- Of large caliber (or conduction) → have a diameter between 3 cm and 0.7 cm.
- Medium-sized (or distribution) → have a diameter between 7 mm (0.7 cm) and 0.1 mm.
- Arterioles → arteries that have a diameter of 100 μ (0.1 mm) down.
Let's now go to see the different characteristics of these types of artery.
- Large gauge
This class of arteries has 3 tonics, which from inside to outside are:
- The intimate tunic is made up of a simple endothelium (simple pavement epithelium) resting on a lamina of loose connective tissue (basal lamina). Between the inner layer and the external tunic there is a thin elastic lamina called internal elastic lamina.
- The medium tunic is made up of a series of overlapping layers of elastic membranes.In the space between these membranes are collagen fibrils and a few smooth muscle fibrocellules, arranged concentrically. Between the medium and the external cassock the external elastic lamina is present.
- The adventitia habit is relatively thin, formed of fibrillar connective tissue with collagen and elastic fibrils. Since this wall is the most external and therefore the furthest from the lumen of the vase, it can not draw nourishment directly from the blood of the vessel. Its tropism is due to the vasa vasorum, a network of small vases that run in the thickness of this wall.
- Medium caliber
Also this class of arteries has a three-toned structure.
- The intimate tunic is very similar to that of the large caliber arteries, or a thin layer of endothelial cells resting on the connective lamina. Also in this case between the inner and the lower tunic the internal elastic lamina is present.
- The medium tunic is characterized by the important presence of smooth muscle fibrocellules arranged either circularly or helically. We have called the medium-caliber "distribution" arteries, and this is because, thanks to the medium muscle tonic, they play an important role in regulating blood pressure. The external elastic lamina is present between the medium and the external tunic.
- The adventitia habit is very thin, connectivale and presents vasa vasorum.
- Small caliber
- Intimately made of endothelium, with little visible elastic lamina.
- Medium tunic consisting of two or three layers of smooth muscle fibrocellules arranged circularly.
- Very thin adventitia , connectivale.