DP Biology (last assessment 2024)
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6.2 The blood system

Description

Nature of science:
Theories are regarded as uncertain—William Harvey overturned theories developed by the ancient Greek philosopher Galen on movement of blood in the body. (1.9)Understandings:

  • Arteries convey blood at high pressure from the ventricles to the tissues of the body.
  • Arteries have muscle cells and elastic fibres in their walls.
  • The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.
  • Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillary.
  • Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.
  • Valves in veins and the heart ensure circulation of blood by preventing backflow.
  • There is a separate circulation for the lungs.
  • The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.
  • The sinoatrial node acts as a pacemaker.
  • The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles.
  • The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.
  • Epinephrine increases the heart rate to prepare for vigorous physical activity.

Applications and skills:

  • Application: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump.
  • Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.
  • Application: Causes and consequences of occlusion of the coronary arteries.
  • Skill: Identification of blood vessels as arteries, capillaries or veins from the structure of their walls.
  • Skill: Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure.

Theory of knowledge:

  • Our current understanding is that emotions are the product of activity in the brain rather than the heart. Is knowledge based on science more valid than knowledge based on intuition?

Utilization:

  • Understanding of the structure of the cardiovascular system has allowed the development of heart surgery.

Syllabus and cross-curricular links:
Biology
Topic 2.2 Water
Topic 2.3 Carbohydrates and lipids
Topic 6.4 Gas exchange
Topic 6.6 Hormones, homeostasis and reproduction

Aims:

  • Aim 6: A heart dissection is suggested as a means of studying heart structure.
  • Aim 8: The social implications of coronary heart disease could be discussed.

 

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