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Transportation in human beings is carried out by the network of tubes called blood vessels. Arteries, veins, and capillaries are the three types of blood vessels. They are different from each other in terms of function and structure.
The heart pumps out oxygenated blood with high pressure and arteries carry this high-pressure blood away from the heart to the various organs of the body. Arteries have thick, muscular, and elastic walls to withstand this high pressure to maintain blood pressure.
Arteries: Definition
Arteries are the type of blood vessels that transport blood from the heart to the various organs.
In general, they carry oxygenated blood but pulmonary and umbilical arteries are the exceptions as they carry deoxygenated blood.
The arteries are subdivided into two types according to their relative composition of elastic and muscle tissues.
- Elastic arteries: They are large-sized conducting arteries. Their walls stretch to accommodate sudden pressure of blood arising from the left ventricle of the heart during systole (contraction of the heart to pump out the blood). Example: Aorta.
- Muscular arteries: They are medium-sized distributing arteries. These arteries are the branches formed by elastic arteries and they have more smooth muscles. Example: Brachial artery.
Arteries: Structure
Arteries are tube-like structures having three layers.
- Outer layer: It is made up of connective tissues, collagen fibers, and elastic fibers. This layer provides support to the blood vessels.
- Middle layer: It is made up of smooth muscles, collagen fibers, and a larger number of elastic fibers. This layer provides strength and elasticity.
- Inner Endothelium: It is composed of very smooth epithelial cells that help in minimizing friction.
The lumen of the arteries is small due to the presence of thick walls. The small lumen creates the high pressure inside the arteries that are required to carry blood from the heart to the extreme points of various organs. High pressure also prevents the backflow of the blood.
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Why do arteries have thick walls?
- As the heart contracts, it pumps blood into the elastic arteries called the aorta with high pressure.
- To withstand this high pressure, arteries have thick, muscular and elastic walls. The blood then moves to the smaller muscular arteries and then to the arterioles.
- These arterioles further connect to the capillaries.
- The pressure of the blood does not remain the same throughout its flow.
- The pressure is greatest when blood is pumped out of the heart into arteries and the pressure falls when the heart relaxes between the beats.
An example to relate thick walls and small lumen
While spraying water into the garden have you ever decreased the nozzle size of the water pipe with your thumb to increase the pressure. This is the same scenario with arteries. Thick walls decrease the lumen size of the arteries which increases the pressure inside them. High pressure is necessary so that the blood reaches the extreme ends and does not flow backward.
Sample Questions:
Ques: How high blood pressure causes harm? (Marks 2)
Ans: Blood pressure increases when the artery walls become less elastic and force the heart to work harder to supply enough blood to the body. This condition may further lead to the blockage of arteries and heart attack or stroke may occur.
Ques: Why does the heart pump out blood with high pressure? (Marks 1)
Ans: The heart pumps out blood with great pressure to make sure the blood reaches the extreme ends of the various organs.
Ques: How low blood pressure causes harm? (Marks 2)
Ans: With low pressure, inadequate blood reaches the organs. This can cause dizziness and lightheadedness due to the lack of oxygen transport. This may further lead to heart stroke, attack, or kidney failure.
Ques: What is atherosclerosis? (Marks 2)
Ans: Atherosclerosis is the hardening and narrowing of arteries due to the deposition of plaque. This plaque can be of fats, cholesterol, or other substances. This condition can block the blood flow that may lead to stroke.
Ques: Why don't arteries have valves? (Marks 2)
Ans: The function of valves is to prevent backflow. Blood flows with great pressure inside the arteries and does not go back as the heart is pumping out the blood to the arteries. Since high-pressure flow prevents backflow, arteries do not need valves.
Also Read:
| Nutrition in Amoeba | Transportation in Animals and Plants |
| Control and Coordination | Reproduction in Plants |
Things to remember
- Arteries have thick, muscular, and elastic walls to withstand the high pressure of blood pumped out of the heart during systole. Thick walls help to regulate blood pressure. Hardening of arteries due to the deposition of cholesterol is known as atherosclerosis.
- High blood pressure is necessary to make sure blood reaches the extreme ends of the various organs. The pressure difference between arterioles and capillaries also plays an important role in this.
- It is important to regulate the blood pressure as very high or low pressure may lead to a heart attack. Very high pressure may damage the elasticity of the walls of arteries and very low pressure will lead to an inadequate supply of blood to the organs.
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