AS LEVEL- Biology- Transport in Animals (1)

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  • Transport in animals (1)
    • Need for transport systems
      • High metabolic demands- lots of nutrients are needed
      • Small SA:V ratio- Large diffusion distances within the body
      • Hormones + enzymes are made in one place + needed in another
      • Food is digested down in one organ + breakdown products are needed in another
      • Waste products are produced in all cells but need to be transported to excetory organs
    • Circulatory systems
      • Open- *Very few blood vessels *transport medium flows in direct contact with the tissues *Returns to the heart through an open ended vessel* Doesn't carry O2 or CO2 but transports food, nitogeous waste + cells involved in the immune system
      • Closed- *Transport medium contained in blood vessels *Not in direct contact with the tissues *Medium is under pressure as it's pumped around the body + returns back to the heart + Pressure of blood is maintained *Blood flows faster + blood flow can be directed
      • Single- *Blood flows through the heart once in each circulation *Blood passes through two sets of capillaries before returning back to the heart *Pressure is quite low so returns to the heart very slowly
      • Double- *Blood passes through the heart twice in each complete circulation *Blood is pumped to the lungs + then goes back *Blood is then pumped around the whole body before going back to the heart *Blood only passes through one capillary network in each pump *Pressure is maintained
    • Blood vessels
      • Arteries
        • Strcture-*Thick wall- Small lumen which maintains pressure *Thick layer of elastic fibres- Stretch + recoil narrowing the lumen which helps maintain pressure *Thick layer of smooth muscle- Contracts to narrow the lumen to maintain pressure of the blood *Smooth endothelium- reduces friction so allows blood to flow easily *Thick layer of collagen- Provides strength + gives the limit to what it can stretch to withstand pressure
        • Function- Carries oxygenated blood AWAY from the heart to the body
      • Arterioles
        • Structure- *Lots more smooth muscle in the wall- Contract + relax to control the blood flowing into the capillary networks *Less elastic fibres- Blood has less surge as they are further away from the heart
        • Function-Carries oxygenated blood AWAY from the heart to the body
      • Capillaries
        • Structure- *Walls are one cell thick- Provides a short diffusion pathway *Diameter of lumen is 7.5-8 micrometers- Red blood cells travel in a single file giving more room for exchange *Gaps are present between the walls fo the endothelium cells which allow substances to be exchanged
        • Function- Links the arterioles + venules. They form an extensive network through all of the tissues of the body + are the main site of exchange
      • Venules
        • Structure-*Very thin walls *Very little elastic fibres *Smooth muscle *No valves
        • Function-  Carries deoxygenated blood from the body TO the heart
      • Veins
        • Structure- *Large lumen- To contain the large volume of blood + to reduce friction as less blood is in contact with the endothelium *Endothelium is smooth- Reduces friction *Thin layer of elastic fibres- There is no surge in blood so they don't have to stretch in response *Thin layer of smooth msucle *Thick layer of collagen- For strength to prevent the vwin from collapsing under low pressure
        • Function-  Carries deoxygenated blood from the body TO the heart


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