What you need to know
- 7.13(i)Calculate cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate..
- 7.13(ii)heart rateThe number of heartbeats per minute. and ventilation rate are controlled by the cardiovascular control centreThe region in the medulla oblongata that controls heart rate through nerves to the SAN. and the ventilation centreThe region in the medulla oblongata that controls the rate and depth of breathing. in the medulla oblongata.
- 7.14adrenalineA hormone from the adrenal glands that prepares the body for action, for example by raising heart rate. in the fight or flight response.
Spirometer volumes are 7B 8. The full nervous system is Topic 8, so name these medulla centres and their effects without a reflex-arc essay. Adrenaline is not a peptide-hormone transcription lesson; that is 7C 1. Numbers below are illustrative.
By the end, you should be able to…
- Calculate cardiac output from heart rate and stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat., with units.
- State how the two medullary centres change heart rate and ventilation.
- Describe adrenaline’s role in fight or flight without a drug dose.
Build your understanding
Cardiac output is a product
cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. is the volume of blood one ventricleA lower chamber of the heart. Its thick muscular wall pumps blood into an artery. pumps per minute. Cardiac output = heart rateThe number of heartbeats per minute. × stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat.. Heart rate is beats per minute. Stroke volume is the volume ejected per beat. Keep the volume unit consistent. Illustrative rest: 70 beats per minute × 70 cm³ = 4900 cm³ per minute, which is 4.9 dm³ per minute. These are round teaching numbers, not your pulse.
In exercise both heart rate and stroke volume can rise, so cardiac output rises. Illustrative exercise: 140 × 110 cm³ = 15400 cm³ per minute = 15.4 dm³ per minute. A higher cardiac output delivers oxygen faster and removes carbon dioxide faster, alongside the increase in ventilation. Do not call cardiac output a rate of breathing.
Follow the process
If you are given the time for one cardiac cycleThe sequence of events in one heartbeat: atrial systole, ventricular systole and diastole., heart rate = 60 ÷ time in seconds. Illustrative: one cycle takes 0.833 s, so heart rate = 60/0.833 = 72 beats per minute. Stroke volume 75 cm³ gives cardiac output = 72 × 75 = 5400 cm³ per minute = 5.4 dm³ per minute. Rearrange the same product if the question gives cardiac output and asks for stroke volume. These figures are a method, not a resting value to memorise.
Follow the process (continued)
Exercise control, in the order to write: working muscle produces more carbon dioxide → carbon dioxide in the blood lowers pHA measure of how acidic or alkaline a solution is, based on its H⁺ ion concentration. Below 7 is acidic, above 7 is alkaline. → chemoreceptors inform the medulla → the ventilation centreThe region in the medulla oblongata that controls the rate and depth of breathing. increases rate and depth of breathing, and the cardiovascular centre makes the sinoatrial nodeThe pacemaker: a patch of tissue in the right atrium wall that sends out a wave of excitation across the atria. fire more often. adrenalineA hormone from the adrenal glands that prepares the body for action, for example by raising heart rate., in a sudden demand, also raises heart rate and the force of contraction. Neither centre nor the hormone starts the beat. The SAN still does.
Centres in the medulla
The cardiovascular control centreThe region in the medulla oblongata that controls heart rate through nerves to the SAN. and the ventilation centre are in the medulla oblongata. Chemoreceptors detect a rise in carbon dioxide and the associated fall in blood pH, and they inform these centres. The ventilation centre then increases the rate and depth of breathing. The cardiovascular centre sends nerve impulses that raise the heart rate at the SAN. A fall in carbon dioxide does the opposite.
The heart remains myogenicDescribes heart muscle that contracts by itself, without needing nerve impulses.. The centre does not “tell every cell to contract”. It changes how often the SAN fires. Low oxygen can also stimulate chemoreceptors, but carbon dioxide is the main driver of ventilation you should write first. Topic 8 will add more nervous-system detail. Here, name the centres and the effects.
Adrenaline is the fight or flight hormone
In a sudden threat or a sudden demand, the adrenal glands release adrenaline. It increases heart rate and the force of contraction, so cardiac output rises. breathing rateThe number of breaths taken per minute. increases and bronchioles widen, which supports a higher ventilation. Blood is directed toward skeletal muscle. Together with the nerve supply to the SAN, this prepares the body for rapid ATPAdenosine triphosphate: the molecule that releases energy for cell processes when it is hydrolysed to ADP and Pi. use.
