Blood Vessels Flashcards
How many miles of blood vessels are there in the human body ?
60,000
What 3 components do blood vessels always have ?
- Endothelium
- Smooth muscle layer
- Connective tissue
What are the 3 concentric layers that form the structure of blood vessels ?
- Tunica intima
- Tunica media
- Tunica adventitia
What is the tunica intima ?
Endothelial cell layer plus connective tissue in contact with the lumen
What is the tunica media ?
Smooth muscle cells and connective tissue bordered by a distinctive inner boundary (internal elastic lamina) and outer boundary (external elastic lamina) made of elastic fibres
What is the tunica adventitita ?
Connective tissue
What are examples of elastic arteries ?
The aorta and pulmonary trunk
What are features of elastic arteries ?
- Wide lumen
- Very thick walls with a thick tunica media
- Large amounts of elastic fibres and collagen to prevent overexpansion
- Incorporate vasa vasorum into their tunica adventitia to provide oxygen to the smooth muscle cells in the vessel themselves
Features of muscular arteries
- A thick tunica media of smooth muscle to manage high arterial pressure
- Smooth muscle cells orientated in a circular not longitudinal direction
What are arterioles ?
End-arteries found just before entrance to capillary beds
Features of arterioles
- Approx 100um in diameter
- Smooth muscle cells orientated circularly and wrap around vessel
- Smooth muscle wrapping around entrance acts as a sphincter, regulating blood flow
- Pressure needs to be high enough to get through capillaries, but low enough not to rupture them
What are capillaries ?
Thin, fragile blood vessels forming a dense, tight network known as a capillary bed
What is the role of capillaries ?
The principal site of exchange between blood and tissue fluid
What are sinusoids ?
Specialised, widened capillaries that can permit a greater passage of erythrocytes.
They are found in bone marrow, spleen, lymph nodes and liver.
What are the 3 types of capillary endothelium ?
- Continuous- most capillaries
- Fenestrated- capillaries in endocrine glands
- Discontinuous- sinusoids
What do venules do ? What is their main feature ?
Permit the exit of deoxygenated blood from capillary beds.
They don’t have a thick tunica media as pressure is low.
How are varicose veins formed ?
If valves weaken and become incompetent, blood can pool in the veins leading to their distension
What is the blood-brain barrier ?
The interface between blood and the tissues of the brain parenchyma
What features of the BBB create a highly selective barrier ?
- A strong, endothelium
- Specialised tight junctions between endothelial cells
- The presence of additional cell barriers including astrocytes and pericytes
