Veins – types, structure, functions. The most common diseases of the veins

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Veins are the types of blood vessels in our body. Blood vessels are essential for the transport of blood. The blood carries oxygen and other nutrients to various tissues in the body, enabling them to function. The heart and blood vessels make up the cardiovascular system. This system includes a complex network of vessels with different structures and functions.

Veins – basic information

The veins are the blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; the exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. Unlike veins, arteries carry blood away from the heart. The veins are thinner than the arteries and are often closer to the skin. Most veins have valves to prevent backflow.

The veins carry blood from the periphery to the heart, and its color depends on where they lead it: if from the perimeter to the right atrium, the blood is dark cherry (as it is deprived of oxygen and rich in metabolic products), while in the veins leading from the lungs to in the left atrium, blood is bright red (due to high oxygenation).

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Veins – types

The same tissues make up the arteries and veins, but the veins are thinner and have less muscle layer, which allows them to retain more blood. The veins typically contain about 70% of the blood in the body at any given time. Veins are classified in many ways, including superficial and deep, pulmonary and systemic, and large and small.

1. Superficial veins are those that are closer to the surface of the body and have no corresponding arteries.
2. Deep veins they are deeper in the body and have corresponding arteries.
3. Piercing veins flow from the superficial to the deep veins. They are usually found in the legs and feet.
4. Connecting veins are the veins that directly connect the superficial veins with the deep veins.
5. Pulmonary veins is a group of veins that supply oxygenated blood from the lungs to the heart.
6. System veins they drain the body tissues and deliver deoxygenated blood to the heart.

Most veins are equipped with one way valves to prevent blood from flowing in the opposite direction.

The veins are translucent, so the color of the vein that appears outside the body is largely determined by the color of the venous blood, which is usually dark red due to its low oxygen content. The veins appear blue because of the low oxygen level in the vein. The color of the vein can be influenced by the characteristics of a person’s skin, the amount of oxygen carried in the blood, and the size and depth of the vessels. When the vein is empty of blood and removed from the body, it appears grayish white.

Fishing lines are the smallest type of veins. They have very thin walls to hold a lot of blood. They deliver low-oxygen blood through the capillaries from the arteries directly into the veins. The blood then travels back to the heart through a series of veins of increasing size and a layer of muscle.

See also: The work of the heart and its disorders. What are the most common heart diseases? [WE EXPLAIN]

Veins – construction

The walls of the veins consist of three layers.

1. Outer membrane (Latin: tunica adventitia): It consists of collagen and elastin. This layer allows the blood vessels to expand or contract, depending on the type of vein or artery. This feature is important for blood pressure control.
2. Endothelium (Latin endothelium): This is the layer of squamous cells that line the inner surface of blood vessels and lymph vessels. Endothelial cells create a barrier between vessels and tissue and control the flow of substances and fluids in and out of the tissue.
3. Muscle layer: it contains circular smooth muscles that regulate the lumen of the blood vessel, and thus the blood flow.

Veins – functions

The veins are used to return blood from the organs to the heart. The veins are also called “capacitive vessels” because most of the blood volume (60%) is contained in the veins. In the bloodstream oxygenated blood is pumped through the left ventricle through the arteries to the muscles and organs of the body, where nutrients and gases are exchanged in the capillaries.

After cell waste and carbon dioxide are collected in the capillaries, blood is directed through the vessels that converge together to form veins that continue to converge to form larger veins. The deoxygenated blood is drawn through the veins to the right atrium of the heart, from where it is transported to the right ventricle, from where it is pumped through the pulmonary arteries to the lungs. In a small bloodstream the pulmonary veins return oxygenated blood from the lungs to the left atrium, which flows into the left ventricle, completing the cycle of blood circulation.

The return of blood to the heart is assisted by the action of the muscles and by the movement of the chest during breathing. Standing or sitting for long periods of time can cause low venous blood return to the heart following venous (vascular) shock. Fainting may occur, but usually the baroreceptors in the aortic sinuses initiate the baroreceptor reflex so that angiotensin II and norepinephrine stimulate vasoconstriction and the heart rate is increased to restore blood flow.

