Arteries and veins: what are the differences between them?

Both arteries and veins are types of blood vessels in the cardiovascular system

An artery carries blood away from the heart, and a vein brings blood back to the heart.

Blood vessels are necessary to transport blood throughout the body. Blood carries oxygen and nutrients to various tissues in the body, allowing them to function.

The heart and blood vessels make up the cardiovascular system. This system contains a complex network of vessels with different structures and functions.

In this article, we discuss the differences between arteries and veins. We also highlight the different types of blood vessels and how they work as part of the cardiovascular system.

Arteries and veins: definitions

Arteries and veins are types of blood vessels that transport blood throughout the body.

Blood vessels form two systems, leading to and from the heart. These two systems form the circulatory system.

The systemic circulation supplies oxygen and other vital substances to organs, tissues and cells.

The systemic arteries transport oxygen-rich blood from the left ventricle to the rest of the body. The low-oxygen blood then collects in the systemic veins and is sent to the right atrium.

The pulmonary circulation is where fresh oxygen enters the blood.

The pulmonary arteries transport low-oxygen blood from the right ventricle to the lungs. The pulmonary veins then transport oxygen-rich blood back to the heart through the left atrium.

Capillaries are the third type of blood vessel in the body. They supply blood directly to the organs.

Some numbers

There are more than 95 thousand kilometers of blood vessels in the body of a healthy adult. More than seven thousand liters of blood are pumped through them every day. The size of the blood vessels varies from 25 mm
(aortic diameter)
to eight microns
(capillary diameter).

Down with atherosclerosis!

Atherosclerosis is one of the most common vascular diseases. It is characterized by the formation of fatty plaques on the walls of the arteries. Find out how to prevent atherosclerosis.

Types of arteries

There are three types of arteries:

Elastic arteries

Elastic arteries are large vessels leaving the heart. For example, they include the pulmonary artery and aorta. The aorta is the main artery that carries blood away from the heart.

The heart forcibly pumps out blood to move it throughout the body. Elastic arteries must be flexible to cope with the rush of blood. They expand when the heart pumps out blood.

Elastin is a protein found in many tissues that provides flexibility to organs, including elastic arteries.

Muscular arteries

Elastic arteries carry blood to muscular arteries such as the femoral or coronary arteries.

Smooth muscle fibers make up the walls of muscle arteries. Muscles allow these arteries to expand and contract. These changes in size control how much blood moves through the arteries.

Arterioles

Arterioles are the smallest type of arteries. They distribute blood from larger arteries through networks of capillaries.

The outer layer of arterioles also contains smooth muscle, which regulates expansion and contraction.

What is blood pressure?

Blood pressure is the force with which blood presses against the walls of the arteries. It increases when the heart contracts and pumps out blood, and decreases when the heart muscle relaxes. Blood pressure is stronger in the arteries and weaker in the veins. Blood pressure is measured with a special device - tonometer
.
Pressure readings are usually recorded in two numbers. Thus, normal blood pressure for an adult is considered to be 120/80
.
The first number, systolic pressure
, is a measure of the pressure during a heartbeat.
The second is diastolic pressure
- the pressure during relaxation of the heart.

Such dangerous excess weight

Professor Sergei Boytsov, chief specialist in preventive medicine at the Russian Ministry of Health and Social Development, talks about how extra pounds affect the heart and blood vessels.

Pressure is measured in the arteries and expressed in millimeters of mercury. In the capillaries, the pulsation of the heart becomes invisible and the pressure in them drops to approximately 30 mm Hg. Art. A blood pressure reading can tell your doctor how your heart is working. If one or both numbers are higher than normal, this indicates high blood pressure. If it’s lower, it means it’s reduced. High blood pressure indicates that the heart is working too hard: it requires more effort to push blood through the vessels. It also indicates that a person has an increased risk of heart disease.

Types of Veins

Arteries and veins are designed roughly the same, but veins are thinner and have less muscle, which allows them to hold more blood. Veins typically contain about 70% of the body's blood at one time.

