Location of VSMCs in the blood vessel wall

The vessel wall is made up of three distinct layers which vary slightly in composition between individual arteries/veins. The layer which is exposed to the circulating blood is the tunica intima, which is covered on the lumenal side by a single flattened sheet of endothelial cells lying on basement membrane of collagen type IV. In some arteries, such as the aorta and coronary arteries, there are also VSMCs in the intima. The role of the intima is to provide a smooth, non-thrombogenic surface and to act as a permeability barrier to cells and macromolecules. Beneath the intima is the internal elastic lamina, which is a sheet of fenestrated elastic fibres. The cell layer beneath this is the tunica media which contains longitudinal, spirally arranged SMCs interspersed with elastin fibers and an extracellular matrix rich in collagen I, fibronectin, and proteoglycans. The VSMCs are surrounded by a basement membrane containing collagen IV, laminin and heparan sulfate [1]. The outermost layer is the tunica adventitia, which is separated from the media by the external elastic lamina, and contains fibroblasts surrounded by collagen, proteoglycan matrix, vasa vasorum and innervation [2] (see Figure 1).

Internal elastic lamina Intima

Figure 1. The blood vessel wall is made up of three distinct layers which vary slightly in composition between different arteries and veins; the tunica intima, the tunica media (containing VSMCs), and the tunica adventitia. These layers are separated by the internal and the external elastic lamina (see section 1.1).

External elastic lamina

Internal elastic lamina Intima

External elastic lamina

Adventitia

Media

Figure 1. The blood vessel wall is made up of three distinct layers which vary slightly in composition between different arteries and veins; the tunica intima, the tunica media (containing VSMCs), and the tunica adventitia. These layers are separated by the internal and the external elastic lamina (see section 1.1).

Adventitia

Media

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