Homéostasie phosphocalcique et remodelage osseux: Sytème endocrine.

Summary

This video explains the concept of phosphocalcic homeostasis, which involves the regulation of calcium and phosphate concentrations in the body. The balance of these minerals is crucial for various bodily functions, such as cellular signaling, energy transfer, and bone health. The video covers how calcium and phosphate are absorbed, excreted, and distributed, and the role of hormones like PTH, vitamin D, and calcitonin in maintaining this balance. It also explores the structure and remodeling of bones, the interaction between different cells involved in bone metabolism, and how hormonal regulation influences calcium and phosphate levels.

Takeaways

• 😀 Phosphocalcique homeostasis refers to the regulation of phosphate and calcium levels in the body to maintain balance.
• 😀 Calcium plays key roles in cellular signaling, muscle contraction, blood clotting, and neuron excitability.
• 😀 Phosphate is essential for forming membranes, generating ATP, and regulating pH balance.
• 😀 The daily intake of calcium and phosphate is approximately 1 gram each, but absorption rates are not 100%.
• 😀 Around 35% of calcium is absorbed in the intestine, and phosphate has a similar absorption rate with minimal excretion.
• 😀 Most calcium is stored in bones (99%), with small amounts present in intracellular and extracellular fluids.
• 😀 Phosphate in the body (800g) is mostly found in bones, with smaller portions in cells as phospholipids and phosphates.
• 😀 Homeostasis of phosphocalcique is regulated by hormones like PTH (parathyroid hormone), vitamin D, and calcitonin.
• 😀 PTH stimulates calcium absorption in the kidneys, increases calcium release from bones, and decreases phosphate absorption.
• 😀 Vitamin D enhances calcium absorption in the intestines, supports bone formation, and works synergistically with PTH.
• 😀 Calcitonin helps to lower calcium levels by reducing bone resorption and has a minor effect on phosphate levels.

Q & A

What is phosphocalcic homeostasis?

Phosphocalcic homeostasis refers to the processes and mechanisms that regulate the concentrations of phosphorus (or phosphates) and calcium in the body, keeping them at stable levels to maintain balance. This regulation is crucial for various bodily functions.

Why is calcium more important than phosphorus in homeostasis?

Although both calcium and phosphorus are essential for various functions, calcium tends to be more critical in homeostasis. This is because calcium plays key roles in cellular signaling, muscle contraction, blood clotting, and neuronal excitability, while phosphorus is mainly involved in energy production and structural functions like membrane formation.

How much calcium and phosphorus is ingested daily?

The daily intake of calcium and phosphorus is approximately 1000 mg or 1 gram. However, not all of this is absorbed by the intestines, with about 35% of calcium being absorbed and around 65% of phosphate.

What are the main ways calcium is eliminated from the body?

Calcium is mainly eliminated through fecal excretion (800-900 mg) and urinary excretion (100-200 mg).

Where is most of the body's calcium stored?

Around 99% of the body's calcium is stored in the bones, which contain approximately 1 to 1.5 kg of calcium. The remaining 1% is found in extracellular and intracellular fluids.

What are the three main fractions of calcium in the extracellular fluid?

In the extracellular fluid, calcium is divided into three fractions: 40-44% bound to proteins like albumin, 10% complexed with anions like citrate and phosphate, and 50% in its ionized form, which is the active form.

How is phosphorous distributed in the body?

Phosphorus is primarily stored in the bones (85-95% of total phosphorus), where it is part of hydroxyapatite. The rest is found in intracellular and extracellular compartments, mainly in the form of phospholipids, phosphate esters, and inorganic phosphate.

What hormones regulate phosphocalcic homeostasis?

Phosphocalcic homeostasis is primarily regulated by parathyroid hormone (PTH), vitamin D, and calcitonin. These hormones act on various organs, including the intestines, kidneys, and bones, to maintain calcium and phosphorus balance.

What role does parathyroid hormone (PTH) play in calcium regulation?

PTH increases blood calcium levels by stimulating calcium release from bones (resorption), increasing calcium reabsorption in the kidneys, and activating vitamin D to enhance calcium absorption in the intestines. It also decreases phosphate levels by reducing phosphate reabsorption in the kidneys.

How does vitamin D contribute to calcium and phosphate regulation?

Vitamin D plays a key role in increasing calcium absorption in the intestines and enhancing bone resorption. It also works with PTH to increase calcium release from bones and may have a minor effect on calcium and phosphate reabsorption in the kidneys.