American Academy of Professional Coders (AAPC) Practice Exam

What do flat bones consist of?

1. A single layer of spongy bone

2. Multiple thin layers of compact bone

3. A layer of spongy bone between two thin layers of compact bone

4. Only compact bone

The correct answer is: A layer of spongy bone between two thin layers of compact bone

Flat bones consist of a structure where a layer of spongy bone is sandwiched between two thin layers of compact bone. This anatomical arrangement allows flat bones to be both lightweight and strong, making them efficient in providing protection to underlying organs and serving as a site for muscle attachment. The spongy bone adds to the bone's strength and flexibility while reducing overall weight. Flat bones include structures such as the skull, ribs, and sternum, which require both resilience and a certain level of protection for the body. In contrast, other structures mentioned do not accurately represent flat bones. For instance, a single layer of spongy bone would lack the protective and supportive features provided by the outer compact bone. Multiple thin layers of compact bone would not provide the necessary cushioning and flexibility that spongy bone offers within flat bones. Lastly, flat bones are not made up entirely of compact bone, as this would compromise their overall structural integrity and functional adaptability.