Basics of the venous system of the lower limbs

woman with damaged leg veins at doctor's appointment

The particular structure of the venous vessels and the composition of their walls determines their capacitive properties. Veins differ from arteries in that they are thin-walled tubes and lumens of relatively large diameter. In addition to the walls of the arteries, the composition of the venous walls includes smooth muscle elements, elastic fibers and collagen, among which there are many more.

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.

Collagen fibers under normal conditions maintain the normal configuration of the vessel, and if an extreme impact is exerted on the vessel, these fibers maintain it. Collagen vessels do not participate in the formation of tone within the vessel and also do not affect vasomotor reactions, since smooth muscle fibers are responsible for their regulation.

Veins are made up of three layers:

  • adventitia - outer layer;
  • middle - middle layer;
  • intimate - the inner layer.

There are elastic membranes between these layers:

  • internal, which is more pronounced;
  • exterior, which is slightly different.

The median membrane of the veins is mainly composed 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 venous vessel diameter. The larger the diameter of the vein, the more developed the muscle layer. The number of smooth muscle elements increases from top to bottom. The muscle cells that make up the central membrane are found in a network of collagen fibers, which are highly curled in both the longitudinal and transverse directions. These fibers straighten only when there is a strong stretching of the venous wall.

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

The outer layer of the vein, or adventitia, is a dense network of collagen fibers, which create a kind of skeleton, as well as a small number of muscle cells, which have a longitudinal arrangement. This muscle layer develops with age; can be seen most clearly 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 a dense band.

The structure of the venous 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 is small. The degree of vascular extensibility depends on two elements of the venous wall: smooth muscle and collagen fibers. The stiffness of the venous walls during their strong dilation depends on the collagen fibers, which prevent the veins from stretching very much only under conditions of a significant increase in pressure inside the vessel. If the changes in intravascular pressure are physiological in nature, then the smooth muscle elements are responsible for the elasticity of the venous walls.

Venous valves

vein valve of the leg

Venous vessels have an important feature - they have valves with which centripetal blood flow in one direction is possible. The number of valves, as well as their location, serve to provide blood flow to the heart. On the lower limb, the greatest number of valves are located in the distal regions, i. e. slightly below the place where the mouth of a large tributary is located. In each of the highways 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 foot perforators, also have a valvular apparatus. Often, perforators can enter deep veins in multiple candlestick-like trunks, preventing retrograde blood flow along with the valves.

Venous valves usually have a bicuspid structure, and their distribution in a particular segment of the vessel depends on the degree of functional load. The structure for the base of the cusps of the venous valves, which is made up of connective tissue, is a spur of the inner elastic membrane. The cusp of the valve has two surfaces covered with endothelium: one on the side of the sinus, the other on the side of the lumen. Smooth muscle fibers located at the base of the valves, directed along the axis of the vein, as a result of the change of direction towards the transverse, create a circular sphincter that prolapses into the sinus of the valve in the form of a kind of edge attachment. The valve stroma is formed by smooth muscle fibers, which are grouped in the form of a fan at the valve flaps. With the help of an electron microscope, you can find elongated thickenings - nodules that are located on the free edge of the valve cusps of the large veins. According to the scientists, these are a kind of receptors that register when the valves close. The cusps of an intact valve are longer than the diameter of the vessel, therefore, if they are closed, longitudinal folds are observed on them. The excessive length of the valve leaflet, in particular, is due to physiological prolapse.

The venous valve is a structure robust enough to withstand pressures up to 300 mmHg. Art. However, some of the blood is discharged into the sinuses of the valves of the large veins through thin tributaries that do not have valves flowing into them, as a result of which the pressure above the cusps of the valves decreases. In addition, the retrograde blood wave is scattered around the edge of the attack, which leads to a decrease in its kinetic energy.

With the help of life-long fibrophleboscopy, one can imagine how the venous valve works. After the retrograde blood wave enters the sinuses of the valve, its cusps move and close. The nodules transmit a signal that they have touched the muscle sphincter. The sphincter begins to expand until it reaches the diameter where the valve flaps reopen 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 mouth of the draining veins occurs, which leads to a decrease in venous hypertension to a safe level.

