Cardiovascular System


Cardiac conduction system

  • Cardiovascular system- body's transport system which includes the heart and the blood vessels. 
  • During execerise, an effecient cardiovascular system is important as the heart pumps blood through the blood vessels to deliver oxygen to the working muscles and gather waste products e.g. carbon dioxide
  • Blood travels in through the atria and out through the venticles.
  • Heart muscle is myogentic as the beat starts in the tissue itself with an electrical signal in the sinoatrial node (SAN)- mass of cardiac muscle found in the wall of the right atrium that generates the heartbeat.

Electrical signal spreads through the heart in this order:

  • From SAN, the impulse spreads through the wall of the atria causing them to contract (atrial systole)
  • Impulse passes through the atrioventricular node (AVN)- which relays the impulse between the upper and lower sections of the heart- where it is delayed for 0.1 seconds to enable the atria to contract before ventricular systole begins.
  • Impulse then travels through the bundle of his, which branches off in two, and into the Purkinje fibres which causes contraction (ventricular systole)
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Factors affecting the conduction system

Ensures that heart rate increases during exercise to allow the working muscles to receive more oxygen. 

Neutral control mechanism

Involves the sympathetic nervous system which stimulates the heart to beat faster and the parasympathetic nervous system that returns heart rate to resting level. Both co-ordinated in the cardiac control centre in the medulla oblongata.

  • Chemoreptors -> detect increase in blood carbon dioxide-> cardiac control centre -> sympathetic system -> SAN increases heart rate
  • Baroreceptors -> detect increase in blood pressure -> cardiac control centre -> parasympathetic system -> SAN decreases heart rate
  • Proprioceptors -> detect change in muscle movement-> cardiac control centre -> sympathetic system -> SAN increases heart rate. 

Hormonal control mechanism

Adrenaline is released by the sympathetic nerves and cardiac nerves during exercise in order to stimulate the SAN which increases both speed and force of contraction increasing cardiac output. Results in more oxygenated blood being pumped to the working msucles for energy. 

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Impact of physical activity on stroke volume.

Stroke volume- volume of blood pumped out by the left ventricle in each contraction.

  • Venous return- the return of blood to the right side of the heart via the vena cava. When this increases, stroke volume increases. 
  • Starlings law- the elasticity of the cardic fibres increase during the diastole phase to allow for a greater force of contraction. This increases ejection fraction- percentage of blood pumped out of the left ventricle per beat.

Starlings law -> increased venous return -> greater diastolic filling of the heart -> cardiac muscle streched -> more force of contraction -> increased ejection fraction. 

Stroke volume increases as exercise intensity increases. Only the case for up to 40-60% of maximum effort. When a performer reaches this point, stroke volume plateaus as the ventricles do not have enough time to fill up with blood and can't pump as much out. 

Systole occurs when the heart contracts to pump blood out, and diastole occurs when the heart relaxes after contraction

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Impact of physical activity on heart rate.

Heart rate- number of times the heart beats per minute.

In response to exercise:

  • Increases depending on the intensity of exercise. 
  • Higher intensity = higher heart rate. 
  • Trained performer has a greater heart rate range beacuse their resting heart rate is lower and their maximum heart rate increases. 

Regular aerobic training will result in more cardiac muscle. Cardiac hypertrophy- heart becomes stronger due to thickening of the muscular wall. Results in the heart being able to pump more blood per contraction which means in doesnt have to pump as often. 

Known as bradycardia- when there is a decrease in resting heart rate to below 60 beats per minute. When this occurs, oxygen delievery to the muscles improves as there is less oxygen needed for contractions of the heart. 

Maximum heart rate is 220 minus your age. 

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Impact of physical activity on cardiac output.

Cardiac output- volume of blood pumped out of the heart ventricles per minute. If stroke volume or heart rate increases, then cardiac output will increase.

Cardiac output = Stroke volume x Heart rate.

