Calcium Metabolism Review

Summary

This clinical review video explores the key aspects of calcium metabolism, focusing on the homeostasis of calcium levels in the blood. It explains how calcium is stored in bones, with a small percentage circulating in fluids, and highlights the role of hormones such as parathyroid hormone and vitamin D in regulating calcium levels. The video also discusses the processes of calcium absorption, the impact of kidney and bone health, and how calcium supports functions like muscle contraction and blood coagulation. It provides an in-depth look at the physiological mechanisms ensuring proper calcium balance and bone strength.

Takeaways

• 😀 The goal of calcium homeostasis is to maintain blood calcium levels, not bone calcium levels, as blood calcium is crucial for cellular and tissue functions.
• 😀 About 99% of the body's calcium is stored in bones as hydroxyapatite, while the remaining 1% is in extracellular fluids and plasma.
• 😀 Half of the calcium circulating in extracellular fluids is bound to proteins, and the other half exists as ionized calcium.
• 😀 The body’s only source of calcium is through diet, and the primary route of excretion is through urine.
• 😀 Calcium plays vital roles in bone mineralization, blood coagulation, muscle contraction, hormone secretion, glycogen metabolism, cell division, and heart function.
• 😀 Calcitonin, released by the thyroid gland, helps lower calcium levels by promoting bone deposition, decreasing intestinal absorption, and increasing calcium excretion in urine.
• 😀 Parathyroid hormone (PTH) is released when calcium levels are low, promoting bone resorption, calcium reabsorption in the kidneys, and increased calcium absorption in the intestines (with the help of vitamin D).
• 😀 Vitamin D is essential for calcium metabolism and is synthesized in the skin following UVB exposure, converting cholesterol to vitamin D.
• 😀 Vitamin D also has non-calcium-related benefits, such as boosting immunity and improving mood, particularly in winter months when sunlight exposure is reduced.
• 😀 The synthesis of active vitamin D involves several organs: the skin, liver, and kidneys. The liver and kidneys help activate vitamin D for calcium absorption and bone resorption.
• 😀 The kidneys play a critical role in calcium metabolism by regulating calcium reabsorption and excretion, which affects blood calcium levels and the risk of kidney stones.
• 😀 Bone remodeling involves the continuous formation and breakdown of bone tissue, with osteoblasts building bone and osteoclasts breaking it down. A balance between these processes is crucial for maintaining bone mass.

Q & A

What is the primary goal of calcium homeostasis?

The primary goal of calcium homeostasis is to maintain the blood calcium level at a constant level, ensuring cellular and tissue functions are normal.

Where is the majority of calcium in the body located?

About 99% of calcium in the body is stored in bones as hydroxyapatite crystals, which make bones strong.

What are the main functions of calcium in the body?

Calcium is crucial for bone mineralization, blood coagulation, muscle contraction, hormone secretion, glycogen metabolism, and cell division. It's also essential for heart function.

How does the body respond to high calcium levels?

When calcium levels are high, the thyroid gland releases calcitonin, which promotes calcium storage in bones, decreases calcium absorption in the intestines, and reduces calcium reabsorption in the kidneys.

What happens when blood calcium levels are too low?

When calcium levels drop, the parathyroid glands release parathyroid hormone, which increases calcium release from bones, enhances calcium absorption in the intestines, and prevents calcium loss in the kidneys.

What role does vitamin D play in calcium metabolism?

Vitamin D is essential for calcium absorption in the gut and helps maintain proper calcium levels in the blood. It also helps activate the parathyroid hormone and supports immune function.

How is vitamin D synthesized in the body?

Vitamin D is synthesized in the skin when exposed to UVB rays from sunlight, converting cholesterol into vitamin D. It can also be obtained from dietary sources like fortified milk, cod liver oil, and seafood.

What are the three organs involved in the synthesis of vitamin D?

The skin, liver, and kidneys are involved in the synthesis of vitamin D. The skin produces vitamin D from cholesterol, the liver converts it into 25-hydroxyvitamin D, and the kidneys convert it into the active form, 1,25-dihydroxyvitamin D.

How do the parathyroid glands regulate calcium levels?

The parathyroid glands release parathyroid hormone in response to low blood calcium levels. This hormone stimulates calcium release from bones, increases calcium reabsorption in the kidneys, and activates vitamin D to enhance calcium absorption in the intestines.

What factors are necessary for calcium absorption in the gastrointestinal system?

For calcium absorption to occur efficiently, normal intestinal function, adequate dietary calcium intake, and sufficient vitamin D levels are required. Conditions like short bowel syndrome or vitamin D deficiency can impair calcium absorption.