HNF 462 1st Edition Lecture 14Outline of Last LectureI. General Vitamin D Cont.a. Storageb. Excretionc. Functionsd. Deficiencye. Toxicityf. Sun ExposureII. Transcription FactorsIII. Vitamin A in DNAIV. Vitamin D in DNAOutline of Current LectureI. Absorptiona. Transporter Mediatedb. Paracellular DiffusionII. BioavailabilityIII. Transport and ExcretionIV. Calcium Concentration Regulationa. PTHb. Calcitriolc. CalcitoninV. Calcium and BoneCurrent Lecture: Calcium1. Absorptiona. Transporter MediatedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Active transport with calcium transport 1 (TRPV6) into intestinal cellii. Once in the cell, calcium binds to calbindin protein, which shuttles it through the cytoplasmiii. ATP hydrolyzer pumps calcium into the bloodb. Paracellular Diffusioni. Transport through openings between cells when calcium concentration is highii. Opens tight junctions between cells to allow the passing of calcium2. Bioavailabilitya. Not high: only ~1/3 of what you eat will be absorbed into the bloodb. Enhancersi. Pregnancy/lactation/young ageii. Ingesting with foodc. Inhibitorsi. Phytates, oxalates, and fiberii. Increasing ageiii. Estrogen deficiencyiv. Divalent cations and mineralsv. Fatty acids via insoluble calcium soaps3. Transport and Excretiona. Transporti. About half of calcium in blood is bound to protein, and about half is unboundii. Small portion forms complexes with sulfate, phosphate, and citrateb. Excretion via urine, feces, and sweat4. Calcium Concentration Regulation: concentration of calcium in the blood is tightly controlled; concentration is much lower in the cell than outside the cell (~10,000 times lower)a. PTH: Increase calcium levels in bloodi. In kidney: increases synthesis of calcitriol (hydroxylation of 25-hydroxyl D3) = increases absorption of kidneyii. In bone: stimulates osteoclasts (break down bone to release calcium into blood)b. Calcitriol: Increase calcium levels in bloodi. Small Intestine: increase expression of calcium transporters = increase absorptionii. Kidney: decrease synthesis of calcitriol when calcitriol levels in blood are high (negative feedback mechanism—prevents kidney from producing too much)iii. Bone: stimulates activity of osteoclastsiv. Parathyroid Gland: Inhibits PTH release (negative feedback—prevents overly-high levels of calcium)c. Calcitonin: Decreases calcium concentration in the bloodi. Kidney: inhibits calcium and phosphorus reabsorptionii. Bone: inhibits osteoclast activityiii. Parathyroid Gland: inhibits PTH secretion5. Calcium and Bonea. Trabecular bone: larger surface area and higher metabolic activity compared to cortical boneb. Active form of D3 and PTH stimulates production of RANKL produced by osteoblasts. RANKL binds to surface of osteoclasts, which stimulates maturation of osteoclasts so they can break down bonePTH Calcitriol CalcitoninSerum Calcium Increase Increase DecreaseBone Calcium Decrease Decrease IncreaseRenal Calcium AbsorptionIncrease Increase DecreaseIntestinal Calcium AbsorptionIncrease Increase No
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