The internal environment ismulticellular organismThe environment in which the cells ofExtracellular fluid。The internal environment is directly carried out by cellsSubstance exchangeIt is the environment where cells live directly.Cellular metabolismOxygen required and variousNutrientsIt can only be taken from the internal environment, but is produced by cell metabolismcarbon dioxideAnd metabolic end products also need to be directly discharged into the internal environment, and thenblood circulationTransport, by breathing andExcretory organExcretion.In addition, the internal environment is also the place where cells live and move.Therefore, the internal environment is important for the survival of cells and the maintenance of normal cellsphysiological functionVery important.The relative stability of the internal environment is the primary condition for the free and independent survival of the body.[1]
Chinese name
internal environment
Foreign name
internal environment
Presenter
Claude Bernard
Interpretation
The environment in which the cells of multicellular organisms live directly in the body
body fluid(body fluid) includesIntracellular fluidandExtracellular fluid。The body fluid volume of normal adults accounts for about 60% of the body weight, of which extracellular fluid accounts for1/3，The intracellular fluid accounts for 2/3 of the total fluid, and about 3/4 of the extracellular fluid is distributed in the cell gap, which is calledInterstitial fluidorTissue fluid（tissuefluid）；The rest about 1/4 continuously circulates in the blood vessels, that is, plasma.In addition, there are a small amount of lymph andcerebrospinal fluid。[2]
Physiological definition
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Most cells in the human body do not contact with the outside world, but bathe in the bodyExtracellular fluidTherefore, extracellular fluid is the environment where cells directly contact and live.Physiology will focus onmulticellular organisms The internal environment of the body is the extracellular fluid around the internal cells.
PlasmaTissue fluidAnd lymph are both extracellular fluids, which together constitute the direct environment for cell life in the body.blood corpuscleThe living liquid environment is plasma,Capillary wallOfepithelial cellsThe internal environment of refers toplasmaandTissue fluid。Because extracellular fluid resides deep inside the body, it is calledinternal environment, used to distinguish it from the survival of the bodyExternal environment。[2]
Plasma is the most active part of the internal environment and the constituent of blood.staycirculatory organsUnder the action ofcardiovascular systemZhongchuan flows continuously and communicates with other extracellular fluids (tissue fluid and lymph), thus forming the body fluid connection of the whole body.
The plasma in the artery flows along the arteryblood capillaryandArterial end, many of which will pass throughCapillary wallget intoTissue fluid。Tissue fluid exists inHistiocyteInterstitial fluid is also called interstitial fluid.The cells of most tissues are bathed in the tissue fluid, and are carried out with the tissue fluidSubstance exchangeTherefore, tissue fluid is the environment in which most cells in the body live directly.
The tissue fluid contains cellsMetabolitesMost of the substances inside can be reabsorbed by the venous end of capillaries and enter the plasma;A small part isLymphatic capillariesAbsorptionLymph, also calledLymph。
The lymph in the lymphatic capillaries converges into the lymphatic vessels and passes throughLymphatic circulationFrom left to rightSubclavian veinImportplasmaMiddle, entering the heart and participating in the whole bodyblood circulation。A lot oflymphocyteandPhagocyteFor these cells, lymph is their direct living environment.
internal environment
cerebrospinal fluid: YesBrain cellInternal environment for direct survival——Tissue fluid；Cerebrospinal fluid also belongs to the internal environment.In fact, we can understand cerebrospinal fluid as tissue fluidHistiocyteIt's brain cells.
SoExtracellular fluidIn essenceSalt solution, similar to sea water.To some extent, this reflects that life originated from the ocean.
Tissue fluidThe composition and content of lymph are similar to that of plasma, but not completely the same. The main difference is that plasma contains more protein, while tissue fluid and lymphprotein content very seldom.The components of tissue fluid and lymph are most similar.
Physical and chemical properties of internal environment
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Due to the continuous development between cells and internal environment, and between internal environment and external environmentSubstance exchangeTherefore, the constant changes of cell metabolism and external environment will inevitably affect the internal environmentPhysical and chemical properties, such asPH、osmotic pressure, temperature, etc., but the internal environment can maintain relative stability through the regulation of the body.
Take pH value as an example:
The human body will produce manyAcids, such aslactic acid、carbonic acid；People's food (such as vegetables and fruits) often contains someAlkaline substance(e.gsodium carbonate)。These acidic and alkalinematerialEntering the blood will change the pH value of the blood.But in the blood, there are manyBuffering effectSubstance of——Buffer materialEach pair of buffer substances is composed ofweak acidAnd a corresponding strong alkali salt, such as H ₂CO≮ and NaHCO ∨, NaHtwoPOfourAnd NatwoHPOfourEtc.When the bodyStrenuous exerciseA large amount of lactic acid, carbonic acid and other substances are produced in the muscle and enter the blood.After lactic acid enters the blood, it reacts with NaHCO ≮ in the blood to generateSodium lactateAnd H ₂ CO ≮, which is a weak acid and unstable, easy to be decomposed into CO ₂ and H ₂ O, so it has little impact on the pH value of blood.The increased CO ₂ in blood will stimulate respiratory activityNervous center, enhance breathing movement, increaseVentilatory capacityTo expel CO ₂ from the body.When Na ₂ CO ∨ enters the blood, it reacts with H ₂ CO ∨ in the blood to generateBicarbonate, and excessive bicarbonate can be excreted by the kidney.In this way, due to the regulation of buffer substances in the blood, the pH value of the blood will not occurBig changesIt is generally stable between 7.35 and 7.45.Others of internal environmentPhysical and chemical properties, such as temperatureosmotic pressure, contents of various chemicals, etcnervous systemAnd body fluids, through various organsSystem coordinationActivities can also be maintained in a relatively stable state.