Adrenaline is not a treatment plan and not a dose. Do not describe an auto-injector. In this specification it is the hormone of the fight or flight response. It modifies the myogenic heart. It does not replace the SAN.
NOT: the brain does not start each heartbeat, and cardiac output is not a sum.
- Cardiac output = heart rate x stroke volume
- Carbon dioxide is the main ventilation signal
- Both centres are in the medulla
- The SAN remains the pacemaker
Two traps this diagram blocks
- Do not add heart rate to stroke volume.
- Do not say adrenaline replaces the sinoatrial node.
From the diagram alone
Question
Explain how a rise in blood carbon dioxide increases both breathing and heart rate. [4]
Show a model answer
Chemoreceptors detect the rise in carbon dioxide and the fall in pH. They inform the medulla. The ventilation centre increases the rate and depth of breathing, and the cardiovascular centre makes the sinoatrial node fire more often.
Make your reasoning visible
Build the explanation
X happens because Y, leading to Z. X: both breathing and heart rateThe number of heartbeats per minute. rise in exercise. Y: extra carbon dioxide lowers blood pHA measure of how acidic or alkaline a solution is, based on its H⁺ ion concentration. Below 7 is acidic, above 7 is alkaline. and chemoreceptors report that to the medulla. Z: the ventilation centreThe region in the medulla oblongata that controls the rate and depth of breathing. increases breathing, and the cardiovascular centre increases how often the sinoatrial nodeThe pacemaker: a patch of tissue in the right atrium wall that sends out a wave of excitation across the atria. fires, so oxygen delivery and carbon dioxide removal both speed up. Incomplete: “The brain makes the heart beat.” Improved: “The SAN still starts each beat. The medulla only changes the rate, using the carbon dioxide signal.”
Units on the product
beats/min × cm³/beat = cm³/min. Divide by 1000 if you want dm³/min.
CO₂ before a nerve essay
High CO₂, chemoreceptor, medulla, then heart rate and ventilation.
Avoid this misconception
The claim: cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. is heart rate plus stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat., and the brain starts each beat.
The correction: Cardiac output is heart rate multiplied by stroke volume. The SAN starts each beat. The medulla and adrenalineA hormone from the adrenal glands that prepares the body for action, for example by raising heart rate. change the rate.
Who speeds up your heart when you run?
The SAN starts every heartbeat. In exercise, extra CO₂ is detected and the medulla raises how often the SAN fires and how deeply and often you breathe. In a fright, adrenaline does the same to the heart.
What the model shows
A fictional person resting, running and recovering, or having a fright, with the control pathway lit up and cardiac output worked out.
What to look for
Which arrows light first, how cardiac output = heart rate × stroke volume changes, and what still happens with the nerve cut.
What it tells us
Cardiac output is a product. The ventilation and cardiovascular centres in the medulla respond to CO₂. Adrenaline raises heart rate and force. The heart is myogenic.
Be careful what you claim
Illustrative values only.
Try it in the model: press Play and watch the arrows from the muscle to the medulla.
Heart rate, breathing and adrenaline
Follow a fictional person through 2 minutes of rest, 6 minutes of activity and 8 minutes of recovery, or a sudden fright, and watch CO₂, the medulla and adrenaline change heart rate and breathing. All values are illustrative.
What you see
- A control diagram: working muscle, blood CO₂ and pH, chemoreceptors, the ventilation and cardiovascular centres in the medulla oblongata, the lungs, the heart with its SAN, and the adrenal glands. Arrows light up when a signal is passing.
- A timeline of 2 minutes at rest, 6 minutes of activity or a fright, and 8 minutes of recovery, with cardiac output on the graph and the working on the card.
How to use it
- Choose the activity, Exercise or Fright, and whether the nerve from the centre to the SAN is connected. Then play or drag Time.
What it shows
- Cardiac output = heart rate × stroke volume, with units (7.13).
- How the medulla’s centres raise heart rate and ventilation in response to CO₂ (7.13), and how adrenaline acts in fight or flight (7.14).
Limits of the model
- All values are illustrative and round, not anyone’s pulse. Real control also involves stretch receptors, temperature and signals from the brain at the start of exercise.
- Cutting the nerve is a thought experiment to show the heart is myogenic, not a procedure.
Guided tour · step 1 of 8
In Session, just below these steps, press Play and let it run past minute 4.
