Lymphatic System

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The lymphatic system consists of a network of low pressure lymphatic vessels and lymphoid tissues/organs (eg spleen, tonsils). The vessels are responsible for transporting fluids back to the blood that has filtered out from capillaries into the tissue spaces. The vessels form a one-way system to the heart.

• colourless clear fluid – similar to blood but with less protein

Structure of lymphatic vessels
Begin as ‘blind’ ended porous lymph capillaries that weave between tissue cells and blood capillaries. Occur everywhere that there are capillaries except for bone and teeth and CNS.

Endothelial cells that form walls of lymphatic capillaries are not tightly bound – they loosely over lap  flaps form minivalves. Fine filament anchor the endothelial cells to the surrounding tissues  when there is an increase in interstitial fluid, the filaments pull on the endothelial cells, the flaps  fluid can enter lymphatic capillary. When fluid pressure becomes greater in lymphatic vessel  endothelial cell flaps are forced back together  lymph does no leak out into tissues and forces it along vessel.

From lymphatic capillaries, the lymph flows through successively larger lymph vessels. The lymphatic capillaries converge to form collecting vessels, that often travel along with veins and arteries in a common connective tissue sheath. Collecting vessels converge to form larger lymphatic trunks  two collecting ducts (right lymphatic duct and thoracic duct)  drains into subclavian vein

Lymphatic collecting vessels – have three tunics like veins.

Lymph nodes:
Lymph is filtered through nodes for cleansing – phagocytic macrophages in node destroy any microorganisms and other debris that has entered lymph

Also play a role in activating the immune system.

Begin as minute blind ended endothelial sacks in intercellular spaces of all tissues – in lower limb they are mostly in the skin and dermal plexus.

The end sacs join together  delicate plexus of small vessels within interstitial spaces  continue to join together in tissues around arterioles and venules  progressively unite to form larger collecting vessels.

In lower limb most of the collecting vessels begin on the dorsum of the foot and around ankle  run up medial side of leg, close to saphenous vein  end at inguinal lymph nodes.
Second, smaller group – begins on heel and lateral side of foot  run up back of calf to popliteal lymph gland  efferents join deep lymphatics. A valve is at every 2-3mm.

Some deeper lymphatics usually run alongside posterior tibial and peroneal arteries

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