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Gas exchange
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Gas exchange is the biological process by which gases move passively by diffusion across a surface. Typically, this surface is - or contains - a biological membrane that forms the boundary between an organism and its extracellular environment.
Gases are constantly consumed and produced by cellular and metabolic reactions in most living things, so an efficient system for gas exchange between, ultimately, the interior of the cell(s) and the external environment is required. Small, particularly unicellular organisms, such as bacteria and protozoa, have a high surface-area to volume ratio. In these creatures the gas exchange membrane is typically the cell membrane. Some small multicellular organisms, such as flatworms, are also able to perform sufficient gas exchange across the skin or cuticle that surrounds their bodies. However, in most larger organisms, which have a small surface-area to volume ratios, specialised structures with convoluted surfaces such as gills, pulmonary alveoli and spongy mesophyll provide the large area needed for effective gas exchange. These convoluted surfaces may sometimes be internalised into the body of the organism. This is the case with the alveoli, which form the inner surface of the mammalian lung, the spongy mesophyll, which is found inside the leaves of some kinds of plant, or the gills of those molluscs that have them, which are found in the mantle cavity.
In aerobic organisms, gas exchange is particularly important for respiration, which involves the uptake of oxygen (O
2) and release of carbon dioxide (CO
2). Conversely, in oxygenic photosynthetic organisms such as most land plants, uptake of carbon dioxide and release of both oxygen and water vapour are the main gas-exchange processes occurring during the day. Other gas-exchange processes are important in less familiar organisms: e.g. carbon dioxide, methane and hydrogen are exchanged across the cell membrane of methanogenic archaea. In nitrogen fixation by diazotrophic bacteria, and denitrification by heterotrophic bacteria (such as Paracoccus denitrificans and various pseudomonads),[1] nitrogen gas is exchanged with the environment, being taken up by the former and released into it by the latter, while giant tube worms rely on bacteria to oxidize hydrogen sulfide extracted from their deep sea environment,[2] using dissolved oxygen in the water as an electron acceptor.
Contents
[hide]
1 Physical principles of gas-exchange
1.1 Diffusion and surface area
1.2 Interaction with circulatory systems
2 Mammals
2.1 Exchange membrane
2.2 Alveolar air
2.3 Pulmonary circulation
3 Other vertebrates
3.1 Fish
3.2 Amphibians
3.3 Reptiles
3.4 Birds
4 Plants
5 Invertebrates
6 Summary of main gas exchange systems
7 See also
8 References
Physical principles of gas-exchange[edit]
Diffusion and surface area[edit]
The exchange of gases occurs as a result of diffusion down a concentration gradient. Gas molecules move from a region in which they are at high concentration to one in which they are at low concentration. Diffusion is a passive process, meaning that no energy is required to power the transport, and it follows Fick’s Law:[citation needed]
J = − D d φ d x {\displaystyle J=-D{\frac {d\varphi }{dx}}}
In relation to a typical biological system, where two compartments ('inside' and 'outside'), are separated by a membrane barrier, and where a gas is allowed to spontaneously diffuse down its concentration gradient:[citation needed]
J is the flux, the amount of gas diffusing per unit area of membrane per unit time. Note that this is already scaled for the area of the membrane.
D is the diffusion coefficient, which will differ from gas to gas, and from membrane to membrane, according to the size of the gas molecule in question, and the nature of the membrane itself (particularly its viscosity, temperature and hydrophobicity).
φ is the concentration of the gas.
x is the position across the thickness of the membrane.
dφ/dx is therefore the concentration gradient across the membrane. If the two compartments are individually well-mixed, then this is simplifies to the difference in concentration of the gas between the inside and outside compartments divided by the thickness of the membrane.
The negative sign indicates that the diffusion is always in the direction that - over time - will destroy the concentration gradient, i.e. the gas moves from high concentration to low concentration until eventually the inside and outside compartments reach equilibrium.
Fig. 1. Fick's Law for gas-exchange surface
Gases must first dissolve in a liquid in order to diffuse across a membrane, so all biological gas exchange systems require a moist environment.[3] In general, the higher the concentration gradient across the gas-exchanging surface, the faster the rate of diffusion across it. Conversely, the thinner the gas-exchanging surface (for the same concentration difference), the faster the gases will diffuse across it.[4]
In the equation above, J is the flux expressed per unit area, so increasing the area will make no difference to its value. However, an increase in the available surface area, will increase the amount of gas that can diffuse in a given time.[4] This is because the amount of gas diffusing per unit time (dq/dt) is the product of J and the area of the gas-exchanging surface, A:
d q d t = J A {\displaystyle {\frac {dq}{dt}}=JA}
Single-celled organisms such as bacteria and amoebae do not have specialised gas exchange surfaces, because they can take advantage of the high surface area they have relative to their volume. The amount of gas an organism produces (or requires) in a given time will be in rough proportion to the volume of its cytoplasm. The volume of a unicellular organism is very small, therefore it produces (and requires) a relatively small amount of gas in a given time. In comparison to this small volume, the surface area of its cell membrane is very large, and adequate for its gas-exchange needs without further modification. However, as an organism increases in size, its surface area and volume do not scale in the same way. Consider an imaginary organism that is a cube of side-length, L. Its volume increases with the cube (L3) of its length, but its external surface area increases only with the square (L2) of its length. This means the external surface rapidly becomes inadequate for the rapidly increasing gas-exchange needs of a larger volume of cytoplasm. Additionally, the thickness of the surface that gases must cross (dx in Fick's Law) can also be larger in larger organisms: in the case of a single-celled organism, a typical cell membrane is only 10 nm thick;[5] but in larger organisms such as roundworms (Nematoda) the equivalent exchange surface - the cuticle - is substantially thicker at 0.5 µm.[6]
Interaction with circulatory systems[edit]
Fig. 2. A comparison between the operations and effects of a cocurrent and a countercurrent flow exchange system is depicted by the upper and lower diagrams respectively. In both it is assumed (and indicated) that red has a higher value (e.g. of temperature or the partial pressure of a gas) than blue and that the property being transported in the channels therefore flows from red to blue. Note that channels are contiguous if effective exchange is to occur (i.e. there can be no gap between the channels).