Working muscle respires faster and makes more CO₂. CO₂ in the blood lowers its pH. Chemoreceptors detect this and inform the medulla oblongata. The ventilation centre increases the rate and depth of breathing, and the cardiovascular centre makes the SAN fire more often.
Session
Questions
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Calculate cardiac output if heart rate is 60 beats per minute and stroke volume is 80 cm³. Give the unit.
Show suggested answer
4800 cm³ per minute, or 4.8 dm³ per minute.
Practice question
Retrieval and explanation · suggested answer
Where are the cardiovascular control centre and the ventilation centre?
Show suggested answer
In the medulla oblongata.
Practice question
Retrieval and explanation · suggested answer
How does a rise in blood carbon dioxide change ventilation?
Show suggested answer
Chemoreceptors detect it. The ventilation centre increases the rate and depth of breathing.
Practice question
Retrieval and explanation · suggested answer
State two effects of adrenaline in the fight or flight response.
Show suggested answer
Any two of: higher heart rate, stronger contraction, higher cardiac output, faster breathing, widened bronchioles, more blood flow to skeletal muscle.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Illustrative: at rest, heart rate 60 and stroke volume 75 cm³. During a fright, heart rate doubles and stroke volume rises by 20 cm³. Calculate both cardiac outputs. Does the fright response have to be exercise? Assume adrenaline was released.
Show a hint
Multiply each pair. Then use 7.14.
Explore the reasoning
Rest: 60 × 75 = 4500 cm³/min. Fright: heart rate 120, stroke volume 95, so 120 × 95 = 11400 cm³/min. Adrenaline can cause this pattern in fight or flight without a training session. The volumes are invented. A real ECG or a real diagnosis is not implied.
Recall this lesson
Lesson recall questions
Question 1 of 5: How does increasing stroke volume as well as heart rate raise oxygen delivery?
Cardiac output and ventilation control
Practice question
Retrieval and explanation · suggested answer
How does increasing stroke volume as well as heart rate raise oxygen delivery?
Lesson: 7B 7: Controlling the Heart and Breathing Rates
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Activity changes the rate; the node still starts the beat
7B · Controlling the Heart and Breathing RatesThe British Heart Foundation describes the heartbeat as starting at the sinoatrial node, and the pace as changing with activity and emotion. That supports the split you need:…Specification 7.13(i)Read & use the scienceClose article
Why this matters
The British Heart Foundation describes the heartbeat as starting at the sinoatrial node, and the pace as changing with activity and emotion. That supports the split you need: the SAN is the origin, and the rate is adjustable. Their page does not set out adrenaline or the medulla by name, so do not pretend it lists 7.14. 7.13 and 7.14: cardiac output, medullary control of rate, and adrenaline in fight or flight.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.13(i) Calculate cardiac output.
Use the science
Why is “the BHF says adrenaline is the pacemaker” an over-reading?
Explore a possible response
The page describes the sinoatrial node starting the signal and the pace changing with activity. Adrenaline is a specification hormone that modifies rate. It is not the pacemaker, and it is not a claim you should paste onto that page.
Explore the source
- British Heart Foundation: how a healthy heart worksBritish Heart Foundation
Stress hormones are measurable chemistry
7B · Controlling the Heart and Breathing RatesMedlinePlus describes catecholamines, including epinephrine or adrenaline, as hormones released during physical or emotional stress. Their effects include increased heart rate and blood flow to muscles. A clinician…Specification 7.14Read & use the scienceClose article
Why this matters
MedlinePlus describes catecholamines, including epinephrine or adrenaline, as hormones released during physical or emotional stress. Their effects include increased heart rate and blood flow to muscles. A clinician can measure catecholamines in blood or urine, but one high value needs context because stress, timing and other causes matter. The connection to 7.14 is a blood-borne signal that changes an organ’s activity; the sinoatrial node remains the origin of a normal heartbeat. A faster pulse is therefore not proof that adrenaline alone caused it, and it is not evidence that the medulla oblongata has stopped controlling rate.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.14 Adrenaline in the fight-or-flight response.
Use the science
How can adrenaline increase heart rate without becoming the heart’s pacemaker?
Explore a possible response
Adrenaline changes the rate at which pacemaker cells fire and affects cardiac activity. The sinoatrial node remains the source of the normal initiating electrical impulse.
Explore the source
- Catecholamine testsUS National Library of Medicine