Histology of Blood Vessels

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  1. What are the three layers of a blood vessel?
    Tunica intima, tunica media and tunica adventitia
  2. What type of blood vessel only consists of the tunica intima?
  3. What are each of the three tunics mainly composed of?
    • Tunica intima - endothelium
    • Tunica media - smooth muscle and elastic fibres, in varying proportions
    • Tunica adventitia - CT with collagen
  4. What are the different subdivisions of afferent vessels (arteries)?
    • Elastic arteries
    • Muscular arteries
    • Arterioles
  5. Give an example of an elastic artery
    The aorta
  6. What is the function of the aorta?
    To conduct blood at high pressure and shock absorption (the elastic component dampens pulsatory blood flow)
  7. Which tunic is the most developed in the aorta?
    Tunica media
  8. What is the tunica media mainly composed of in the aorta?
    Elastic fibres arranged in laminae (sheets)
  9. What is the vasa vasorum?
    Small blood vessels in the tunica adventitia that nourish the outer 2/3 of the tunica media and adventitia
  10. What is the function of muscular arteries?
    To distribute blood in relation to varying demand throughout the body
  11. List the layers of a muscular artery
    Tunica intima, prominent internal elastic lamina, tunica media, tunica adventitia
  12. What is the tunica media mainly composed of in muscular arteries?
    Mainly smooth muscle and elastic fibres
  13. What nervous system regulates the smooth muscle in muscular arteries?
    Sympathetic nervous system
  14. How many layers of smooth muscle are in arterioles?
    Any afferent vessel with less than 5 layers of smooth muscle is classed as an arteriole (rather than a small muscular artery)
  15. How many layers of smooth muscle are in a metarteriole?
  16. What is the function of arterioles?
    The create peripheral resistance to slow the rate of flow and cause a drop in blood pressure, and regulate the amount of blood entering a capillary bed
  17. Give examples of different types of microcirculation
    • Precapillary spinchters
    • Precapillary anastamosis
    • Arterial portal system
    • Venous portal system
  18. What is a precapillary sphincter?
    A single band of smooth muscle located in capillary beds
  19. What is the role of precapillary sphincters?
    Through contraction/relaxation they direct blood flow to different parts of a capillary bed
  20. What is the role of a precapillary anastamosis?
    This allows blood to bypass a whole capillary bed and go straight into the venous system without undergoing gas exchange
  21. Give an example of an a) arterial portal system b) venous portal system?
    • a) kidney glomerulus
    • b) hepatic portal system
  22. Give two adaptations of capillaries that make them good at gas exchange
    • Thin wall
    • High surface area:volume ratio
  23. What is a pericyte?
    An undifferentiated cell that can differentiate into a smooth muscle cell to change a capillary into a metarteriole
  24. What are the three different types of capillaries?
    • Continuous capillaries
    • Fenestrated capillaries
    • Sinusoids
  25. What are fenestrated capillaries?  Give an example of where they might be located
    • Fenestrated capillaries have pores in their walls.  These can either be open or closed.
    • Kidney (open fenestrae), small intestine (closed fenestrae)
  26. Which is more permeable - continuous or fenestrated capillaries?
    Fenestrated capillaries
  27. What structure do sinusoids lack?
    Basal lamina
  28. Where would you find sinusoids in the body?
    Liver and spleen
  29. What are the different subdivisions of efferent vessels (venous system)?
    • Venules (post capillary and muscular venules)
    • Large, medium and small veins
  30. What is the function of efferent vessels?
    Capacitance/storage of blood
  31. What is the function of an a) post capillary venule b) muscular venule?
    • a) exchange 
    • b) capacitance
  32. How can you distinguish veins from arteries on histological section?
    Veins have a thin wall, no elastic laminae and  thin media compared to arteries.  Larger veins also have valves present.
  33. What is the function of valves within veins?
    To prevent back flow of blood and act as muscular pumps
  34. Give an example of a large vein
    Caudal vena cava
  35. What tunic is most prominent in the caudal vena cava?
    The tunica adventitia
  36. True or false: lymphatic vessels have valves?
  37. What do lymphatic vessels carry?
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Histology of Blood Vessels
Vet Med - Module 10
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