الفهرس 
Introduction
Cartilage and bone growthOnly 14 pages are availabe for public view
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Abstract
Euthyroid status is essential for normal skeletal development and adult bone maintenance. Hypothyroidism in children causes growth arrest, delayed bone maturation, and epiphyseal dysgenesis. so the present work is carried out to show the effect of hypothyroidism and thyroxin treatment on the postnatal development of skeletal system in albino rat.
This study was conducted on 60 adult female and 15 adult male Albino rats. Female rats were mated with a single male overnight. Female rats were singly housed and randomly divided into 3 groups: Control group: (20) rats in this group was given distilled water from the 10th gestational day till the end of the study, Experimental group (a): (20) rats in this group was given carbimazole to be congenitally hypothyroid in a dose of 6 microgram /gram body weight daily. The drug was administered from the 10thgestational day till the end of pregnancy and the administration continued until eight weeks postnatal and Experimental group (b): (20) rats in this group was given carbimazole before birth (on 10th day of gestation) in a dose of 6 microgram /gram body weight daily and thyroxin at birth in a dose of 10 microgram/kg /day and the administration continued until eight weeks postnatal.
For each group, the offspring sacrificed at the following ages: newborn, 2weeks, 8weeks, 11weeks, 16weeks and 20weeks. 6 tibia and lumbar vertebrae disarticulated, extracted, fixed in 10% Formaldehyde solution for 24 h -72 h, decalcified, dehydrated, embedded in Paraffin blocks, cut at 5micrometer, stained by Heamatoxylin and eosin staining, Masson’s trichrome and toluidine blue stains and examined by light microscopy. The tibia and lumbar vertebrae were taken and prepared for examination by electron microscope. Weight, tail length and crown rump length were measured at ages 8wks, 11wks, 16 wks and 20 wks. In addition, the thickness of epiphyseal cartilage plate of tibia and thickness of epiphyses of lumbar vertebrae were measured at ages 8wks, 11wks, 16 wks and 20 wks at magnification 100 using image analyzer (Leica Q 500 M.C) in histology department, Faculty of medicine, Assiut University. Comparsion between control, treated and rehabilitated was done by ANOVA test.
Histological examination of the proximal end of tibia and epiphyses of the lumbar vertebrae of carbimazole treated group at newborn and two weeks old revealed crowded chondrocytes in zone of reserve cartilage, abnormally arranged and exhibits swollen nuclei with marked dilation in lacunae. The matrix reveals areas devoid of cells. In zone of proliferation, the chondrocytes appear disorganized with loss of the normal longitudinal arrangement. At age of two weeks failure of the secondary ossification center to appear as compared to control and thyroxin treated group.
At age of eight weeks the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae revealed disorganization in the arrangement of growing chondrocytes especially in the proliferative zone. The proliferating cell zone is the most affected layer; its cells appeared deformed with loss of its longitudinal arrangement and abnormally stained with accumulation of acidophilic material in the cytoplasm. Some cells in zone of hypertrophy exhibits degeneration.
At age of 11weeks the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae revealed more preserved reserve cell zone than that in control group. The proliferating cell zone is the most affected layer; its cells appear disorganized with dilated lacunae and wide areas of matrix devoid of cells. In zone of hypertrophy there is marked dilation of the lacunae with degeneration in chondrocytes.
At age of 16 weeks old the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae revealed an apparent increase in thickness as compared to control group. The proliferating cell zone appears disorganized with dilated lacunae and abnormal staining.
At age of 20 weeks old the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae revealed swollen proliferating cell zone with dilated lacunae.
The matrix of the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae showed less staining with toluidine blue and Masson’s trichrome.
Electron microscopic results in reserve cell zone revealed shrunken cells with excessive vacuolization of the cytoplasm. Abnormal shape and position of nuclei is observed with the rough endoplasmic reticulum less numerous and the collagen fibers in the extracellular matrix are less apparent. In proliferating cell zone, the nuclei are eccentrically located and pyknotic, the outline of nuclear membrane not well demarcated.
Morphometric results at age of eight weeks old showed marked decrease in thicknness the epiphyseal growth plate of tibia and epiphysis of lumbar vertebrae as compared to control and thyroxin treated group.
Thyroxin replacement revert most of these changes when given immediately at birth.
Conclusion
from the present study it was observed that hypothyroidism has marked effect on the bone growth, especially epiphyseal growth plate in long bone and the epiphyses of lumbar vertebrae. So once hypothyroidism is diagnosed thyroxin replacement must be started immediately.