Blood Vessels Diagram

Blood vessels are nothing but a network of hollow pipe-like structures that transport blood throughout our body. It forms a major component of the circulatory system along with the heart. They transport not only blood but also the oxygen and nutrients throughout the body tissues. Furthermore, they take carbon dioxide and waste products away from the tissues.

Labelled Diagram of Blood Vessels

Blood Vessels – Description

• There are three major types of blood vessels, namely the veins, arteries and the capillaries.
• The arteries usually transport blood away from the heart, while the veins transport blood towards the heart.
• The arteries mostly carry oxygenated blood, with the exception of umbilical and pulmonary arteries that carry deoxygenated blood to the placenta and lungs, respectively, for oxygenation.
• The veins mostly transport deoxygenated blood from the body tissues to the heart.
• The capillaries are the connecting blood vessels found between veins and arteries. They are the smallest vessels where the nutrients and oxygen are exchanged with tissues.
• The blood vessels in the circulatory system have three tunics or layers – tunica externa, tunica intima and tunica media.
• The tunica externa or tunica adventitia layer comprises the outer connective tissue. It is the thickest layer in veins.
• The middle layer of smooth muscle is the tunica media. This is the thickest layer in arteries and has varying amounts of elastic fibres in the large and medium-sized arteries.
• The inner lining of endothelial cells is called the tunica intima. It is the thinnest layer typically made of simple squamous epithelium. It is surrounded by another thin layer made of connective tissue, and it is interlaced with the help of elastic bands called the internal elastic lamina.
• Furthermore, the arteries can be classified based on the amounts of elastic fibres and smooth muscles that contribute to the thickness of the blood vessels. They can be large elastic arteries, medium muscular arteries and small arteries and arterioles.
• The large elastic arteries have considerable amounts of elastic fibres in the middle layer or the tunica media. This allows recoiling and expansion in the cardiovascular system during the normal cardiac cycle. Also, this helps in maintaining the constant blood flow during the diastole. The aorta, pulmonary trunk, brachiocephalic trunk, the left subclavian artery, and the left common carotid artery are some examples of large elastic arteries.
• The medium muscular arteries mostly contain smooth muscle fibres. This feature allows these blood vessels to adjust their diameter and thus controls the blood flow to different parts of the body. The radial, femoral and axillary arteries are some examples of medium muscular arteries.
• The small arteries and arterioles regulate the filling of the blood capillaries and thus directly provide arterial pressure in the cardiovascular system.
• Likewise, veins are classified into three classes – large veins, small and medium veins, and the venules.
• The large veins have some smooth muscle layers in the tunica media and the thickest tunica externa. The portal vein, superior vena cava and inferior vena cava are some examples of large veins.
• The small and medium veins have only a few smooth muscles and a thick tunica externa. The deeper veins of the forearm and leg and the superficial veins in the lower and upper limbs are some examples of small and medium veins.
• The smallest veins or venules drain blood from the capillaries to the veins.

Comparison between an Artery and Vein

Significance

The blood vessels transport blood, nutrients, oxygen, and hormones to the body tissues. They also help in carrying toxins or waste away from the tissue. Thus they are vital to sustain life as all of our body tissues depend on their functionality.

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