the cranial base, the bony floor under the brain, which also is the dividing line between the cranium and the face.the cranial vault, the bones that cover the upper and outer surface of the brain.The nature of skeletal growth The craniofacial complex can be divided into four areas that grow rather differently: by direct or surface apposition- formation of new cells occurs in the periosteum, and extracellular material, secreted there, is mineralized and becomes new bone.The nature of skeletal growth Growth of the bone is possible: In contrast, when mineralization takes place, interstitial growth becomes impossible.Growth of soft tissues is called interstitial growthand it occurs at all points within the tissue.The fact that the extracellular material of the skeleton becomes mineralized leads to an important distinction between growth of the soft tissues of the body and the hard or calcified tissues.Although tissues throughout the body secrete extracellular material, this phenomenon is particularly important in the growth of the skeletal system, where extracellular material later mineralizes.Hypertrophy occurs in a number of special circumstances but is a less important mechanism.The nature of skeletal growth All three of these processes occur in skeletal growth. the third is that cells secrete extracellular material, which contribute to an increase in size independent of the number or size of the cells themselves.hyperplasia is an increase in the number of the cells.hypertrophy is an increase in the size of individual cells.The nature of skeletal growth At the cellular level, there are only three possibilities for growth: when the facial growth pattern is viewed against the perspective of the cephalocaudal gradient, the mandible, being farther away from the brain, tends to grow more and longer than the maxilla, which is closer.the facial skeleton grows much longer and thus in the adult forms a much larger proportion of the scull than in the child.after the age of 6 years, there is little further growth of the cranium because the brain has nearly reached its adult size.The infant has a relatively much larger cranium and a much smaller face at the same time that growth of the genital tissues accelerates rapidly.lymphoid tissues proliferate far beyond the adult amount in late childhood, and then undergo involution.general body tissues, including muscle, bone, and viscera, show an S-shaped curve, with a slowing of growth during childhood and an acceleration at puberty.
growth of the neural tissues is nearly complete by 6 or 7 years of age.Picture showes the curves for growth of the four major tissue systems of the body: One reason for gradients of growth is that different tissue systems that grow at different rates are concentrated in various parts of the body. This means that there is an axis of increased growth extending from the head toward the feet. At birth, the legs represent about one third of the total body length, while in the adult, they represent about half.Īll of these changes, which are a part of the normal growth pattern, reflect the "cephalocaudal gradient of growth“. and faster growth of the trunk and limbs ( lower limbs grow more than upper limbs).There is progressive reduction of the relative size of the head (from almost 30% of the total body lenght at birth to about 12% of the adult).Picture illustrates the change in overall body proportions that occurs during normal growth and development:
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