Veins are blood vessels that move blood toward the heart. Maximum veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, transport oxygenated blood from the lungs to the left upper chamber of the heart. The deoxygenated form of hemoglobin (deoxyhemoglobin) in venous blood makes it appear dark. In contrast to veins, an artery is a vessel that carries blood away from the heart.Veins are fewer muscular than arteries and are oftentimes closer to the skin. There are valves in maximum veins to prevent backflow.
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Types of Veins
Veins are present throughout the body that carries blood back to the heart. Veins are classified in -superficial vs. deep, large vs. small and pulmonary vs. systemic.
Superficial veins are closer to the surface of the body and become no corresponding arteries.
Deep veins are deeper in the body and become corresponding arteries.
Perforator veins drain from the superficial veins to the deep veins. These veins are usually associated in the lower limbs and feet.
Communicating veins that directly join superficial to deep veins.
Pulmonary veins that deliver oxygenated blood from the lungs to the heart.
Systemic veins deliver deoxygenated blood to the heart.
Most veins are hold valves to prevent blood flowing in the backward direction. Veins are translucent, so the color a vein is usually dark red as a result of its low oxygen content. The color of a vein can be influenced by the characteristics of a person’s skin, how much oxygen is being taken in the blood, and how big and deep the vessels are.
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The largest veins in the body are the venae cavae. These are two large veins –superior vena cava & inferior vena cava which enter the right atrium of the heart from above and below. The superior vena cava brings blood from the upper limbs and head to the right atrium of the heart, whereas the inferior vena cava brings blood from the lower limbs and abdomen to the heart. The inferior vena cava is retroperitoneal and runs to the right and approximately parallel to the abdominal aorta with the spine. Large veins stuff into these two veins and tinier veins into these. Together this makes the venous system.
The main veins maintain a relatively constant position, the location of veins person to person can reveal quite a lot of difference.
The superior and inferior venae cavae carry almost deoxygenated blood from the upper and lower systemic circulations.The pulmonary veins carry moderately oxygenated blood from the lungs to the heart.
The portal venous system is a series of veins that shortly join two capillary beds. Examples -hepatic portal vein and hypophyseal portal system.
The peripheral veins transport blood from the limbs and hands and feet.
The Venous Drainage of the Upper Limb
The chief superficial veins of the upper limb are the cephalic and basilic veins. The veins are placed inside the subcutaneous tissue of the upper limb.
The cephalic vein originates from the dorsal venous interface of the hand. It ascends the antero-lateral aspect of the upper limb, reaching anteriorly at the elbow. Through the shoulder, the cephalic vein travels within the deltoid and pectoralis major muscles and enters the axilla region via the clavipectoral triangle. In the axilla, the cephalic vein terminates by connecting the axillary vein.
The basilic vein arises from the dorsal venous network of the hand. It ascends the medial phase of the upper limb. At the edge of the teres major muscle, the vein moves deep into the arm. Here, it connects with the brachial veins to make the axillary vein.
Through the elbow, the cephalic and basilic veins are joined by the median cubital vein.
The upper limb deep veins are situated under the deep fascia.
They have paired veins that append and occupy either side of an artery. The brachial veins are the biggest in size and are located either side of the brachial artery. The beats of the brachial artery help the venous return. Veins that are structured in this process are identified as vena comitantes.
Perforating veins run within the deep and superficial veins of the upper limb, uniting the two systems.
The Venous Drainage of the Lower Limb
The Deep Veins of the Lower Limb
The deep venous drainage system is positioned beneath the deep fascia of the lower limb. The deep veins accompany and share the name of the major arteries.
The Gluteal Region
The gluteal area is drained by superior and inferior gluteal veins.
When the popliteal vein has entered the thigh, known as the femoral vein. The femoral vein is located anteriorly, following the femoral artery.
The profunda femoris vein is the other main venous structure in the thigh. Via perforating veins, it empties blood from the thigh muscles. It then empties within the femoral vein.
The femoral vein leaves the thigh by moving under the inguinal ligament, it is distinguished as the external iliac vein in the inguinal ligament.
The Foot and Leg
The venous arrangement of the foot is the dorsal venous arch, which mostly empties into the superficial veins. Some veins of the arch enter deep into the leg, making the anterior tibial vein.
On the plantar aspect, medial and lateral plantar veins arise in the foot. These veins join to form the posterior tibial and fibular veins. The posterior tibial vein follows the posterior tibial artery, penetrating the leg posteriorly to the medial malleolus of the ankle.
On the posterior aspect of the knee, the anterior tibial, posterior tibial and fibular veins join to form the popliteal vein. The popliteal vein enters the thigh through the adductor canal.
The Superficial Veins of the Lower Limb
There are two major superficial veins – the great saphenous vein, and the small saphenous vein. The lower limb superficial veins run in the subcutaneous tissue.
The great saphenous vein is made by the dorsal venous arch of the foot, and the dorsal vein of the great toe. It rises up the medial side of the leg, moving anteriorly to the medial malleolus, and posteriorly to the medial condyle at the knee joint.
As the vein runs up the leg, the great saphenous vein ends by draining into the femoral vein shortly inferior to the inguinal ligament.
The small saphenous vein is made by the dorsal venous arch of the foot, and the dorsal vein of the little toe. It runs up the posterior side of the leg, moving posteriorly to the lateral malleolus of the ankle, along with the lateral border of the calcaneal tendon. It goes within the two heads of the gastrocnemius muscle and drains into the popliteal vein in the popliteal fossa.
Microscopically, the walls of veins have three layers: an inner layer, known as the tunica intima; a middle layer, known as the tunica media; and an outer layer known as the tunica adventitia. Each layer has a number of sublayers. The tunica intima varies from the inner layer of an artery: many veins, especially in the arms and legs, have valves to prevent backflow of blood, and the elastic membrane lining the artery is absent in the vein, which consists fundamentally of endothelium and scant connective tissue. The tunica media, which are, in general, much thinner than those of arteries, as veins do not function primarily in a contractile manner and are not subject to the high pressures of systole, as arteries are. The outer layer consists chiefly of connective tissue and is the thickest layer of the vein. As in arteries, there are tiny vessels called vasa vasorum that supply blood to the walls of the veins and other minute vessels that carry blood away.
Veins serve to return blood from organs to the heart.In systemic circulation oxygenated blood is pumped by the left ventricle within the arteries to the muscles and organs. After taking up cellular waste the de-oxygenated blood is carried by veins to the right atrium of the heart, which transfers the blood to the right ventricle, wherever it is then pumped within the pulmonary arteries to the lungs. In pulmonary circulation the pulmonary veins deliver oxygenated blood from the lungs to the left atrium, which empties into the left ventricle, making the cycle of blood circulation.
Veins Clinical Significance
Venous insufficiency is a common disorder of the venous system and is usually disclosed as spider veins or varicose veins.
The postphlebitic syndrome is venous insufficiency that happens following deep vein thrombosis.
Deep vein thrombosis
Deep vein thrombosis is a situation in which a blood clot forms in a deep vein. This is usually the veins of the legs, although it can also occur in the veins of the arms.
The portal veins are located in the abdomen and transport blood through to the liver. Portal hypertension is linked to cirrhosis of the liver or obstructing clot or compression from tumors or tuberculosis lesions.