controlling the heart and breathing rates

what is cardiac volume

• The volume of blood pumped at each heartbeat

what is cardiac output

• Cardiac output (CO) is the term used to describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time

• An average adult has a cardiac output of roughly 4.7 litres of blood per minute when at rest

• Individuals who are fitter often have higher cardiac outputs due to having thicker and stronger ventricular muscles in their hearts

• Cardiac output increases when an individual is exercising

  • This is so that the blood supply can match the increased metabolic demands of the cells

  • In trained atheltes heart rate begins to increase before the exercise begins

what is heart rate

• Heart rate is the number of times a heart beats per minute

  • This can also be described as the number of cardiac cycles per minute

What is stroke volume

• Stroke volume is the volume of blood pumped out of the left ventricle during one cardiac cycle

how to calculate cardiac output

Cardiac output = heart rate x stroke volume

• The equation can be rearranged to find the heart rate and stroke volume if required:

  • Heart rate = cardiac output ÷ stroke volume

  • Stroke volume = cardiac output ÷ heart rate

• Cardiac output is measured in cm³ min^-1

• Heart rate is measured in beats per min (bpm)

• Stroke volume is measured in cm³

what changes does body do to accommodate cells requiring more oxygen and producing mroe CO2 during exercise?

• Increase the rate and depth of breathing which will increase the amount of oxygen entering the lungs and bloodstream, while getting rid of more carbon dioxide

• Increase the heart rate which will transport the oxygen (and glucose) to the muscles much faster, while removing the additional carbon dioxide produced due to the increased rate of respiration

what is cardiovascular control centre

• Situated in the medulla oblongata of the brain

• It unconsciously controls the heart rate by controlling the rate at which the sinoatrial node (SAN) generates electrical impulses

how are changes in internal environment of the body detected

• Chemical, stretch and pressure receptors called baroreceptors and cehmoreceptors in the lining of the blood vessels and the chambers of the heart send nerve impulses to the cardiovascular cotnrol centre

• The cardiovascular control centre in the medulla oblongata will respond by sending impulses to the SAN along sympathetic or parasympathetic neurones

effect of sympathetic nervous system via autonomic nervous system

• Sympathetic neurones is excitatory so will increase the rate at which the SAN generates electrical impulses, thus speeding up the heart rate

  • These neurones form part of the sympathetic nervous system which prepares the body for action ('fight or flight' response) and increases the heart rate during exercise

what do impulses that travel down sympathetic nerve do? Effect?

• Nerve impulses that travel down the sympathetic nerve from the cardiovascular control centre to heart release noradrenaline to stimulate the SAN

• This increases the frequency of the signals from the pacemaker region, so heart beats more quickly

• Branches of this sympathetic nerve also pass into the ventricles, so they also increase the force of contraction

effect of parasympathetic nervous system via autonomic nervous system

• Parasympathetic neurones are inhibitory and will decrease the rate at which the SAN fires, thus slowing down the heart rate

  • These neurones form part of the parasympathetic nervous system which calms the body down after action ('rest and digest' response) and decreases the heart rate after exercise

what do impulses that travel down parasympathetic neurones do?

• Nerve impulses in parasympathetic nerve release acetylcholine, inhibiting SAN and slowing heart down

what are baroreceptors

• Baroreceptors are found in the aortic and carotid bodies and they are stimulated by high and low blood pressure

• Important in the feedback control of the heart rate during exercise

• At rest, they send a steady stream of signals back through sensory neurons to the cardiovascular control centre in the brain

what do baroreceptors do during exercise?

• At beginning of exercise, the blood vessels dilate in response to hormone adrenaline which is reelased in anticipation of exercise

• Due to vasodialtion, blood pressure falls a little

• This reduces stretch on baroreceptios

• Due to this reduced stimulation the cardiovascular control centre immediately sends signals along sympathetic nerve which screte neurotransmitter noradrenalin

• Noradrenalin binds to receptors on SAN to fire more frequently

• The heart rate speeds up and increase the blood pressure again by constricting blood vessels

What do baroreceptiors do when exercise stops?- low blood pressure

• When exercise stops, blood pressure in the arteries increases as the heart continues to pump harder and faster than it needs to, and so the baroreceptors are stretched

• They respond by sending more sensory nerve impulses to the cardiovascular control centre which sends impulses through parasympathetic system which secrete acetylcholone.

• Acetylcholien binds to receptors on SAN causing it to fire less frequently

• Sow down heart rate and cause blood vessels to become wider and so blood pressure reduces

what are chemoreceptors

• Chemoreceptors are found in the medulla oblongata, as well as in the aortic and carotid bodies

• They are stimulated by changes in the levels of carbon dioxide and oxygen in the blood, as well as blood pH

what do chemoreceptors do when CO2 levels go up and so pH of blood goes down?

• Detected by chemoreceptors which send impulses to cardiovascular control centre

• It sends impulses along sympathetic neurones which secrete the neurotransmitter noradrenaline

  • Noradrenaline binds to receptors on SAN causing it to fire more frequently

• Heart rate speeds up so more blood flow to lungs so more CO2 removed from blood and O₂ / CO₂ and pH levels return to normal

what do chemoreceptors do when low CO2

• Detected by chemoreceptors which send impulses to cardiovascular control centre

• It sends impulses along parasympathetic neurones which secrete the neurotransmitter acetylcholine

  • Acetylcholine binds to receptors on SAN causing it to fire less frequently

• Heart rate slows down and O₂ / CO₂ and pH levels return to normal

what happens to heart rate hwen you are stressed?

• Sympathetic nerve stimulates the adrenal medulla to release hormone adrenaline

• It is carried around body in blood and binds to receptors in target organs eg SAN

• Adrenaline stimulates the cardiovascular contorl centre in the brain, increasing the impulses in the sympathetic neurones which supply heart

• Also causes SAN to increase freq of excitation and so heart rate increases

• Suppleis oyu wiht extra oxygen and glucose for msucles and brian in case you need to run or fight

effect on other blood vessels when you exercise?

• Sympahtetic system sends fewer impulses to many blood vessels causing contraction of smooth muscles lining vessels, thus narrowing or closing vessels

• This diverts blood flow from less important areas to provide mroe blood to heart and muscles