In multicellular organisms therefore, specialised respiratory organs such as gills or lungs are often used to provide the additional surface area for the required rate of gas exchange with the external environment. However the distances between the gas exchanger and the deeper tissues are often too great for diffusion to meet gaseous requirements of these tissues. The gas exchangers are therefore frequently coupled to gas-distributing circulatory systems, which transport the gases evenly to all the body tissues regardless of their distance from the gas exchanger.[7]
Some multicellular organisms such as flatworms (Platyhelminthes) are relatively large but very thin, allowing their outer body surface to act as a gas exchange surface without the need for a specialised gas exchange organ. Flatworms therefore lack gills or lungs, and also lack a circulatory system. Other multicellular organisms such as sponges (Porifera) have an inherently high surface area, because they are very porous and/or branched. Sponges do not require a circulatory system or specialised gas exchange organs, because their feeding strategy involves one-way pumping of water through their porous bodies using flagellated collar cells. Each cell of the sponge's body is therefore exposed to a constant flow of fresh oxygenated water. They can therefore rely on diffusion across their cell membranes to carry out the gas exchange needed for respiration.[8]
In organisms that have circulatory systems associated with their specialized gas-exchange surfaces, a great variety of systems are used for the interaction between the two.
In a countercurrent flow system, air (or, more usually, the water containing dissolved air) is drawn in the opposite direction to the flow of blood in the gas exchanger. A countercurrent system such as this maintains a steep concentration gradient along the length of the gas-exchange surface (see lower diagram in Fig. 2). This is the situation seen in the gills of fish and many other aquatic creatures.[9] The gas-containing environmental water is drawn unidirectionally across the gas-exchange surface, with the blood-flow in the gill capillaries beneath flowing in the opposite direction.[9][10][11] Although this theoretically allows almost complete transfer of a respiratory gas from one side of the exchanger to the other, in fish less than 80% of the oxygen in the water flowing over the gills is generally transferred to the blood.[9]
Alternative arrangements are cross current systems found in birds.[12][13] and dead-end air-filled sac systems found in the lungs of mammals.[14][15] In a cocurrent flow system, the blood and gas (or the fluid containing the gas) move in the same direction through the gas exchanger. This means the magnitude of the gradient is variable along the length of the gas-exchange surface, and the exchange will eventually stop when an equilibrium has been reached (see upper diagram in Fig. 2).[9] Cocurrent flow gas exchange systems are not known to be used in nature.
Mammals[edit]
Fig. 3. An alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. They occur in the mammalian lung. They are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood.
The gas exchanger in mammals is internalized to form lungs, as it is in most of the larger land animals.[citation needed] Gas exchange occurs in microscopic dead-end air-filled sacs called alveoli, where a very thin membrane (called the blood-air barrier) separates the blood in the alveolar capillaries (in the walls of the alveoli) from the alveolar air in the sacs.
Exchange membrane[edit]
Fig. 4. A histological cross-section through an alveolar wall showing the layers through which the gases have to move between the blood plasma and the alveolar air. The dark blue objects are the nuclei of the capillary endothelial and alveolar type I epithelial cells (or type 1 pneumocytes). The two red objects labeled "RBC" are red blood cells in the alveolar capillary blood.
The membrane across which gas exchange takes place in the alveoli (i.e. the blood-air barrier) is extremely thin (in humans, on average, 2.2 μm thick).[14] It consists of the alveolar epithelial cells, their basement membranes and the endothelial cells of the pulmonary capillaries (Fig. 4).[14][16] The large surface area of the membrane comes from the folding of the membrane into about 300 million alveoli, with diameters of approximately 75-300 µm each. This provides an extremely large surface area (approximately 145 m2) across which gas exchange can occur.[14]
Alveolar air[edit]
Fig. 5. The changes in the composition of the alveolar air during a normal breathing cycle at rest. The scale on the left, and the blue line, indicate the partial pressures of carbon dioxide in kPa, while that on the right and the red line, indicate the partial pressures of oxygen, also in kPa (to convert kPa into mm Hg, multiply by 7.5).
Fig. 6. A diagrammatic histological cross-section through a portion of lung tissue showing a normally inflated alveolus (at the end of a normal exhalation), and its walls containing the alveolar capillaries (shown in cross-section). This illustrates how the alveolar capillary blood is completely surrounded by alveolar air. In a normal human lung all the alveoli together contain about 3 liters of alveolar air. All the alveolar capillaries contain about 100 ml blood.
Air is brought to the alveoli in small doses (called the tidal volume), by breathing in (inhalation) and out (exhalation) through the respiratory airways, a set of relatively narrow and moderately long tubes which start at the nose or mouth and end in the alveoli of the lungs in the chest. Air moves in and out through the same set of tubes, in which the flow is in one direction during inhalation, and in the opposite direction during exhalation.
