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2.7.10Inquiry Process

The Mammalian Heart — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 82 of 160

📚 IB Biology HL Hub / Topical Revision
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Section 1 of 4Structure and Blood Flow

2.7.10 The Mammalian Heart

The septum keeps oxygenated and deoxygenated blood apart.

1
Deoxygenated blood from the body enters the right atrium through the vena cava.
2
It passes through the tricuspid valve into the right ventricle, which pumps it through the pulmonary valve into the pulmonary artery towards the lungs.
3
Oxygenated blood returns through the pulmonary veins into the left atrium.
4
It passes through the bicuspid valve into the left ventricle, which has a much thicker muscular wall.
5
The left ventricle pumps blood through the aortic valve into the aorta for distribution around the body.

Section 2 of 4Controlling the Heartbeat

Myogenic contraction
  • Cardiac muscle contracts on its own without nerve stimulation; the heart is therefore described as myogenic.
Sinoatrial node
  • A cluster of cells in the right atrium wall acts as the pacemaker, sending waves of excitation across both atria.
Atrioventricular node
  • The wave reaches this node, which delays it briefly so that the atria finish emptying before the ventricles contract.
Conducting fibres
  • The signal then passes down the septum and through Purkyne fibres, so the ventricles contract from the apex upwards.
ChamberWall thicknessPumps blood to
Right ventricleThinnerLungs
Left ventricleThickestWhole body

Section 3 of 4Modifying Heart Rate

Modifying Heart Rate
Cardiovascular centre
  • The medulla oblongata adjusts heart rate in response to carbon dioxide and pH detected by chemoreceptors.
Sympathetic nerve
  • Impulses from this nerve speed up the pacemaker and raise heart rate during exercise or stress.
Vagus nerve
  • Impulses along the vagus nerve slow the pacemaker and lower heart rate during rest.
Adrenaline
  • This hormone from the adrenal glands increases the rate and force of contraction.

Section 4 of 4Exam Checklist & Tips

2.7.10 – Key Points for the Exam

  • Myogenic Initiating its own contraction without a nerve impulse, as cardiac muscle does.
  • Sinoatrial node The natural pacemaker of the heart located in the right atrium.
  • Atrioventricular valve A valve between atrium and ventricle that prevents backflow into the atrium.
  • Septum The muscular wall separating the left and right sides of the heart.
  • Purkyne fibres Specialised fibres that spread the signal rapidly through the ventricle walls.

Common Mistakes

  • Saying the heart is neurogenic because it is controlled by the brain; nerves only adjust the rate.
  • Labelling the left side of the diagram as the viewer's left, when it is the patient's left.
  • Forgetting that the pulmonary artery carries deoxygenated blood.
  • Stating that the atria and ventricles contract together.

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