Anatomical structure of the venous pelvis of the lower limbs

The veins of the lower limbs are divided non-superficial and deep.

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

The saphenous veins in the foot area form two networks: the plantar cutaneous venous network and the cutaneous venous network of the dorsum of the foot. Common dorsal digital veins, which enter the cutaneous venous network of the dorsum of the foot, due to the fact that they anastomose together, form the dorsal cutaneous 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 lateral marginal vein (v. Marginalis lateralis). On the lower leg, these veins have a continuation in the form of large and small saphenous veins, respectively. On the plantar surface of the foot the subcutaneous venous plantar arch stands out which, extensively anastomosed with the marginal veins, sends the intercapital veins into each of the interdigital spaces. The intercapital 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 extremity (v. Safena 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, folds around the medial condyle, goes to the inside of the thigh from the back of the knee joint. In the area of the lower leg, the GSV is located near the saphenous nerve, with the help of which the skin of the foot and lower leg is innervated. This feature of the anatomical structure should be taken into account during phlebectomy, as 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 paresthesias and causalgies.

In the thigh area, the great saphenous vein can have one to three trunks. In the area of the oval fossa (saphenous hiatus) is the mouth of the GSV (saphenofemoral anastomosis). At this point its terminal section makes a curvature through the seropid process of the broad fascia of the thigh and, due to the perforation of the ethmoid plate (lamina cribrosa), flows into the femoral vein. The location of the saphenofemoral anastomosis can be located 2-6 m below the place where the pupar ligament is located.

The great saphenous vein is joined along its entire length by numerous tributaries that carry blood not only from the lower limbs, the external genital organs, the anterior abdominal wall, but also from the skin and subcutaneous tissue located in the gluteal region. In a normal state, the great saphenous vein has a lumen width of 0. 3 - 0. 5 cm and has five to ten pairs of valves.

Permanent venous trunks that flow into the terminal section of the great saphenous vein:

  • v. external pudenda - external genital, or shame, vein. The occurrence of reflux in this vein can lead to perineal varicose veins;
  • v. epigastrica superfacialis - superficial epigastric vein. This vein is the most constant inflow. During surgery, this vessel acts as an important reference point by which it is possible to determine the immediate proximity of the saphenofemoral anastomosis;
  • v. circumflexa ilei superfacialis - superficial vein. This vein is located around the ileum;
  • v. accessory saphenous medialis - posterior medial vein. This vein is also called the accessory medial saphenous vein;
  • v. saphenous accessory lateralis - anterolateral vein. This vein is also called the accessory lateral saphenous vein.
the location of the veins in the leg

The external marginal vein of the foot (v. Marginalis lateralis) continues with a small saphenous vein (v. Safena parva). It runs along the back of the lateral ankle, then goes up: first along the outer edge of the Achilles tendon, then along its posterior surface, located near the midline of the posterior surface of the lower leg. From this point on, the little saphenous can have one trunk, sometimes two. Near the small saphenous vein is the medial cutaneous nerve of the calf (n. Cutaneus surae medialis), for 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 third of the leg, penetrates the area of the deep fascia, located between its leaves. Reaching the popliteal fossa, the SSV passes through the deep leaf of the fascia and most often connects to the popliteal vein. However, in some cases, the small saphenous vein passes over the popliteal fossa and connects with the femoral vein or with tributaries of the deep thigh vein. In rare cases, the SSV flows into one of the tributaries of the great saphenous vein. In the area of the upper third of the leg between the small saphenous vein and the great saphenous vein system, many anastomoses are formed.

The largest permanent inflow near the mouth of the small saphenous, which has an epifascial seat, is the femoro-popliteal vein (see Femoropoplitea), or Giacomini's vein. This vein connects the SSV with a large saphenous vein located in the thigh. If reflux occurs through the Giacomini vein from the GSV pool, due to this, varicose expansion of the small saphenous vein can begin. However, the opposite mechanism can also work. If valvular insufficiency of the SSV occurs, a varicose transformation can be observed in the femoro-popliteal vein. Furthermore, the great saphenous vein will also be involved in this process. This must be taken into consideration during surgery, as if preserved, the femoro-popliteal vein may be the reason for the return of the 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, and in the knee and thigh area.

