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Biology IB HL - 6.2 The Blood System Part 3
This deck covers key concepts about the blood system, focusing on capillaries, veins, and venules. It includes the structure and function of these components, as well as the mechanisms that aid blood flow.
What do capillaries join back into?
After material exchange has occurred, capillaries will pool into venules which will in turn collate into larger veins
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Key Terms
Term
Definition
What do capillaries join back into?
After material exchange has occurred, capillaries will pool into venules which will in turn collate into larger veins
What are capillaries surrounded by? What is the purpose?
They are surrounded by a basement membrane which is permeable to necessary materials
What may be present in the endothelial layer of capillaries?
They may contain pores to further aid in the transport of materials between tissue fluid and blood
What holds endothelial cells together?
The capillary wall may be continuous with endothelial cells held together by tight junctions to limit permeability of large molecules
What may capillaries look like in kidneys?
In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores)
What does it mean if a capillary is sinusoidal? Where might it be found?
Some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells (e.g. in liver)
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| Term | Definition |
|---|---|
What do capillaries join back into? | After material exchange has occurred, capillaries will pool into venules which will in turn collate into larger veins |
What are capillaries surrounded by? What is the purpose? | They are surrounded by a basement membrane which is permeable to necessary materials |
What may be present in the endothelial layer of capillaries? | They may contain pores to further aid in the transport of materials between tissue fluid and blood |
What holds endothelial cells together? | The capillary wall may be continuous with endothelial cells held together by tight junctions to limit permeability of large molecules |
What may capillaries look like in kidneys? | In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores) |
What does it mean if a capillary is sinusoidal? Where might it be found? | Some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells (e.g. in liver) |
What forces materials into tissue fluid? | The higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid |
What is carried in tissue fluid back into the venules? | Materials that enters the capillaries at body tissues include carbon dioxide and urea (wastes produced by the cells) |
What is the function of veins? | Veins transport blood to the heart at low pressure |
What blood pressure do veins receive? | They receive blood that has passed through capillary networks, across which pressure has dropped due to the slow flow of blood |
How does the structure of the tunica media differ in veins? | The tunica media is much thinner in veins |
Why is the tunica media thinner in veins? | There is no need for a thick muscular and elastic layer as veins don't have to maintain or withstand high pressure |
How does the lumen of veins differ from arteries? | The lumen of veins is much wider in diameter than that of arteries |
What is the purpose of the larger lumen in veins? | 3 | A larger lumen helps to ensure that blood returns to the heart at an adequate speed A large lumen reduces friction between the blood and the endothelial layer of the vein The rate of blood flow is slower in veins but a larger lumen means the volume of blood delivered per unit of time is equal |
What special feature do veins have? | These prevent the back flow of blood that can result under low pressure, helping return blood to the heart |
What helps push blood through veins? | Movement of the skeletal muscles pushes the blood through the veins, and any blood that gets pushed backwards gets caught in the valves; this blood can then be moved forwards by the next skeletal muscle movement |
Can a pulse be found in veins? | A pulse is absent in veins; the pressure changes taking place due to the beating of the heart are no longer present |
What is the role of venules? | Venules connect the capillaries to the veins |
What is the composition of venules? | They have few or no elastic fibres and a large lumen |
Why do venules have few or no elastic fibres? | As the blood is at low pressure after passing through the capillaries there is no need for a muscular layer to maintain pressure |
Why do venules have a large lumen? | The large lumen enables a large volume of blood to be transported |
How do skeletal muscles help in the passage of blood? | When the skeletal muscles contract, they squeeze the vein and cause the blood to flow from the site of compression |
Apart from skeletal muscles, what other contraction can help push blood up veins? | Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse |
Why is a circulatory system needed? | All organisms need to transport materials to where they are needed inside their tissues |
What is the alternative to a circulatory system and when is it used? | Small organisms (or relatively inactive animals like jellyfish) can rely on diffusion alone to transport oxygen, carbon dioxide and nutrients around their bodies |