During each inhalation, at rest, approximately 500 ml of fresh air flows in through the nose. Its is warmed and moistened as it flows through the nose and pharynx. By the time it reaches the trachea the inhaled air's temperature is 37 °C and it is saturated with water vapor. On arrival in the alveoli it is diluted and thoroughly mixed with the approximately 2.5–3.0 liters of air that remained in the alveoli after the last exhalation. This relatively large volume of air that is semi-permanently present in the alveoli throughout the breathing cycle is known as the functional residual capacity (FRC).[15]
At the beginning of inhalation the airways are filled with unchanged alveolar air, left over from the last exhalation. This is the dead space volume, which is usually about 150 ml.[17] It is the first air to re-enter the alveoli during inhalation. Only after the dead space air has returned to the alveoli does the remainder of the tidal volume (500 ml - 150 ml = 350 ml) enter the alveoli.[15] The entry of such a small volume of fresh air with each inhalation, ensures that the composition of the FRC hardly changes during the breathing cycle (Fig. 5).[15] The alveolar partial pressure of oxygen remains very close to 13–14 kPa (100 mmHg), and the partial pressure of carbon dioxide varies minimally around 5.3 kPa (40 mmHg) throughout the breathing cycle (of inhalation and exhalation).[15] The corresponding partial pressures of oxygen and carbon dioxide in the ambient (dry) air at sea level are 21 kPa (160 mmHg) and 0.04 kPa (0.3 mmHg) respectively.[15]
Fig. 7. A highly diagrammatic illustration of the process of gas exchange in the mammalian lungs, emphasizing the differences between the gas compositions of the ambient air, the alveolar air (light blue) with which the alveolar capillary blood equilibrates, and the blood gas tensions in the pulmonary arterial (blue blood entering the lung on the left) and venous blood (red blood leaving the lung on the right). All the gas tensions are in kPa. To convert to mm Hg, multiply by 7.5.
This alveolar air, which constitutes the FRC, completely surrounds the blood in the alveolar capillaries (Fig. 6). Gas exchange in mammals occurs between this alveolar air (which differs significantly from fresh air) and the blood in the alveolar capillaries. The gases on either side of the gas exchange membrane equilibrate by simple diffusion. This ensures that the partial pressures of oxygen and carbon dioxide in the blood leaving the alveolar capillaries, and ultimately circulates throughout the body, are the same as those in the FRC.[15]
The marked difference between the composition of the alveolar air and that of the ambient air can be maintained because the functional residual capacity is contained in dead-end sacs connected to the outside air by long, narrow, tubes (the airways: nose, pharynx, larynx, trachea, bronchi and their branches and sub-branches down to the bronchioles). This anatomy, and the fact that the lungs are not emptied and re-inflated with each breath, provides mammals with a "portable atmosphere", whose composition differs significantly from the present-day ambient air.[18]
The composition of the air in the FRC is carefully monitored, by measuring the partial pressures of oxygen and carbon dioxide in the arterial blood. If either gas pressure deviates from normal, reflexes are elicited that change the rate and depth of breathing in such a way that normality is restored within seconds or minutes.[15]
Pulmonary circulation[edit]
Main article: Pulmonary circulation
All the blood returning from the body tissues to the right side of the heart flows through the alveolar capillaries before being pumped around the body again. On its passage through the lungs the blood comes into close contact with the alveolar air, separated from it by a very thin diffusion membrane which is only, on average, about 2 μm thick.[14] The gas pressures in the blood will therefore rapidly equilibrate with those in the alveoli, ensuring that the arterial blood that circulates to all the tissues throughout the body has an oxygen tension of 13−14 kPa (100 mmHg), and a carbon dioxide tension of 5.3 kPa (40 mmHg). These arterial partial pressures of oxygen and carbon dioxide are homeostatically controlled. A rise in the arterial P C O 2 {\displaystyle P_{{\mathrm {CO} }_{2}}} , and, to a lesser extent, a fall in the arterial P O 2 {\displaystyle P_{{\mathrm {O} }_{2}}} , will reflexly cause deeper and faster breathing till the blood gas tensions return to normal. The converse happens when the carbon dioxide tension falls, or, again to a lesser extent, the oxygen tension rises: the rate and depth of breathing are reduced till blood gas normality is restored.
Since the blood arriving in the alveolar capillaries has a P O 2 {\displaystyle P_{{\mathrm {O} }_{2}}} of, on average, 6 kPa (45 mmHg), while the pressure in the alveolar air is 13 kPa (100 mmHg), there will be a net diffusion of oxygen into the capillary blood, changing the composition of the 3 liters of alveolar air slightly. Similarly, since the blood arriving in the alveolar capillaries has a P C O 2 {\displaystyle P_{{\mathrm {CO} }_{2}}} of also about 6 kPa (45 mmHg), whereas that of the alveolar air is 5.3 kPa (40 mmHg), there is a net movement of carbon dioxide out of the capillaries into the alveoli. The changes brought about by these net flows of individual gases into and out of the functional residual capacity necessitate the replacement of about 15% of the alveolar air with ambient air every 5 seconds or so. This is very tightly controlled by the continuous monitoring of the arterial blood gas tensions (which accurately reflect partial pressures of the respiratory gases in the alveolar air) by the aortic bodies, the carotid bodies, and the blood gas and pH sensor on the anterior surface of the medulla oblongata in the brain. There are also oxygen and carbon dioxide sensors in the lungs, but they primarily determine the diameters of the bronchioles and pulmonary capillaries, and are therefore responsible for directing the flow of air and blood to different parts of the lungs.
