PTH AND BONE PHYSIOLOGY 2024-01.pdf

BONE AND PTH PHYSYOLOGY Dr. Miguel Alejandro Dávalos Benítez Rheumatologist OBJECTIVES 1. Understand the mechanisms of absorption and excretion of calcium and phosphate 2. Explain the role of Calcium in bone formation, structure, and remodeling. 3. Identify the functions of Vitamin D along with its...

BONE AND PTH PHYSYOLOGY Dr. Miguel Alejandro Dávalos Benítez Rheumatologist OBJECTIVES 1. Understand the mechanisms of absorption and excretion of calcium and phosphate 2. Explain the role of Calcium in bone formation, structure, and remodeling. 3. Identify the functions of Vitamin D along with its absorption mechanisms and its interaction with the normal calcium and phosphate metabolism. 4. Describe the hormonal regulation of Calcium and phosphate. 1. Special focus in PTH role and Calcitonin. INTRODUCTION Calcium is normally regulated precisely. Calcium plays a key rol in many physiological processes. The neurones are sensitive in changes of calcium: Hypercalcemia: Depression of the nervous system. Hypocalcemia: The nervous system becomes more excited. The normal value is 9.4 mg/dL = 2.4 millimoles of calcium per liter. DISTRIBUTION Calcium: 0.1 % is extracellular. 1% in the cells. 98.9% in bones. Phosphate: secretion of PTH. o Increase of calcium concentration -> decreases activity of PTH. o Excess of calcium on the diet. o Excess of vitamin D on the diet. o Bone resorption for different causes than PTH. o Changes in the extracellular fluid calcium ion concentrations are detected by a calcium-sensing receptor in the parathryoid cell membranes. EFFECTS OF PTH Calcium sensing receptor: is a G protein-coupled receptor that, when stimulated by calcium ions, activates phospholipase C and increases intracellular inositol 1, 4, 5 – triphosphate and diacylglycerol formation -> decreases PTH secretion. CALCITONIN oPeptide hormone is secreted by the thyroid gland, in the parafollicular cells. oDecrease plasma calcium concentration. oOpposite to PTH effects. oThe primary stimulus for calcitonin secretion is increased extracellular fluid of calcium concentration. CALCITONIN EFFECTS OF CALCITONIN oDecrease the absorptive activities and the osteolytic effect of the osteocytic membrane. oDecrease formation of new osteoclast. oThe effect of calcitonin in children is much greater because bone remodeling occurs rapidly in them. oAny reduction of the calcium ion concentration by calcitonin leads to a powerful stimulation of PTH. BIBLIOGRAPHY 1. Hall, J. E. (2020). Guyton and Hall textbook of medical physiology, chapter 80, 14th edition, pages 991-1004. 2. Saunders (2010). Netter’s concise orthopaedic anatomy, second edition, chapter 1.