Introduction Vitamin D and PTH play an important role in calcium homeostasis skin, liver, parathyroid gland, kidney, bone, and small intestine all play a role increased PTH and Vitamin D leads to increase serum calcium levels Vitamin D Physiology Overview Vitamin D and PTH play an important role in calcium homeostasis skin, liver, parathyroid gland, kidney, bone, and small intestine all play a role Increased PTH and Vitamin D leads to increase serum calcium levels Synthesis 7-Dehydrocholesterol precursor to calcitriol is stored in the skin where UV exposure converts it to previtamin D3. cholecalciferol (Vitamin D3) Previtamin D3 is then bound to vitamin-D binding protein (DBP) where it is carried to the liver and metabolized to 25-hydroxyvitamin D3 25-hydroxyvitamin D3 when calcium is low, parathyroid hormone (PTH) levels become elevated which activates 1-alpha-hydroxylase in the kidney 1-alpha-hydroxylase converts 25-hydroxyvitamin D to the active Vitamin D (calcitriol) laboratory study of choice to determine Vitamin D deficiency 1,25-dihydroxyvitamin D3 (Vitamin D, calcitriol) active form that controls calcium homeostasis in body by targeting intestines and bones (see function below) Function ↑ serum Ca2+ and phosphate via ↑ absorption of calcium and phosphate from the intestine ↑ bone resorption of Ca2+ and phosphate recall PTH functions to ↑ serum Ca2+ but ↓ serum phosphate Regulation PTH stimulates 1,25-(OH)2 vitamin D production hypocalcemia/hypophoshatemia stimulates 1,25-(OH)2 vitamin D production 1,25-(OH)2 vitamin D feedback negatively on itself PTH Physiology Synthesis secreted by the chief cells of parathyroid Function ↑ serum Ca2+ and ↓ serum phosphate in response to hypocalcemia/hypomagnesemia via ↑ bone resorption of calcium and phosphate (bone is destroyed) PTH receptor is on the osteoblasts which secretes IL-1 to activated osteoclasts ↑ kidney resorption of calcium in distal convoluted tubule ↓ kidney resorption of phosphate ↑ 1,25-(OH)2 vitamin D production Clinical Conditions Conditions related to PTH hypoparathyrodism pseudohypoparathyroidism renal osteodystrophy Conditions related to Vitamin D Rickets
QUESTIONS 1 of 4 1 2 3 4 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ13.18) Which of the following statements is correct regarding Vitamin D? QID: 4653 Type & Select Correct Answer 1 1,25-dihydrocholecalciferol is the best laboratory study to determine a Vitamin D deficiency 27% (1141/4154) 2 25-hydroxycholecalciferol is the active form of Vitamin D 6% (265/4154) 3 24,25-dihydroxycholecalciferol is an inactive form of Vitamin D 53% (2204/4154) 4 1,25-dihydrocholecalciferol is converted to 25-hydroxycholecalciferol in the kidney 8% (319/4154) 5 The half-life of 1,25-dihydrocholecalciferol is longer than 25-hydroxycholecalciferol 5% (196/4154) L 4 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK
All Videos (2) Podcasts (1) Physiology | Endocrine | lecture 5 | Calcium homeostasis | Dr.Nagi | Arabic Basic Science - PTH & Vit D Physiology 4/10/2022 499 views 0.0 (0) Dr.Nagi - Live Physiology - Lecture 46 - Endocrine (7) - Part 1 - Calcium Homeostasis Basic Science - PTH & Vit D Physiology 4/10/2022 503 views 0.0 (0) Basic Science⎪PTH & Vit D Physiology Orthobullets Team Basic Science - PTH & Vit D Physiology Listen Now 12:10 min 7/3/2020 238 plays 5.0 (1)