It is only as a result of accurately maintaining the composition of the 3 liters alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation, respiration will be slowed down or halted until the alveolar P C O 2 {\displaystyle P_{{\mathrm {CO} }_{2}}} has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide “waste”. In fact the total concentration of carbon dioxide in arterial blood is about 26 mM (or 58 ml/100 ml),[19] compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood).[15] This large concentration of carbon dioxide plays a pivotal role in the determination and maintenance of the pH of the extracellular fluids. The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body’s extracellular fluid carbon dioxide and pH homeostats
If these homeostats are compromised, then a respiratory acidosis, or a respiratory alkalosis will occur. In the long run these can be compensated by renal adjustments to the H+ and HCO3− concentrations in the plasma; but since this takes time, the hyperventilation syndrome can, for instance, occur when agitation or anxiety cause a person to breathe fast and deeply[20] thus blowing off too much CO2 from the blood into the outside air, precipitating a set of distressing symptoms which result from an excessively high pH of the extracellular fluids.[21]
Oxygen has a very low solubility in water, and is therefore carried in the blood loosely combined with hemoglobin. The oxygen is held on the hemoglobin by four ferrous iron-containing heme groups per hemoglobin molecule. When all the heme groups carry one O2 molecule each the blood is said to be “saturated” with oxygen, and no further increase in the partial pressure of oxygen will meaningfully increase the oxygen concentration of the blood. Most of the carbon dioxide in the blood is carried as HCO3− ions in the plasma. However the conversion of dissolved CO2 into HCO3− (through the addition of water) is too slow for the rate at which the blood circulates through the tissues on the one hand, and alveolar capillaries on the other. The reaction is therefore catalyzed by carbonic anhydrase, an enzyme inside the red blood cells.[22] The reaction can go in either direction depending on the prevailing partial pressure of carbon dioxide. A small amount of carbon dioxide is carried on the protein portion of the hemoglobin molecules as carbamino groups. The total concentration of carbon dioxide (in the form of bicarbonate ions, dissolved CO2, and carbamino groups) in arterial blood (i.e. after it has equilibrated with the alveolar air) is about 26 mM (or 58 ml/100 ml),[19] compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood).[15]
Other vertebrates[edit]
Fish[edit]
Fig. 8. Gills of tuna showing filaments and lamellae
The dissolved oxygen content in fresh water is approximately 8–10 ml/liter compared to that of air which is 210 ml/liter.[23] Water is 800 times more dense than air[24] and 100 times more viscous.[23] Therefore, oxygen has a diffusion rate in air 10,000 times greater than in water.[23] The use of sac-like lungs to remove oxygen from water would therefore not be efficient enough to sustain life.[23] Rather than using lungs, gaseous exchange takes place across the surface of highly vascularized gills. Gills are specialised organs containing filaments, which further divide into lamellae. The lamellae contain capillaries that provide a large surface area and short diffusion distances, as their walls are extremely thin.[25] Gill rakers are found within the exchange system in order to filter out food, and keep the gills clean.
Gills use a countercurrent flow system that increases the efficiency of oxygen-uptake (and waste gas loss).[9][10][11] Oxygenated 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 steep concentration gradients along the entire length of each capillary (see the diagram in the "Interaction with circulatory systems" section above). Oxygen is able to continually diffuse down its gradient into the blood, and the carbon dioxide down its gradient into the water.[10] The deoxygenated water will eventually pass out through the operculum (gill cover). Although countercurrent exchange systems theoretically allow an almost complete transfer of a respiratory gas from one side of the exchanger to the other, in fish less than 80% of the oxygen in the water flowing over the gills is generally transferred to the blood.[9]
Amphibians[edit]
Amphibians have three main organs involved in gas exchange: the lungs, the skin, and the gills, which can be used singly or in a variety of different combinations. The relative importance of these structures differs according to the age, the environment and species of the amphibian. The skin of amphibians and their larvae is highly vascularised, leading to relatively efficient gas exchange when the skin is moist. The larvae of amphibians, such as the pre-metamorphosis tadpole stage of frogs, also have external gills. The gills are absorbed into the body during metamorphosis, after which the lungs will then take over. The lungs are usually simpler than in the other land vertebrates, with few internal septa and larger alveoli; however, toads, which spend more time on land, have a larger alveolar surface with more developed lungs. To increase the rate of gas exchange by diffusion, amphibians maintain the concentration gradient across the respiratory surface using a process called buccal pumping.[26] The lower floor of the mouth is moved in a "pumping" manner, which can be observed by the naked eye.
Reptiles[edit]
All reptiles breathe using lungs. In squamates (the lizards and snakes) ventilation is driven by the axial musculature, but this musculature is also used during movement, so some squamates rely on buccal pumping to maintain gas exchange efficiency.[27]
Due to the rigidity of turtle and tortoise shells, significant expansion and contraction of the chest is difficult. Turtles and tortoises depend on muscle layers attached to their shells, which wrap around their lungs to fill and empty them.[28] Some aquatic turtles can also pump water into a highly vascularised mouth or cloaca to achieve gas-exchange.[29][30]
Crocodiles have a structure similar to the mammalian diaphragm - the diaphragmaticus - but this muscle helps create a unidirectional flow of air through the lungs rather than a tidal flow: this is more similar to the air-flow seen in birds than that seen in mammals.[31] During inhalation, the diaphragmaticus pulls the liver back, inflating the lungs into the space this creates.[32][33] Air flows into the lungs from the bronchus during inhalation, but during exhalation, air flows out of the lungs into the bronchus by a different route: this one-way movement of gas is achieved by aerodynamic valves in the airways.[34][35]
Birds[edit]
Main article: Bird anatomy § Respiratory system
Fig. 10. Inhalation-exhalation cycle in birds.
Fig. 9. A diagrammatic representation of the cross-current respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from right to left in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram).[12] Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.
Birds have lungs but no diaphragm. They rely mostly on air sacs for ventilation. These air sacs do not play a direct role in gas exchange, but help to move air unidirectionally across the gas exchange surfaces in the lungs. During inhalation, fresh air is taken from the trachea down into the posterior air sacs and into the parabronchi which lead from the posterior air sacs into the lung. The air that enters the lungs joins the air which is already in the lungs, and is drawn forward across the gas exchanger into anterior air sacs. During exhalation, the posterior air sacs force air into the same parabronchi of the lungs, flowing in the same direction as during inhalation, allowing continuous gas exchange irrespective of the breathing cycle. Air exiting the lungs during exhalation joins the air being expelled from the anterior air sacs (both consisting of "spent air" that has passed through the gas exchanger) entering the trachea to be exhaled (Fig. 10).[13] Selective bronchoconstriction at the various bronchial branch points ensures that the air does not ebb and flow through the bronchi during inhalation and exhalation, as it does in mammals, but follows the paths described above.
