Body Fluids (301)

Study Notes

Body fluids, or biofluids, are liquids originating from inside living people. They include excreted or secreted fluids as well as body water.
The major component of body fluids is body water.
Approximately 60-65% of body water is inside cells (intracellular fluid).
The remaining 35-40% is outside cells (extracellular fluid), including interstitial fluid, lymph, and blood.

In adults, body fluids make up 55% of a female's and 60% of a male's total body mass.
Intracellular fluid (ICF) accounts for about 2/3 of the total body fluid, located inside cells.
Extracellular fluid (ECF) is outside cells, including interstitial fluid, which is between cells.
ECF also includes blood plasma, lymph, cerebrospinal fluid, synovial fluid, aqueous humor, perilymph, and pleural fluid.

Organic Substances: Glucose, amino acids, fatty acids, hormones, and enzymes.
Inorganic Substances: Sodium, potassium, calcium, magnesium, chloride, phosphate, sulfate, and bicarbonate.

The figure shows the distribution of body solids and fluids in a lean adult. It highlights the percentage of solids and fluids in both males and females.

The cytosol, also known as intracellular fluid (ICF) or cytoplasmic matrix, is a liquid inside cells.
It's a complex mixture of water and dissolved substances, including ions (e.g. sodium, potassium) and large molecules (e.g., proteins).
ICF ion concentrations differ from extracellular fluid. This difference is crucial for various cellular processes.
The cytosol is a site of numerous cellular processes like signal transduction and cytokinesis.
It's also responsible for transporting metabolites throughout the cell.

The cytosol plays a vital role in multiple cellular processes, including signal transduction and cellular processes of cytokinesis.
This fluid is also important in transporting metabolites within the cell.

The ECF usually refers to all body fluids outside the cells, helping to create a constant environment for cellular operation.
It's found in blood, lymph, body cavities and channels (e.g., brain and spinal cord), and muscle and other tissues.

Interstitial fluid bathes most tissues, excluding fluids in lymph and blood vessels.
Blood plasma is the yellow/gray-yellow, protein-containing portion of blood.
Transcellular fluid, a part of ECF, comprises about 2.5% of the whole.

The breakdown of extracellular fluid demonstrates the dominant percentage within the interstitial fluid.

ECF is crucial in maintaining water and electrolyte balance.
This fluid is involved in excreting and absorbing water between the body and environment.
Ions must be exchanged to maintain homeostasis. This exchange is done through cellular processes or filtration in the kidneys.

### Constituents of ECF

Main Cations: Sodium (136-145 mEq/L), Potassium (3.5-5.5 mEq/L), Calcium (2.2-2.6 mEq/L)
Main Anions: Chloride (99-109 mEq/L), Bicarbonate (22-26 mM)
ECF is generally poorer in proteins compared to ICF.

The table demonstrates differences in ion concentrations between ECF and ICF.
ICF has a higher concentration of potassium and lower concentration of sodium.
ECF has a higher concentration of sodium and a lower concentration of potassium.

Two barriers (plasma membrane and blood vessel walls) divide and separate the ICF, interstitial fluid, and plasma.
Fluid balance is achieved when the required amounts of water and solutes are proportionately distributed among the compartments.
Water is the largest component of the body, making up 45-75% of total body mass

This occurs when a fluid loss exceeds intake, leading to hypovolemia.
Insufficient fluid intake and excessive losses (e.g., vomiting, diarrhea, wounds) are causes.

This is excess fluid in blood vessels (hypervolemia).
Possible causes include inflammatory processes, low osmotic pressure, or high venous pressure.

Total body water percentage varies with age and body fat. Infants have the highest percentage, decreasing as individuals age.

The illustration shows the percentage of water in tissues across different age groups.

Blood, urine, milk, saliva, semen, sweat, tears, mucous, vaginal secretions, vomit, amniotic fluid, pleural fluid, aqueous humor, cerebrospinal fluid, and synovial fluid.