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Unformatted text preview: BoneEndocrinology and BoneEndocrinology and Pathology Bone Endocrinology and Bone Endocrinology and Physiology Vitamin D3cholecalciferol Majority of D3 formed in skin by ultraviolet irradiation of 7dehydrocholesterol Converted by liver to 25 Hydroxycholecalciferol 25Hydroxycholecalciferol converted by kidney to 1,25Dihydrocholecalciferol BoneEndocrinology and BoneEndocrinology and Physiology 1,25Dihydrocholecalciferol has a “hormonal” effect to promote intestinal absorption of calcium and to a lesser effect phosphorus BoneEndocrinology and BoneEndocrinology and Physiology Parathyroid hormone necessary for conversion of 25Hydrocholecalciferol to 1,25Dihydrocholecalciferol in the kidney High plasma levels of calcium suppress parathyroid hormone and therefore reduce further uptake of calcium from the gi tract by indirectly reducing the availability of 1,25Dihydrocholecalciferol BoneEndocrinology and BoneEndocrinology and Physiology Parathyroid hormone secreted by the parathyroid gland in response to low blood calcium Two direct effects on calcium extraction from bone Parathyroid hormone Parathyroid hormone Rapid phase”osteolysis”calcium pump activated to release calcium phosphate salts from bone fluid around osteocytes Slow phase activation of osteoclasts to mobilize more calcium salts Bone Endocrinology and Bone Endocrinology and Physiology Calcitonin produced by the thyroid gland Production is stimulated by high blood levels of calcium Decreases osteoclastic activity while stimulating osteoblastic activity BoneEndocrine Pathology BoneEndocrine Pathology Hypoparathyroidismlow parathyroid hormone May be due to gland malfunction or due to surgical removal May result in muscle tetany and even death due to low circulating blood calcium Bone Endocrine Pathology Bone Endocrine Pathology Hyperparathyroidismgenerally a result of a parathyroid gland tumor “Secondary Hyperparathyroidism “ may be dietary “bran disease” from long term dietary intake of feeds high in phosphorous and low in calcium Results in increased osteoclastic activity and a resultant decreased bone density. Bone Pathology Bone Pathology BonePathology BonePathology Bone cysts incomplete endochondral ossification– results in “potholes” in the articular cartilage BonePathology BonePathology Fractures May be large and horrible or small and innocuous BonePathology BonePathology Epiphysitis inflammation of the growth plate May be mild or severe Often a result of poor nutritional management and husbandry BonePathology BonePathology Degenerative joint disease may be the result of trauma, poor nutrition, infection, or of a hereditary nature (conformation ?) BonePathology BonePathology Navicular disease chronic degenerative change of the distal sesamoid bone in the horse Very common in American Quarterhorses Typically in horses 8 years or older Many have under run heels and poor foot conformation ...
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- Spring '07