Final answer:
Lymphatic capillaries are highly permeable due to minivalves in their walls that open to allow interstitial fluid and larger molecules to enter when interstitial pressure increases. Collagen filaments also aid in this process. The lymphatic system transports and filters lymph before returning it to the bloodstream.
Step-by-step explanation:
Lymphatic capillaries owe their permeability to the presence of numerous minivalves in their walls. These minivalves function as one-way gates that respond to increases in interstitial pressure. When the pressure is low, the minivalves close to prevent backflow. As the pressure increases, they open up, allowing fluids and larger molecules such as proteins from the tissues to enter the lymphatic system. This is further facilitated by the collagen filaments that anchor the capillaries, which pull on the endothelial cell flaps as interstitial pressure rises, widening the spaces between cells for more accessible fluid entry.
The lymph fluid, once inside the lymphatic capillaries, is transported throughout the lymphatic system and is filtered through lymph nodes before being returned to the bloodstream. This system plays a crucial role in maintaining fluid balance in the body and in immune function by transporting white blood cells and filtering out pathogens.