Venules are the smallest type of vein. They have very thin walls in order to hold a lot of blood. They pump low-oxygen blood through capillaries from the arteries directly into the veins. The blood then returns to the heart through a series of veins of increasing size and muscle.

There are two main types of veins: pulmonary and systemic.

Systemic veins are further classified into:

Deep veins : These veins usually have a corresponding artery nearby and are found in muscle tissue. These veins may have a one-way valve to prevent blood from flowing backwards.
Superficial veins : These veins do not have an artery of the same name nearby and are found close to the surface of the skin. They may also have a one-way valve.
Connecting veins : These small veins allow blood to flow from the superficial veins to the deep veins.

Basics of the venous system of the lower extremities

The peculiar structure of venous vessels and the composition of their walls determines their capacitive properties. Veins differ from arteries in that they are tubes with thin walls and lumens of relatively large diameter. Just like the walls of arteries, the composition of the venous walls includes smooth muscle elements, elastic and collagen fibers, among which there are much more of the latter.

In the venous wall, structures of two categories are distinguished: - supporting structures, which include reticulin and collagen fibers; - elastic-contractile structures, which include elastic fibers and smooth muscle cells.

Under normal conditions, collagen fibers maintain the normal configuration of the vessel, and if the vessel is exposed to any extreme impact, then these fibers maintain it. Collagen vessels do not take part in the formation of tone inside the vessel, and they also do not affect vasomotor reactions, since smooth muscle fibers are responsible for their regulation.

Veins consist of three layers: - adventitia - outer layer; - media - middle layer; - intima - inner layer.

Between these layers there are elastic membranes: - internal, which is more pronounced; - external, which differs very little.

The middle lining of the veins consists mainly of smooth muscle cells, which are located along the perimeter of the vessel in the form of a spiral. The development of the muscle layer depends on the width of the diameter of the venous vessel. The larger the diameter of the vein, the more developed the muscle layer is. The number of smooth muscle elements increases from top to bottom. The muscle cells that make up the tunica media are located in a network of collagen fibers that are highly convoluted in both the longitudinal and transverse directions. These fibers straighten only when a strong stretch of the venous wall occurs.

Superficial veins, which are located in the subcutaneous tissue, have a very developed smooth muscle structure. This explains the fact that superficial veins, unlike deep veins located at the same level and having the same diameter, perfectly resist both hydrostatic and hydrodynamic pressure due to the fact that their walls have elastic resistance. The venous wall has a thickness that is inversely proportional to the size of the muscle layer surrounding the vessel.

The outer layer of the vein, or adventitia, consists of a dense network of collagen fibers, which create a kind of frame, as well as a small number of muscle cells that are longitudinally located. This muscle layer develops with age and can be most clearly observed in the venous vessels of the lower extremities. The role of additional support is played by venous trunks of more or less large size, surrounded by dense fascia.

The structure of the vein wall is determined by its mechanical properties: in the radial direction the venous wall has a high degree of extensibility, and in the longitudinal direction it has a low degree. The degree of vessel distensibility depends on two elements of the venous wall - smooth muscle and collagen fibers. The rigidity of the venous walls during their strong dilatation depends on collagen fibers, which prevent the veins from stretching too much only under conditions of a significant increase in pressure inside the vessel. If changes in intravascular pressure are physiological in nature, then smooth muscle elements are responsible for the elasticity of the venous walls.

Venous valves

Venous vessels have an important feature - they have valves, with the help of which centripetal blood flow in one direction is possible. The number of valves, as well as their location, serves to ensure blood flow to the heart. On the lower limb, the largest number of valves are located in the distal sections, namely slightly below the place where the mouth of the large inflow is located. In each of the trunks of the superficial veins, the valves are located at a distance of 8-10 cm from each other. Communicating veins, with the exception of valveless perforators of the foot, also have a valve apparatus. Often, perforators can flow into deep veins with several trunks that resemble candelabra in appearance, which prevents retrograde blood flow along with the valves.

