Syllabus Edition

First teaching 2023

First exams 2025

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Changes in Blood Supply to Organs (HL) (HL IB Biology)

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Naomi H

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Naomi H

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Changes in Blood Supply to Organs

  • The role of the circulatory system is to supply the cells of the body with oxygen and nutrients, and to remove the waste products of metabolism
  • The requirements of the cells in different parts of the body will differ depending on the activity levels of the body, e.g.
    • During exercise the muscles will require more oxygen and glucose to fuel muscle contraction, so will need an increased blood supply
    • After a meal the digestive system will require more oxygen and glucose to fuel digestion and absorption, so will need an increased blood supply
  • The circulatory system can divert blood flow to increase or decrease the blood supply to different organs
    • This is achieved by vasodilation or vasoconstriction in the arterioles that supply the capillary beds in different parts of the body
  • The blood supply to the organs may change as follows:
    • Skeletal muscles
      • During sleep the skeletal muscles are relaxed and blood flow to these muscles is relatively low
      • During wakefulness some muscle groups will be working to keep the body upright, and blood flow will increase
      • There will be a large increase in blood flow during physical exercise, as rapid contraction of many muscle groups will occur
    • Gut
      • Soon after a meal the blood flow to the gut will increase
      • Blood flow decreases during exercise so that more blood can be diverted to the skeletal muscles
    •  Brain
      • The blood flow to the brain remains relatively constant regardless of the activity levels of the body, as it carries out processes that need to occur all the time
      • Blood flow increases slightly during a stage of sleep known as REM
    • Kidneys
      • Blood flow does not change significantly on the basis of activity level, but will increase slightly during sleep and rest, and decrease slightly during prolonged exercise

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.