The unidirectional airflow through the parabronchi exchanges respiratory gases with a crosscurrent blood flow (Fig. 9).[12][13] The partial pressure of O2 ( P O 2 {\displaystyle P_{{\mathrm {O} }_{2}}} ) in the parabronchioles declines along their length as O2 diffuses into the blood. The capillaries leaving the exchanger near the entrance of airflow take up more O2 than capillaries leaving near the exit end of the parabronchi. When the contents of all capillaries mix, the final P O 2 {\displaystyle P_{{\mathrm {O} }_{2}}} of the mixed pulmonary venous blood is higher than that of the exhaled air, but lower than that of the inhaled air.[12][13]
Plants[edit]
Gas exchange in plants is dominated by the roles of carbon dioxide, oxygen and water vapor. CO
2 is the only carbon source for autotrophic growth by photosynthesis, and when a plant is actively photosynthesising in the light, it will be taking up carbon dioxide, and losing water vapor and oxygen. At night, plants respire, and gas exchange partly reverses: water vapor is still lost (but to a smaller extent), but oxygen is now taken up and carbon dioxide released.[36]
Fig. 11. A stylised cross-section of a euphyllophyte plant leaf, showing the key plant organs involved in gas exchange
Plant gas exchange occurs mostly through the leaves. Gases diffuse into and out of the intercellular spaces within the leaf through pores called stomata, which are typically found on the lower surface of the leaf. Gases enter into the photosynthetic tissue of the leaf through dissolution onto the moist surface of the palisade and spongy mesophyll cells. The spongy mesophyll cells are loosely packed, allowing for an increased surface area, and subsequently an increased rate of gas-exchange. Uptake of carbon dioxide necessarily results in some loss of water vapor,[37] because both molecules enter and leave by the same stomata, so plants experience a gas exchange dilemma: gaining enough CO
2 without losing too much water. Therefore, water loss from other parts of the leaf is minimised by the waxy cuticle on the leaf's epidermis. The size of a stoma is regulated by the opening and closing of its two guard cells: the turgidity of these cells determines the state of the stomatal opening, and this itself is regulated by water stress. Plants showing crassulacean acid metabolism are drought-tolerant xerophytes and perform almost all their gas-exchange at night, because it is only during the night that these plants open their stomata. By opening the stomata only at night, the water vapor loss associated with carbon dioxide uptake is minimised. However, this comes at the cost of slow growth: the plant has to store the carbon dioxide in the form of malic acid for use during the day, and it cannot store unlimited amounts.[38]
Fig. 12. High precision gas exchange measurements reveal important information on plant physiology
Gas exchange measurements are important tools in plant science: this typically involves sealing the plant (or part of a plant) in a chamber and measuring changes in the concentration of carbon dioxide with an infrared gas analyzer. If the environmental conditions (humidity, CO
2 concentration, light and temperature) are fully controlled, the measurements of CO
2 uptake and water release reveal important information about the CO
2 assimilation and transpiration rates. The intercellular CO
2 concentration reveals important information about the photosynthetic condition of the plants.[39][40] Simpler methods can be used in specific circumstances: hydrogencarbonate indicator can be used to monitor the consumption of CO
2 in a solution containing a single plant leaf at different levels of light intensity,[41] and oxygen generation by the pondweed Elodea can be measured by simply collecting the gas in a submerged test-tube containing a small piece of the plant.
Invertebrates[edit]
The mechanism of gas exchange in invertebrates depends their size, feeding strategy, and habitat (aquatic or terrestrial).
Fig. 13. Diagram representing the body structure of Porifera. The diagram shows the mechanism of water uptake for sponges. Yellow: pinacocytes, red: choanocytes, grey: mesohyl, pale blue: water flow
The sponges (Porifera) are sessile creatures, meaning they are unable to move on their own and normally remain attached to their substrate. They obtain nutrients through the flow of water across their cells, and they exchange gases by simple diffusion across their cell membranes. Pores called ostia draw water into the sponge and the water is subsequently circulated through the sponge by cells called choanocytes which have hair-like structures that move the water through the sponge.[42]
Fig. 14. Cnidarians are always found in aquatic environments, meaning that their gas exchange involves absorbing oxygen from water.
The cnidarians include corals, sea anemones, jellyfish and hydras. These animals are always found in aquatic environments, ranging from fresh water to salt water. They do not have any dedicated respiratory organs; instead, every cell in their body can absorb oxygen from the surrounding water, and release waste gases to it. One key disadvantage of this feature is that cnidarians can die in environments where water is stagnant, as they deplete the water of its oxygen supply.[43] Corals often form symbiosis with other organisms, particularly photosynthetic dinoflagellates. In this symbiosis, the coral provides shelter and the other organism provides nutrients to the coral, including oxygen.
Fig. 15. Cross section of a nematode.
The roundworms (Nematoda), flatworms (Platyhelminthes), and many other small invertebrate animals living in aquatic or otherwise wet habitats do not have a dedicated gas-exchange surface or circulatory system. They instead rely on diffusion of CO
2 and O
2 directly across their cuticle.[44][45] The cuticle is the semi-permeable outermost layer of their bodies.
Other aquatic invertebrates such as most molluscs (Mollusca) and larger crustaceans (Crustacea) such as lobsters, have gills analogous to those of fish, which operate in a similar way.
Fig. 16. Photographic representation of spiracles.
