Which receptors are stimulated by the drop in PaO2 that occurs when lowlanders travel to high altitudes?

White blood cells (WBCs) are also called ________. 

Fill in the blank(s) with the appropriate word(s).

The ____ hormones are made of amino acids and do not cross cell membranes easily. 

A. steroidal B. nonsteroidal C. prostaglandins D. gonadal E. adrenal