The human body requires a steady supply of oxygenated blood to properly function. While arteries transport the oxygenated blood away from the heart and into parts of the body, another system of blood vessels exists to move deoxygenated blood. These are called veins. Today, we’re going to look at the structure and function of veins while we also identify and explore the largest vein in the body.
By the time we’re finished, you’ll have a good idea of how veins work in our body.
What is a Vein?
Generally speaking, a vein is a type of blood vessel that carries deoxygenated blood to the heart. Some exceptions to this rule exist, such as umbilical veins and pulmonary veins. These types of veins carry oxygenated blood to the heart. Veins are found in humans and many other animals alike.
Unlike arteries that are muscular and tend to run deep in the human body, veins are comparatively superficial and thinner than arteries. Let’s look a little closer at veins by identifying the anatomy and function of veins.
The Anatomy of a Vein
At first glance, the anatomy of a vein is very similar to that of an artery. The vein walls have three layers just like arteries, and they are the same ones including:
- Tunica externa: the outermost layer of the vein walls, composed of connective tissue but less than that of arteries. This is the thickest layer of the vein and also contains vasa vasorum.
- Tunica media: the middle layer of the vein that is made of smooth muscle tissue.
- Tunica intima: the portion of the vein that comes into contact with the blood flowing through it, made of endothelial cells.
- Lumen: the hollow portion of veins and arteries through which blood flows.
A major difference between veins and arteries is that veins are generally thinner, but they have a wider lumen than arteries.
Other differences include that veins generally flow away from the heart, are not rounded like arteries, transport blood at low pressure, and have valves that maintain a single direction of flow. Arteries do not possess such valves at all.
The presence of valves is incredibly important in the extremities of the body where blood flow is slower and more susceptible to the forces of gravity. The valves in veins prevent the backflow of blood.
The unique qualities of veins make it easy to distinguish them from arteries. However, it’s important to note that there are several types of veins.
Types of Veins
Several types of veins exist in the body. They have unique functions or locations that set them apart from the others. Let’s take a quick look at how some of these veins are classified.
Generally speaking, we can break down four types of veins into two dichotomies. These are not the only types of veins that exist, and we are only going to give a basic overview of their functions.
Superficial Veins vs Deep Veins
Superficial veins are the veins closest to the surface of the body, and those are easily seen in humans’ hands. Deep veins are those that are located deep in the body and interact with arteries.
Pulmonary Veins vs Systemic Veins
The pulmonary veins are those that bring oxygenated blood from the lungs and into the heart. Systemic veins are those that carry deoxygenated blood from tissues throughout the body back to the heart. There, it enters the pulmonary circuit so that it can be oxygenated. The majority of the veins in a human’s body are systemic.
Other types of veins, like perforator veins or communicating veins, exist. However, the brief overview that we’ve provided should give you enough
What is the Largest Vein in the Body?
The largest vein in the human body is the inferior vena cava. The inferior vena cava measures upwards of 3 cm in diameter depending on the individual and about 22 cm in length. As you might imagine, the inferior vena cava is located close to the heart where many of the other largest blood vessels are located.
The inferior vena cava is one of two very large veins that return blood to the heart. The other one is called the superior vena cava. Despite their names seemingly hinting at their size, the names are actually derived from their anatomical positions in the body. Superior is located above and the inferior is located below relative to the heart.
Meanwhile, the superior vena cava, the superior portion of the venae cavae, has a diameter of 2.4 cm and measures just about 7 cm long. That makes it slightly smaller in diameter than the inferior vena cava and much shorter.
The job of the largest vein in the body is to return deoxygenated blood to the heart. The veins accomplish this by emptying the deoxygenated blood into the right atrium of the heart.
The fact that these two veins are this large is interesting because veins tend to be smaller than arteries on the whole. Also, the size of the venae cavae all but ensures that no other veins could match them for size. That means few other veins have the diameter of these two.
What is an Artery?
Arteries are thicker, more muscular blood vessels with a smaller lumen relative to veins. These blood vessels are tasked with carrying oxygenated blood from the heart to various parts of the body.
Arteries carry blood under pressure, and they lack the valves that we see in veins. These vessels are very important to the body, and they can get quite large. For example, the aorta is the largest artery in the body, and it measures about one inch in diameter and measures over one foot long. This is much longer than any of the veins present in the human body.
Arteries and veins work in conjunction to deliver oxygenated and deoxygenated blood throughout the body. Although they have numerous similarities at first glance, the two types of blood vessels are very distinct from one another when you take a closer look.
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