The lymphatic system is a one-way system because it functions to return excess tissue fluid to the circulation (Applegate, 2000, 287). It only flows in one direction. The blood vascular system is a two-way system because it brings oxygen and nutrients to the tissues via the arteries, and takes carbon dioxide and waste products away from the tissues via the veins.
35.3 Lymphatic vessels resemble veins in that they have thin walls, and they have valves to prevent backflow (Applegate, 20000, 289).
35.4 Lymphatic capillaries differ from blood capillaries in that they begin in the tissue spaces as blind-ended sacs, whereas blood capillaries are extensions of arterioles (Applegate, 2000, 288). The endothelium of the lymphatic capillaries is also different in that the simple squamous cells overlap to form a one-way valve which lets tissue fluid in but does not let anything out. This differs from blood capillaries in which there is two-way exchange across the endothelium.
35.5 The function of the lymphatic vessels is to return excess tissue fluid to the circulation (Applegate, 2000, 287). They are also responsible for the absorption of fats and fat-soluble vitamins from the digestive system. This occurs in special lymphatic capillaries known as lacteals, which are found in the center of the villi in the small intestine.
35.6 Lymph fluid has a similar composition to blood plasma (Applegate, 2000, 287)). As blood passes through the capillaries, fluids pass through the capillary walls at the arterial end and becomes interstitial fluid. Ninety percent of this fluid is returned to the capillaries, but the rest remains as interstitial fluid, along with small protein molecules which also leak from the capillaries. When the pressure of the interstitial fluid builds up, it is resorbed by the lymphatic capillaries and is then known as lymph.
35.7 There is no pump in the lymphatic system such as the heart in the cardi...