Answer:
The correct answer is ''originate as closed-ended tubes associated with blood capillary networks.''
Explanation:
The lymphatic vessel system begins within the tissues in the form of tubes closed at one end called lymphatic capillaries (chyliferous in the intestine). These have an internal endothelial lining, similar to that of blood capillaries. These vessels are found in greater numbers in the skin, the digestive tract, and the respiratory system. The tissue fluid penetrates the lymphatic capillaries by diffusion, with the help of a small indirect pressure gradient, which gives it the arterial pressure. The walls of the lymphatic capillaries offer little resistance to the entry of substances; they are more permeable than capillaries in the blood system. The tiny capillaries form larger vessels, similar to the venules and veins of the blood vessel system. The walls are thinner than those of the veins of the blood system and its valves much more numerous.
