What are blood vessels?
Blood vessels are hollow organs. With a length of around 150,000 kilometers, these tubular, hollow structures create an interconnected network that runs through our entire body. Connected in series, it would be possible to circumnavigate the earth almost 4 times.
Blood vessels: structure
The vessel wall encloses a cavity, the so-called lumen, in which the blood flows – always in one direction only. The wall of smaller vessels is usually single-layered, that of larger vessels three-layered:
- Inner layer (intima, tunica intima): Thin layer of endothelial cells. It seals the vessel and ensures the exchange of substances and gases between the blood and the vessel wall.
- Middle layer (media, tunica media): Consists of smooth muscle and elastic connective tissue, the proportions of which vary depending on the vessel. Regulates the width of the vessel.
- Outer layer (adventitia, tunica externia): Consists of collagen fibers and elastic nets, surrounds the blood vessels on the outside and anchors them to surrounding tissue.
The various blood vessels in the body differ in length, diameter and thickness of the vessel wall. Depending on the function of the blood vessels, the individual wall layers are more or less pronounced or not present at all.
What is the function of blood vessels?
Blood vessels transport blood – and therefore oxygen, nutrients, hormones etc. – throughout the body. – through the whole body.
Last but not least, the numerous, kilometer-long blood vessels store several liters of blood (about five liters in adults).
Where are the blood vessels located?
The blood vessels run through the entire body to ensure an optimal supply. Some are located superficially under the skin, others deep down, embedded in tissue or muscles.
On its way through the body, the blood passes through different types of vessels. Together they form an interconnected network and guarantee the uninterrupted flow of blood in one direction, from the heart to the periphery and from there back to the heart:
This large blood circulation (systemic circulation) starts in the left side of the heart: it pumps oxygen-rich blood into the body via the main artery (aorta). Thick main branches (arteries) branch off from the aorta, which divide into smaller and smaller blood vessels (arterioles) and finally merge into the smallest vessels (capillaries). These form a finely branched capillary network through which oxygen and nutrients are delivered to the surrounding tissue. The now deoxygenated, nutrient-poor blood flows from the capillary network into slightly larger vessels (venules). The venules in turn flow into veins that carry the blood via the superior and inferior vena cava back to the heart, namely to the right side of the heart.
Arteries and veins together make up 95 percent and therefore the majority of blood vessels. They are usually located close to each other. The remaining five percent is made up of capillaries.
Only a few parts of the body have no blood vessels at all. These include the outermost layer of the skin as well as the cornea, hair and nails, tooth enamel and the cornea of the eye.
Artery
Arteries transport blood from the heart to the periphery. You can read more about this type of blood vessel in the article Artery.
Aorta
The aorta is the largest artery in the body. You can read more about it in the article Aorta.
Veins
Veins bring blood from the periphery back to the heart. You can read more about this in the article Veins.
Upper and lower vena cava
You can find out everything you need to know about the two largest veins in the body in the article Vena cava.
Portal vein
Blood from the abdominal cavity is transported to the liver via the portal vein. You can read more about this special vein in the article Portal vein.
Capillaries
Arteries and veins are connected to each other via a network of very fine vessels. You can find out more about this in the article Capillaries.
What problems can blood vessels cause?
“Varicose veins, which mainly occur on the legs, are dilated, tortuous superficial veins. They develop when the blood cannot drain properly from the veins, which can have various causes. Varicose veins can also form in other parts of the body, such as the oesophagus.
Inflammation of superficial veins with the formation of blood clots is called thrombophlebitis. It mainly occurs in the legs. If blood clots form in deep veins, this is called phlebothrombosis.
Other diseases of the blood vessels include Raynaud’s syndrome, giant cell arteritis and chronic venous insufficiency (chronic venous insufficiency).
