Lymphatic System Why we need a Lymphatic System: Since the heart pumps with such a high pressure and force, it forces some fluid out of the capillaries, meaning that some fluid pumped by the heart does not make it back to the heart (this fluid is not exactly blood, but instead interstitial fluid and plasma) Lymphatic vessels collect this interstitial fluid that leaves the vessels and brings it back into circulation Stuff leaks in between the endothelial cells lining the blood vessel (bigger proteins and molecules won’t get out but smaller things like water/small proteins will) The reason shit leaks out is because there are cells on the outsides of the blood vessels that need to be fed by things like hormones, glucose, etc. If they were tightly sealed then they would just die (O2 is so small it can literally just go right through the endothelial cells) How Lymphatic Vessels Move Fluid: Lymph reenters the blood circulation at the very end of the systemic circulation, this is because the pressure here is at its lowest and therefore easiest to get lymph back into Lymph valves allow for lymph to move unidirectionally and prevent fluid from moving backward Smooth muscle surrounding the lymph vessels also contract in order to keep fluid moving unidirectionally Lymph reenters specifically into the subclavian veins which feed into the superior vena cava The Lymphatic System’s Role in Immunity: Infection is typically localized and does not actually enter the bloodstream, just the surrounding tissue of the infected area B cells and T cells are a part of the adaptive immune system which reacts to specific antigens and have a much more powerful effects against them Macrophages typically fight off more types of invaders but aren’t as effective as B/T cells are against specific invaders The body will take these antigens/invaders and sweep them up into the lymphatic system, specifically to a lymph node which has B/T cells that can specialize and mount a response to the attack Lymph nodes kind of act as filters for the lymph before giving it back into blood circulation Lipids & Protein Transport in the Lymphatic System: Chylomicrons containing fats cannot readily diffuse into the blood vessels but can enter the lymphatic system Lacteals are the lymphatic vessels found surrounding the small intestine Basically, things that need to get into the blood but can’t necessarily fit go in through the lymphatic vessels and eventually into the bloodstream What Actually is Lymph: Lymph is technically once it is actually in the lymphatic vessel, before it is just called extracellular fluid About 50% less protein in lymph than in the blood (typically smaller proteins) Lymph is primarily made up of water We produce about 3 L of lymph per day (20 L is squeezed out but 17 L are diffused back in)