The smallest blood vessels measure only five micrometers. To give you some perspective, a strand of human hair measures about 17 micrometers. But if you took all the blood vessels out of an average child and laid them out in one line, the line would stretch over 60, miles. There are three kinds of blood vessels: arteries, veins, and capillaries.
Each of these plays a very specific role in the circulation process. Arteries carry oxygenated blood away from the heart. Arteries also contain a strong, muscular middle layer that helps pump blood through the body. This type of blood capillaries allows the movement of red blood cells , white blood cells , and serum proteins. They occur in adrenal glands, bone marrow, and lymph nodes.
The three types of blood capillaries are shown in figure 3. Veins are the blood vessels that drain deoxygenated blood towards the heart.
After undergoing microcirculation, deoxygenated blood is collected in the venules along with other metabolic wastes. The venules are small blood vessels branched out from the veins. They drain the deoxygenated blood to the veins. The pressure of the venous blood is lesser than that of arteries. The major driving force of the blood in the veins is the muscle contractions. Veins comprise valves, which prevents the reverse blood flow. The formation of a vein from blood capillaries is shown in figure 4.
Figure 4: Formation of a Vein. The diameter of a vein may vary from 1 mm to 1. The vein wall is made up of three tissue layers: tunica adventitia, tunica media, and tunica intima. The tunica adventitia is composed of connective tissue layer and forms the strong outer covering of the vein. The tunica media is composed of a thin smooth muscle layer and the tunica intima is composed of a lining of a smooth endothelial layer.
The veins drain blood to the largest veins called vena cava. The superior and inferior vena cava drain blood to the right atrium of the heart. The anatomy of a vein is shown in figure 5. Capillaries: Capillaries are the fine-branching blood vessels that form a network between arterioles and venules. Veins: Veins are the tube forming parts of the circulation system that drain deoxygenated blood towards the heart. Veins: The diameter of a vein is higher than that of a capillary. Capillaries: The wall of the capillary is one-cell thick.
Veins: The wall of the vein consists of several cell layers. Capillaries: Capillaries do not consist of veins. Capillaries: Capillaries form a highly branched network called the capillary bed. These are where the blood deposits oxygen into the tissues so they can respire. So, if you think about how gas transport works they need to have:.
Finally, the deoxygenated blood flows into veins to begin its journey back to the heart. Now remember the capillaries contain low pressure blood to pass on to veins so the veins don't need thick walls like arteries.
But without high pressure to keep the blood moving they will need a way to keep blood moving in the right direction often against gravity - i. So that is the key differences between the structure of these vessels varies and how it relates to their function. What is the difference between arteries, veins and capillaries?
Therefore, they need to have: Thick muscular walls Plenty of elastic tissue to spring back to their original shape A thin lumen to keep pressure high enough for it to reach the tissues Next the blood flows into capillaries.
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