M01.10.05 Artery

The arterial system is essential in distributing oxygenated blood from the heart to tissues throughout the body. Each type of artery has distinct structural adaptations suited to its functional demands. Here’s an overview of the histological features of muscular arteries, with a focus on the coronary arteries.

1. Overview of Arterial Structure

Arteries are typically composed of three primary layers:

• Tunica Intima: The innermost layer, consisting of endothelial cells, a subendothelial layer, and a thin internal elastic lamina.
• Tunica Media: The middle layer, primarily smooth muscle cells interspersed with elastin, providing structural integrity and elasticity.
• Tunica Adventitia: The outer layer, made up of connective tissue, collagen, and elastin fibers, supports the vessel.

Each layer varies in thickness and structure between different types of arteries, allowing them to meet specific circulatory requirements.

2. Histology of Muscular Arteries

Muscular arteries, also called distributing arteries, include the coronary arteries. They regulate blood flow to various organs and are adapted to their high-pressure environment.

• Tunica Intima: Contains an endothelium, subendothelial connective tissue, and a prominent internal elastic lamina that appears as a wavy line under a microscope.
• Tunica Media: Composed of multiple layers of smooth muscle cells interspersed with elastic fibers. The smooth muscle here is capable of vasoconstriction and vasodilation, allowing the artery to adjust its diameter based on physiological needs.
• Tunica Adventitia: Thinner than the tunica media, it contains connective tissue and sometimes small blood vessels (vasa vasorum) that supply the outer layers of the artery itself.

Key Features:

• Thick tunica media with high smooth muscle content.
• Internal and external elastic laminae visible under histological staining.

3. Histology of the Coronary Arteries

Coronary arteries, as muscular arteries, exhibit unique features to support continuous blood flow under varying pressures, essential for myocardial perfusion.

• Tunica Intima: The endothelial layer here is closely associated with the subendothelial connective tissue and an internal elastic lamina. In the coronary arteries, the intima may thicken with age or in response to atherosclerotic changes.
• Tunica Media: Characterized by a high concentration of smooth muscle cells, similar to other muscular arteries, but with slightly more elastic fibers to help accommodate pulsatile blood flow to the heart muscle.
• Tunica Adventitia: Contains vasa vasorum, as well as sympathetic and parasympathetic nerve fibers. These nerves help regulate vasodilation and vasoconstriction based on cardiac demand.

Large coronary artery

Key Features:

• Adapted to withstand continuous pulsatile flow.
• Rich sympathetic innervation allows dynamic regulation of blood flow.
• Prone to atherosclerosis, especially with aging or high-risk factors.

4. Clinical Relevance: Coronary Artery Disease (CAD)

The coronary arteries are prone to atherosclerosis, where plaques form within the tunica intima, leading to a reduced lumen and compromised blood flow. CAD can lead to myocardial ischemia, angina, and myocardial infarction if left untreated.

Summary Points

• Muscular Arteries: Thick tunica media for vasoconstriction/vasodilation, distinct internal and external elastic laminae.
• Coronary Arteries: Similar to other muscular arteries but have added elasticity and vasa vasorum. Vulnerable to atherosclerotic changes impacting cardiac function.