Introduction
In the human body, blood is the fluid that transports oxygen and nutrients to various body tissues. The oxygenated and deoxygenated blood is transported separately to and from the heart. The blood vessels help in the proper circulation of the blood.
What Are the Blood Vessels in the Human Body?
Blood vessels are channels through which blood is circulated throughout the body. The vessels have two closed systems of tubes that begin and end at the heart, like a closed circuit. The heart vessels and blood vessels together form the circulatory system. According to the function and structure, the blood vessels are classified into:
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Arteries.
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Veins.
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Capillaries.
What Are Arterial Blood Vessels?
Arteries carry the blood away from the heart. Arteries help to carry oxygenated blood from the heart to various parts of the body. Blood pumped from the ventricles reaches large elastic arteries, which again branch into smaller arteries and finally give rise to microscopic arteries called arterioles. Arterioles help in the regulation of blood flow into the tissue capillaries. Systemic arteries transport oxygen-rich blood to the blood tissues, and pulmonary arteries transport low-oxygenated blood from the right ventricle to the lungs. Ten percent of the total blood volume is present in the systemic arterial system.
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Structure of Artery:
The arterial wall consists of three layers
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Tunica intima.
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Tunica media.
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Tunica externa or tunica adventitia.
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Tunica Intima:
The innermost layer is also called the tunica interna. It is made up of simple squamous epithelium covered with connective tissue and a basement membrane with elastic fibers.
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Tunica Media:
The middle layer and the thickest layer. It is made up of smooth muscles and helps in providing support for the vessels, changing the diameter of the vessel. This helps in the regulation of blood flow and blood pressure.
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Tunica Externa:
The outermost layer attaches the vessel to the outer surrounding tissues. Consists of connective tissue with varied amounts of elastic fibers and collagen fibers.
This connective tissue layer is dense when adjacent to the tunica media and loose connective tissue when adjacent to the periphery of the vessel.
What Are Capillaries?
Arteries and veins are connected by tiny blood vessels called capillaries. They are the smallest but most numerous. The exchange of materials between the blood and tissue cells is carried out by the capillaries. The metabolically active tissues have an extensive network of capillaries. Skeletal muscle, kidney, and liver have an extensive capillary network, and connective tissue has a less capillary network. The tissues that lack a capillary network are the epidermis of the skin, the lens, and the cornea of the eyes.
What Are Veins?
Veins carry blood toward the heart. From arteries, the blood passes through capillaries and enters the veins. From capillaries, blood enters the smallest veins called venules and progressively flows into the larger veins, and finally reaches the heart. In pulmonary circulation, the pulmonary veins transport the oxygen-rich blood. It reaches the left atrium from the lungs. Systemic veins transport the blood with less oxygen content from various body tissues to the right atrium.
What Is the Structure of Veins?
Similar to arteries, veins also have three layers. The smooth muscle connective tissue is less compared to the arteries. Veins are thinner than arteries, and the blood in veins has less pressure.
Due to the thin and less rigid nature of veins, they can hold more blood than arteries. The veins carry 70 % of the total blood volume. Venous valves are present in medium and large veins to prevent the backflow of blood.
What Are the Functions of Blood Vessels?
The blood vessels help in the transportation of blood to various organs and tissues in the body. The blood helps to deliver oxygen and nutrients to the tissues. Also, carry away carbon dioxide and waste products from the body's organs.
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Arteries:
Strong, macular blood vessels carry oxygen-rich blood from the heart to various body tissues. Arteries pose a larger force and pressure for carrying the blood and do not carry large amounts of blood. Only 10-15 percent of blood is present in the arteries.
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Arterioles:
Smaller blood vessels are branches of the arteries. Arteries and arterioles are flexible and help to maintain blood pressure.
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Capillaries:
Tiny blood vessels that connect the arteries and veins. Capillaries have thin walls where the oxygen and nutrients from the blood can reach the organs and tissues. Other functions are the exchange of nutrients and taking away waste products from the tissues.
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Venules:
Veins begin as tiny venules and gradually get larger. They collect blood from the capillaries.
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Veins:
Deoxygenated blood reaches back to the heart through veins. The thin, less elastic walls help to manage high pressure and volume of blood. The valves present in the veins prevent the backflow of the blood.
What Are the Circulatory Pathways?
The blood vessels are divided to form two circulatory pathways
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Pulmonary circulation.
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Systemic circulation.
Pulmonary Circulation:
The pump for the pulmonary circulation is the right ventricle. The deoxygenated blood from the right ventricle reaches the lungs and transports back the oxygen-rich blood to the left atrium.
Systemic Circulation:
The pump for the systemic circulation is the left ventricle. The functional blood supply to all the body tissues is achieved through this circulation. The body tissues receive oxygen and nutrients through this circulation and carry back carbon dioxide and other waste products. The oxygenated blood is carried from the left ventricle and transported through arteries and capillaries, and reaches the body tissues. From tissues, the deoxygenated blood returns to the venous system and reaches the right atrium of the heart.
What Are the Major Systemic Arteries and Veins?
Systemic arteries are the branches of the aorta. The branches of ascending portion of the aorta are
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Ascending aorta.
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Aortic arch.
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Descending aorta.
The descending aorta divides into
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Thoracic aorta.
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Abdominal aorta.
In systemic circulation, the capillaries merge with venules and converge to form larger veins and reach the superior or inferior vena cava, which opens onto the right atrium.
How Does Fetal Circulation Occur?
Fetal blood circulation depends on maternal circulation, from which oxygen and nutrients are obtained. And also carries away carbon dioxide and waste products.
The umbilical cord has two umbilical arteries and one umbilical vein. Umbilical arteries help to carry fetal blood to the placenta, and from there, it reaches the fetus through the umbilical veins.
Conclusion
Blood vessels carry out proper circulation of the blood throughout the body. Any obstruction of the blood vessels can lead to certain clinical conditions. Keeping the blood vessels healthy is important to improve the circulation and health. Eating a healthy balanced diet, limiting consumption of sodium, cholesterol, and saturated fats is important in maintaining healthy circulation. Other risk factors that cause various heart diseases are alcohol consumption and smoking.
