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Bone+Endocrinology+and+Pathology - Bone­Endocrinology and...

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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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