In response to exercise: 

  • Increase in cardiac output due to increase in heart rate/stroke volume. 
  • Will increase with the increase in intensity of exercise until maximum intensity is reached (plateaus)

During exercise, a trained performer will be able to transport more oxygen to the working muscles as they have a greater maximum cardiac output. 

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Impact of physical activity on the health of the p

  • Heart disease- Coronary heart disease occurs when the coronary arteries experience atherosclerosis- become blocked due to a build up of fatty deposits. Caused by high blood pressure, high cholesterol, lack of exercise and smoking. This decreases the supply volume of oxygenated blood to the heart. 
  • High blood pressure- force exerted by the blood against the blood vessel wall. Pressure comes from the heart as it pumps blood around the body. High blood pressure puts extra strain on the ateries and the heart and can increase the chance of heart attacks, heart failure etc. Regular aerobic exercise can reduce blood pressure.
  • Cholesterol levels- Low-density lipoprotiens transport cholestorol in the blood to the tissues- classed as bad since they increase risk of heart disease. High-density lipoprotiens transport excess cholesterol in the blood back to the liver to be broken down. Classed as good as they decrease risk of heart disease. Regular aerobic exercise helps reduce LDL levels and increase HDL levels. 
  • Stroke- occurs when the bloody supply to the brain is cut off, causing the barin cells to die. Can led to brain damage, disability and death. Two types of stroke:
    • Ischaemic strokes: blood clot stops supply of blood to the brain.
    • Haemorrhagic strokes: weakened blood vessel supplying the brain bursts. 
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Cardiovascular drift

Cardiovascular drift- a progressive decrease in stroke volume and arterial blood pressure, together with a progressive rise in heart rate despite intensity remaining the same. 

  • Occurs during prolonged exercise in a warm enviroment. 
  • Reduction in plasma volume occurs from the increase in sweating response of the body. This in return reduces venous return and stroke volume. 
  • Heart rate therefore increases to compensate and maintain cardiac output

Cardiovascular drift occurs because:

  • Heart rate increases and stroke decreases
  • after 10 minutes in a warm conditions
  • caused by reduced plasma volume
  • reduced venous return
  • cardiac output increases due to more energy needed to cool the body/sweat
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Blood vessels

Veins- transport deoxygenated blood back to the heart (with the exception of the pulmonary vein)

  • Have thin, muscle/elastic tissue layers
  • Valves to prevent backflow of blood
  • Lumen is large to ensure the low pressure of blood is transported effeciently

Arteries- transport oxygenated blood around the body (with the exception of the pulmonary artery)

  • Have thick, elastic walls and thick layers of muscle
  • Small lumen to ensure high blood pressure is maintained as it travels around the body.

Capillaries- slows down blood flow and allows the exchange of nutrients with the tissus to take place by diffusion.

  • one cell thick to allow one red blood cell through at one time.
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Blood pressure

Blood pressure- force exerted by the blood against the blood vessel wall 

Blood flow x Resistance

During exercise, the heart contracts with more force so blood leaves the heart under higher pressure so the working muscles recieve the extra oxygen they require.

This is the systolic pressure (when the ventricles are contracting)

The lower pressure occurs when the ventricles relax (diastolic pressure)

Blood pressure is different in the various blood vessels due to distance of the vessels from the heart. 

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Venous return

Venous return- return of blood to the right side of the heart via the vena cava

  • 70% of the total volume of blood is conatained in the veins at rest, meaning a large volume of blood can be returned when needed (exercise)
  • During exercise, the amount of blood returning to the heart (venous return) increases.

Active mechanisms aid venous return:

  • Skeletal muscle pump- When muscles contract/relax they change shape which means the muscles press on nearby veins and cause a pumping effect- squeezing the blood towards the heart
  • Respiratory pump- the muscles that are used during inhalation and exhalation cause a change in pressure in the chest and abdominal cavities. This compresses nearby veins and squeezes the blood towards the heart.
  • Pocket valves- ensures blood travels in one direction (towards the heart) and prevent backflow
  • Thin layer of muscle in the walls of the veins to help squeeze the blood back to the heart
  • Gravity helps return blood to the upper half of the body.

