Difference Between Capillaries and Veins

Capillaries vs Veins

Veins and capillaries are two different types of vessels but often mistakenly used terms. Therefore, a proper understanding is necessary about these important parts of the circulatory system to avoid mistakes. Usually, oxygenated blood travels through main arteries, divides into specific arteries designed for the organs and tissues, further divides into capillaries, and finally reaches the organs and tissues. Then, deoxygenated blood from the organs and tissues come back to the heart through veins. These important parts of the circulatory system would be easy to understand if the differences and particular characteristics are understood, and this article would be a great help for that.

What are Veins?

The veins are the blood vessels that carry blood towards the heart. Veins carry deoxygenated blood from the tissues to the heart and remain contracted if there is no blood inside the vessels. Veins run close to the skin, and these generally thin structures contain valves to keep the flowing direction always towards the heart. The wall of a vein consists of three layers known as tunica externa, tunica media, and tunica intima. The tunica externa is thick; it is made up of connective tissues. The tunica media is made up of smooth muscles, and the tunica intima is made up of endothelial cells. Veins of the lower part of body collect blood into one vessel called inferior vena cava and the veins of the upper part collects into another vessel called superior vena cava, both these connect to the right atrium of the heart. Usually, veins are also known as capacitance vessels, as altogether all the veins contain about 60% of the whole blood volume of the body.

What are Capillaries?

Capillaries are the smallest functional parts of the blood circulation, as those contribute in microcirculation. Usually, the capillaries interconnect venules and arterioles. The capillaries can exchange water, oxygen, carbon dioxide, hormones, nutrients, and many more between the blood stream and the surrounding tissues. Capillary beds cover the organs according to the function and make an efficient exchange of gases, nutrients, and wastes. The wall of capillaries or these micro vessels contains only one cell layer. This one endothelial cell-layered wall of capillaries facilitates the exchange of the contents.

What is the difference between Veins and Capillaries?

• Veins are more complex and larger in structure, but capillaries are simple and very small structures. In fact, veins contain three made up of three different layers containing connective tissues, smooth muscles, and endothelial layer. However, capillaries have only one layer of endothelial cells.

• Veins contribute to the macro circulation of blood while capillaries function in the microcirculation.

• Capillaries contribute in exchange of gas, nutrients, waste products, hormones, and many other constituents between blood stream and the tissues, whereas veins function in transporting those between different parts of the body.

• Veins contain deoxygenated blood except pulmonary and umbilical veins, but capillaries have both oxygenated and deoxygenated blood.