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