Interstitial Fluid
Interstitial fluid is a vital liquid found in the spaces surrounding and between cells in both humans and animals. It originates from plasma that leaks out of capillaries and serves crucial functions, including transporting oxygen and nutrients to cells while removing waste products. This fluid is formed continuously, and once it has served its purpose, it moves into the lymphatic system, where it is referred to as lymph. The term "interstitial" is derived from the Latin word meaning "standing between," reflecting its role in the small spaces between cells. About 10% of blood volume is converted into interstitial fluid, with the majority being recirculated back into the bloodstream.
Maintaining the balance of interstitial fluid is essential for bodily functions, as low fluid levels can lead to issues such as cellular dehydration. Specialized neurons, called osmoreceptors, help regulate fluid levels by triggering thirst when concentrations of nutrients and solutes in the fluid rise. Additionally, interstitial fluid serves as an important tool for medical diagnostics, as it mirrors the nutrient composition of blood and can assist in monitoring conditions like diabetes through continuous glucose monitoring. It also plays a role in oncology, as it contains proteins and biomarkers that can provide insights into tumor characteristics and aid in the development of targeted treatments.
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Interstitial Fluid
Interstitial fluid is a liquid that is found in the spaces around and between cells in humans and animals. It is made up of plasma that comes out of the capillaries and surrounds and bathes the cells. Interstitial fluid helps to transport oxygen and nutrients into cells and waste products out. When interstitial fluid has fulfilled its purpose and has aged, it moves into the lymph nodes where it is simply known as lymph.
Background
The word interstitial comes from the Latin word institi, which means "standing between." The term is used often in medicine to refer to body parts or components that are between other things, especially where the space between is small. Since cells in any living being are packed closely together with little space between them, the fluid that does seep between them is known as interstitial fluid.
Fluids in the body can be found either inside cells, which is called intracellular fluid, or outside of cells, which is known as extracellular fluid. Intracellular fluid is the cytoplasm, or liquid center, of the cell. About two-thirds of the water found in the human body is contained in the intracellular fluid, while the remaining water is in the extracellular fluid. Extracellular fluid occurs in three forms: cerebrospinal fluid, which is in the spinal cord and brain; intravascular fluid, which is inside the circulatory system; and the interstitial fluid that is over and between the cells.
The fluid in the human body begins as blood plasma. Blood is made up of red blood cells that carry oxygen, white blood cells that fight infection, and platelets, which help clots to form to stop bleeding after an injury. These elements are carried in blood plasma, the liquid that flows through the circulatory system delivering the blood components to all parts of the body. Blood flows under pressure from the beating of the heart; that pressure increases as the blood moves from the larger arteries into the smaller capillaries, which are the smallest blood vessels that carry blood to the furthest parts of the body. As this pressure increases, the blood plasma is forced out of the capillary walls. It is at this point in the process known as interstitial or tissue fluid.
The fluid carries with it some of the nutrients found in the blood, including glucose, salt, and minerals such as calcium, potassium, and magnesium. It also carries amino acids, fatty acids, and various types of enzymes. The fluid distributes these to the cells as needed and removes waste products. Fresh interstitial fluid is made constantly and the older fluid is retired. The fluid to be replaced moves to the lymph nodes. The lymph nodes are small, pea-sized glands located throughout the body. They are part of the body's immune system and responsible for helping to remove waste products and infections from the body. Most people become aware of their lymph nodes when an infection causes the nodes in the neck, armpits, and/or groin to swell and hurt.
The interstitial fluid moves into the lymph nodes and becomes known as lymph. The lymph nodes provide a very important function in this process. It is estimated that about 10 percent of blood volume is converted to interstitial fluid as it circulates; the remaining 90 percent is picked back up by the veins and recirculated. If the lymphatic system did not draw in the spent interstitial fluid and process it through the lymph nodes for removal from the body, the body would swell with fluid. This sometimes happens when the process is interrupted by disease or medication and is a condition known as edema.
Overview
With so much of the body made up of fluid, to function properly it is important for the body to maintain correct fluid levels. Interstitial fluid plays a role in this process. When fluid levels begin to drop too low because of evaporation or the ingestion of too much salt, the blood contains less interstitial fluid and the nutrients and waste products it carries grow more concentrated. This can result in cellular dehydration as fluids move from inside the cells to make up for the reduction of interstitial fluid. To compensate, special neurons, or nerve cells, known as osmoreceptors respond to the higher concentrations of nutrients and other solutes in the interstitial fluid and trigger thirst. The fluid balance is restored when an individual drinks liquids.
Its role carrying nutrients throughout the body also makes interstitial fluid an important diagnostic tool for physicians treating several types of illnesses. Interstitial fluid contains all the nutrients that blood does, and in roughly the same proportions. A physician treating diabetes can take advantage of this by providing a patient with a continuous glucose monitor. Maintaining an appropriate blood glucose level is important for people with diabetes, and many rely on frequent testing of small drops of blood to determine their levels. With a continuous blood glucose monitor, a small sensor placed under the skin reads the glucose levels in the interstitial fluid. This checks the blood glucose level every few minutes without the need for frequent testing.
Interstitial fluid can also be helpful to physicians treating cancer. Since the fluid surrounds all cells—including cancer cells—it contains proteins and other components released by the cells. It also contains molecules that are unique to the tumors that serve as biomarkers, or biological indicators, of the presence of tumors as well as clues to their development and makeup. These biomarkers can allow physicians to study and analyze the properties of tumors and how they are formed, and can help in developing new and better ways to treat different types of tumors.
Bibliography
"Definition of Interstitial." MedicineNet, 13 May 2016, www.medicinenet.com/script/main/art.asp?articlekey=9587. Accessed 18 Nov. 2016.
"Diabetes Management: A Look at Interstitial Fluid Glucose Sensors." British Columbia Pharmacy Association, 23 Aug. 2021, www.bcpharmacy.ca/tablet/summer-21/look-interstitial-fluid-glucose-sensors. Accessed 25 Nov. 2024.
Gromov, Pavel et al. "Tumor Interstitial Fluid—A Treasure Trove of Cancer Biomarkers." Biochima et Biophysica Acta, Nov. 2013. www.ncbi.nlm.nih.gov/pubmed/23416532. Accessed 25 Nov. 2024.
"Interstitial Fluid." National Cancer Institute, www.cancer.gov/publications/dictionaries/cancer-terms?cdrid=703283. Accessed 25 Nov. 2024.
"Interstitial Fluid." Diabetes Digital Media Ltd, 29 Oct. 2023, www.diabetes.co.uk/body/interstitial-fluid.html. Accessed 25 Nov. 2024.
Scanlan, J., Huxley, VH., Korthius, RJ. "The Interstitium." Capillary Fluid Exchange: Regulation, Functions, and Pathology. Morgan & Claypool Life Sciences, 2010.