Physiology of venous and lymphatic vessels Microcirculation The

Physiology of venous and lymphatic vessels

Microcirculation ● The microcirculation is the blood flow through blood vessels smaller than 100 µm (i. e. arterioles, capillaries, and venules). ● Function: 1. Transport of cells, oxygen and other substances to/from the tissues 2. Regulation of body temperature

Microcirculation consists of 3 components: 1. Haemomycrocyrculation (arterioles, precapillares, postcapillares venules, arterioles-venules anastomosis) n 2. Substance’ transport to intercticium, where some hydrostatic and oncotic pressure creates n 3. Limphatic vessels – their walls more thin than in arteriales and don’t contain basal membrane. Intercellular cracks – they are the main way of penetration of tissue fluid into the lumen of lymphatic vessels n

Morpho-functional properties of venous system n Veins are the vessels, which are carry out blood from organs, tissues to heart in right atrium. Only pulmonary vein carry out blood from lungs in left atrium. There are superficial (skin) and deep veins. They are very stretching and have a low elasticity. Valves are present in veins. Plexus venosus are storage of blood. Blood moving in veins under gravity.

Mechanism of regulation n Difference of pressure in venous system is a cause of blood moving. From the place of high pressure blood moving to the place of low pressure. n Negative pressure in chest is a cause of blood moving. n Contraction of skeletal muscles, diaphragm pump, peristaltic movement of veins walls are the causes of moving.

Blood flow in veins n Blood flows through the blood vessels, including the veins, primarily, because of the pumping action of the heart, although venous flow is aided by the heartbeat, the increase in the negative intrathoracic pressure during each inspiration, and contractions of skeletal muscles that compress the veins (muscle pump).

Venous pressure n Venous pressure is pressure of blood, which are circulated in veins. n Venous pressure in healthy person is from 50 to 100 mm H 2 O. n Increase of venous pressure in physiological condition may be in the action of physical activity. Determine of venous pressure is called phlebotonometry and give for doctors information about activity of right atrium.

Methods for assessing blood flow in the veins Magnetic resonance venography of normal sinuses of the brain (posterior -lateral projection).

Phlebography n а – atria wave –contraction of right atrium n с – passing of carotid artery pulse on vein n х – systole of ventricles n v – ventricular – filling of atrium by blood n y – passing of blood in right atria

Lymphatic system n The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. n The lymphatic system is a major component of the immune system.

Morpho-functional properties of lymphatic system n n n Lymph system has capillaries, vessels, where present valves, lymphatic nodes. In lymphatic nodes are lymphopoiesis, depo of lymph, their function is barrierfilter. Lymph flow in vein system through the chest lymph ductus. Functions of lymph: 1. support of constant level of volume and components of tissue fluid; 2. transport of nutritive substances from digestive tract in venous system; 3. barrier-filter function. 4. take place in immunology reactions.

Lympathatic system n The lymphatic system has three primary functions. First of all, it returns excess interstitial fluid to the blood. n The second function of the lymphatic system is the absorption of fats and fat-soluble vitamins from the digestive system and the subsequent transport of these substances to the venous circulation. n The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease.

Lymphatic capillaries n Lymphatic capillaries begin as one side closed capacities, which are drained by smallest lymphatic vessels. n Pressure of lymph inside the capillary is lower than in intracellular space, which helps to lymph flow. Capillary wall has basal membrane and one layer of endotheliocytes.

Lymph -The lymphatic capillaries are responsible for returning interstitial fluid and proteins to the vascular compartment. -Lymph capillaries merge into large thoracic duct which empties into the large veins. -Lymph vessels have smooth muscle for movement and surrounding skeletal muscle contractions and contain open ends.

Lymph n n n Lymph originates as blood plasma that leaks from the capillaries of the circulatory system, becoming interstitial fluid, and filling the space between individual cells of tissue. Plasma is forced out of the capillaries by hydrostatic pressure, and as it mixes with the interstitial fluid, the volume of fluid accumulates slowly. Most of the fluid is returned to the capillaries by osmosis (about 90% of the former plasma). The excess interstitial fluid is collected by the lymphatic system by diffusion into lymph capillaries, and is processed by lymph nodes prior to being returned to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid.

Lymphatic circulation n n The lymphatic system acts as a secondary circulatory system, except that it collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due to peristalsis, the operation of semilunar valves in the lymph veins, and the milking action of skeletal muscles. Like veins, lymph vessels have one-way, semilunar valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.

Function of Limphatic node 1. Lymph nodes play role of filtration barrier. This function possible due to the presence of macrophages and net of reticular fibers in the lumen of the sinuses. 2. Lymph nodes are organs of lymphopoiesis (B - and Tlymphocytes) 3. Lymph nodes – they are deposit of lymph. The main drains of the lymphatic system in which lymph flows in to the venous system is the Lymphatic thoracic duct and cervical lymphatic duct, which collects lymph from the head and surrounding areas.

Ultrasound examination of lymph nodes

Production of lymph n Fluid efflux normally exceeds influx across the capillary walls, but the extra fluid enters the lymph and drains through them back into the blood. This keeps the interstitial fluid pressure from rising and promotes the turnover of tissue fluid. n The normal 24 -hour lymph flow is 2 -4 L.

Mechanism of lymph flow n Lymph flow is due to movements of skeletal muscle, the negative intrathoracic pressure during inspiration, the suction effect of high velocity flow of blood in the veins in which the lymphatic vessels terminate, and rhythmic contractions of the walls of the large lymph ducts. n Since lymph vessels have valves that prevent backflow, skeletal muscle contractions push the lymph toward the heart. n Pulsations of arteries near lymphatic vessels may have a similar effect.

Thymus n The thymus is an organ located in the upper anterior portion of the chest cavity. n The thymus plays an important role in the development of the immune system in early life, and its cells form a part of the body's normal immune system. n It is most active before puberty, after which it shrinks in size and activity in most individuals and is replaced with fat. n Function: Production (maturation) of T cells.

Spleen The spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. n The spleen is the largest collection of lymphoid tissue in the body. n It is regarded as one of the centres of activity of the reticuloendothelial system. n Its absence leads to a predisposition to certain infections. n Function: n – – Blood reservoir Destruction of old red blood cells Immune functions Blood cells production in embryogenesis

Tonsils n Tonsils are clusters of lymphatic tissue just under the mucous membranes that line the nose, mouth, and throat (pharynx). n There are three groups of tonsils. n The pharyngeal tonsils are located near the opening of the nasal cavity into the pharynx. When these tonsils become enlarged they may interfere with breathing and are called adenoids.

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