Choose one of the following topics for your initial post:
A. Let's start by discussing the structure of our blood vessels. Let's each take a characteristic of (1) arteries, (2) veins, or (3) capillaries. Build upon wh
...
Choose one of the following topics for your initial post:
A. Let's start by discussing the structure of our blood vessels. Let's each take a characteristic of (1) arteries, (2) veins, or (3) capillaries. Build upon what your classmates say to enable us to have a fuller understanding of these vessels that are essential for our existence.
All blood vessels are composed of three layers: the tunica intima, tunica media, and tunica adventitia except the capillaries have only a tunica intima layer.
• Tunica intima (also called tunica interna) -inner most layer - is simple squamous epithelium surrounded by a connective tissue basement membrane with elastic fibers.
• Tunica media - middle layer - is primarily smooth muscle and is usually the thickest layer. It not only provides support for the vessel but also changes vessel diameter to regulate blood flow and blood pressure
• Tunica externa (also called tunica adventitia) - outermost layer - which attaches the vessel to the surrounding tissue. This layer is connective tissue with varying amounts of elastic and collagenous fibers. The connective tissue in this layer is quite dense where it is adjacent to the tunic media, but it changes to loose connective tissue near the periphery of the vessel.
Arteries:
Arteries carry blood away from the heart.
Pulmonary arteries transport blood that has a low oxygen (deoxygenated) content from the right ventricle to the lungs.
Systemic arteries transport oxygenated blood from the left ventricle to the body tissues There are two main types of arteries found in the body:
• Elastic arteries: nearest the heart (aorta and pulmonary arteries) that contain much more elastic tissue in the tunica media than muscular arteries which allows them to maintain a relatively constant pressure gradient despite the constant pumping action of the heart.
• Muscular arteries: contain more smooth muscle cells in the tunica media layer than the elastic arteries.
Veins:
Veins carry blood toward the heart. After blood passes through the capillaries, it enters the smallest veins, called venules. From the venules, it flows into progressively larger and larger veins until it reaches the heart.
In the pulmonary circuit, the pulmonary veins transport blood from the lungs to the left atrium of the heart. This blood has a high oxygen content because it has just been oxygenated in the lungs. Systemic veins transport blood from the body tissue to the right atrium of the heart. This blood has a reduced oxygen content because the oxygen has been used for metabolic activities in the tissue cells.
The walls of veins have the same three layers as the arteries but there is less smooth muscle and connective tissue. This makes the walls of veins thinner than those of arteries, which is related to the fact that blood in the veins has less pressure than in the arteries.
Almost 70 percent of the total blood volume is in the veins at any given time because veins can hold more blood due to the fact that the walls of the veins are thinner and less rigid than arteries.
Medium and large veins have venous valves, similar to the semilunar valves associated with the heart, that help keep the blood flowing toward the heart. Venous valves are especially important in the arms and legs, where they prevent the back flow of blood in response to the pull of gravity.
Capillaries:
Capillaries, the smallest and most numerous of the blood vessels, form the connection between the vessels that carry blood away from the heart (arteries) and the vessels that return blood to the heart (veins).
The primary function of capillaries is the exchange of materials between the blood and tissue cells.
Capillaries are thin-walled vessels composed of a single endothelial layer. Because of the thin walls of the capillary, the exchange of nutrients and metabolites occurs primarily via diffusion. The arteriolar lumen regulates the flow of blood through the capillaries. Capillaries have only a tunica intima layer and no smooth muscle is present. About 5 percent of the total blood volume is in the systemic capillaries at any given time.
References
• SEER Training Modules. Classification & Structure of Blood Vessels. U. S. National Institutes of Health, National Cancer Institute. Retrieved January 26, 2023, from: https://training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html
https://training.seer.cancer.gov/images/anatomy/cardiovascular/artery_wall.jpg
https://training.seer.cancer.gov/images/anatomy/cardiovascular/vein.jpg
https://training.seer.cancer.gov/images/anatomy/cardiovascular/capillaries.jpg
• Tucker, W. D., Arora, Y., & Mahajan, K. (2022). Anatomy, Blood Vessels. In StatPearls.
StatPearls Publishing. Retrieved January 26, 2023, from: https://pubmed.ncbi.nlm.nih.gov/29262226/
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