Artery Histology
Arteries
- Carry blood away from the heart; vessel diameter decreases as we move down the arterial tree.
- Walls comprise
- Tunica intima (inner): smooth endothelial cells reduce friction with blood flowing through the vessel lumen.
- Tunica media (middle): comprises smooth muscle cells and fenestrated sheets of elastic tissue; the elastic allows for recoil.
- Tunica adventitia (outer): tunica adventitia is the collagenous outermost layer; vaso vasorum are small blood vessels that travel through this layer in larger arteries.
Artery Types
Elastic arteries
- Include the aorta, the largest artery in the body
- Abundant elastic fibers in tunica media
Muscular arteries
- Include the arteries that distribute blood to major body regions (such as the femoral artery in the thigh)
- Have thick layer of tunica media, abundant smooth muscle cells
- Two distinct sheets of elastic tissue not identified in our histological samples:
- The external elastic lamina lies just deep to the tunica adventitia, and covers the tunica media
- Internal elastic lamina deep to basement membrane
Arterioles
- The smallest arterial vessels; these carry blood to the capillary beds in target tissues
- Larger arterioles comprise all three tunics (smaller arterioles may not)
- Despite having only a few layers of smooth muscle cells in their tunica media, arterioles are the primary site of blood flow regulation
Smooth muscle cells
- Vascular smooth muscle cells (VSMC) display phenotypic plasticity, as they can function as contractile or synthesizing units depending on environmental signals
- As contractile cells, vascular smooth muscle cells maintain arteriole tone to regulate local blood flow
- Synthesize extracellular components, including elastic, reticular, and collagenous fibers
- Inflammation triggers the synthesis of extracellular components, which exacerbates plaque formation
- May facilitate plaque stability by maintaining fibrous caps