WordNet

hand over one and receive another, approximately equivalent; "exchange prisoners"; "exchange employees between branches of the company"
chemical process in which one atom or ion or group changes places with another
reciprocal transfer of equivalent sums of money (especially the currencies of different countries); "he earns his living from the interchange of currency" (同)interchange
the act of changing one thing for another thing; "Adam was promised immortality in exchange for his disobedience"; "there was an interchange of prisoners" (同)interchange
(chess) gaining (or losing) a rook in return for a knight or bishop; "black lost the exchange"
(chess) the capture by both players (usually on consecutive moves) of pieces of equal value; "the endgame began after the exchange of queens"
a workplace for buying and selling; open only to members
the act of giving something in return for something received; "deductible losses on sales or exchanges of property are allowable"
a mutual expression of views (especially an unpleasant one); "they had a bitter exchange"
give to, and receive from, one another; "Would you change places with me?"; "We have been exchanging letters for a year" (同)change, interchange
attack with gas; subject to gas fumes; "The despot gassed the rebellious tribes"
the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container (同)gaseous state
a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely
a unit of force equal to the force exerted by gravity; used to indicate the force to which a body is subjected when it is accelerated (同)gee, g-force
changed for (replaced by) something different

PrepTutorEJDIC

…‘を'『取り替える』;(…と)…‘を'取り替える《+『名』+『for』+『名』》 / …‘を'『取り交わす』;(人と)…‘を'取り交わす《+『名』+『with』+『名』〈人〉》 / (化幣が)両替される / 〈U〉〈C〉(物の物との)『取り替え』《+『of』+『名』+『for』+『名』》;(相手と物を)『交換すること』《+『of』+『名』(複数)+『with』+『名』〈人〉》 / 〈C〉交換物,取り替え品 / 〈C〉取引所;(電話の)交換局 / 〈U〉両替;為替(かわせ),為替相場 / 〈C〉=employment exchange
〈U〉〈C〉『気体』,『ガス』 / 〈U〉(灯用・燃料用)ガス / 〈U〉《米話》=gasoline / 〈U〉(麻酔用の)亜酸化窒素,笑気(laughing gas);毒ガス(mustard gas, tear gasなど) / 〈U〉《話》むだ話,ばか話 / 〈C〉《単数形で》とても楽しいこと / 〈敵など〉‘を'毒ガスで攻撃する / 《米話》〈車〉‘に'ガソリンを入れる《+『up』+『名,』+『名』+『up』》 / 長々とむだ話をする

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/26 23:30:47」(JST)

wiki en

Gas exchange is a biological process through which different gases are transferred in opposite directions across a specialized respiratory surface. Gases are constantly required by, and produced as a by-product of, cellular and metabolic reactions, so an efficient system for their exchange is extremely important. It is linked with respiration in animals, and both respiration and photosynthesis in plants.^[1]

In respiration, oxygen (O
2) is required to enter cells, while waste carbon dioxide (CO
2) must be removed; the opposite is true for photosynthesis, in which CO
2 enters plants and O
2 is released.^[1] The exchange of gases essentially occurs as a result of diffusion down a concentration gradient: gas molecules moving from an area of high concentration to low concentration.

Diffusion

Diffusion follows Fick’s Law. It is a passive process (no energy is required) affected by factors such as the surface area available, the distance the gas molecules must diffuse across and the concentration gradient.

Gases must first dissolve in a liquid in order to diffuse across a membrane, so all gas exchange systems require a moist environment.^[2]

In single-celled organisms, diffusion can occur straight across the cell membrane; as organisms increase in size, so does the distance gases must travel across. (Their surface area-to-volume ratio also decreases.) Diffusion alone is not efficient enough and specialized respiratory systems are required. This is the case with humans and with fish that have evolved circulatory systems: these are able to transport the gases to and from the respiratory surface and maintain a continuous concentration gradient.^[3]

In humans

Gas exchange in humans. Oxygen and carbon dioxide diffuse between a capillary and an alveolus.

Both oxygen and carbon dioxide are transported around the body in the blood through arteries, veins and capillaries. They bind to hemoglobin in red blood cells, although oxygen does so more effectively. Carbon dioxide also dissolves in the plasma or combines with water to form bicarbonate ions (HCO−
3). This reaction is catalyzed by the carbonic anhydrase enzyme in red blood cells.^[4]

The main respiratory surface in humans is the alveoli,^[5] which are small air sacs branching off from the bronchioles in the lungs. They are one cell thick and provide a moist and extremely large surface area for gas exchange to occur. Capillaries carrying deoxygenated blood from the pulmonary artery run across the alveoli. They are also extremely thin, so the total distance gases must diffuse across is only around 2 cells thick. An adult male has about 300 million alveoli, each ranging in diameter from 75 to 300 µm.