Physicochemical properties of plasma
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Blood bag
PH: 7.35~7.45
Temperature: about 37 ℃
osmotic pressure：When the temperature is about 37 ℃, the osmotic pressure is 770kPa (equivalent to 7pressureLeft and right, 5330mmHgMmHg, and equivalent tonormal saline）
Substance exchange
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Most cells in the human body are not associated with plasmadirect contact Therefore, these cells are associated withblood capillaryPlasma inNot directconductSubstance exchange。However, most cells of the human body are bathed inTissue fluidMedium,Intracellular fluidThere is only one layer between it and tissue fluidcell membraneTherefore, water and all substances that can pass through the cell membrane are exchanged between these two parts of body fluid;Oxygen required by cells, etcNutrientsEntering cells;Cellogeniccarbon dioxideAnd other wastes enter the tissue fluid.Because the tissue fluid is constantly formed, and the tissue fluid is constantly flowing back into the blood, it constantly provides the needed nutrients for cells and transports metabolic wastes.This is how the cells exchange substances with their internal environment.Blood circulates continuously in blood vessels, on the one hand, it exchanges tissue fluid with various parts of the human body;On the other handLung, kidney, stomach, intestine and other organsThey have close relations.This can make peoplesomatic cellContinuously communicate with the outside world through the internal environmentSubstance exchange。
So,The internal environment is the medium of material exchange between cells and the external environment.
From the transportation andExchange processAs can be seen,blood circulationNormal operation can avoid the depletion of substances in the internal environment due to the continuous use of cells, which helps to maintain the relatively constant composition of the internal environment,Steady state of internal environmentIt's the cells that work normallyLife activitiesRequired.Once the blood circulation is blocked, the normal life activities of cells will be affected, and life may be endangered in serious cases.
In vivo cells exchange substances with the external environment through the internal environment.The various nutrients in the food we eatdigestive systemOfDigestion and absorption, enterVillus of small intestineCapillaries inside, absorbed intocirculatory system。These nutrients are dissolved in plasma and transported to various parts of the body with blood circulationTissue and organIn, byHistiocyteUse.The external air passes throughrespiratory tractget intoAlveoli。The walls of the alveoli are very thin, and they are all composed of a flat layerepithelial cellsComposition.At this time, the oxygen in the alveoli can pass through the alveolar wall andCapillary wall, entering the blood, andhemoglobinCombined, and then transported to various tissues and organs of the body along with the blood circulation, which are used by tissue cells.In this way, oxygen and various nutrients in the external environment are absorbed by tissue cells.
HistocyteMetabolic processWaste generated in, such as excess water in human bodyinorganic saltas well asurea、uric acid, carbon dioxide, etcHuman cellsHarmful substances enter the tissue gap through the cell membraneTissue fluidAnd then diffuses into capillaries orLymphatic capillaries, enter the circulation system.When the blood flows through the capillaries outside the alveolar wall, the carbon dioxide in the blood passes throughCapillary wallAnd the alveolar wall enter the alveoli. At this time, the alveoli shrink and the carbon dioxide is expelled from the body through exhalation.When the blood flows through the kidney, the excess water, inorganic salts, urea, uric acid, etc. in the blood form urine, which is excreted through urination.Some metabolic wastes can also be excreted through skin sweat.
It can be seen from the above that various nutrients absorbed by the digestive system and oxygen exchanged by the respiratory system must pass throughcirculatory systemCan be transported to all cells in the body;andsomatic cellThe waste generated by metabolism should also be transported to the excretory system through the circulatory system and discharged from the body.thus it can be seen,circulatory system、digestive system、respiratory systemandexcretory systemThese four systems are directly related to the metabolism of human cells.Through the close cooperation of these four systems, every tissue cell of the human body can interact with the external environmentSubstance exchangeHas.The close cooperation of these four systems isendocrine systemAnd the regulation of the nervous system.
When we do a lot of exercise, a lot oflactic acidEntering the plasma will cause a decrease in pH (i.e., an increase in acidity).The reason why our plasmaPHIt can still be maintained at 7.35~7.45, mainly becauseBicarbonateIons.It is formed after reacting with lactic acidSodium lactateandcarbonic acid。Carbonic acid decomposes to produce carbon dioxide.carbon dioxideConcentration increase, stimulates breathingNervous center, so that carbon dioxide can be discharged.
