In my field, human anatomy and physiology (A&P), like many others, it is customary to end each textbook chapter with a concept review and self-testing exercises. For the first five editions of my Anatomy & Physiology—The Unity of Form and Function, I titled my end-of-chapter feature “Chapter Review” and its first section, “Review of Key Concepts.” I followed the traditional practice of summarizing the chapter in short declarative sentences like these:

• Microvilli are short surface extensions of the plasma membrane that increase a cell’s surface area. They are especially well developed on absorptive cells, as in the kidney and small intestine. On some cells, they play a sensory role.
• Parathyroid hormone is secreted by the parathyroid glands in response to hypocalcemia. It raises blood Ca2+ levels by indirectly stimulating osteoclasts, inhibiting osteoblasts, promoting calcitriol synthesis, and promoting Ca2+ conservation by the kidneys.