Unlike the invertebrates groups mentioned so far, insects are usually terrestrial, and exchange gases across a moist surface in direct contact with the atmosphere, rather than in contact with surrounding water. The insect's exoskeleton is impermeable to gases, including water vapor, so they have a more specialised gas exchange system, requiring gases to be directly transported to the tissues via a complex network of tubes. This respiratory system is separated from their circulatory system. Gases enter and leave the body through openings called spiracles, located laterally along the thorax and abdomen. Similar to plants, insects are able to control the opening and closing of these spiracles, but instead of relying on turgor pressure, they rely on muscle contractions.[46] These contractions result in an insect's abdomen being pumped in and out. The spiracles are connected to tubes called tracheae, which branch repeatedly and ramify into the insect's body. These branches terminate in specialised tracheole cells which provides a thin, moist surface for efficient gas exchange, directly with cells.[47]
The other main group of terrestrial arthropod, the arachnids (spiders, scorpion, mites, and their relatives) typically perform gas exchange with a book lung.[48]
Summary of main gas exchange systems[edit]
Surface area
Diffusion distance
Maintaining concentration gradient
Respiratory organs
Human Total alveoli = 70–100 m2[49] Alveolus and capillary (two cells) Constant blood flow in capillaries; breathing Lungs
Fish Many lamellae and filaments per gill Usually one cell Countercurrent flow Gills
Insects Specialised tracheole cell One cell Buccal pumping Spiracles
Sponges Ostia pores One cell Water movement None
Flatworms Flat body shape Usually one cell Countercurrent flow None
Cnidarians Oral arms Usually one cell Water movement None
Reptiles Many lamellae and filaments per gill Alveolus and capillary (two cells) Countercurrent flow Lungs
Amphibians Many lamellae and filaments per gill Alveolus and capillary (two cells) or one cell Countercurrent flow Lungs, skin and gills
Plants High density of stomata; air spaces within leaf One cell Constant air flow Stomata
See also[edit]
Respiratory system
References[edit]
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Jump up ^ C.Michael Hogan. 2011. Sulfur. Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the environment, Washington DC Archived October 28, 2012, at the Wayback Machine.
Jump up ^ Piiper J, Dejours P, Haab P & Rahn H (1971). "Concepts and basic quantities in gas exchange physiology". Respiration Physiology. 13: 292–304. doi:10.1016/0034-5687(71)90034-x. CS1 maint: Uses authors parameter (link)
^ Jump up to: a b Kety SS (1951). "The theory and applications of the exchange of inert gas at the lungs and tissues". Pharmacological Reviews. 3: 1–41.
Jump up ^ Schneiter, R; Brügger, B; Sandhoff, R; Zellnig, G; Leber, A; Lampl, M; Athenstaedt, K; Hrastnik, C; Eder, S; Daum, G; Paltauf, F; Wieland, FT; Kohlwein, SD (1999). "Electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of the lipid molecular species composition of yeast subcellular membranes reveals acyl chain-based sorting/remodeling of distinct molecular species en route to the plasma membrane". The Journal of Cell Biology. 146 (4): 741–54. PMID 10459010.
Jump up ^ Cox, G. N. (1 July 1981). "Cuticle of Caenorhabditis elegans: its isolation and partial characterization". The Journal of Cell Biology. 90 (1): 7–17. doi:10.1083/jcb.90.1.7.
Jump up ^ Flegr, Jaroslav. "Frozen Evolution". Frozen Evolution. Retrieved 21 March 2017.
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^ Jump up to: a b c d e f Campbell, Neil A. (1990). Biology (Second ed.). Redwood City, California: Benjamin/Cummings Publishing Company, Inc. pp. 836–838. ISBN 0-8053-1800-3.
^ Jump up to: a b c Hughes GM (1972). "Morphometrics of fish gills". Respiration physiology. 14: 1–25. doi:10.1016/0034-5687(72)90014-x.
^ Jump up to: a b Storer, Tracy I.; Usinger, R. L.; Stebbins, Robert C.; Nybakken, James W. (1997). General Zoology (sixth ed.). New York: McGraw-Hill. pp. 668–670. ISBN 0-07-061780-5.
^ Jump up to: a b c d Scott, Graham R. (2011). "Commentary: Elevated performance: the unique physiology of birds that fly at high altitudes". Journal of Experimental Biology. 214: 2455–2462. doi:10.1242/jeb.052548.
^ Jump up to: a b c d Ritchson, G. "BIO 554/754 – Ornithology: Avian respiration". Department of Biological Sciences, Eastern Kentucky University. Retrieved 2009-04-23.
^ Jump up to: a b c d e Williams, Peter L; Warwick, Roger; Dyson, Mary; Bannister, Lawrence H. (1989). Gray’s Anatomy (Thirty-seventh ed.). Edinburgh: Churchill Livingstone. pp. 1278–1282. ISBN 0443 041776.
^ Jump up to: a b c d e f g h i j Tortora, Gerard J.; Anagnostakos, Nicholas P. (1987). Principles of anatomy and physiology (Fifth ed.). New York: Harper & Row, Publishers. pp. 570–580. ISBN 0-06-350729-3.
Jump up ^ "Gas Exchange in humans". Retrieved 19 March 2013.
Jump up ^ "Dead space volume - Oxford Reference". doi:10.1093/oi/authority.20110803095704195.
Jump up ^ Lovelock, James (1991). Healing Gaia: Practical medicine for the Planet. New York: Harmony Books. pp. 21–34, 73–88. ISBN 0-517-57848-4.
^ Jump up to: a b Diem, K.; Lentner, C. (1970). "Blood – Inorganic substances". in: Scientific Tables (Seventh ed.). Basle, Switzerland: CIBA-GEIGY Ltd. p. 571.
Jump up ^ Shu, BC; Chang, YY; Lee, FY; Tzeng, DS; Lin, HY; Lung, FW (2007-10-31). "Parental attachment, premorbid personality, and mental health in young males with hyperventilation syndrome". Psychiatry Research. 153 (2): 163–70. doi:10.1016/j.psychres.2006.05.006. PMID 17659783.
Jump up ^ "eMedicine - Hyperventilation Syndrome: Article by Edward Newton, MD". Retrieved 2007-12-20.
Jump up ^ 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. CS1 maint: Uses authors parameter (link)
^ Jump up to: a b c d M. b. v. Roberts; Michael Reiss; Grace Monger (2000). Advanced Biology. London, UK: Nelson. pp. 164–165.
Jump up ^ Tyson, P. D.; Preston-White, R.A. (2013). The Weather and Climate of Southern Africa (Second ed.). Cape Town, South Africa: Oxford University Press. p. 14. ISBN 9780195718065.
Jump up ^ Newstead James D (1967). "Fine structure of the respiratory lamellae of teleostean gills". Cell and Tissue Research. 79: 396–428. doi:10.1007/bf00335484.
