The heart sends returned blood to the lungs, where oxygen is exhaled and carbon dioxide is inhaled.

Abnormalities in metabolism are MOST likely caused by dysfunction of the:

A. pancreas. B. thyroid gland. C. adrenal gland. D. parathyroid gland

Nonsteroidal hormones bind to receptors on the surface of the cell and activate a(n) ________ that causes enzymes inside the cell to be turned on. 

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