AQA Biology 4.2.2.2
The heart and blood vessels
Your heart is two pumps side by side. Follow the blood through both, then see how arteries, veins, capillaries and lungs are each built for their job.
Triple Science · Foundation tier
Start here
Two fingers on your wrist.
Press two fingers lightly on the inside of your wrist, below your thumb. You can feel a pulse: a surge of blood with every heartbeat.
If you had to guess, is the blood you can feel moving away from your heart, or back towards it?
The heart · a double circulation
Follow one red blood cell round the circuit.
The right side of the heart pumps blood to the lungs. The left side pumps it to the rest of the body. So blood passes through the heart twice on every complete circuit: a double circulatory system.
Stop 1 of 10
The cell is in the vena cava.
Where does it go next?
Thicker on the left
Both ventricles pump the same volume of blood. The left ventricle has the thicker, more muscular wall because it pumps blood all round the body, at higher pressure. The right ventricle only pumps to the lungs.
Valves
Valves between the atria and ventricles, and where the arteries leave the ventricles, stop blood flowing backwards. You don't need their names.
Coronary arteries
The heart muscle can't use the blood passing through its chambers. Coronary arteries branch off the aorta and supply the heart muscle with oxygenated blood.
Pacemakers
A group of cells in the right atrium acts as a natural pacemaker and controls the resting heart rate. An artificial pacemaker is an electrical device that corrects an irregular heart rate.
Blood vessels · structure and function
Arteries away, veins back, capillaries in between.
Artery
- Carries blood away from the heart, at high pressure.
- Thick muscular wall, with elastic fibres that stretch and recoil with each beat.
- Narrow lumen. No valves along its length: the pressure keeps blood moving one way.
Vein
- Carries blood back to the heart, at low pressure.
- Thinner wall and a wide lumen.
- Valves stop the low-pressure blood flowing backwards.
Capillary
- Links arteries to veins, in a dense network through every tissue.
- Wall one cell thick: a short diffusion distance.
- Oxygen and glucose diffuse out to the cells; carbon dioxide and waste diffuse in.
Pressure falls all the way round: highest in the arteries, lower in the capillaries, lowest in the veins.
The lungs · gas exchange
Trachea, bronchi, alveoli, capillaries.
Air passes down the trachea, into the two bronchi, and on to millions of tiny air sacs, the alveoli. Each alveolus is wrapped in a network of capillaries.
Oxygen diffuses from the air in the alveoli into the blood. Carbon dioxide diffuses from the blood into the alveoli, and is breathed out.
- Very large surface area from so many alveoli.
- Thin walls, so a short diffusion distance.
- A dense capillary network and good blood supply, which keeps the concentration gradient steep.
Think again · arteries and veins
“Arteries carry oxygenated blood and veins carry deoxygenated blood.”
Your call
ChooseThe pulmonary vein carries blood from the lungs to the left atrium. Which blood is in it?
Sort
Artery, vein or capillary?
Place each feature with the vessel it belongs to.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Equations · rate calculations
Tap the quantity you want to find.
Equation
Rate of blood flow
Side by side: multiply.
One over the other: divide.
Tap the quantity you want to find.
Written out
rate of blood flow = volume of blood ÷ time
- V
- volume of blood
- cm³ or dm³
- R
- rate of blood flow
- cm³/min or dm³/min
- t
- time
- min
Equation
Heart rate
Side by side: multiply.
One over the other: divide.
Tap the quantity you want to find.
Written out
heart rate = number of beats ÷ time
- N
- number of beats
- beats
- HR
- heart rate
- beats per minute
- t
- time
- min
Command words in this lesson
- Describe
- Say what the structure is like or where blood goes. No reasons needed.
- Explain
- Link each feature to what it does: thick wall, so it withstands high pressure.
- Calculate
- Rate = amount ÷ time, with the time in minutes for a per-minute answer.
Key fact
Blood passes through the heart twice on each circuit. Arteries carry it away from the heart, veins carry it back, and capillaries are where substances are exchanged.
Key note · AQA 4.2.2.2
The heart and blood vessels
- Double circulation: right side → lungs → left side → body. Blood passes through the heart twice per circuit.
- Four chambers. Vena cava → right atrium; right ventricle → pulmonary artery; pulmonary vein → left atrium; left ventricle → aorta.
- Left ventricle has the thickest wall: it pumps to the whole body at higher pressure. Valves stop backflow.
- Coronary arteries supply the heart muscle. Natural pacemaker: cells in the right atrium. Artificial pacemaker: electrical device for an irregular rate.
- Arteries: away, thick elastic wall, high pressure. Veins: towards, valves, low pressure. Capillaries: one cell thick, exchange.
- Lungs: trachea → bronchi → alveoli. Large surface area, thin walls, dense capillary network. Rate = amount ÷ time.
Photograph this card. Tomorrow, cover it and say each line first.
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Mixing up which vessel goes where?
Diagrams are schematic and not to scale. The heart is drawn as you face the patient, so the patient's right side is on your left.