The numerous body fluids in the human body , consisting mainly of water , can be roughly subdivided into those that circulate in fluid systems and those that occur within certain spaces (compartments). This separation is more formal, since the apparently “standing” liquids, such as B. the aqueous humor of the eye, formed ( secreted ) in certain places and reabsorbed ( resorbed ) elsewhere and thus subject to a (albeit very slow) flow.
In addition, a distinction can be made between intracellular and extracellular fluid. But the intracellular space is also subject to constant exchange ( diffusion through membranes as a result of cellular metabolism ). Lean muscle tissue contains approximately 75% water in its cells. The blood plasma contains 90 to 95% water, the body fat 25% water and the bones also have a water content of 22%. The water, like the blood, serves to transport oxygen and nutrients to the organs and their cells as well as the removal of metabolic products ("waste"). The amount of water in the body and the volume of the large compartments are hormonally regulated , among other things .
Extracellular fluid that does not circulate in a circuit
Liquids that circulate in circuits (extracellular)
Blood is used to transport oxygen and nutrients to the organs and their cells as well as to remove metabolic products and waste. In addition, hormones and other active substances are transported between the cells. 55% of the blood is blood plasma , which consists of up to 95% water , the rest are other substances dissolved in the carrier water.
Blood is pumped from the right and left halves of the heart and circulates in the blood vessels . In it swim red blood cells ( erythrocytes ), white blood cells ( leukocytes ) and blood platelets ( thrombocytes ).
Lymph fulfills two tasks in the body: on the one hand, it is part of the immune system by transporting pathogens to the lymph nodes ; on the other hand, as part of digestion , it transports molecules that are too large to be transported directly from the tissue into the bloodstream, such as Proteins and lipids from the digestive tract.
Saliva is produced in the salivary glands and then released in the mouth. It contains a digestive enzyme, α-amylase , which breaks down the polysaccharides contained in food , and mucin and immunoglobulin A as protection against pathogens.
Secretions of the pancreas
On the one hand, bile serves to digest fat, in which the bile salts it contains envelop the water-insoluble lipids and form micelles , which can then be absorbed by the intestinal mucosa. In addition, with their help, drugs and their breakdown products as well as physiological breakdown products (e.g. bilirubin ) are excreted in the stool.
The bile is produced in the liver , stored in the gallbladder and released into the intestine via the bile ducts . Here part of the bile is reabsorbed into the blood via the intestinal mucosa , the other part is excreted with the stool.
Secretions and excreta, fluid excretion
Urine is produced in the kidneys . Its elimination is the regulation of fluid and electrolyte balance and the elimination of metabolic waste products , particularly in the degradation of proteins and nucleotides resulting nitrogen - compounds .
Sweat is used to regulate the heat balance due to the evaporation cold that occurs during its evaporation, it keeps the skin supple and its pH value constant. It also contains sexually and individually specific fragrances.
- Breast milk
- Vaginal secretions of the woman
- Tear fluid
- Nasal secretions
- Ejaculate ( semen )
- Menstrual fluid
Other fluid spaces (compartments)
- Aqueous humor of the eye
- Cerebrospinal fluid (cerebrospinal fluid)
- Pleural fluid
- Pericardial fluid
- Synovia (joint fluid)
- Amniotic fluid
- Ear wax (cerumen)
As well as diseases:
Amount of fluid, fluid spaces and compartments
The percentage of water distribution in the fluid spaces of humans (EZR, IZR) differs depending on age (it decreases from around 75% in newborns to 55% in adults). In women, the total amount of fluid in the body is about 5% to 10% less than in adult men. In adults, the total water content of approx. 65% of the respective total body weight is distributed in a ratio of 3: 2 between the intracellular and extracellular spaces.
Exchange of body fluids
During sexual intercourse and erotic acts such as kissing , small amounts of body fluids are exchanged. If someone is infected with a pathogen, diseases can be transmitted through the exchange of body fluids . It has been scientifically proven that kissing, when healthy, strengthens the immune system .
