World Book Trivia Challenge--10/15-human Body

The exchange of carbon dioxide and oxygen occurs in the alveoli. Each alveolus is surrounded by a network of small blood vessels. Like the alveoli, these vessels have extremely thin walls.

Nervous tissue carries signals. It permits various parts of the body to communicate with one another.

The epidermis forms the outermost layer of the skin. It serves as a barrier between the outside world and the inner tissues of the body.

Except for water, all of the chief molecules in the body contain the element carbon. The most important carbon-containing molecules are large, complicated compounds called macromolecules. There are four main kinds of macromolecules in the body: carbohydrates, lipids, proteins, and nucleic acids.

Skeletal muscles are attached to the bones. They move the bones of the arms, legs, fingers, and other parts of the skeleton. We can consciously control the skeletal muscles, and so they are known as voluntary muscles. The fibers that make up a skeletal muscle have alternate light and dark crossbands called striations.

The blood vessels form a branching network of about 60,000 miles (100,000 kilometers). They can be divided into three types (1) Arteries carry blood from the heart. (2) Veins carry blood to the heart. (3) Capillaries connect the arteries and veins.

Much brain activity occurs at the conscious level. We are aware of decisions made at this level and can voluntarily control them. Other activity occurs at the subconscious level. This activity regulates the smooth muscles and is beyond voluntary control.

The cells of red bone marrow—the soft, fatty core of many bones—produce new blood cells and release them into the bloodstream. Yellow bone marrow, the most common type of marrow in the adult skeleton, stores fat. Yellow bone marrow does not normally produce blood cells.

The hypothalamus links the nervous and endocrine control systems.

Red blood cells, also called erythrocytes carry oxygen to body tissues and remove carbon dioxide.