Makindo Medical Notes

Related Subjects:Calcium Physiology

Calcium is an essential mineral that plays a critical role in numerous physiological processes, including bone health, muscle contraction, nerve transmission, blood clotting, and cellular signaling. It is the most abundant mineral in the human body, with about 99% of it stored in bones and teeth.

Distribution of Calcium

• Calcium is distributed in the body as follows:
  • 99% in bones and teeth, providing structural support and serving as a reservoir for calcium.
  • 1% in extracellular fluid and soft tissues, involved in various metabolic functions.
  • Normal serum calcium levels are tightly regulated, typically ranging from 8.5 to 10.5 mg/dL (2.1 to 2.6 mmol/L).

Functions of Calcium

• Bone Health:
  • Calcium, along with phosphate, forms hydroxyapatite crystals that provide strength and structure to bones and teeth.
  • Bone acts as a dynamic reservoir, releasing and absorbing calcium as needed to maintain serum levels.
• Muscle Contraction:
  • Calcium ions are essential for muscle contraction, including skeletal, cardiac, and smooth muscle.
  • During muscle contraction, calcium binds to troponin, causing a conformational change that allows actin and myosin interaction.
• Nerve Transmission:
  • Calcium plays a crucial role in the release of neurotransmitters at synaptic junctions, facilitating nerve impulse transmission.
  • Calcium influx into nerve terminals triggers the release of neurotransmitter-containing vesicles into the synaptic cleft.
• Blood Clotting:
  • Calcium is a vital component of the coagulation cascade, necessary for the activation of various clotting factors.
• Cellular Signaling:
  • Calcium acts as a second messenger in various cellular signaling pathways, regulating processes such as hormone secretion, enzyme activity, and cell growth.

Regulation of Calcium Levels

• Calcium homeostasis is tightly regulated by several hormones:
  • Parathyroid Hormone (PTH):
    • Secreted by the parathyroid glands in response to low serum calcium levels.
    • Increases calcium levels by stimulating bone resorption, increasing renal calcium reabsorption, and promoting the activation of vitamin D.
  • Calcitriol (Active Vitamin D):
    • Produced in the kidneys from its precursor forms under the influence of PTH.
    • Enhances calcium absorption from the gastrointestinal tract and increases renal calcium reabsorption.
  • Calcitonin:
    • Secreted by the thyroid gland in response to high serum calcium levels.
    • Lowers calcium levels by inhibiting bone resorption and increasing renal calcium excretion.
• Calcium balance is also influenced by dietary intake and absorption, renal excretion, and bone remodeling processes.

Clinical Relevance

• Hypocalcemia (low calcium levels):
  • Causes: Hypoparathyroidism, vitamin D deficiency, chronic kidney disease, and certain medications.
  • Symptoms: Muscle cramps, tetany, seizures, cardiac arrhythmias, and numbness/tingling in the extremities.
  • Treatment: Calcium supplementation (oral or intravenous) and addressing the underlying cause.
• Hypercalcemia (high calcium levels):
  • Causes: Hyperparathyroidism, malignancies, excessive vitamin D intake, and certain medications.
  • Symptoms: Nausea, vomiting, constipation, polyuria, polydipsia, confusion, and in severe cases, cardiac arrhythmias and coma.
  • Treatment: Hydration, bisphosphonates, calcitonin, and addressing the underlying cause.
• Osteoporosis:
  • A condition characterized by reduced bone mass and increased fracture risk.
  • Associated with aging, menopause, chronic glucocorticoid use, and other risk factors.
  • Treatment: Calcium and vitamin D supplementation, weight-bearing exercise, and medications such as bisphosphonates or selective estrogen receptor modulators (SERMs).
• Rickets and Osteomalacia:
  • Conditions resulting from vitamin D deficiency, leading to impaired bone mineralization.
  • Rickets occurs in children, causing bone deformities, while osteomalacia occurs in adults, leading to bone pain and fractures.
  • Treatment: Vitamin D and calcium supplementation, along with addressing the underlying cause.

Summary

Calcium is a vital mineral involved in bone health, muscle contraction, nerve transmission, blood clotting, and cellular signaling. Its regulation is tightly controlled by hormonal mechanisms, dietary intake, renal excretion, and bone remodeling. Abnormal calcium levels can lead to significant clinical issues, highlighting the importance of understanding calcium physiology and maintaining its balance.