57. Biochemical composition, molecular organization and metabolism in bone tissue. Bone mineralization – main mechanisms, hormonal effects. Calcium metabolism and factors influencing calcium homeostasis.

Metabolism of Calcium and Phosphorus

Calcium:

• Functions: Vital for bone structure, muscle contraction, nerve transmission, blood clotting, and enzyme activity.
• Sources: Dietary intake from dairy products, leafy greens. Absorbed in the small intestine, mainly in the duodenum and jejunum.
• Storage: 99% stored in bones and teeth as hydroxyapatite. The remaining 1% is found in blood and extracellular fluids.
• Homeostasis: Maintained by the balance between dietary intake, intestinal absorption, renal excretion, and bone resorption and formation.

Metabolism of Calcium and Phosphorus

• Phosphorus:
• Functions: Essential for bone structure, energy production (ATP), nucleic acids, and cell membranes (phospholipids).
• Sources: Dietary intake from meat, dairy, nuts, and grains. Absorbed in the small intestine.
• Storage: 85% stored in bones and teeth, the rest in cells and extracellular fluids.
• Homeostasis: Regulated by dietary intake, renal excretion, and bone metabolism.

Regulation

Hormonal Regulation:

• Parathyroid Hormone (PTH):
• Source: Parathyroid glands.
• Function: Increases blood calcium levels by stimulating bone resorption, increasing renal reabsorption of calcium, and promoting activation of vitamin D.