When systolic blood pressure increases, venous return increases as the pressure in the blood vessels are higher so the blood travels quicker. 

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Transportation of oxygen

  • 3% dissolves into plasma.
  • 97% combines with haemoglobin to form oxyhaemoglobin.

At the tissues, oxygen is released from oxyhaemoglobin due to the lower pressure of oxygen that exists there. This is known as oxyhaemoglobin dissociation. 

In the muscles, oxygen is stored by myoglobin- stores oxygen in the muscle fibres which can be used quickly when exercise begins. Has a higher affinity for oxygen that haemoglobin and will store the oxygen in the microchondria ("powerhouse of the cell"- where respiration and energy production occurs) until it is utilsed by the muscles. 


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Oxyhaemoglobin dissociation curve

Helps us understand how haemoglobin in our blood carries and releases oxygen. The curve represents the relationship between oxygen and haemoglobin.

At rest the high partial pressure of oxygen in the lungs means the haemoglobin is saturated with oxygen. In the tissues, the partial pressure of oxygen is lower, so the haemoglobin gives some of its oxygen to the tissues

During exercise, the curve shifts to the right. This is because when muscles require more oxygen, the dissociation of oxygen from haemoglobin in the blood capillaries to the muscle tissue occurs more readily. This shift is known as the Bohr shift - when an increase in blood carbon dioxide and a decrease in blood PH results in a reduction of the affinity of haemoglobin and oxygen.

Three factors for the increase in dissociation of oxygen from haemoglobin so more oxygen is readily available for the working muscles (remember the word blood):

  • Increase in blood temperature during exercise 
  • Partial pressure of blood carbon dioxide increases during exercise
  • Blood pH- more carbon dioxide will lower the pH in the body. This causes oxygen to dissociate form haemoglobin more quickly (Bohr shift)
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Redistribution of blood

During exercise, muscles require more oxygen so more blood needs to be redirected to them in order to meet the increase in oxygen demand. 

Vascular shunt mechanism- the redistribution of cardiac output.

This mechanism is important to ensure:

  • More blood goes to the heart, because it needs more oxygen to beat faster with more force
  • More blood goes to the working muscles, as they need more oxygen for energy and waste products to be removed such as carbon dioxide and lactic acid. 
  • More blood goes to the skin to cool the body down
  • Blood flow to the brain remains constant to mainatin function

Important to ensure the gut is empty as a full gut woud result in more blood being directed towards the stomach instead of the working muscles. This would have a negative effect on performance as less oxygen will be readily availble. 

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Control of blood flow

Blood pressure and blood flow are controlled by the vasomotor centre located in the medulla oblongata.

During exercise, increase in carbon dioxide and lactic acid are detected by the chemoreceptors, which stimulates the vasomotor centre and redistributes blood flow through vasoconstriction and vasodilation. 

Vasoconstriction- narrowing of the blood vessels to reduce blood flow to the capillaries. 

Vasodilation- widening of the blood vessels to increase blood flow to the capillaries. 

In exercise, vasodilation will occur in the aterioles to supply the working muscles with more oxygen. Whereas vasodilation will occur in the arterioles supplying non-essential organs such as the intestines and liver. 

Pre-capillary sphincters aid blood redistribution as the tiny rings located at the opening of the capillaries contract, blood flow is restricted. When they relaxed, blood flow increases. 

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Arterio-venous difference (A-V02 diff)

A-VO2- difference between the oxygen content of the arterial blood arriving at the muscles and the venous blood leaving the muscles. 

The difference in the volume of oxygen in the arteries and the veins. 

At rest, A-VO2 diff is low, as not much oxygen is required by the muscles. 

During exercise, more oxygen is needed from the blood for the muscles, so the A-VO2 diff is high. This increase will affect gaseous exchange at the alveoli, so more oxygen is taken in and more carbon dioxide is removed. 

Training increases the A-VO2 diff as trained performers can extract a greater amount of oxygen from the blood.

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