Which structures are extremely small vessels that absorb excess fluid from tissue spaces?

Lymph capillaries are extremely small vessels designed to absorb excess fluid that accumulates in tissue spaces, facilitating the maintenance of fluid balance in the body. They are a critical component of the lymphatic system, which helps transport lymph—a fluid containing white blood cells, proteins, and waste products—back into circulation.

The structure of lymph capillaries allows them to effectively take up interstitial fluid, which can change in volume depending on various factors like activity levels and capillary permeability. These capillaries have a very thin wall that is permeable to larger molecules and fluids, unlike blood capillaries, which primarily transport blood and are less permeable.

Additionally, while lymph vessels play a role in transporting lymph away from tissues, they are larger than lymph capillaries and thus do not perform the primary function of absorbing excess fluid. Lymph nodes are involved in filtering lymph and are not responsible for fluid absorption. Capillaries, while crucial for exchanging nutrients and gases in tissues, are part of the circulatory system and do not specialize in absorbing excess interstitial fluid in the manner that lymph capillaries do.