Inhaled oxygen is able to diffuse into the capillaries from the alveoli, while CO
2 from the blood diffuses in the opposite direction into the alveoli. The waste CO
2 can then be exhaled out of the body. Continuous blood flow in the capillaries and constant breathing maintain a steep concentration gradient.

Varying response

During physical exercise, excess carbon dioxide is produced as a result of increased respiration, and muscles and cells require increased oxygen. The body responds to this change by increasing the breathing rate, maximizing the rate of possible gas exchange.^[6]

In plants

High precision gas exchange measurements reveal important information on plant physiology

Gas exchange in plants is dominated by the roles of carbon dioxide and water vapor. CO
2 is the only carbon source for autotrophic organisms, making it essential for the conversion of light into sugar during photosynthesis. Due to the high differences in water potential in the plant versus the surrounding air, water vapor tends to evaporate from plants. Gas exchange is mediated through pores (known as stomata and located mainly on the lower side of leaves) that underlie a complex regulatory system. As the condition of the stomata unavoidably influences both the CO
2 and water vapor exchanges, plants experience a gas exchange dilemma: gaining enough CO
2 without losing too much water.^[7]

Gas exchange measurements are common tools in plant science. If the environmental conditions (humidity, CO
2 concentration, light and temperature) is fully controlled, the measurements of CO
2 uptake and water release reveal important information about the CO
2 assimilation and transpiration rates and the intercellular CO
2 concentration, which reveal important information about the photosynthetic condition of the plants.^[8]^[9]

Oxygen, essential for respiration during the night, plays a minor role in plants' gas exchange as it is always present in sufficient amounts.

In fish

Fish must extract oxygen dissolved in water, not air, which has led to the evolution of gills and opercula. Gills are specialized organs containing filaments and lamellae: the lamellae contain capillaries and provide a large surface area and short diffusion distance, as they are extremely thin.^[10]

Water is drawn in through the mouth and passes over the gills in one direction while blood flows through the lamellae in the opposite direction. This countercurrent maintains a steep concentration gradient. Oxygen is able to continually diffuse down its gradient into the blood, and the CO
2 into the water.^[11]

Summary of main systems

	Large surface area	Short diffusion distance	Maintained concentration gradient
Human	Total alveoli = 70–100 m²^[12]	Alveolus and capillary (two cells)	Constant blood flow in capillaries; breathing
Fish	Many lamellae and filaments per gill	Usually one cell	Countercurrent flow
Plant	High density of stomata; air spaces within leaf	One cell	Constant air flow

Other examples

Insects such as crickets do not have an inner skeleton, so they exchange gases across structures known as trachea and tracheoles: tubes that run directly into the insect's body. Air enters the trachea through spiracles and diffuses into the respiring tissues.^[13]

Amphibians are able to use their skin as a respiratory surface. They also have lungs and sometimes gills can be used.

References

^ ^a ^b "Gas exchange". Retrieved 19 March 2013.
^ Piiper J, Dejours P, Haab P & Rahn H (1971). "Oncepts and basic quantities in gas exchange physiology". Respiration Physiology 13: 292–304. doi:10.1016/0034-5687(71)90034-x.
^ Kety SS (1951). "The theory and applications of the exchange of inert gas at the lungs and tissues". Pharmacological Reviews 3: 1–41.
^ Raymond H & Swenson E (2000). "The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs". Respiration physiology 121: 1–12. doi:10.1016/s0034-5687(00)00110-9.
^ "Gas Exchange in humans". Retrieved 19 March 2013.
^ Wasserman K, Whipp B, Koyal S & Beaver W (1973). "Anaerobic threshold and respiratory gas exchange during exercise". Journal of Applied Physiology 35.
^ K. Raschke (1976). "How Stomata Resolve the Dilemma of Opposing Priorities". Phil. Trans. R. Soc. Lond. B. 273: 551–560.
^ S Von Caemmerer, GD Farquhar (1981). "Some relationships between the biochemistry of photosynthesis and gas exchange of leaves". Planta 153: 376–387.
^ Portable Gas Exchange Fluorescence System GFS-3000. Handbook of Operation (PDF), March 20, 2013
^ Newstead James D (1967). "Fine structure of the respiratory lamellae of teleostean gills". Cell and Tissue Research 79: 396–428. doi:10.1007/bf00335484.
^ Hughes GM (1972). "Morphometrics of fish gills". Respiration physiology 14: 1–25. doi:10.1016/0034-5687(72)90014-x.
^ Basset J, Crone C, Saumon G (1987). "Significance of active ion transport in transalveolar water absorption: a study on isolated rat lung". The Journal of physiology 384: 311–324.
^ "Gas Exchange in Insects". Retrieved 19 March 2013.

External links

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