Jump up ^ Brainerd, E. L. (1999). "New perspectives on the evolution of lung ventilation mechanisms in invertebrates". Experimental Biology Online. 4 (2): 1–28. doi:10.1007/s00898-999-0002-1.
Jump up ^ Taylor, E. W.; Campbell, H. A.; Leite, C; Abe, A. S.; Wang, T. "Respiration in reptiles". Comparative Biochemisitry and Physiology A - Molecular and Integrative Physiology. 148: S110=S111. doi:10.1016/j.cbpa.2007.06.431.
Jump up ^ Klein, Wilfied; Abe, Augusto; Andrade, Denis; Perry, Steven (2003). "Structure of the posthepatic septum and its influence on visceral topology in the tegu lizard, Tupinambis merianae (Teidae: Reptilia)". Journal of Morphology. 258 (2): 151–157. doi:10.1002/jmor.10136. PMID 14518009.
Jump up ^ Orenstein, Ronald (2001). Turtles, Tortoises & Terrapins: Survivors in Armor. Firefly Books. ISBN 978-1-55209-605-5.
Jump up ^ Feder, Martin E.; Burggren, Warren W. (1985). "Cutaneous gas exchange in vertebrates: design, patterns, control and implications" (PDF). Biological Reviews. 60 (1): 1–45. doi:10.1111/j.1469-185X.1985.tb00416.x.
Jump up ^ Farmer, CG; Sanders, K (2010). "Unidirectional airflow in the lungs of alligators". Science. 327 (5963): 338–340. doi:10.1126/science.1180219. PMID 20075253.
Jump up ^ Farmer, C. G.; Carrier D. R. (2000). "Pelvic aspiration in the American alligator (Alligator mississippiensis)". Journal of Experimental Biology. 203 (11): 1679–1687. PMID 10804158.
Jump up ^ Munns, S. L.; Owerkowicz, T.; Andrewartha, S. J.; Frappell, P. B. (2012). "The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus". Journal of Experimental Biology. 215 (5): 845–852. doi:10.1242/jeb.061952. PMID 22323207.
Jump up ^ Farmer, C. G.; Sanders, K. (2010). "Unidirectional airflow in the lungs of alligators" (PDF). Science. 327 (5963): 338–340. Bibcode:2010Sci...327..338F. doi:10.1126/science.1180219. PMID 20075253.
Jump up ^ Schachner, E. R.; Hutchinson, J. R.; Farmer, C. (2013). "Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria". PeerJ. 1: e60. doi:10.7717/peerj.60. PMC 3628916  . PMID 23638399.
Jump up ^ Whitmarsh J, Govindjee (1999). "Chapter 2: The Basic Photosynthetic Process". In Singhal GS, Renger G, Sopory SK, Irrgang KD, Govindjee. Concepts in Photobiology: Photosynthesis and Photomorphogenesis. Boston: Kluwer Academic Publishers. p. 13. ISBN 978-0-7923-5519-9.
Jump up ^ K. Raschke (1976). "How Stomata Resolve the Dilemma of Opposing Priorities". Phil. Trans. R. Soc. Lond. B. 273: 551–560.
Jump up ^ Ting, I P (1985). "Crassulacean Acid Metabolism". Annual Review of Plant Physiology. 36 (1): 595–622. doi:10.1146/annurev.pp.36.060185.003115.
Jump up ^ S Von Caemmerer; GD Farquhar (1981). "Some relationships between the biochemistry of photosynthesis and gas exchange of leaves". Planta. 153: 376–387.
Jump up ^ Portable Gas Exchange Fluorescence System GFS-3000. Handbook of Operation (PDF), March 20, 2013
Jump up ^ BBC Bitesize - GCSE Biology - Gas exchange in plants
Jump up ^ Anderson, D. (2001) Invertebrate Zoology Oxford University Press
Jump up ^ "Cnidarian Respiratory System". www.study.com. Retrieved 20 March 2017.
Jump up ^ "Nematode Respiratory System". www.study.com. Retrieved 20 March 2017.
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Jump up ^ Lane, N. J.; Harrison, J. B. (1986). "Junctions and the cytoskeleton in insect tissues". Journal of Cell Biology. 103 (5): A69–A69.
Jump up ^ Klowden, M. J. 2007. Physiological systems in insects. Elsevier/Academic Press. pp. 440-442
Jump up ^ Garwood, Russell J. & Edgecombe, Gregory D. (September 2011). "Early Terrestrial Animals, Evolution, and Uncertainty". Evolution: Education and Outreach. New York: Springer Science+Business Media. 4 (3): 489–501. doi:10.1007/s12052-011-0357-y. ISSN 1936-6426. Retrieved 2015-07-21.
Jump up ^ 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. CS1 maint: Uses authors parameter (link)
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text:
Midnight sun
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Midnight sun (disambiguation).
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2013) (Learn how and when to remove this template message)
The Altafjord in Alta, Norway, bathed in the midnight sun.
Midnight sun at the North Cape on the island of Magerøya in Norway
The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the sun remains visible at the local midnight.
Contents
[hide]
1 Details
2 Time zones and daylight saving time
3 White nights
4 Duration
5 See also
6 References
7 Further reading
8 External links
Details[edit]
Around the summer solstice (approximately 21 June in the Northern Hemisphere and 22 December in the Southern Hemisphere), the sun is visible for the full 24 hours, given fair weather. The number of days per year with potential midnight sun increases the closer towards either pole one goes. Although approximately defined by the polar circles, in practice the midnight sun can be seen as much as 55 miles (90 km) outside the polar circle, as described below, and the exact latitudes of the farthest reaches of midnight sun depend on topography and vary slightly year-to-year.
