{"id":1677,"date":"2024-04-09T15:04:50","date_gmt":"2024-04-09T19:04:50","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&p=1677"},"modified":"2025-10-17T19:31:06","modified_gmt":"2025-10-17T23:31:06","slug":"vitamin-d-and-calcitriol","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/vitamin-d-and-calcitriol\/","title":{"raw":"Review Reminder: Sources of and Roles of Vitamin D and Calcitriol - Important in Maintaining Blood Calcium Levels and Bone Density","rendered":"Review Reminder: Sources of and Roles of Vitamin D and Calcitriol – Important in Maintaining Blood Calcium Levels and Bone Density"},"content":{"raw":"*Vitamin D2<\/strong> (ergocalciferol) and vitamin D3<\/strong> (cholecalciferol) can be formed in the skin<\/strong> by epithelial cells upon exposure to UV.\u00a0 Alternatively dietary<\/strong> Vitamins D2 and D3 can be ingested in the form of oily fish<\/strong>, meat,<\/strong> supplemented dairy and plant-based products<\/strong> (e.g., milk, yogurt, soy milk),<\/strong> daily vitamins<\/strong> as well as various plant, fungi (e.g., some mushrooms) and yeast sources.\r\n\r\nOnce synthesized by the skin, or ingested by the digestive tract, vitamin D3 is carried to the liver,<\/strong> where hepatocytes convert it to a calcitriol precursor,<\/strong> which is converted to calcitriol<\/strong> by proximal tubular cells in the kidney.<\/strong>\u00a0 Calcitriol is a hormone which is able to help regulate blood calcium levels<\/strong>.\u00a0 Specifically, calcitriol is released and active when blood calcium levels are low.\u00a0 Calcitriol helps to increase blood calcium levels<\/strong> and maintain homeostasis by performing 3 functions:\r\n
    \r\n \t
  1. Calcitriol facilitates the absorption of dietary calcium and phosphate in the intestine<\/strong>, which leads to more calcium and phosphate entering the bloodstream.<\/li>\r\n \t
  2. Calcitriol increases the reabsorption of calcium within the nephron<\/strong>, which leads to less calcium being excreted in the form of urine, and therefore more calcium being retained in the bloodstream.<\/li>\r\n \t
  3. Calcitriol promotes osteoblasts to release RANKL<\/strong>, a signalling protein, which activates osteoclasts to dissolve bone matrix and release the calcium and phosphate which is taken up by the bloodstream, increasing blood calcium levels.<\/li>\r\n<\/ol>","rendered":"

    *Vitamin D2<\/strong> (ergocalciferol) and vitamin D3<\/strong> (cholecalciferol) can be formed in the skin<\/strong> by epithelial cells upon exposure to UV.\u00a0 Alternatively dietary<\/strong> Vitamins D2 and D3 can be ingested in the form of oily fish<\/strong>, meat,<\/strong> supplemented dairy and plant-based products<\/strong> (e.g., milk, yogurt, soy milk),<\/strong> daily vitamins<\/strong> as well as various plant, fungi (e.g., some mushrooms) and yeast sources.<\/p>\n

    Once synthesized by the skin, or ingested by the digestive tract, vitamin D3 is carried to the liver,<\/strong> where hepatocytes convert it to a calcitriol precursor,<\/strong> which is converted to calcitriol<\/strong> by proximal tubular cells in the kidney.<\/strong>\u00a0 Calcitriol is a hormone which is able to help regulate blood calcium levels<\/strong>.\u00a0 Specifically, calcitriol is released and active when blood calcium levels are low.\u00a0 Calcitriol helps to increase blood calcium levels<\/strong> and maintain homeostasis by performing 3 functions:<\/p>\n

      \n
    1. Calcitriol facilitates the absorption of dietary calcium and phosphate in the intestine<\/strong>, which leads to more calcium and phosphate entering the bloodstream.<\/li>\n
    2. Calcitriol increases the reabsorption of calcium within the nephron<\/strong>, which leads to less calcium being excreted in the form of urine, and therefore more calcium being retained in the bloodstream.<\/li>\n
    3. Calcitriol promotes osteoblasts to release RANKL<\/strong>, a signalling protein, which activates osteoclasts to dissolve bone matrix and release the calcium and phosphate which is taken up by the bloodstream, increasing blood calcium levels.<\/li>\n<\/ol>\n","protected":false},"author":1370,"menu_order":28,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"Pictures coming soon!","pb_authors":["zoe-soon"],"pb_section_license":"cc-by-nc-sa"},"chapter-type":[48],"contributor":[60],"license":[57],"class_list":["post-1677","chapter","type-chapter","status-web-only","hentry","chapter-type-standard","contributor-zoe-soon","license-cc-by-nc-sa"],"part":41,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1677","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/users\/1370"}],"version-history":[{"count":4,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1677\/revisions"}],"predecessor-version":[{"id":4488,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1677\/revisions\/4488"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/parts\/41"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1677\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/media?parent=1677"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapter-type?post=1677"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/contributor?post=1677"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/license?post=1677"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}