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What are the three layers of a blood vessel?
Tunica intima, tunica media and tunica adventitia
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What type of blood vessel only consists of the tunica intima?
Capillary
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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
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What are the different subdivisions of afferent vessels (arteries)?
- Elastic arteries
- Muscular arteries
- Arterioles
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Give an example of an elastic artery
The aorta
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What is the function of the aorta?
To conduct blood at high pressure and shock absorption (the elastic component dampens pulsatory blood flow)
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Which tunic is the most developed in the aorta?
Tunica media
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What is the tunica media mainly composed of in the aorta?
Elastic fibres arranged in laminae (sheets)
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What is the vasa vasorum?
Small blood vessels in the tunica adventitia that nourish the outer 2/3 of the tunica media and adventitia
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What is the function of muscular arteries?
To distribute blood in relation to varying demand throughout the body
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List the layers of a muscular artery
Tunica intima, prominent internal elastic lamina, tunica media, tunica adventitia
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What is the tunica media mainly composed of in muscular arteries?
Mainly smooth muscle and elastic fibres
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What nervous system regulates the smooth muscle in muscular arteries?
Sympathetic nervous system
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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)
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How many layers of smooth muscle are in a metarteriole?
One
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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
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Give examples of different types of microcirculation
- Precapillary spinchters
- Precapillary anastamosis
- Arterial portal system
- Venous portal system
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What is a precapillary sphincter?
A single band of smooth muscle located in capillary beds
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What is the role of precapillary sphincters?
Through contraction/relaxation they direct blood flow to different parts of a capillary bed
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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
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Give an example of an a) arterial portal system b) venous portal system?
- a) kidney glomerulus
- b) hepatic portal system
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Give two adaptations of capillaries that make them good at gas exchange
- Thin wall
- High surface area:volume ratio
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What is a pericyte?
An undifferentiated cell that can differentiate into a smooth muscle cell to change a capillary into a metarteriole
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What are the three different types of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Sinusoids
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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)
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Which is more permeable - continuous or fenestrated capillaries?
Fenestrated capillaries
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What structure do sinusoids lack?
Basal lamina
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Where would you find sinusoids in the body?
Liver and spleen
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What are the different subdivisions of efferent vessels (venous system)?
- Venules (post capillary and muscular venules)
- Large, medium and small veins
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What is the function of efferent vessels?
Capacitance/storage of blood
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What is the function of an a) post capillary venule b) muscular venule?
- a) exchange
- b) capacitance
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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.
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What is the function of valves within veins?
To prevent back flow of blood and act as muscular pumps
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Give an example of a large vein
Caudal vena cava
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What tunic is most prominent in the caudal vena cava?
The tunica adventitia
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True or false: lymphatic vessels have valves?
True
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What do lymphatic vessels carry?
Lymph
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