Vein valves usually have a bicuspid structure, and how they are distributed in a particular segment of the vessel depends on the degree of functional load. The framework for the base of the venous valve leaflets, which consist of connective tissue, is the spur of the internal elastic membrane. The valve leaflet has two endothelial-covered surfaces: one on the sinus side, the second on the lumen side. Smooth muscle fibers located at the base of the valves, directed along the axis of the vein, as a result of changing their direction to transverse, create a circular sphincter that prolapses into the sinus of the valve in the form of a kind of attachment rim. The valve stroma is formed by smooth muscle fibers, which run in fan-shaped bundles onto the valve leaflets. Using an electron microscope, you can detect oblong-shaped thickenings - nodules, which are located on the free edge of the valve leaflets of large veins. According to scientists, these are peculiar receptors that record the moment when the valves close. The leaflets of an intact valve are longer than the diameter of the vessel, so if they are closed, longitudinal folds are observed on them. The excessive length of the valve leaflets, in particular, is due to physiological prolapse.

The venous valve is a structure that has sufficient strength that can withstand pressures of up to 300 mmHg. Art. However, part of the blood is discharged into the sinuses of the valves of large veins through the thin tributaries that do not have valves flowing into them, which is why the pressure above the valve leaflets decreases. In addition, the retrograde blood wave is scattered against the rim of the attachment, which leads to a decrease in its kinetic energy.

With the help of fibrophleboscopy performed during life, you can imagine how the venous valve works. After the retrograde wave of blood enters the sinuses of the valve, its leaflets begin to move and close. The nodules transmit a signal that they have touched to the muscle sphincter. The sphincter begins to expand until it reaches the diameter at which the valve flaps open again and reliably block the path of the retrograde blood wave. When the pressure in the sinus rises above the threshold level, the opening of the draining veins occurs, which leads to a decrease in venous hypertension to a safe level.

Anatomical structure of the venous system of the lower extremities

The veins of the lower extremities are divided into superficial and deep.

The superficial veins include the cutaneous veins of the foot, located on the plantar and dorsal surfaces, large and small saphenous veins and their numerous tributaries.

The saphenous veins in the foot area form two networks: the cutaneous venous plantar network and the cutaneous venous network of the dorsum of the foot. The common dorsal digital veins, which enter the cutaneous venous network of the dorsum of the foot, as a result of the fact that they anastomose with each other, form the cutaneous dorsal arch of the foot. The ends of the arch continue in the proximal direction and form two trunks running in the longitudinal direction - the medial marginal vein (v. marginalis medialis) and the marginal lateral vein (v. marginalis lateralis). On the lower leg, these veins are continued in the form of the large and small saphenous vein, respectively. On the plantar surface of the foot, a subcutaneous venous plantar arch stands out, which, widely anastomosing with the marginal veins, sends the intercapitate veins to each of the interdigital spaces. The intercapitate veins, in turn, anastomose with those veins that form the dorsal arch.

The continuation of the medial marginal vein (v. marginalis medialis) is the great saphenous vein of the lower limb (v. saphena magna), which along the anterior edge of the inner side of the ankle passes to the lower leg, and then, passing along the medial edge of the tibia, goes around the medial condyle, exits to the inner thigh at the back of the knee joint. In the area of the lower leg, the GSV is located near the saphenous nerve, through which the skin on the foot and lower leg is innervated. This feature of the anatomical structure must be taken into account during phlebectomy, since damage to the saphenous nerve can cause long-term and sometimes life-long disturbances in the innervation of the skin in the lower leg area, as well as lead to paresthesia and causalgia.

In the thigh area, the great saphenous vein can have from one to three trunks. In the area of the oval-shaped fossa (hiatus saphenus) there is the mouth of the GSV (saphenofemoral anastomosis). At this point, its terminal section bends through the seropid process of the lata fascia of the thigh and, as a result of perforation of the cribriform plate (lamina cribrosa), flows into the femoral vein. The location of the saphenofemoral anastomosis can be 2-6 m below where the pupart's ligament is located.

