The Cardiovascular System 7: The Vascular System 1

Arteries are thick-walled blood vessels that carry blood away from the heart to the body tissues under relatively high blood pressure. They have strong and elastic walls that allow them to withstand the pressure generated by the pumping of the heart. Arteries are responsible for delivering oxygenated blood to the tissues and organs throughout the body.

The pulmonary arteries are the only arteries in the adult body that carry deoxygenated blood. All other arteries carry oxygenated blood.

Arteries consist of three distinct layers of tissues. These layers are known as the tunica interna, tunica media, and tunica externa. The tunica interna is the innermost layer, also referred to as the tunica intima. It is composed of endothelial cells and a thin layer of connective tissue. The tunica media is the middle layer, consisting of smooth muscle cells and elastic fibers. It provides support and helps regulate blood flow. The tunica externa is the outermost layer, made up of connective tissue and collagen fibers. It provides structural support and protection to the artery.

The tunica interna is the correct answer because it is the only tunic that is present in all types of blood vessels. The tunica interna, also known as the intima, is the innermost layer of blood vessels and is composed of endothelial cells. It is found in all types of blood vessels, including arteries, veins, and capillaries. The tunica externa and tunica media are present in some blood vessels but not all, while the elastic lamina is a specific layer found in arteries. Therefore, the tunica interna is the only tunic that is consistently present in all types of blood vessels.

When arterial smooth muscles are stimulated, they contract, causing a reduction in the diameter of the blood vessel. This process is known as vasoconstriction.

The tunica interna is composed of a simple squamous epithelium called endothelium that rests on a basement membrane containing both elastic and collagenous fibers. It is an extension of the endocardial lining of the heart. Its extreme smoothness prevents abnormal blood clotting, and the endothelial cells also secrete biochemicals that inhibit platelet aggregation.

The internal elastic lamina is a layer that separates the tunica intima from the tunica media in arteries. It is only found in arteries and is composed of elastin, a protein that provides elasticity and strength to the arterial walls. This layer helps maintain the structure and function of the arteries, allowing them to expand and contract with the flow of blood.

Fenestrae are gaps that allow substances to diffuse to nourish the underlying cells. This gives the internal elastic lamina its crinkled appearance.

The tunica media is the middle layer in large arteries and is responsible for maintaining the elasticity and strength of the arteries. It contains several layers of elastic fibers, which allow the arteries to stretch and recoil with each heartbeat. Additionally, the tunica media consists of smooth muscle fibers that help regulate the diameter of the arteries and control blood flow. It also has a thick layer of elastic connective tissue, which further contributes to the elasticity of the arteries.

The correct answer is "tunica externa, thin, elastic collagen, CT fibers". The tunica externa refers to the outer wall of the artery, which is relatively thin in these vessels. It mainly consists of elastic collagen and connective tissue fibers. These fibers attach and anchor the vessel to surrounding tissue.

The tunica externa contains minute vessels called capillaries, which give rise to blood supply and provide a pathway to the more external cells of the arterial wall. These vessels are known as vasa vasorum, which means vessels of vessels.

The elasticity of arteries allows them to passively change their diameter in response to changes in blood pressure. This enables the arteries to withstand the force of the blood and also stretch to accommodate the sudden increase in blood volume that accompanies each ventricular contraction.

The term "contractility" refers to the ability of arteries to actively change their diameter. This process is controlled by the sympathetic division of the autonomic nervous system. Specifically, the smooth muscle of the tunica media layer of arteries is innervated by the sympathetic nervous system.

When sympathetic input is inhibited, it means that the sympathetic nervous system, which is responsible for the "fight or flight" response, is not activated. In this state, the smooth muscle fibers in the blood vessels relax, causing the diameter of the blood vessels to increase. This increase in diameter is known as vasodilation, which allows for increased blood flow and decreased blood pressure.

Arterioles are small arterial branches that deliver blood to a capillary network. These vessels are microscopic in size and their structures resemble that of the large arteries. However, as they approach the capillaries, their walls become thinner and thinner.

The smaller arterioles that lead to the capillaries consist of their endothelium surrounded by only a single layer of smooth muscle fibers. This arrangement allows for precise control of blood flow and regulation of blood pressure. The endothelium acts as a barrier between the blood and the surrounding tissue, while the smooth muscle fibers can contract or relax to adjust the diameter of the arterioles, thereby controlling the amount of blood flow to the capillaries.