A 12-year-old girl fractures her right radius and ulna in a motor accident. Her arm is placed in a cast extending over the elbow, which nearly eliminates movement of her forearm muscles. Which of the following will occur in her forearm muscles after several weeks in the cast?
The primary function of blood vessels in skeletal muscles is to supply nutrients and remove metabolic waste products from the muscle tissues. Prolonged increases in metabolic rate lead to growth of the vasculature; decreases in metabolic rate lead to vascular rarefaction, i.e., loss of capillaries as well as other types of blood vessels. In other words, blood vessels grow where they are needed and regress when they are not needed. When a limb is immobilized in a cast, the muscles are inactive and their metabolic rate decreases. This decrease in metabolic rate leads to a decrease in capillarity in the skeletal muscles by mechanisms that are poorly understood. When the metabolic rate of immobilized skeletal muscle decreases, the oxygen consumption of the muscle decreases, which is likely to cause an initial increase in both myoglobin oxygen saturation and intracellular pO2.
Decreased capillarity
Decreased intracellular pO2
Decreased myoglobin oxygen saturation
Increased metabolic rate