Final answer:
The structure of lymphatic capillaries, including their one-way valve system formed by overlapping endothelial cells and anchoring collagen fibers, enables them to absorb interstitial fluid, proteins, fats, and other larger molecules, and transport them through the lymphatic system for eventual return to the circulatory system.
Step-by-step explanation:
The structure of lymphatic capillaries is intimately related to their function in the body's circulatory and immune systems. These capillaries are formed by a one cell-thick layer of endothelial cells.
They are designed with overlapping cell flaps, which operate like one-way valves, allowing the entry of interstitial fluid when the pressure outside the vessel is high. Once inside, the fluid becomes known as lymph, and as it moves through the lymphatic system, it is cleaned of debris and pathogens at lymph nodes before eventually being returned to the circulatory system.
Collagen fibers anchor the capillaries to surrounding tissue, and fluctuating pressures in the interstitial space cause these fibers to pull on the endothelial flaps. This mechanism ensures that the lymphatic system can absorb excess fluid from the tissues as well as larger molecules like proteins and fats that cannot readily enter blood capillaries.
Lymphatic vessels also play a role in transporting absorbed fats from the intestine and delivering them to the blood, thus highlighting its importance in lipid metabolism.