Chapter 4 The Skeletal System 139 Because the discs receive no blood supply, they must rely upon changes in posture and body position to produce a pumping action that brings in nutrients and flushes out metabolic waste products with an influx and outflow of fluid. Because maintaining a fixed body position curtails this pumping action, sitting in one position for a long period of time can negatively affect disc health. Check Your Understanding 1. List the five regions of the vertebral column, from upper to lower. 2. What is the functional purpose of the vertebrae increasing in size from the cervical region down to the lumbar region? 3. What is the function of the intervertebral discs? The Intervertebral Discs Intervertebral (in-ter-VER-teh-bral) discs composed of fibrocartilage provide cushioning between all of the articulating vertebral bodies except those that are fused. These discs serve as shock absorbers and allow the spine to bend. The differences in the anterior and posterior thicknesses of these discs produce the normal cervical, thoracic, and lumbar curves. In a normal adult, the discs account for approximately one-quarter of the height of the spine. When a person is lying in bed during overnight sleep, the discs absorb water and expand slightly. During periods of upright standing and sitting, when the discs are bearing weight, they lose a small amount of fluid and are compressed. For this reason, people are as much as three- fourths of an inch taller when they first arise in the morning. Injury and progressive aging reduce the water retention capability of the discs, accounting for diminished standing height in elderly individuals. © Body Scientific International Figure 4.15 Three types of abnormal spinal curvature. What are some causes of abnormal curvature? Scoliosis Kyphosis Lordosis Lateral deviation of spine Exaggerated lumbar curve Accentuated thoracic curve Copyright Goodheart-Willcox Co., Inc.