The lymphatic system

The lymphatic system is closely associated with the cardio-vascular system and connects with it. The lymphatic system removes tissue fluid and proteins from the tissue spaces and returns it to the blood via the subclavian veins. This fluid in the lymphatic vessels is called lymph. The system also transports fats from the small intestine to the blood, and it plays an important role in protecting the body against infection.

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The parts of the lymphatic system are:

^ lymphatic capillaries, vessels and trunks: these are tubes that carry the fluid ^ lymphatic nodes: arranged in groups throughout the body ^ lymphatic organs: such as the spleen, thymus gland and tonsils

^ lymphatic ducts: there are two ducts, the right lymphatic duct and the thoracic duct, which empty into the right and left subclavian veins

^ lymph: the fluid flowing through the vessels.

Lymphatic capillaries begin as blind-end tubes forming a network among the tissue spaces. Their walls are very thin and allow fluid, larger proteins and particles to pass through. Because these larger particles and proteins are unable to pass through blood vessel walls, they are returned to the blood via the lymphatic system. These minute lymphatic capillaries then join together to form larger lymphatic vessels. Lymphatic vessels are very similar to veins in structure, but have thinner walls and a greater number of valves to prevent backward flow.

All lymphatic vessels drain into lymphatic nodes. These are strategically placed in groups along the path of the vessels. Many afferent vessels enter a node, but only one or two efferent vessels

Posterior auricular

Occipital lymphatic nodes

Cervical lymphatic nodes

Figure 2.14 The lymphatic system of the head.

Anterior auricular lymph glands

Posterior auricular

Occipital lymphatic nodes

Anterior auricular lymph glands

Mandibular lymphatic nodes

Cervical lymphatic nodes

Figure 2.14 The lymphatic system of the head.

Mandibular lymphatic nodes leave. Lymphatic nodes are small, bean-shaped structures up to 2 cm in length. Here the lymph is filtered, foreign substances are trapped and destroyed, and lymphocytes are produced that combat infection and disease. The efferent vessels leaving the nodes join to form lymphatic trunks. These empty into two main ducts:

J thoracic duct: this receives lymph from the left arm, left side of the head and chest and all the body below the ribs; it empties into the left subclavian vein

| right lymphatic duct: this receives lymph from the right upper quarter of the body, i.e. the right arm, right side of head and chest; it then empties into the right subclavian vein.

In this way the lymph is transported from the tissue spaces back to the blood. Any malfunction or blockage of the lymphatic system will result in swelling of the tissues known as oedema.

The speed at which lymph flows through the system depends on many factors, for example the contraction and relaxation of muscles help its return, as do negative pressure and movement of the chest during respiration. Exercise is therefore very important in aiding the flow of lymph. Areas of stasis and oedema can be improved by moving the joints and exercising the muscles

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Figure 2.15 Cross-section of a lymphatic node.

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Figure 2.15 Cross-section of a lymphatic node.

of the swollen area. The volume of lymph passing into the capillaries and vessels depends on the pressure inside and outside the vessels.

Massage is very effective at speeding up the flow of lymph in the lymphatic vessels and thereby increasing the drainage of tissue fluid. Long effleurage strokes exert pressure and push the lymph along in the vessels towards the nearest set of lymphatic nodes (remember always move towards the nearest set of lymphatic nodes). The pressure (petrissage) manipulations squeeze the tissues. This pressure increases the amount of tissue fluid passing into the vessels to be drained away.

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