Neurogenic and hypovolemic shock (hypovolaemia) can also cause fainting. In these cases, the smooth muscles surrounding the veins relax and the veins fill with most of the blood in the body, keeping the blood out of the brain and causing you to pass out. Jet pilots wear pressure suits to maintain blood pressure and return venous blood to the heart from grand circulation.

The arteries are viewed as carrying oxygenated blood to the tissues, while the veins carry the deoxygenated blood back to the heart. This includes the large bloodstream, the much larger of the two blood circuits in the body that carries oxygen from the heart to the body’s tissues. However, in the small bloodstream, the arteries carry the deoxygenated blood from the heart to the lungs, and the veins return blood from the lungs to the heart.

The difference between veins and arteries is in the direction of their flow (from the heart through the arteries, back to the heart through the veins), not the oxygen content. In addition, deoxygenated blood that is transferred from the tissues back to the heart for re-oxygenation in the systemic circulation still contains some oxygen, although this is much less than that carried through the systemic arteries or pulmonary veins.

While most veins carry blood back to the heart, there is one exception. The portal veins carry blood between the capillary beds. Capillary beds are a network of blood vessels that connect the venules to the arterioles and allow materials to be exchanged across the membrane from blood to tissues and vice versa.

For example, the portal vein of the liver takes blood from the capillaries in the digestive tract and transports it to the capillaries in the liver. The blood is then drained in the digestive tract and spleen, where it is drawn in through the liver’s veins, and blood is drawn back to the heart. Since it is an important function in mammals, damage to the portal vein of the liver can be dangerous. Blood clotting in the hepatic portal vein can cause portal hypertension, which reduces blood flow to the liver.

Veins – diseases

The most common diseases of the veins include:

Venous diseases – venous insufficiency

Venous insufficiency is the most common disease of the venous system and is usually manifested by spider veins (telangiectasia) or varicose veins. Several types of treatment are used, depending on the specific type and pattern of the patient’s veins and the physician’s preferences. Treatment may include, inter alia, e.g. intravenous thermal ablation, stripping (angiology), total or partial excision of a vein, sclerotherapy.

Vein diseases – deep vein thrombosis

Deep vein thrombosis is a condition where a blood clot forms in a deep vein. These are usually the leg veins, although it can also occur in the arm veins. Immobilization, active cancer, obesity, traumatic injury and birth defects that increase the likelihood of blood clots are risk factors for deep vein thrombosis. The condition can cause the affected limb to swell, pain and rash on the skin. At worst, deep vein thrombosis may spread, or part of the clot may break loose and land in the lungs, which is called a pulmonary embolism.

The decision to treat deep vein thrombosis depends on the size of the disease, the person’s symptoms, and risk factors. It usually includes anticoagulant medications to prevent blood clots from forming or to reduce the size of a clot.

See also: The six most common symptoms of thrombosis

Vein diseases – portal hypertension

Portal veins are located in the abdomen and carry blood to the liver. Portal hypertension is associated with cirrhosis or liver disease, or other conditions such as hepatic vein thrombosis (Buddha-Chiari syndrome) or compression of tumors, or tuberculous lesions. When the pressure in the portal veins increases, a collateral circulation develops, causing visible veins such as esophageal varices.

Vein diseases – varicose veins

Varicose veins are deformed veins that usually appear on the thighs, calves and under the knees. It is not only an aesthetic problem, but also a health problem, because it means problems with blood circulation and is one of the symptoms of chronic venous disease. They appear when blood does not return to the heart from the veins, but gradually accumulates in the vessels and leads to their dilatation.

At first they appear as small spider veins visible on the legs, and gradually they become more and more convex and visible. Varicose veins are also associated with unpleasant ailments, which include leg swelling, a feeling of heavy legs, burning, tingling, and calf cramps.