Along its entire length, the great saphenous vein is joined by many tributaries that carry blood not only from the area of the lower extremities, from the external genitalia, from the area of the anterior abdominal wall, but also from the skin and subcutaneous tissue located in the gluteal region. In normal condition, the great saphenous vein has a lumen width of 0.3 - 0.5 cm and has from five to ten pairs of valves.

Permanent venous trunks that drain into the terminal portion of the great saphenous vein:

v. pudenda externa - external genital, or pudendal, vein. The occurrence of reflux along this vein can lead to perineal varicose veins;
v. epigastrica superfacialis - superficial epigastric vein. This vein is the most constant tributary. During surgery, this vessel serves as an important landmark by which the immediate proximity of the saphenofemoral anastomosis can be determined;
v. circumflexa ilei superfacialis – superficial vein. This vein is located around the ilium;
v. saphena accessoria medialis – posteromedial vein. This vein is also called the accessory medial saphenous vein;
v. saphena accessoria lateralis – anterolateral vein. This vein is also called the accessory lateral saphenous vein.

The external marginal vein of the foot (v. marginalis lateralis) continues with the small saphenous vein (v. saphena parva). It runs along the back of the lateral malleolus, and then goes up: first along the outer edge of the Achilles tendon, and then along its back surface, located next to the midline of the back surface of the leg. From this moment on, the small saphenous vein may have one trunk, sometimes two. Next to the small saphenous vein is the medial cutaneous nerve of the calf (n. cutaneus surae medialis), thanks to which the skin of the posteromedial surface of the leg is innervated. This explains the fact that the use of traumatic phlebectomy in this area is fraught with neurological disorders.

The small saphenous vein, passing through the junction of the middle and upper thirds of the leg, penetrates the zone of deep fascia, located between its layers. Reaching the popliteal fossa, the SVC passes through a deep layer of fascia and most often connects with the popliteal vein. However, in some cases, the small saphenous vein passes over the popliteal fossa and connects with either the femoral vein or tributaries of the deep femoral vein. In rare cases, the SVC flows into one of the tributaries of the great saphenous vein. In the area of the upper third of the leg, many anastomoses are formed between the small saphenous vein and the system of the great saphenous vein.

The largest permanent estial tributary of the small saphenous vein, which has an epifascial location, is the femoropopliteal vein (v. Femoroplitea), or vein of Giacomini. This vein connects the SVC with the great saphenous vein located on the thigh. If reflux occurs along the Giacomini vein from the GSV basin, this can cause varicose veins of the small saphenous vein. However, the opposite mechanism can also work. If valvular insufficiency of the SVC occurs, then varicose transformation can be observed in the femoropopliteal vein. In addition, the great saphenous vein will also be involved in this process. This must be taken into account during surgery, since if preserved, the femoropopliteal vein may be the reason for the return of varicose veins in the patient.

Deep venous system

Deep veins include veins located on the back of the foot and sole, on the lower leg, as well as in the knee and thigh area.

The deep venous system of the foot is formed by paired companion veins and arteries located near them. The companion veins encircle the dorsum and plantar region of the foot in two deep arcs. The dorsal deep arch is responsible for the formation of the anterior tibial veins - vv. tibiales anteriores, the plantar deep arch is responsible for the formation of the posterior tibial (vv. tibiales posteriores) and receiving peroneal (vv. peroneae) veins. That is, the dorsal veins of the foot form the anterior tibial veins, and the posterior tibial veins are formed from the plantar medial and lateral veins of the foot.

In the lower leg, the venous system consists of three pairs of deep veins - the anterior and posterior tibial veins and the peroneal vein. The main load for the outflow of blood from the periphery is placed on the posterior tibial veins, into which, in turn, the peroneal veins drain.

