Systemic veins

Veins are a type of blood vessel that return deoxygenated blood from organs back to the heart for reoxygenation. These are different from the arteries, which deliver oxygenated blood from heart to the rest of the body.

After blood delivers oxygen to the tissues and picks up carbon dioxide, it returns to the heart through a system of veins. The capillaries, where the gaseous exchange occurs, merge into venules and these converge to form larger and larger veins until the blood reaches either the superior vena cava or inferior vena cava, which drain into the right atrium.

There are four types of veins:
*Deep veins are located within muscle tissue
*Superficial veins are closer to the skin’s surface
*Pulmonary veins transport blood that’s been filled with oxygen by the lungs to the heart
*Systemic veins

Systemic veins are located throughout the body from the legs up to the neck, including the arms and trunk. Systemic veins transport blood from the body tissue to the right atrium of the heart. This blood has a reduced oxygen content because the oxygen has been used for metabolic activities in the tissue cells.

The systemic veins may be arranged into three groups:
(1) The veins of the heart.
(2) The veins of the upper extremities, head, neck, and thorax, which end in the superior vena cava.
(3) The veins of the lower extremities, abdomen, and pelvis, which end in the inferior vena cava.

The inferior vena cava, also referred to as the posterior vena cava, is the largest vein in the human body. The superior vena cava is a large vein located in the upper anterior mediastinum. It is responsible for carrying deoxygenated blood from the upper body (head, neck, upper limbs, and some organs of the chest) to the heart.
Systemic veins

Pulmonary veins

Veins are types of blood vessels which carry blood towards the heart. These carry deoxygenated blood from tissues back to the heart. Pulmonary veins are blood vessels that carry oxygen-rich blood from lungs to the left atrium where it is returned to the systemic circulation.

Pulmonary veins are the only veins in the adult human body, which contain a higher percentage of oxygenation of blood than their arterial counterpart, the pulmonary arteries. All other veins carry oxygen-poor blood.

Pulmonary veins are located between lungs and the heart. Pulmonary veins play an important role in respiration by receiving oxygenated blood in the alveoli and draining it into the left atrium.

Many smaller blood vessels converge in each of lungs (right and left) to form a pair of pulmonary veins. Each pair leaves its respective lung through a spot known as the hilum, or root. From there, pulmonary veins travel to the heart and connect with left atrium.

The pulmonary veins can become distended in congestive heart failure (left-sided heart failure), resulting in pulmonary edema. Damage to the pulmonary veins epithelial lining can cause pleural effusions as well.

There are typically four pulmonary veins, two draining each lung:
*Right superior: drains the right upper and middle lobes
*Right inferior: drains the right lower lobe
*Left superior: drains the left upper lobe
*Left inferior: drains the left lower lobe
Pulmonary veins

Functions of veins

There are three types of blood vessels:
*Arteries
*Veins
*Capillaries

Veins are a type of elastic blood vessel that return deoxygenated blood from body organs back to the heart. Arteries transport blood away from the heart while veins move blood back to the heart.

Deoxygenated blood that flows into the veins is collected within tiny blood vessels called capillaries. Capillaries are the smallest blood vessels in the body. These tiny blood vessels have thin walls. Capillaries are where oxygen and nutrients are exchanged for carbon dioxide and waste.

Veins can be categorized into four main types: pulmonary, systemic, superficial, and deep veins.
*Pulmonary veins carry oxygenated blood from the lungs to the heart
*Systemic veins return deoxygenated blood from the rest of the body to the heart.
*Superficial Veins: these veins work in unison to collect blood from skin and surrounding superficial tissues
*Deep Veins: Once blood enters these deep veins, blood is pumped to the heart as these large muscles contract, moving blood along the circulatory system

The main vein in your body is the vena cava. The superior vena cava is in the upper right part of human chest. It carries blood from head, neck, arms and chest back to the heart.

The walls of veins are made up of three different layers:
Tunica externa
Tunica media
Tunica intima
Functions of veins