Understanding Fluid Compartments in the Human Body

Compartments in the Body
The human body is mostly made up of fluid. There are different types of fluid throughout the body that is required for homeostasis. The fluid in the body is separated by cell membranes and capillary membranes. Fluid is stored in the body in intracellular and extracellular compartments. The intracellular fluid (ICF) make up approximately 66% of fluid in the cells. Inside the cells, solutes such as oxygen, electrolytes, and glucose dissolve for the metabolic process. The composition of ICF is primarily potassium. The extracellular compartment holds approximately 33% of fluid that surrounds the outside of the cells in the body. The composition of extracellular fluid is primarily sodium. The extracellular compartment

is broken down into the interstitial compartment which surrounds the cells and the intravascular compartment in the vascular system. Most of the extracellular fluid (ECF) is in interstitial compartment.
Movement of Fluid in the Body
Active Transport
Small particles can move across cell membranes more easily than larger particles. Active transport is used when solutes are trying to move from an area of less concentration to an area of more concentration and energy is required. Energy is used when sodium and potassium molecules move across the concentration gradient. The sodium potassium pump moves sodium from ICF to ECF and it moves potassium from ECF to ICF.
Passive Transport
Passive transport does not use energy to move particles.

One mechanism utilized for passive transport is diffusion. When the concentration of particles is higher in area the particles diffuse to an area of lower concentration from the constant motion of particles. The rate of diffusion can increase when the temperature of the solution is increased because this causes the motion of molecules to increase. Another mechanism utilized in passive transport is osmosis. Osmosis occurs when water moves to an area of higher concentration to equalize the concentration between the cell membranes. Osmotic pressure is the power a solution has to draw water across the membrane. The higher concentration has more osmotic pressure and draws water across the membrane. In the extracellular compartment, oncotic pressure pulls water from the interstitial compartment to the intravascular compartment to equalize the concentrations and maintain volume in the vascular system. Lastly, filtration is utilized to move fluid and particles together across the membrane. Filtration takes place from a higher pressure to lower pressure. Hydrostatic pressure is the pressure a fluid uses to force fluid from greater pressure to an area of less

pressure.
IV fluids
Effect of Fluids
The goal of intravenous therapy (IV) therapy is to correct a fluid deficit. There are many causes for fluid deficit, such as dehydration, or burns. Fluid and electrolyte balance is a key factor in homeostasis. There are three types of fluid solutions are used to correct a fluid or electrolyte imbalance. Additionally, crystalloids are solutions that contain small particles, and colloids are solutions that contain bigger particles. Hypertonic solutions have a high concentration of solutes. The concentration of solutes is higher than the concentration in the body. An isotonic solution has the same concentration as body fluids. The osmolality of isotonic solutions most resembles the fluid in the body. A hypotonic solution has a lower concentration of solutes than body fluids.
Hypertonic Solutions
A hypertonic solution in used in fluid overload of when fluids need to be shifted.

Through osmosis, water is shifted out of the cells and pulled into the vascular system. Hypertonic solutions provide calories and other electrolytes. Examples of hypertonic solution include 3% saline, D5/0.9% saline, D5/0.45% saline, and D5LR.
Isotonic solution
An isotonic solution is used to replenish volume from fluid loss. The solution stays in the vascular system to help increase the volume of blood. Examples of isotonic solutions include 0.9% saline, D5/0.225% saline, lactated ringers, whole blood, and packed red blood cells. D5W is also considered isotonic, but quickly converts to hypotonic because the body metabolizes the glucose.
Hypotonic solutions
Hypotonic fluids are used to expand the intracellular space. Hypotonic solutions provide sodium, and chloride. Other electrolytes and calories are not in hypotonic solutions. Examples of hypotonic solutions include 0.45% saline, 0.225%

saline.