lab9 - 9 The Skeletal System Objectives In this chapter we...

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52 9 The Skeletal System Objectives In this chapter we will study two developmental disorders of the skull—acrania and craniosynostosis; spina bifida, a developmental disorder of the vertebral column; some of the causes of lower back pain later in life; and skeletal disorders of the feet, specifically foot deformities and heel pain. Diagnosing Skeletal Disorders This chapter focuses on disorders of some of the groups of bones that compose the skeleton, and examines skeletal problems at the organ and system level as opposed to the tissue level treated in the previous chapter. The methods used to diagnose the disorders discussed in this chapter are largely the same as those described in the previous chapter. Developmental Disorders of the Skull Developmental defects that occur during the formation of the bones of the skull can be so minor that they have little or no effect or so major that they cause death. This discussion focuses on two defects of the skull: acrania and craniosynostosis. Acrania Acrania (“without skull”) is the almost complete absence of a calvaria, or skull cap, at birth. It is sometimes accompanied by defects in the vertebral column and by anencephaly, the absence or rudimentary development of the cerebrum, cerebellum, and brainstem. Acrania results from the failure of an embryonic structure called the neural tube to complete its development. It occurs in approximately 0.1% of live births and results in death shortly after birth. Craniosynostosis Normal human babies are born with unfused cranial bones that are able to shift enough to allow their heads to fit through the birth canal. The cranial bones become rigidly joined by sutures 1 to 2 years after birth. Craniosynostosis occurs when one or more of the cranial sutures fuses prematurely during the first 18 to 20 months of life. It occurs in about 5 out of 100,000 live births and twice as often in males as in females. Premature closure of a suture results in lack of bone growth at right angles to the suture and compensatory growth at the sutures that remain open. For example, if the coronal suture closes prematurely, the head cannot grow normally in a fronto-occipital direction but shows excessive growth in a lateral direction, perpendicular to the sagittal suture. As a result, the head is abnormally wide (left to right) and short (front to rear). Craniosynostosis produces a deformed, sometimes asymmetric skull, often accompanied by mental retardation or other neurological dysfunctions. However, surgical intervention can limit brain damage and improve the child’s appearance. The cause of craniosynostosis is not known with certainty. One theory is that the mesenchyme—the embryonic connective tissue that gives rise to bone— lacks enzymes that normally inhibit premature ossification. This hypothesis is supported by the finding that craniosynostosis is often accompanied by
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This note was uploaded on 11/16/2011 for the course SCIENCE Anatomy an taught by Professor Tory during the Spring '11 term at Kennesaw.

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lab9 - 9 The Skeletal System Objectives In this chapter we...

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