Blood vessels are made up of three layers. Tunica Intima is the inner lining of blood vessels. It is made up of squamous endothelium. The other two layers are tunica media (middle) and tunica externa (external).
Blood Vessels
Blood vessels are the closed fixed pathway (tube) through which blood flows. Blood flows through blood vessels in all organisms having a closed circulatory system. Blood vessels include a network of arteries, veins, capillaries, arterioles and venules. Blood vessels transport nutrients, chemical substances and oxygen to various tissues and also take away carbon dioxide and other waste products from the tissue.
Arteries carry blood from the heart to various tissues, i.e. away from the heart, and veins carry blood from various tissues and organs back to the heart, i.e. towards the heart. The exchange of gases and various substances between the blood and tissue occurs at capillaries. Arteries carry oxygenated blood and veins carry deoxygenated blood except for pulmonary artery and pulmonary vein that carry deoxygenated blood and oxygenated blood, respectively.
Blood Vessels Structure
Blood vessels, both arteries and veins are made up of three layers of tissues. The three layers of blood vessels are as follows:
- Tunica Intima – It is the innermost layer. Tunica intima is made up of squamous endothelium.
- Tunica Media – It is the middle layer of blood vessels. Tunica media is made up of smooth muscles and elastic fibres. It is thicker in arteries compared to veins.
- Tunica Externa – It is the outermost layer of blood vessels. It is also known as tunica adventitia. Tunica externa is made up of connective tissues. It is made up of fibrous connective tissues with collagen fibres.
Tunica Intima
It is the inner lining of blood vessels. Tunica intima is made up of a single layer of squamous endothelial cells. It is supported by elastic lamina. The endothelial cells of tunica intima are in direct contact with the blood flowing through a blood vessel.
The inner lining of blood vessels consists of:
- Pavement endothelium – The endothelial cells are oval, polygonal or fusiform with oval or round nuclei.
- Subendothelial layer – It is made up of delicate connective tissue. The connective tissue is more developed in the bigger vessels.
- Elastic lamina – It is made up of elastic fibres. It is present in elastic arteries. It is thin in minute arteries but in larger arteries and aorta, it has significant thickness. It has small perforations, hence, it is also called a fenestrated membrane.
The muscular arteries, arterioles, capillaries and veins are made up of endothelial cells. The elastic arteries consist of endothelial cells covered by elastic fibres.
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