaker" as the firing rate will determine heart rate
• 2. Atrioventricular (AV) node. the AV node collects the impulse and delays it for 0.1 seconds to allow the atria to finish contracting. it then releases this impulse to the bundle of His
• 3. Bundle of His. located in the septum of the heart, the Bundle of His splits the impulse into two, ready to be distributed through each separate ventricle
• 4. Bundle branches. these carry the impulse to the base of each ventricle
• 5. purkinje fibres. these distribute the impulse through the ventricle walls, causing them to contract
• the cardiac cycle

  the cardiac cycle is the process of cardiac muscle contraction and the movement of blood through its chambers. one complete cardiac cycle represents the sequence of events involved in a single heart beat. it is referred to as a cycle as it never stops. at rest, one complete cycle takes 0.8 seconds and has two distinct phases

  1. cardiac diastole: the relaxation phase of of cardiac muscle where the chambers fill with blood
  2. cardiac systole: the contraction phase of cardiac muscle where the blood is forcibly ejected into the aorta and pulmonary artery
• diastole

  • as the atria and then ventricles relax, they expand drawing blood into the atria
  • the pressure in the atria increases opening the AV valves
  • blood passively enters the ventricles
  • SL valves are closed to prevent blood from leaving the heart
• atrial systole

  • the atria contract, forcing remaining blood into the ventricles

  ventricular systole

  • the ventricles contract, increasing the pressure closing the AV valves to prevent backflow into the atria
  • SL valves are forced open as blood is ejected from the ventricles into the aorta and pulmonary artery
• Conduction system controlling the cardiac cycle

  1. No electrical impulse causes diastole and the cardiac muscle relaxes

  2. SA node fires and electrical impulse through the atria walls to the AV node. AV node delays the impulse. this causes atrial systole and the atrial muscle contracts

  3. Bundle of His splits and passes the impulse through two branches to the purkinje fibres in both ventricle walls, causing ventricular systole and the ventricular muscle contracts

  4. AV valves close and blood is pushed into the arteries forcing SL valves open until the ventricles finish contracting

  5. SL valves close, atria fill with blood opening the AV valves. blood starts to enter the ventricles

  6. AV valves are forced open and blood is pushed into the ventricles until the atria finish contracting
• heart rate

  the number of times the heart beats per minute. resting heart rate is approximately 72bpm

  • trained athlete
  • rest: 50bpm
  • sub-maximal: 95-120bpm
  • untrained performer
  • rest: 72bpm
  • sub-maximal: 100-130
• stroke volume

  the volume of blood ejected from the left ventricle per beat

  • trained performer
  • rest: 100ml
  • sub-max/max: 160-200ml
  • untrained performer
  • rest: 70ml
  • sub-max/max: 100-120ml
• cardiac output

  the volume of blood ejected from the left ventricle per minute

  CO = SV X HR

  • trained performer
  • rest: 5l/min
  • sub-max: 15-20ml/min
  • max: 30-40l/min
  • untrained performer
  • rest: 5l/min
  • sub-max: 10-15l/min
  • max: 20-30l/min
• bradycardia


  a resting heart rate below 60bpm
• venous return

  the return of the blood to the right atria through the veins
• sub-maximal exercise

  a low to moderate intensity of exercise within a performer's aerobic capacity
• maximal exercise

  a high intensity of exercise above a performer's aerobic capacity that will induce fatigue
• during sub-maximal intensity exercise, heart rate can plateau as the performer reaches a comfortable, steady state. this plateau represents the supply meeting demand for oxygen delivery and waste removal. there is also

  • an anticipatory rise due to the release of the hormone adrenaline
  • a rapid increase in HR at the start of exercise to increase blood flow and oxygen in line with exercise intensity
  • a steady HR sustained as oxygen supply meets demand
  • a rapid decrease in HR as recovery is entered and the action of the muscle pump is reduced
  • a more gradual decrease in HR to resting levels
• during maximal intensity exercise, heart rate does not plateau as exercise intensity continues to increase. there is still a growing demand for oxygen and waste removal which HR must continually strive to meet.
• stroke volume response to exercise

  stroke volume is able to increase due to the following:

  • increased venous return (the volume of blood that returns to the heart from the body). during exercise, venous return increases, and so there is a greater volume of blood returning to the heart and filling the ventricles. this is due to the squeezing action of muscular contraction around the veins known as the muscle pump
  • the Frank-Starling mechanism, which shows increased venous return leads to an increased strove volume, due to an increased stretch of ventricle walls and so force of contraction
• stroke volume reaches a plateau during sub-maximal intensity due to:

  • increased heart rate towards maximal intensities does not allow enough time for ventricles to completely fill with blood in the diastolic phase. this limits the Frank-starling mechanism
  • this occurs at around 40-60% maximal intensity
• heart rate regulation

  the autonomic nervous system (ANS) involuntarily regulates heart rate and determines the firing rate of the SA node. the higher the firing rate of the SA node, the higher the heart rate. from the medulla oblongata in the brain, the cardiac control centre (CCC) receives information from the sensory nerves and sends direction through motor nerves to change HR
• neural control

  • chemoreceptors located in the muscles, aorta and carotid arteries inform the CCC of chemical changes in the blood stream, such as increased levels of CO2 and lactic acid
  • proprioceptors located in the muscles, tendons and joints inform the CCC of motor activity
  • baroreceptors located in the blood vessel walls inform the CCC of increased blood pressure
• intrinsic control

  • temperature changes will affect the viscosity of the blood and speed of nerve impulse transmission
  • venous return changes will affect the stretch in the ventricle walls, force of ventricular contraction and therefore stroke volume
• hormonal control

  • adrenaline and noradrenaline are released from the adrenal glands increasing the force of ventricular contraction (therefore SV) and increasing the spread of electrical activity through the heart (therefore HR)
• the CCC actions either an increase or decrease in stimulation of the SA node, which will raise or lower heart rate. if an increase in HR is required, the sympathetic nervous system is actioned, releasing adrenaline, noradrenaline and sending stimulation to the SA node via the accelerator nerve. this will increase heart rate. if a decrease in heart rate is required, the parasympathetic nervous system is actioned to inhibit these effects via the vagus nerve, lowering the heart rate
• cardiac control centre (CCC)

  a control centre in the medulla oblongata responsible for HR regulation
• sympathetic nervous system

  part of the autonomic nervous system responsible for increasing HR, specifically during exercise
• parasympathetic nervous system

  part of the autonomic nervous system responsible for decreasing HR, specifically during recovery
• the vascular system

  a dense network of blood vessels and the blood which they carry in one direction around the human body. this ensures oxygen and nutrients are delivered to all respiring cells for energy production, and waste is removed efficiently. the blood is made of 45% cells and 55% plasma fluid, which:

  • transports nutrients such as oxygen and glucose
  • protect and fight disease
  • maintain the internal stability (homeostasis) and regulate temperature
• arteries and arterioles

  carry oxygenated blood from the heart to muscles and organs. the main artery is the aorta and carries blood at a high pressure from the left ventricle. arteries subdivide into arterioles to slow blood flow

  • arteries have a large layer of smooth muscle and elastic tissue to cushion and smooth the pulsating blood flow
  • arterioles have a large layer of smooth muscle allowing vasoconstriction and vasodilation, regulating blood pressure. they also have a ring of smooth muscle surrounding the entry of the capillary bed called pre-capillary sphincters, controlling blood flow
• capillaries

  bring the blood slowly into close contact with the muscle and organ cells for gaseous exchange

  • capillary walls are composed of a single layer of cells, thin enough to allow gas, nutrient and waste exchange