➔ Right side
Right atrium and right ventricle. They deal with deoxygenated blood. The right ventricle pumps blood to the lungs.
Animal Tissues, Organs and Systems » The Heart
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.2.2.2
- How the heart pumps blood around a double circulatory system
- The four chambers of the heart and where blood goes next
- The blood vessels joined to the heart, including the coronary arteries
- How the natural pacemaker and artificial pacemakers control heart rate
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Unlock This CourseThe heart as a pump
Your heart is an organ made mostly of muscle tissue. It beats about 70 times a minute at rest, pushing blood around your body without ever stopping. Blood carries oxygen and dissolved food to every cell and carries waste away.
Humans have a double circulatory system. That means the blood travels through the heart twice on every full trip around the body:
- Circuit 1: the heart pumps blood to the lungs, where gas exchange takes place. The blood picks up oxygen and returns to the heart.
- Circuit 2: the heart pumps this oxygen-rich blood around the rest of the body, then the blood returns to the heart again.
Key terms:
- Double circulatory system: a system in which blood passes through the heart twice on each complete circuit of the body.
- Oxygenated blood: blood carrying a lot of oxygen.
- Deoxygenated blood: blood carrying little oxygen.
The four chambers
The heart has four chambers. The two at the top are the atria (one is an atrium). They receive blood coming into the heart. The two at the bottom are the ventricles. They pump blood out of the heart.
➔ Left side
Left atrium and left ventricle. They deal with oxygenated blood. The left ventricle pumps blood around the rest of the body.
The two sides are kept apart, so oxygenated and deoxygenated blood do not mix inside the heart.
Key terms:
- Atrium: an upper chamber of the heart that receives blood.
- Ventricle: a lower chamber of the heart that pumps blood out.
The blood vessels of the heart
Four large blood vessels carry blood into and out of the heart, and you need to know their names. Follow the blood and the names fall into place.
- The vena cava brings deoxygenated blood from the body into the right atrium.
- Blood passes to the right ventricle.
- The pulmonary artery takes deoxygenated blood from the right ventricle to the lungs.
- The pulmonary vein brings oxygenated blood from the lungs into the left atrium.
- Blood passes to the left ventricle.
- The aorta takes oxygenated blood from the left ventricle to the body.
The word pulmonary means "to do with the lungs", so the pulmonary artery and vein are the vessels linked to the lungs.
Something odd to remember
Vessels that carry blood away from the heart are called arteries, and vessels that carry blood towards it are called veins. So the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood. The direction of flow decides the name, not the oxygen content.
Feeding the heart itself
The blood inside the heart's chambers does not feed the heart muscle. The muscle gets its own supply from the coronary arteries. These branch from the aorta and run over the surface of the heart. They carry oxygen and glucose to the heart muscle so it can respire and keep contracting.
Key term:
- Coronary arteries: blood vessels that supply the heart muscle with oxygenated blood.
The natural pacemaker
The natural resting heart rate is controlled by a group of cells in the right atrium. These cells act as a pacemaker. They send out regular electrical signals that make the heart muscle contract, and so they set the pace of the heartbeat.
Artificial pacemakers
Sometimes the natural pacemaker does not work properly and the heart beats too slowly or in an uneven way. An artificial pacemaker is an electrical device that corrects irregularities in the heart rate. It sends regular electrical signals to the heart to keep it beating at the right rate.
Key terms:
- Pacemaker: a group of cells in the right atrium that controls the natural resting heart rate.
- Artificial pacemaker: an electrical device used to correct irregularities in the heart rate.
Worked example
Trace a drop of blood that has just returned from the big toe. It enters the heart through the vena cava into the right atrium, then the right ventricle. It leaves through the pulmonary artery and goes to the lungs. It comes back through the pulmonary vein into the left atrium, then the left ventricle. It leaves through the aorta and travels to the body. It has passed through the heart twice, which is why the system is called double.
Common mistakes
Many students put the left side of the heart on the left of the page. A diagram shows the heart as if you are facing the person, so the left side of the heart is on the right of the page. Others forget that the pulmonary vein carries oxygenated blood. Check each vessel by asking: is the blood going to the heart or away from it, and where is it going or coming from?
Exam-style question
(a) Explain why the heart is described as part of a double circulatory system. [2 marks]
(b) Name the blood vessel that carries blood from the left ventricle to the body. [1 mark]
(c) Describe the job of the coronary arteries. [2 marks]
(d) A patient's heart beats irregularly. Suggest how a doctor can correct this. [1 mark]
Model answer
(a) Blood passes through the heart twice on each circuit of the body (1). It is pumped to the lungs and then back to the heart before it is pumped to the rest of the body (1).
(b) The aorta (1).
(c) They supply the heart muscle (1) with oxygen and glucose, or oxygenated blood (1).
(d) Fit an artificial pacemaker (1).
Exam tip
In "name the vessel" questions, check the direction of flow first. Blood leaving the left ventricle goes into the aorta. Blood leaving the right ventricle goes into the pulmonary artery.