The intricate network of hollow tubes which is responsible for transporting blood throughout the body are known as blood vessels. They are made up of layers of connective tissue and muscles. The innermost layer of blood vessels is made up of endothelium. The endothelium makes up for the majority of the vessel in capillaries and sinusoids. It also remains continuous with the inner most tissue lining of various organs like brain, lungs, skin and the heart. In the heart the innermost layer is called the endocardium. Blood vessels are very important as they are responsible for delivering nutrients to all parts of the body and carrying the waste material away from the cells.
Varieties of Blood Vessels
Vessel means a hollow container which is used to carry something in it such as a cup, a tube or a bucket. In the same sense, blood vessels are hollow tube shaped containers meant to carry blood. They are present all across the body and help in blood circulation.
1. Arteries
Physical characteristics: The arteries are made up three layers, a tough outer layer of tissue, a middle layer of muscle and a smooth inner layer of epithelial cells. The muscular layer helps the artery to be elastic and strong. Since the inner layer is smooth, the blood flows easily without obstacles.
What they do: The blood vessels which carry oxygenated blood from the heart to other parts of the body are called arteries. The blood is pumped out from the heart via the dorsal artery. This artery then divides into smaller ones to spread throughout the body. When the heart pumps blood, the muscular walls of the arteries expand and fill with blood. They also contract when the heart relaxes, with a force which is strong enough to push the blood throughout the body. This creates an efficient circulation system.
Carotid arteries are blood vessels of the heart. Arteries further branch out into capillaries at which level there is an exchange of oxygen and carbon dioxide at cellular level. The deoxygenated blood is then passed on to the veins which go to the lungs and heart.
2. Capillaries
Physical characteristics: The arteries branch out into capillaries and they are very thin and fragile. Only a single file of blood cells can pass through them at a time and the walls are also one epithelial cell thick.
What they do: Capillaries facilitate the exchange of oxygen and carbon dioxide between the red blood cells and the tissue present around the capillary. A network of capillaries is formed along the arteries and veins which run parallel throughout the body. The waste or deoxygenated blood passes through the wall of the capillaries, into the red blood cells present and then is carried by the veins back to the heart. Excess heat in the body is also regulated by capillaries which is delivered by the blood to the tissue by the capillaries. This is what happens when the skin appears flushed red due to heat.
3. Veins
Physical characteristics: Like the arteries, the veins are also made up of three layers. But in the veins there is less connective tissue and less smooth muscles which make them thinner as compared to arteries. This is why there is lower blood pressure in the veins. Due to the thinner walls, the blood carrying capacity of the veins is higher and at any given time 70% of the total blood is present in the veins. Veins of medium and large size have valves which prevent the back flow of the blood against pull of gravity, especially in the hands and legs. The valves are semilunar and keep the blood going towards the heart.
What they do: Veins are the blood vessels responsible for carrying blood back to the heart. Once the deoxygenated blood is passed from the tissues to the capillaries, it moves to the smallest veins called as venules. Pulmonary vein is the only vein which carries oxygen rich blood. It carries this blood from the lung to the left atrium of the heart. Systemic vein carries deoxygenated blood to the right atrium of the heart from the body tissues, where the oxygen has been used up for metabolic activities.
You may watch a video for a clearer view of these blood vessels:
Health Problems Related to Blood Vessels
Problems of the blood vessel and heart are common, but can be very serious as well. This can be especially important in people suffering from Marfan syndrome and many other related disorders. For this reason, it is important to make an early and accurate diagnosis.
1. Aortic Enlargement
In this condition, especially in a person suffering from Marfan syndrome, the aorta becomes enlarged which is also called aortic dilation. The walls of the aorta can bulge, these problems are very serious because they can lead to tear or rupture of the aorta. In people with Marfan syndrome, there is more risk as this problem is seen at the part closest to the heart
2. Mitral Valve Prolapse
The mitral valve is present in the left side of the heart. When the flaps of this valve are floppy or do not close completely, it is referred to as Mitral valve prolapse. This causes irregular heartbeats, tachycardia and shortness of breath. There might be leaking of the mitral valve which, if high, would require surgery.
3. Aortic Regurgitation
In this scenario, there is a problem with the aortic valve and it does not close properly. This causes the blood to flow back into the heart. Enlarged aorta can cause this problem. The symptoms would be forceful heartbeats and shortness of breath when performing light activity.
4. Aortic Tear or Rupture
When there is tear or rupture in between layers of the walls of the aorta, it is called aortic dissection. People will experience a sharp, tearing or ripping pain in the chest. Immediate medical attention is required in such cases.
It is of two types – dissection of ascending aorta and the descending aorta. When it occurs in the ascending aorta, immediate surgery is required as it is life-threatening. It is common in Marfan syndrome. When it is in the descending artery, it can be managed by medication and monitoring. If the aorta gets enlarged or blood supply gets inadequate to vital organs, surgery might be required.