The human body constantly performs processes to sustain life. These processes involve the production and management of various biological fluids. These fluids circulate, performing specialized roles that contribute to overall health and function. From transporting nutrients to removing waste, these fluids are integral to maintaining a stable internal environment.
Categories of Body Fluids
Biological fluids are classified as secretions or excretions. Secretions are substances produced and released by cells or glands for a specific physiological function, often within the body or onto a surface.
Excretions are waste products eliminated from the body. These substances are byproducts of metabolic processes and can be harmful if allowed to accumulate. The body removes these wastes to prevent toxic levels. Saliva is a secretion, serving beneficial functions. Urine is an excretion, representing the body’s method of expelling metabolic waste.
Saliva A Secretion
Saliva is a clear fluid present in the mouth, produced primarily by three major pairs of salivary glands: the parotid, submandibular, and sublingual glands, along with smaller glands in the oral tissues. The average daily production of saliva in a healthy adult ranges from 0.75 to 1.5 liters, though this flow can increase significantly with the presence or even thought of food. This fluid is approximately 99.5% water, with the remaining 0.5% consisting of electrolytes, mucus, enzymes, and antibacterial compounds.
Saliva’s functions support oral health and digestion. It lubricates and moistens food, transforming it into a soft mass called a bolus, which facilitates easier chewing, tasting, and swallowing. It also contains enzymes such as salivary amylase (ptyalin) and lingual lipase, which initiate the chemical breakdown of carbohydrates and fats, respectively, even before food leaves the mouth. Beyond digestion, saliva helps to protect teeth by washing away food debris, dead cells, and bacteria, and it maintains an alkaline environment in the mouth to help prevent tooth decay.
Urine An Excretion
Urine is a liquid byproduct formed as the kidneys filter blood. This fluid is primarily composed of water, typically over 95%, with the remaining percentage consisting of dissolved waste products. Key waste components found in urine include urea, creatinine, and uric acid, alongside various electrolytes like sodium, potassium, and chloride. Urea, for instance, is a non-toxic molecule produced in the liver from toxic ammonia and carbon dioxide, which are byproducts of protein breakdown.
The urinary system, which includes the kidneys, ureters, bladder, and urethra, forms and eliminates urine. The kidneys, bean-shaped organs, contain millions of tiny filtering units called nephrons. These nephrons filter blood, reabsorbing necessary substances and collecting waste products to form urine.
Urine then travels from the kidneys through the ureters to the bladder for storage, eventually exiting the body via the urethra. This process removes excess water, metabolic byproducts, and helps regulate blood volume, blood pressure, and maintain the body’s electrolyte and pH balance.