Page 233 - Fundamentals of anatomy physiology

220 Unit 2 Support and Movement 6-7 Exercise, hormones,
Figure 6–13 The Blood Supply to a Mature Bone.
and nutrition affect bone development
Vessels in Bone Articular and the skeletal system
Epiphyseal cartilage
Learning Outcome Discuss the effects of exercise, hormones,
artery and vein and nutrition on bone development and on the skeletal system.

Metaphyseal What factors have the most important effects on the processes
artery and vein of bone remodeling? Exercise, nutrition, and hormones are key.

6 Branches of Periosteum The Effects of Exercise on Bone
nutrient artery
Compact The turnover and recycling of minerals give each bone the
and vein bone ability to adapt to new stresses. The sensitivity of osteoblasts
to electrical events has been theorized as the mechanism
Nutrient artery Medullary that controls the internal organization and structure of bone.
and vein cavity Whenever a bone is stressed, the mineral crystals generate min-
ute electrical fields. Osteoblasts are apparently attracted to
Periosteal Nutrient these electrical fields and, once in the area, begin to produce
arteries and veins foramen bone. This finding has led to the successful use of small elec-
tric fields in stimulating bone healing.
Periosteum
Because of their adaptability, bone shapes reflect the
Connections to Metaphysis forces applied to them. For example, bumps and ridges on
superficial osteons the surface of a bone mark the sites where tendons are at-
Epiphyseal tached. If muscles become more powerful, the correspond-
Metaphyseal line ing bumps and ridges enlarge to withstand the increased
artery and vein forces. Heavily stressed bones become thicker and stron-
ger, and bones that are not subjected to ordinary stresses
complications in the aftermath of the Chernobyl nuclear reac- become thin and brittle. For this reason, regular exercise is
tor incident in 1986. Radioactive compounds released in the an important stimulus for maintaining normal bone struc-
meltdown of the reactor were deposited into the bones of ex- ture. Champion weight lifters typically have massive bones
posed individuals. Over time, the radiation released by their with thick, prominent ridges. In nonathletes (especially
own bones has caused thyroid cancers, leukemia (cancer of the “couch potatoes”), moderate amounts of physical activ-
blood cells, which starts in the red bone marrow), and other ity and weight-bearing activities are essential for stimulat-
potentially fatal cancers. ing normal bone maintenance and maintaining adequate
bone strength.
Checkpoint
12. Describe bone remodeling. Degenerative changes in the skeleton take place after rela-
13. Explain how heavy-metal ions could be incorporated tively brief periods of inactivity. For example, you may use a
crutch to take weight off an injured leg while you wear a cast.
into bone matrix. After a few weeks, your unstressed bones can lose up to a third
of their mass. The bones rebuild just as quickly when you re-
See the blue Answers tab at the back of the book. sume normal weight loading. However, the removal of cal-
cium salts can be a serious health hazard both for astronauts
remaining in a weightless environment and for bedridden or
paralyzed patients who spend months or years without stress-
ing their skeleton.

Nutritional and Hormonal Effects on Bone

Normal bone growth and maintenance depend on a combina-
tion of nutritional and hormonal factors, such as: