Biofluids are the diverse array of liquids found within living organisms, playing fundamental roles in sustaining life. These internal fluids are constantly in motion, facilitating communication and transport throughout the body. Their balance and composition are integral to biological systems.
What Are Biofluids?
Biofluids are water-based liquids containing various dissolved substances, making their chemical composition highly variable depending on their location in the body. They are dynamic, constantly moving within networks like blood and lymphatic vessels. They are found inside cells (intracellular fluid) and outside cells (extracellular fluid), which includes blood plasma, interstitial fluid, and lymph.
They are mostly water (often around 99%), containing electrolytes like sodium, potassium, chloride, and bicarbonate. They also contain proteins, glucose, hormones, and metabolic waste products. This mixture allows them to participate in physiological activities such as nutrient delivery, waste removal, immune defense, and temperature regulation.
Key Biofluids and Their Essential Functions
The body relies on several distinct biofluids, each with specialized components and functions. Blood is a fluid composed of plasma, red blood cells, white blood cells, and platelets. Plasma, about 55% of blood volume, is primarily water, also containing proteins, electrolytes, lipids, and glucose. Red blood cells (erythrocytes) contain hemoglobin, which transports oxygen from the lungs to tissues and carries carbon dioxide back to the lungs. White blood cells defend against pathogens, and platelets clot blood to prevent bleeding.
Urine is a liquid byproduct formed in the kidneys and expelled from the body. It is over 95% water, comprising metabolic wastes like urea, creatinine, and uric acid, along with inorganic salts and dissolved ions. The kidneys filter blood plasma, reabsorbing useful substances and concentrating waste products into urine. This process removes toxins and maintains the body’s water and electrolyte balance.
Cerebrospinal fluid (CSF) is a clear fluid that surrounds the brain and spinal cord. Produced by the choroid plexus within the brain’s ventricles, CSF is about 99% water, containing proteins, glucose, and electrolytes. It provides a protective cushion, absorbing shocks and buffering the central nervous system against trauma. CSF also maintains a stable chemical environment for neuronal function by regulating ion concentrations, delivering nutrients, and removing metabolic waste products.
Saliva, produced by salivary glands, is approximately 99% water, including electrolytes, mucus, enzymes, and antimicrobial agents. Its functions include lubricating and moistening food to aid in chewing and swallowing. Saliva also contains enzymes like amylase and lipase, which initiate carbohydrate and fat digestion. Additionally, saliva helps maintain oral hygiene by cleaning food debris and bacteria, and its buffering capacity neutralizes acids, protecting tooth enamel.
Biofluids in Health Assessment and Diagnostics
Biofluid analysis provides insights into health, enabling disease detection, condition monitoring, and guiding treatment decisions. Blood tests measure glucose levels for diabetes diagnosis and management, or assess cholesterol levels for cardiovascular risk. Analyzing blood components can also reveal infections, anemia, or blood clotting issues.
Urine analysis, or urinalysis, is a common diagnostic tool, indicating kidney function, urinary tract infections, or metabolic disorders by detecting abnormal levels of proteins, glucose, or other substances. Examining cerebrospinal fluid (CSF) obtained through a lumbar puncture can help diagnose neurological conditions such as meningitis, multiple sclerosis, or brain tumors by identifying abnormal proteins, cells, or pathogens. Saliva is also emerging as a non-invasive diagnostic tool for systemic illnesses, including cancers and autoimmune conditions, by analyzing its protein and genetic content. These analyses of biofluids allow healthcare professionals to understand internal bodily processes and detect deviations from normal physiological states.