Places of excretions and products
- Kidneys → urinary bladder → urine
- Lungs , pulmonary alveoli → exhaled air → water vapor
- Liver → bile , gallbladder → large intestine
- Gastrointestinal tract → colon → rectum → anus
- Skin → sweat
- Mucous membranes , exocrine glands → various mucus, also tears on the eye
- Prostate → seminal fluid
- possibly internal or external wounds → blood plasma , blood loss
Calculation of body water
In individuals of normal weight, water is abundant in most parts of the body except adipose tissue . The following calculations are intended for adults with an average physique and are not suitable for overweight or particularly muscular people. The proportions have been greatly simplified and use rounded numbers for quick calculation. In men, 60% of the body mass consists of water. In women, this value is around 55% because of a higher percentage of body fat . This is called total body water .
Two thirds of this water is in the cells and is therefore called intracellular water . The other third is extracellular water .
The extracellular water consists of blood plasma , which is one fifth of the extracellular water, and extracellular fluid, which is the other four fifths. Water is also in other places like the eye , but this can be ignored as a meaningless quantity in the quick calculation.
Estimation of the body water content
There are not many methods that can be used to determine the percentage of body water in the various compartments. The easiest way to get a rough estimate is to calculate an estimate based on body weight, gender and age.
The following are the guideline values of the World Health Organization (WHO) for estimating the water content in people of normal weight:
- Children 60-75% (male / female)
- Women 50–55% (no age information)
- Men 60–65% (no age information)
Measurement of body water content
The total body water can be determined with the mass spectrometer measurement of the deuterium excess in the breath samples of individuals. A known dose of deuterium water (D 2 O) is taken within the body water in a balancing manner and left there. The mass spectrometer then measures the ratio of deuterium to hydrogen (D: H) in the exhaled breathable water vapor. The total body water is then measured precisely from the increase in the breath deuterium content in relation to the release of the ingested D 2 O.
Fluid balance in medicine and care
A fluid balance is used to separately record the import and export of different fluids in a patient; z. B. as an infusion or with food, when sweating or through excretion . It is structured like a kind of table in which the patient or the nursing staff enters the supplied and dispensed fluids in the columns provided. Usually after 24 hours it is calculated whether there is a negative balance (increased excretion) or a barely noticeable deposit (excess) up to visible deposits ( edema ). Even in healthy people there is a range that is initially inconspicuous and not pathological. However, with constant loss of fluid, gradual desiccosis can occur.
The details of fluid intake (metabolism, drinks and food) and fluid output ( micturition ) are usually recorded in milliliters (ml). The accuracy of this measurement can be increased by draining the fluid into collecting vessels via urinary catheters to monitor kidney function and analyzing the composition (samples, urine laboratory values). This can take place at any time, e.g. B. done hourly, fractionated. In addition, it is recorded for certain patients whether the person was able to reach the toilet in time, or whether the bladder emptying in an incontinence aid such. B. a template or an incontinence pad (incorrectly called diaper ) was made.
A precise and daily weight control can also be helpful here. In addition, if there is a diagnostic need, it is also noted whether there was an urge to urinate before micturition. A partial accounting, in which only the export from the bladder is noted, is called the micturition protocol . Notes only about the oral intake of beverages are called drinking log / drinking list .
Problems with abnormal water content
The following problems can be caused by abnormal levels of water in the body (or parts of the body):
In contrast, the various forms of urinary incontinence i. d. Usually not on the liquid / water content in a fabric. Only the amount of fluid in the bladder can be the trigger (intra-individual range of the amount) or possibly not the trigger (pathological) of the urge to urinate.
- Robert F. Schmidt , Gerhard Thews , Florian Lang (Hrsg.): Physiologie des Menschen. 28th edition. Springer, Berlin 2000, ISBN 3-540-66733-4 , chapter 36, p. 778ff (water and electrolyte balance).