The deep venous system of the foot is made up of associated veins and arteries that are located close to them. The companion veins in two deep arches fold around the back and plantar region of the foot. The deep dorsal arch is responsible for the formation of the anterior tibial veins - vv. tibiales anteriores, the deep plantar arch is responsible for the formation of the posterior tibialis (vv. tibiales posteriores) and for the reception of the peroneal veins (vv. peroneae). That is, the dorsal veins of the foot form the anterior tibial veins, and the posterior tibial veins are formed by the medial and lateral plantar 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 fibular vein. The main load on the outflow of blood from the periphery is assigned to the posterior tibial veins, into which, in turn, the peroneal veins are drained.

As a result of the fusion of the deep veins of the leg, a short trunk of the popliteal vein is formed (see Poplitea). The knee vein houses 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 femoro-popliteal canal, it begins to be called the femoral vein.

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

At the level of the joint space, the medial and lateral gastrocnemius vein flows into the popliteal vein from the common mouth or separately, leaving the heads of the gastrocnemius muscle (m. Gastrocnemius).

Near 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 fluke vein flows independently into the popliteal vein or is proximal to or runs into the mouth of the calf veins.

The femoral vein (v. Femoralis) is divided into two parts by most specialists: the superficial femoral vein (v. Femoralis superfacialis) is located farther from the confluence of the deep thigh vein, the common femoral vein (v. Femoralis communis) ) is closest to where the deep vein of the thigh empties. This unit is important both anatomically and functionally.

The most distal large tributary of the femoral vein is the deep thigh vein (v. Femoralis profunda), which flows into the femoral vein approximately 6-8 cm below where the inguinal ligament is located. Slightly lower is the point where the small diameter tributaries enter the femoral vein. These tributaries correspond to small branches of the femoral artery. If the lateral vein, which surrounds the thigh, does not have one trunk, but two or three, then in the same place its lower branch of the lateral vein flows into the femoral vein. In addition to the aforementioned vessels, in the femoral vein, in the place where the mouth of the deep vein of the thigh is located, there is more often the confluence of two companion veins that form the paraarterial venous bed.

In addition to the great saphenous vein, the lateral medial veins that run around the thigh also converge in the common femoral vein. The medial vein is more proximal than the lateral one. The place of its confluence can be located both at the same level as the mouth of the great saphenous vein, and slightly above it.

perforating veins

perforating veins of the leg

Venous vessels with thin walls and different diameters - from a few fractions of a millimeter to 2 mm - are called perforating veins. These veins are often oblique and 15 cm long. Most perforating veins have valves that direct blood flow from the superficial veins to the deep veins. Along with the perforating veins, which have valves, there are those without valve or neutral. These veins are most often located not in the foot. The number of spikes without a valve compared to the valve is 3-10%.

Direct and indirect perforating veins

Direct perforating veins are vessels through which deep and superficial veins are connected to each other. The saphenopliteal junction is the most typical example of a straight perforating vein. There are not many direct perforating veins in the human body. They are larger and in most cases are found in the distal regions of the limbs. For example, the Cockett's perforating veins are found in the tendon part of the lower leg.

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

Both direct and indirect perforating veins often communicate not with the trunk of the saphenous vein itself, but with only one of its tributaries. For example, the Cockett's perforating veins running along the inner surface of the lower third of the leg, on which the development of varicose and post-thrombophlebic diseases is quite often observed, is not connected to the trunk of the same great saphenous vein as the deep veins, but only its posterior branch, the so-called Leonardo's vein. If this feature is not taken into account, this can lead to a relapse of the disease, despite the fact that during the operation the trunk of the great saphenous vein was removed. 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 are found in the lower and middle thirds of the thigh. These perforators are placed transversely to connect the great saphenous vein to the femoral vein. The number of perforators is different: from two to four. Normally, blood flows through these perforating veins exclusively into the femoral vein. The large perforating veins are most often found immediately near the point where the femoral vein enters (Dodd's perforator) and exits (Gunther's) Gunter's canal. There are cases when, with the help of communicating veins, the great saphenous vein connects not with the main trunk of the femoral vein, but with the deep vein of the thigh or with a vein that runs next to the main trunk of the femoral vein. .