What Is Fluid Homeostasis?

The total fluid volume of the human body includes two parts: intracellular fluid and extracellular fluid. Extracellular fluid is divided into two parts: plasma and interstitial fluid. Most interstitial fluids can quickly exchange with intravascular fluids or intracellular fluids, and play a great role in maintaining the body's water and electrolyte balance. The osmotic pressure of the intracellular and extracellular fluids is equal to 290-310 mmol / L. Water can pass through the cell membrane, and the osmotic pressure on both sides of the cell membrane can be kept equal. Any situation that can affect the osmotic pressure of extracellular fluid or intracellular fluid, such as changes in the electrolyte concentration of sodium, potassium, etc., will cause water to move to the one with an increased osmotic pressure, and restore the osmotic pressure of the two.

Fluid balance

Right!

The total fluid volume of the human body includes two parts: intracellular fluid and extracellular fluid. Extracellular fluid is divided into two parts: plasma and interstitial fluid. Most interstitial fluids can quickly exchange with intravascular fluids or intracellular fluids, and play a great role in maintaining the body's water and electrolyte balance. The osmotic pressure of the intracellular and extracellular fluids is equal to 290-310 mmol / L. Water can pass through the cell membrane, and the osmotic pressure on both sides of the cell membrane can be kept equal. Any situation that can affect the osmotic pressure of extracellular fluid or intracellular fluid, such as changes in the electrolyte concentration of sodium, potassium, etc., will cause water to move to the one with an increased osmotic pressure, and restore the osmotic pressure of the two.

The human body fluid balance is mainly adjusted by the kidneys to achieve a constant body environment, which is necessary to ensure the normal metabolism of human cells. ^[1]

The amount of body fluid is related to age, sex and body shape. Adult men's body fluids account for about 60% of body weight, women's 55%, and infants 70%. Two-thirds of the adult's total water is intracellular, and one-third is extracellular. Approximately 3/4 of the extracellular fluid is stored in the interstitial spaces of the cells.

Electrolyte in

The ability of a solute to absorb water (or tension) in water is called osmotic pressure. The osmotic pressure is proportional to the number of particles (molecules or ions) of the solute, and has nothing to do with the charge and size of the particles. Inorganic salt molecules are small and exist in ionic state in water, so the number of particles is large, and the osmotic pressure generated is large; although the glucose molecules are medium and large, they cannot dissociate, and the osmotic pressure generated is second; protein molecules can dissociate, but The molecules are too large, the number of particles is small, and the resulting osmotic pressure is small. The migration of water inside and outside the cell is basically determined by the difference between the osmotic pressure inside and outside the cell membrane. Decreased Na + concentration outside the membrane, that is, low osmotic pressure, water enters the cell, causing intracellular edema; conversely, increased Na + concentration outside the membrane, that is, high osmotic pressure, water out of the cell, causing intracellular dehydration. However, the exchange of water between plasma and interstitial fluid can pass freely because the crystals (inorganic salts, glucose, etc.) have small particles.

During the metabolism of the human body, both acid and alkali are produced, and the [H +] in body fluids often changes, but the human body can make the [H +] in the blood only through the buffering system of the body fluids, the breathing of the lungs, and the regulation of the kidneys. Change in a small range, that is, to maintain the pH value of the blood between 7.35 to 7.45.

HCO3- / H2CO3 in the blood is the most important pair of buffer substances. When the acid in the body increases, HCO3 combines with H + (H + + HCO3 H2CO3 CO2 + H2O) to neutralize the acid; when the alkali increases, H2CO3 releases H + to neutralize the base (OH- + H2CO3 HCO3 + H2O ) To keep the blood pH within the normal range. The effects of the buffer system occur quickly, but the total amount is limited, and ultimately depends on the lungs and kidneys to regulate.

The lungs are an important organ that expels volatile acids (H2CO3) from the body. When the partial pressure of CO2 in the blood increases, the respiratory center is excited, deepening the breathing, accelerating CO2 emission, and reducing the concentration of H2CO3 in the blood. When the partial pressure of CO2 in the blood decreases, the breathing becomes slower and shallower, reducing CO2 emission.

The kidney has the strongest ability to regulate acid-base balance. All non-volatile acids and excess bicarbonate must be excreted through the kidney. Its main function is to excrete H + and absorb Na + and HCO3-.