Veins

The human circulatory system is made up of blood cells, the heart, a network of veins, arteries and the lymphatic system. These four major parts are responsible for performing specific functions to keep the human body active, and healthy. 

Imagine if your blood vessels or veins stop working even for a minute? It seems like a nightmare because without veins, even for a few seconds, a person would die from a sudden cardiac attack. 

Angiology is the branch of human science or anatomy which majorly involves the study of blood vessels, circulatory system, arteries, veins , blood cells, and other diseases.

What are blood vessels? 

Blood vessels are the network of hollow tubes much like a network of pipes. This network of blood vessels is scattered all over the body. These vessels are responsible for carrying blood in both directions, including from the heart to different body parts and from the different parts of the body to the heart. The two types of blood vessels present in the human body are veins and arteries. 

Arteries help in carrying blood, that is rich in oxygen, from the heart to all parts of the body. The blood flows at high speed and high pressure through the arteries. This results in thick elastic walls for the arteries.

What are veins?

Veins are a type of blood vessel that help in carrying blood, that is rich in carbon dioxide, from the organs of the body. They take it back to the heart. The veins have thin walls. They have valves that direct the blood towards the heart. Except for the pulmonary vein, every vein in the body has impure blood. The blood flowing the pulmonary vein flows with low speed and pressure. A large vein that carries blood to the heart from other areas of the body is known as vena cava.The number of beats that occur per minute is called the pulse rate. A normal person has a pulse rate that ranges between 72 and 80 beats per minute on average.

Venous system

It is collecting system formed by the uniting branches as smaller and then larger veins and vena cava leading to the heart.Blood from anterior part of the body is returned to heart by two (in general mammals) anterior vena cava (or precavals), while from the posterior part by single posterior vena cava (or postcaval).

 The Human Heart receives  blood only through two great veins : Superior vena cava from the anterior part and inferior vena cava from posterior part.

 Precaval is formed by the union of common Jugular vein, subclavian vein, intercostal vein and anterior azygos vein. The jugular veins as external and internal jugulars bring blood from head and neck. The right and left external jugulars are connected through jugular anastomosis. The subclavian vein brings blood from forelimbs and shoulders.

 A pair of pulmonary veins come from lungs and open by a common pore into the left auricle.

  In the posterior part the main vein is the dorsal vein which leads to the heart as postcaval. This is formed by the union of one renal vein from each kidney, one hepatic vein, gonadal veins and veins from hind limbs like sciatic and femoral veins.

As a specialty, the venous system forms a portal system in some parts of the body.

Vessels walls(Vein)

Main vessel’s wall consists of 3 layers  : (i) tunica externa (ii) tunica media  (iii) tunica interna.

•     Tunica externa (tunica adventitia) is the outermost fibrous layer (collagen and elastic fibers) with nerve fibers and lymphatic channels
•     Tunica media is the thickest contractile layer that consists of smooth muscles and elastic fibers, this layer is thicker in arteries there by reducing its lumen diameter
•     Tunica interna (tunica intima) is the innermost layer of squamous epithelium also known as endothelium

The human circulatory system

Circulation is the process by which fluids are transported into the body. It is one of the key systems in human beings. 

Blood

Blood is the fluid or liquid that flows throughout our body. It flows through the blood vessels. Blood is composed of various components such as red blood cells or RBCs, white blood cells or WBCs, and platelets. Blood flows through the veins in our body. Some of its important functions are as follows:

• It helps in transporting food from the small intestine to the other organs of the body
• It helps transport oxygen from the lungs to the other parts of the human body
• It also transports waste that is to be removed from the body       

Blood is composed of plasma. The plasma has different types of cells in it. Some of them are as follows:

• The first type of cells present in the plasma is called Red Blood Cells or RBCs which is the source that binds with oxygen
• The second component present in the blood that flows through our veins is White Blood Cells (WBCs) which help in fighting against infections and pathogens 
• Platelets in the blood help in blood clotting, if they did not exist, you may bleed to death

Heart

The heart is the pumping organ of the body. It pumps blood all the time. It helps in transporting blood to all the parts of the body.

Conclusion

Veins are an important part of the human circulatory system, which help in carrying blood, that is carbon-dioxide-rich, from the organs of the body. They take it back to the heart. Except for the pulmonary vein, every vein in the body has impure blood. The blood flowing through the pulmonary vein flows with low speed and pressure.