Lymphatic System Lecture Notes PDF

Lecture Dr.Ahlam Kadhim LYMPHATIC SYSTEM **[Objective:]** 1\. main composition of Lymphatic system. 2.Composition of lymph 3\. Role of Lymphatic System in Controlling Interstitial Fluid volume and pressure LYMPHATIC SYSTEM The lymphatic system represents an accessory route through which fluid...

Lecture Dr.Ahlam Kadhim LYMPHATIC SYSTEM **[Objective:]** 1\. main composition of Lymphatic system. 2.Composition of lymph 3\. Role of Lymphatic System in Controlling Interstitial Fluid volume and pressure LYMPHATIC SYSTEM The lymphatic system represents an accessory route through which fluid can flow from the interstitial spaces into the blood. Most importantly, the lymphatics can carry proteins and large particulate matter away from the tissue spaces, neither of which can be removed by absorption directly into the blood capillaries. **LYMPH CHANNELS OF THE BODY** Almost all tissues of the body have special lymph channels that drain excess fluid directly from the interstitial spaces.. Essentially all the lymph vessels from the lower part of the body eventually empty into the *thoracic duct*, which in turn empties into the blood venous system at the juncture of the *left* internal jugular vein and left subclavian vein. Lymph from the left side of the head, left arm, and parts of the chest region also enters the thoracic duct before it empties into the veins. Lymph from the right side of the neck and head, right arm, and parts of the right thorax enters the *right lymph* *duct* (much smaller than the thoracic duct), which empties into the blood venous system at the juncture of the *right* subclavian vein and internal jugular vein. **Terminal Lymphatic Capillaries and Their Permeability.** Most of the fluid filtering from the *arterial ends* of *blood capillaries* flows among the cells and finally is reabsorbed back into the *venous ends* of the *blood capillaries* but, on average, about one tenth of the fluid instead enters the *lymphatic capillaries* and returns to the blood through the lymphatic system rather than through the venous capillaries. The total quantity of all this lymph is normally only 2 to 3 L/day. There is a special structure of the lymphatic capillaries, the edge of one endothelial cell overlaps the edge of the adjacent cell in such a way that the overlapping edge is free to flap inward, thus forming a minute valve that opens to the interior of the lymphatic capillary. Interstitial fluid, along with its suspended particles, can push the valve open and flow directly into the lymphatic capillary. However, this fluid has difficulty leaving the capillary once it has entered because any backflow closes the flap valve. Thus, the lymphatics have valves at the very tips of the terminal lymphatic capillaries, as well as valves along their larger vessels, up to the point where they empty into the blood circulation. **FORMATION OF LYMPH** Lymph is derived from interstitial fluid that flows into the lymphatics. Therefore, lymph as it first enters the terminal lymphatics has almost the same composition as the interstitial fluid. The protein concentration in the interstitial fluid of most tissues averages about 2 g/dl, and the protein concentration of lymph flowing from these tissues is near this value. Lymph formed in the liver has a protein concentration as high as 6 g/dl, and lymph formed in the intestines has a protein concentration as high as 3 to 4 g/dl. the thoracic duct lymph, which is a mixture of lymph from all areas of the body, usually has a protein concentration of 3 to 5 g/dl. The lymphatic system is also one of the major routes for absorption of nutrients from the gastrointestinal tract, especially for absorption of virtually all fats in food, as. After a fatty meal, thoracic duct lymph sometimes contains as much as 1% to 2% fat. Finally, even large particles, such as bacteria, can push their way between the endothelial cells of the lymphatic capillaries and in this way enter the lymph. As the lymph passes through the lymph nodes, these particles are almost entirely removed and destroyed, **Lymphatic System Plays a Key Role in Controlling Interstitial Fluid Protein Concentration, Volume, and Pressure** It is already clear that the lymphatic system functions as an overflow mechanism to return excess proteins and excess fluid volume from the tissue spaces to the circulation. Therefore, the lymphatic system also plays a central role in controlling the following: \(1) concentration of proteins in the interstitial fluids; as small amounts of proteins leak continuously out of the blood capillaries into the interstitium. Only minute amounts of the leaked proteins return to the circulation by way of the venous ends of the blood capillaries. Therefore, these proteins tend to accumulate in the interstitial fluid, which in turn increases the colloid osmotic pressure \(2) volume of interstitial fluid; The increasing colloid osmotic pressure in the interstitial fluid shifts the balance of forces at the blood capillary membranes in favor of fluid filtration into the interstitium. \(3) The increasing interstitial fluid pressure greatly increases the rate of lymph flow, which carries away the excess interstitial fluid volume and excess protein that has accumulated in the spaces. **[In summery Function of lymph:]** **1-**Reserve of fluid and proteins. **2-**Nutritional function. Lymphatic system is one of major route for absorption of nutrients from the gastrointestinal tract especially for absorption of all fatty meal. **3-** Immune function. Bacteria and other microorganisms in lymph pass through the lymph nodes are destroyed. References : Ganong , Guyton and Hall text book