🦴 Calcium is an essential mineral that underpins bone health, muscle contraction, nerve transmission, blood clotting, and cellular signaling. About 99% of calcium is stored in bones and teeth, while 1% circulates or sits in soft tissues for vital metabolic processes.

📊 Distribution of Calcium

Calcium distribution in the body:
- 🦷 99% in bones and teeth → provides structure and acts as a calcium reservoir.
- 💉 1% in extracellular fluid and soft tissues → supports nerve, muscle, and clotting functions.
- ⚖️ Normal serum calcium range: 2.1–2.6 mmol/L (8.5–10.5 mg/dL), tightly regulated.

⚡ Functions of Calcium

Bone Health 🦴 :
- Combines with phosphate to form hydroxyapatite crystals → bone strength.
- Bone acts as a reservoir, buffering blood calcium fluctuations.
Muscle Contraction 💪 :
- Calcium binds to troponin, enabling actin–myosin interaction.
- Essential for skeletal, cardiac, and smooth muscle activity.
Nerve Transmission 🧠 :
- Triggers neurotransmitter release at synapses.
- Supports rapid communication across the nervous system.
Blood Clotting 🩸 :
- Acts as a cofactor in multiple clotting cascade steps.
Cellular Signaling 📡 :
- Serves as a “second messenger” in hormonal and metabolic pathways.

⚖️ Regulation of Calcium Levels

Maintained by interplay of hormones and organs:
- Parathyroid Hormone (PTH) ⬆️ :
  - Released when calcium is low.
  - Stimulates bone resorption, kidney reabsorption, and vitamin D activation.
- Calcitriol (Active Vitamin D) 🌞 :
  - Produced in kidneys under PTH control.
  - Enhances intestinal calcium absorption and kidney retention.
- Calcitonin ⬇️ :
  - Secreted by thyroid C cells when calcium is high.
  - Inhibits bone resorption and promotes renal excretion.
Balance also depends on diet, renal excretion, and bone turnover.

🏥 Clinical Relevance

Hypocalcemia ⬇️ :
- Causes: Hypoparathyroidism, vitamin D deficiency, CKD, medications.
- Symptoms: Muscle cramps, tetany, seizures, paraesthesia, arrhythmias.
- Treatment: IV or oral calcium, plus correction of underlying cause.
Hypercalcemia ⬆️ :
- Causes: Primary hyperparathyroidism, malignancy, vitamin D excess.
- Symptoms: “Stones, bones, groans, and psychiatric overtones” → renal stones, bone pain, constipation, confusion.
- Treatment: IV fluids, bisphosphonates, calcitonin, treat underlying cause.
Osteoporosis 🦴 :
- Reduced bone density and fracture risk.
- Common in aging and post-menopause.
- Treatment: Calcium + vitamin D, exercise, bisphosphonates, SERMs.
Rickets & Osteomalacia ☀️ :
- Vitamin D deficiency → poor bone mineralization.
- Rickets in children (bowed legs), osteomalacia in adults (bone pain, fragility).
- Treatment: Vitamin D and calcium replacement.

📝 Summary

Calcium is central to skeletal strength, neuromuscular activity, clotting, and intracellular signaling. Its levels are finely tuned by PTH, calcitriol, and calcitonin. Disorders of calcium balance can present dramatically (tetany, arrhythmia, confusion), making it a cornerstone concept in both physiology and clinical medicine.

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Calcium Physiology

📊 Distribution of Calcium

⚡ Functions of Calcium

⚖️ Regulation of Calcium Levels

🏥 Clinical Relevance

📝 Summary

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