As a result of the fusion of the deep veins of the leg, a short trunk of the popliteal vein (v. poplitea) is formed. The knee vein receives the small saphenous vein, as well as the paired veins of the knee joint. After the knee vein enters this vessel through the lower opening of the femoropopliteal canal, it begins to be called the femoral vein.

The sural vein system consists of the paired gastrocnemius muscles (vv. Gastrocnemius), which drain the sinus of the gastrocnemius muscle into the popliteal vein, and the unpaired soleus muscle (v. Soleus), which is responsible for drainage into the popliteal vein of the sinus of the soleus muscle.

At the level of the joint space, the medial and lateral gastrocnemius veins flow into the popliteal vein through a common mouth or separately, emerging from the heads of the gastrocnemius muscle (m. Gastrocnemius).

Next to the soleus muscle (v. Soleus) the artery of the same name constantly passes, which in turn is a branch of the popliteal artery (a. poplitea). The soleus vein drains independently into the popliteal vein or proximal to the place where the opening of the gastrocnemius veins is located, or flows into it. The femoral vein (v. femoralis) is divided by most specialists into two parts: the superficial femoral vein (v. femoralis superfacialis) is located further from the place where the deep vein of the thigh flows into it, the common femoral vein (v. femoralis communis) is located closer to the place where it the deep vein of the thigh enters. This division is important both anatomically and functionally.

The most distal major tributary of the femoral vein is the deep femoral vein (v. femoralis profunda), which joins the femoral vein approximately 6-8 cm below where the inguinal ligament is located. A little lower is the place where the tributaries, which have a small diameter, enter the femoral vein. These tributaries correspond to small branches of the femoral artery. If the lateral vein that surrounds the thigh has not one trunk, but two or three, then at the same place its lower branch of the lateral vein flows into the femoral vein. In addition to the above vessels, the femoral vein, in the place where the mouth of the deep vein of the thigh is located, most often contains the confluence of two companion veins, forming a para-arterial venous bed.

In addition to the great saphenous vein, the common femoral vein also receives the medial lateral vein, which runs around the thigh. The medial vein is more proximal than the lateral vein. The place of its confluence can be located either at the same level with the mouth of the great saphenous vein, or slightly above it.

Perforating veins

Venous vessels with thin walls and varying diameters - from a few fractions of a millimeter to 2 mm - are called perforating veins. These veins are often characterized by an oblique course and are 15 cm long. Most perforating veins have valves that serve to direct the movement of blood from the superficial veins to the deep veins. Along with perforating veins, which have valves, there are valveless, or neutral, veins. Such veins are most often located in the foot. The number of valveless perforators compared to valved ones is 3-10%.

Direct and indirect perforating veins

Direct perforating veins are vessels through which the deep and superficial veins are connected to each other. The most typical example of a direct perforating vein is the saphenopopliteal anastomosis. The number of direct perforating veins in the human body is not so large. They are larger and in most cases are located in the distal areas of the limbs. For example, on the lower leg in the tendon part there are the perforating veins of Cockett.

The main task of indirect perforating veins is to connect the saphenous vein with the muscular vein, which has a direct or indirect connection with the deep vein. The number of indirect perforating veins is quite large. These are most often very small veins, which are mostly located where muscle masses are located.

Both direct and indirect perforating veins often communicate not with the trunk of the saphenous vein itself, but only with one of its tributaries. For example, the perforating veins of Cockett, which run along the inner surface of the lower third of the leg, where the development of varicose and post-thrombophlebic disease is quite often observed, is not connected to the deep veins by the trunk of the great saphenous vein itself, but only by its posterior branch, the so-called vein of Leonardo. If this feature is not taken into account, this can lead to relapse of the disease, despite the fact that the trunk of the great saphenous vein was removed during the operation. In total, there are more than 100 perforators in the human body. In the thigh area, as a rule, there are indirect perforating veins. Most of them are in the lower and middle third of the thigh. These perforators are located transversely, with their help the great saphenous vein is connected to the femoral vein. The number of perforators varies – from two to four. Under normal conditions, blood through these perforating veins flows exclusively into the femoral vein. Large perforating veins can most often be found immediately near the place where the femoral vein enters (Dodd's perforator) and where it exits (Gunther's perforator) from the Gunter's canal. There are cases when, with the help of communicating veins, the great saphenous vein is connected not to the main trunk of the femoral vein, but to the deep vein of the femur or to a vein that runs next to the main trunk of the femoral vein.

