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Blood and the respiratory system
Blood and the respiratory system

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In Act 1, Scene 3 of William Shakespeare’s The Merchant of Venice, Shylock asks Antonio:

… shall I bend low, and in a bondman’s key with bated breath and whisp’ring humbleness say this: “Fair sir, you spet on me on Wednesday last… and for these courtesies I’ll lend you thus much moneys”?

(Shakespeare, 1605, p.28)

Shylock is mockingly implying that he is holding his breath in eager anticipation of lending Antonio money. Although written many years before the physiology of respiration was understood, Shakespeare recognised that breathing is a dynamic process that responds to changes in the environment.

In this course, you have learnt how exchange of O2 and CO2 is mediated by physical factors such as pressure gradients and chemical changes such as bicarbonate buffering and pH. The airways, musculoskeletal system, lungs and nervous system act in concert to make sure that adequate levels of O2 are maintained throughout the body.

Here is a summary of the main points that have been covered in this course:

  • The respiratory system comprises structures that conduct air into and out of the lungs. The conduction zone includes the nasal passages, pharynx, larynx, bronchi and bronchioles. Gas exchange occurs in the respiration zone of the bronchioles, alveolar ducts and alveoli.
  • Exchange of O2 and CO2 is influenced by pressure (atmospheric and partial), surface tension, lung compliance and airway resistance. These factors are altered by respiratory disorders such as asthma, smoking and COPD, which also influence lung capacity.
  • The majority of O2 is carried in the blood bound to haemoglobin that is present in erythrocytes. Most of the CO2 is carried in the blood as bicarbonate, whereas a smaller percentage also binds to haemoglobin.
  • Recessive polymorphisms in the haemoglobin genes can cause anaemias such as sickle cell anaemia and thalassaemia, but may confer protection against infectious disease.
  • Changes in PCO2 and PO2 are detected by chemoreceptors located in the heart, blood vessels and brain. Respiratory centres in the medulla communicate via the peripheral nervous system with the muscles that control ventilation.

This OpenLearn course is an adapted extract from the Open University course SK299 Human biology [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .