Lung–kidney system ↗Renal interstitial cells sense oxygen context
Oxygen delivery relative to renal tissue demand alters hypoxia-inducible signaling in specialized cortical and outer-medullary cells.
KIDNEYS / 08
Sense oxygen.
Activate mineral signals.
Kidneys are endocrine organs as well as filters. Renal oxygen sensing controls erythropoietin, while proximal tubular enzymes contribute to calcitriol production and mineral feedback.
Erythropoietin enters circulation
Kidney-derived EPO rises when appropriate hypoxic signaling recruits transcription and secretion.
Marrow precursors survive and mature
EPO receptor signaling supports erythroid progenitors, while iron availability, inflammation, nutrients, and marrow health constrain output.
Red-cell capacity changes over weeks
New red cells increase oxygen-carrying capacity only after production and maturation; this is not the first acute altitude response.
Liver supplies 25-hydroxyvitamin D
Vitamin D from skin or diet is first converted in liver to the major circulating 25-hydroxy form.
Kidney produces hormonal calcitriol
Proximal tubular CYP27B1 performs 1-alpha hydroxylation under regulation by PTH, FGF23, calcium, phosphate, and other context.
Gut, bone, kidney, and parathyroid respond
Calcitriol-related signaling changes intestinal absorption, renal transport, parathyroid feedback, and bone-mineral dynamics.
CKD disrupts the whole mineral network
Reduced calcitriol production interacts with phosphate retention, FGF23, PTH, calcium, bone turnover, and treatment—not one isolated deficiency.