Extracellular fluid in the context of "Cerebrospinal fluid"

In biology, homeostasis (British also homoeostasis; /ˌhoʊmiəˈsteɪsɪs/ HOH-mee-ə-STAY-sis) is the state of steady internal physical and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits (homeostatic range). Other variables include the pH of extracellular fluid, the concentrations of sodium, potassium, and calcium ions, as well as the blood sugar level, and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.

Homeostasis is brought about by a natural resistance to change when already in optimal conditions, and equilibrium is maintained by many regulatory mechanisms; it is thought to be the central motivation for all organic action. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control center, and an effector. The receptor is the sensing component that monitors and responds to changes in the environment, either external or internal. Receptors include thermoreceptors and mechanoreceptors. Control centers include the respiratory center and the renin-angiotensin system. An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include nuclear receptors that bring about changes in gene expression through up-regulation or down-regulation and act in negative feedback mechanisms. An example of this is in the control of bile acids in the liver.

Body fluids, bodily fluids, or biofluids, sometimes body liquids, are liquids within the body of an organism. In lean healthy adult men, the total body water is about 60% (60–67%) of the total body weight; it is usually slightly lower in women (52–55%). The exact percentage of fluid relative to body weight is inversely proportional to the percentage of body fat. A lean 70 kg (150 lb) man, for example, has about 42 (42–47) liters of water in his body.

The total body of water is divided into fluid compartments, between the intracellular fluid compartment (also called space, or volume) and the extracellular fluid (ECF) compartment (space, volume) in a two-to-one ratio: 28 (28–32) liters are inside cells and 14 (14–15) liters are outside cells.

The kidneys are a pair of organs of the excretory system in vertebrates, which maintain the balance of water and electrolytes in the body (osmoregulation), filter the blood, remove metabolic waste products, and, in many vertebrates, also produce hormones (in particular, renin) and maintain blood pressure. In healthy vertebrates, the kidneys maintain homeostasis of extracellular fluid in the body. When the blood is being filtered, the kidneys form urine, which consists of water and excess or unnecessary substances, the urine is then excreted from the body through other organs, which in vertebrates, depending on the species, may include the ureter, urinary bladder, cloaca, and urethra.

All vertebrates have kidneys. The kidneys are the main organ that allows species to adapt to different environments, including fresh and salt water, terrestrial life and desert climate. Depending on the environment in which animals have evolved, the functions and structure of the kidneys may differ. Also, between classes of animals, the kidneys differ in shape and anatomical location. In mammals, they are usually bean-shaped. Evolutionarily, the kidneys first appeared in fish as a result of the independent evolution of the renal glomeruli and tubules, which eventually united into a single functional unit. In some invertebrates, the nephridia are analogous to the kidneys but nephridia are not kidneys. The metanephridia, together with the vascular filtration site and coelom, are functionally identical to the ancestral primitive kidneys of vertebrates.

Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but which contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intravascular part of extracellular fluid (all body fluid outside cells). It is mostly water (up to 95% by volume), and contains important dissolved proteins (6–8%; e.g., serum albumins, globulins, and fibrinogen), glucose, clotting factors, electrolytes (Na
, Ca
, Mg
, HCO₃, Cl
, etc.), hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and oxygen. It plays a vital role in an intravascular osmotic effect that keeps electrolyte concentration balanced and protects the body from infection and other blood-related disorders.

Blood plasma can be separated from whole blood through blood fractionation, by adding an anticoagulant to a tube filled with blood, which is spun in a centrifuge until the blood cells fall to the bottom of the tube. The blood plasma is then poured or drawn off. For point-of-care testing applications, plasma can be extracted from whole blood via filtration or via agglutination to allow for rapid testing of specific biomarkers. Blood plasma has a density of approximately 1,025 kg/m (1.025 g/ml). Blood serum is blood plasma without clotting factors. Plasmapheresis is a medical therapy that involves blood plasma extraction, treatment, and reintegration.

Saliva (commonly referred as spit or drool) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be extracted), enzymes (such as lingual lipase and amylase), and antimicrobial agents (such as secretory IgA, and lysozymes).

The enzymes found in saliva are essential in beginning the process of digestion of dietary starches and fats. These enzymes also play a role in breaking down food particles trapped within dental crevices, thus protecting teeth from bacterial decay. Saliva also performs a lubricating function, wetting food and permitting the initiation of swallowing, and protecting the oral mucosa from drying out.

The internal environment (or milieu intérieur in French; French pronunciation: [mi.ljø ɛ̃.te.ʁjœʁ]) was a concept developed by Claude Bernard, a French physiologist in the 19th century, to describe the interstitial fluid and its physiological capacity to ensure protective stability for the tissues and organs of multicellular organisms.

Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss of extracellular fluid and should not be confused with dehydration.

Hypovolemia is caused by a variety of events, but these can be simplified into two categories: those that are associated with kidney function and those that are not.