Histology of Cardiac Muscle & Blood Vessels

Histology of Cardiac Muscle & Blood Vessels

• Blood vessels are composed of three layers: tunica intima, tunica media, and tunica adventitia.
• Arteries carry blood away from the heart; veins carry blood toward the heart.
• Capillaries are the smallest blood vessels.
• The heart wall is comprised of three layers: endocardium (inner layer), myocardium (middle layer), and epicardium (outer layer).
• The endocardium is composed of endothelium and a subendothelial layer.
• The myocardium is the thickest layer, made of cardiac muscle.
• The epicardium is the outermost layer, composed of mesothelium and connective tissue.
• Blood vessels (arteries, veins, and capillaries) have different structural features in different locations, sizes, and functions. This allows for efficient transport and exchange.

Learning Objectives

• Students will describe the microscopic structure of the heart wall.
• Students will identify characteristic microscopic features of cardiac muscle.
• Students will describe the microscopic structure of blood vessel walls.
• Students will compare and contrast the microscopic structure of arteries and veins.
• Students will identify microscopic characteristics of various types of arteries.
• Students will identify microscopic characteristics of various types of veins.
• Students will compare and contrast the microscopic structure of various types of capillaries.

Cardiovascular System

• The cardiovascular system is composed of the heart and blood vessels.
• The heart pumps blood throughout the body.
• Blood vessels are a closed network of tubes that transport blood.
• Arteries transport blood away from the heart.
• Veins carry blood toward the heart.
• Capillaries allow exchange of substances between blood and tissues.

Types of Blood vessels

• Arteries: Transport blood away from the heart. They branch becoming smaller progressively.
• Veins: Transport blood toward the heart. They converge into larger channels as they approach the heart, enlarging progressively.
• Capillaries: Smallest vessels forming a network exchanging materials with tissues.

Clinical Notes

• Atherosclerosis is characterized by thickening of the artery wall due to the accumulation of lipids and other substances.
• Coronary arteries are highly susceptible to atherosclerosis, which can obstruct blood flow to the heart.
• An aneurysm is a localized, blood-filled bulge in an artery wall. This can weaken the artery and cause rupture if not treated.

Characteristics of Various Types of Arteries

• Elastic arteries (e.g., aorta) have a significant amount of elastic tissue in the tunica media.
• Muscular arteries (e.g., femoral, brachial) have a relatively thick tunica media with smooth muscle.
• Arterioles, the smallest arteries, have little smooth muscle.

Characteristics of Various Types of Veins

• Large veins (e.g., vena cavae) have a thin tunica media and prominent tunica adventitia.
• Medium-sized veins have a less developed tunica media and a conspicuous tunica adventitia.
• Venules (small veins) lack a tunica media and connect to capillaries and larger veins.

Characteristics of Various Types of Capillaries

• Continuous capillaries have a complete endothelial lining and are found in many tissues.
• Fenestrated capillaries have pores in their endothelial cells and are found in areas with high exchange rates (e.g., kidneys).
• Sinusoidal capillaries have large gaps in their endothelial lining, facilitating the exchange of large molecules and cells (e.g., liver).

Key Differences between Arteries and Veins

• Arteries have thicker walls and a more elastic tunica media
• Veins have thinner walls, more developed connective tissue, and valves.
• Arteries carry blood away from the heart.
• Veins carry blood towards the heart.

Questions and Answers

• Vasa vasorum are present in the tunica adventitia.
• Internal and external elastic laminae are found in large arteries.
• The structure separating the tunica intima and tunica adventitia in a medium sized vein is at 1.
• The epicardium is homologous to the tunica adventitia.
• The muscular venule has a recognizable tunica media.