12.3   True/False

1) The lymphatic vessels and cardiovascular veins are similar in that they operate under low pressure and some larger ones have valves.

2) Lymph flows in one direction only:  toward the heart.

3) The lymph nodes filter bacteria, viruses, and tumor cells from blood on its way back to the heart.

4) Lymph nodes have more efferent vessels draining the node than afferent vessels bringing fluid into the node. 

5) The  most important function of the thymus gland is to destroy worn-out red blood cells and return some of the products to the liver.

6) Natural killers are unique phagocytic defense cells that can kill cancer cells and virus-infected body cells well before the immune system is activated.

7) Injured cells release chemicals such as histamine and kinins that dilate vessels, attract phagocytes and activate pain receptors.

8) The final disposal of cell debris as inflammation subsides is performed by neutrophils.

9) The nonspecific defense by which complement proteins attach to sugars or proteins on the surface of foreign cells is called complement fixation.

10) Chemicals secreted by white blood cells and macrophages exposed to foreign substances that can increase body temperature are called pyrogens.