Anatomy

Veins and arteries consist of three layers:

Tunica adventitia : The outer layer of a blood vessel, composed of collagen and elastin. This layer allows the vessel to expand or contract, depending on the type of vein or artery. This function is important for controlling blood pressure.
Tunica media : This is the middle of the blood vessel. Elastin and muscle fibers form the shell of the carriers. The amount of elastin or muscle varies depending on the type of blood vessel. For example, elastic arteries contain few muscle fibers in their membranes.
Tunica Intima: This name refers to the inner layer of a blood vessel. It mainly contains elastic membranes and tissues and may include valves that help blood move in the right direction.

How is an ultrasound scan of leg veins performed?

From start to finish of the procedure it usually takes 20-30 minutes. Ask the specialist to remove clothing below the waist so that nothing interferes with the diagnosis. Next, the patient lies down on the couch and waits for further instructions. The study can be carried out in different positions: standing, sitting, lying on its side, etc.

The examination algorithm is as follows:

The doctor applies a special gel to the area being examined and then moves the sensor over the skin. On the screen, the ultrasound specialist sees the image and writes down the results. In order to refute or confirm the presence of blood clots, the specialist may ask you to cough or perform a Valsalva test. The doctor may also ask you to hold your breath or strain your legs very hard - this will help determine the condition of the veins during exercise.

The cardiovascular system

The cardiovascular system connects the heart and blood vessels together. The system forms a closed circuit of vessels that transport blood throughout the body.

The cardiovascular system is essential for maintaining life. This is the first major network of organs to develop in embryos.

All body tissues need oxygen and nutrients to survive. They also require the removal of waste, which is a byproduct of metabolism.

Blood is needed both to provide oxygen and nutrients and to remove waste from tissues.

The heart pumps blood throughout the body. It must work constantly and with sufficient force so that all tissues of the body receive enough blood to function. Cardiovascular disorders can have serious consequences.

Cardiovascular diseases are a group of disorders that affect the heart and blood vessels, such as coronary heart disease.

These diseases are the leading cause of death worldwide, accounting for approximately 17.9 million deaths in 2021.

Arteries and veins: conclusions

Arteries are a type of blood vessel that transports blood away from the heart. Veins carry blood back to the heart. Along with capillaries, these blood vessels are responsible for moving blood to the tissues around the body.

The heart pumps blood through a complex system of blood vessels. There are several types of arteries and veins with different functions. For example, some contain more muscle to change the amount of blood they carry.

The cardiovascular system is essential to life. Changes in the heart or blood vessels can be serious and sometimes fatal.

Do I need to prepare for an ultrasound of the veins of the lower extremities?

No special preparation is required to perform the diagnosis. However, for maximum reliability of the results, the doctor will give the following recommendations:

If you take medications regularly, you need to consult a doctor. If it turns out that the tablets can somehow affect the blood flow, the doctor may stop the medications a day before the upcoming procedure. But do not stop taking medications on your own, without consulting your doctor.
The patient must avoid coffee, strong tea, energy drinks and alcohol at least 10 hours before the procedure. You should also refrain from smoking.
If you are prone to swelling, try not to drink a lot of fluids before the ultrasound examination.
On the morning of the procedure, take a shower and remove hair from the skin of your legs. This will make it easier for the doctor to diagnose.
Immediately before the ultrasound examination, empty your bladder to avoid having to interrupt the examination.

The listed recommendations will improve the accuracy of the study. If you have any chronic diseases, especially those that can affect blood pressure or the condition of blood vessels, be sure to tell your doctor. Perhaps the doctor will adjust the rules for conducting the examination.