Midnight Sun seen from airplane while passing Greenland
Because there are no permanent human settlements south of the Antarctic Circle, apart from research stations, the countries and territories whose populations experience the midnight sun are limited to those crossed by the Arctic Circle: the Canadian Yukon, Nunavut, and Northwest Territories, and the nations of Iceland, Finland, Norway, Sweden, Denmark (Greenland), Russia, and the State of Alaska in the United States. A quarter of Finland's territory lies north of the Arctic Circle, and at the country's northernmost point the sun does not set at all for 60 days during summer. In Svalbard, Norway, the northernmost inhabited region of Europe, there is no sunset from approximately 19 April to 23 August. The extreme sites are the poles, where the sun can be continuously visible for half the year. The North Pole has midnight sun for 6 months from late March to late September.
The opposite phenomenon, polar night, occurs in winter, when the sun stays below the horizon throughout the day.
Since the axial tilt of the Earth is considerable (approximately 23 degrees 27 minutes), the sun does not set at high latitudes in local summer.[1] The sun remains continuously visible for one day during the summer solstice at the polar circle, for several weeks only 100 km (62 mi) closer to the pole, and for six months at the pole. At extreme latitudes, the midnight sun is usually referred to as polar day.
At the poles themselves, the sun rises and sets only once each year on the equinox. During the six months that the sun is above the horizon, it spends the days continuously moving in circles around the observer, gradually spiralling higher and reaching its highest circuit of the sky at the summer solstice.
Because of atmospheric refraction, and also because the sun is a disc rather than a point, the midnight sun may be experienced at latitudes slightly below the polar circle, though not exceeding one degree (depending on local conditions). For example, Iceland is known for its midnight sun, even though most of it (Grímsey is the exception) is slightly south of the Arctic Circle. For the same reasons, the period of sunlight at the poles is slightly longer than six months. Even the northern extremities of Scotland (and places at similar latitudes, such as St. Petersburg) experience twilight throughout the night in the northern sky at around the summer solstice.
Observers at heights appreciably above sea level can experience extended periods of midnight sun as a result of the "dip" of the horizon viewed from altitude.
Time zones and daylight saving time[edit]
The term "midnight sun" refers to the consecutive 24-hour periods of sunlight experienced north of the Arctic Circle and south of the Antarctic Circle. Other phenomena are sometimes referred to as "midnight sun", but they are caused by time zones and the observance of daylight saving time. For instance, in Fairbanks, Alaska, which is south of the Arctic Circle, the sun sets at 12:47 am at the summer solstice. This is because Fairbanks is 51 minutes ahead of its idealized time zone (as most of the state is in one time zone) and Alaska observes daylight saving time. (Fairbanks is at about 147.72 degrees west, corresponding to UTC−9 hours 51 minutes, and is on UTC−9 in winter.) This means that solar culmination occurs at about 12:51 pm instead of at 12 noon.
If a precise moment for the genuine "midnight sun" is required, the observer's longitude, the local civil time and the equation of time must be taken into account. The moment of the sun's closest approach to the horizon coincides with its passing due north at the observer's position, which occurs only approximately at midnight in general. Each degree of longitude east of the Greenwich meridian makes the vital moment exactly 4 minutes earlier than midnight as shown on the clock, while each hour that the local civil time is ahead of coordinated universal time (UTC, also known as GMT) makes the moment an hour later. These two effects must be added. Furthermore, the equation of time (which depends on the date) must be added: a positive value on a given date means that the sun is running slightly ahead of its average position, so the value must be subtracted.[2]
As an example, at the North Cape of Norway at midnight on June 21/22, the longitude of 25.9 degrees east makes the moment 103.2 minutes earlier by clock time; but the local time, 2 hours ahead of GMT in the summer, makes it 120 minutes later by clock time. The equation of time at that date is -2.0 minutes. Therefore, the sun's lowest elevation occurs 120 - 103.2 + 2.0 minutes after midnight: at 00.19 Central European Summer time. On other nearby dates the only thing different is the equation of time, so this remains a reasonable estimate for a considerable period. The sun's altitude remains within half a degree of the minimum of about 5 degrees for about 45 minutes either side of this time.
White nights[edit]
Main article: White Night festivals
Locations where the sun remains less than 6 (or 7[3]) degrees below the horizon—above 60° 34’ (or 59° 34’) latitude south of the Arctic Circle or north of the Antarctic Circle—experience midnight twilight instead of midnight sun, so that daytime activities, such as reading, are still possible without artificial light on a clear night.
White Nights have become a common symbol of Saint Petersburg, Russia, where they occur from about 11 June to 2 July,[3] and the last 10 days of June are celebrated with cultural events known as the White Nights Festival.
Duration[edit]
Map showing the dates of midnight sun at various latitudes (left) and the total number of nights.
The midnight sun is visible at the Arctic Circle from 12 June until 1 July. This period extends as one travels north: At Cape Nordkinn, Norway, the northernmost point of Continental Europe, the midnight sun lasts approximately from 14 May to 29 July. On the Svalbard archipelago farther north, it lasts from 20 April to 22 August.[4]
See also[edit]
Environment portal
Pytheas, ancient Greek geographer from Massalia and first person to describe the midnight sun
Eagle Summit, which, because of its altitude, experiences the midnight sun despite being south of the Arctic Circle
Polar night, the opposite phenomenon experienced in winter: a day without sunrise.
Midnight Sun Solar Race Team: With the midnight sun phenomenon, a solar-powered vehicle can continue driving 24 hours a day.
References[edit]
Jump up ^ "What is the Midnight Sun Phenomenon? | Earth Phenomena | Planetary Science". Scribd. Retrieved 2017-08-25.
Jump up ^ H. Spencer Jones, General Astronomy (Edward Arnold, London, 1922), Chapters I-III
^ Jump up to: a b Great Soviet Encyclopedia
Jump up ^ Trygve B. Haugan, ed. Det Nordlige Norge Fra Trondheim Til Midnattssolens Land (Trondheim: Reisetrafikkforeningen for Trondheim og Trøndelag. 1940)
Further reading[edit]
Lutgens F.K., Tarbuck E.J. (2007) The Atmosphere, Tenth Edition, page 39, PEARSON, Prentice Hall, NJ.
External links[edit]
Wikimedia Commons has media related to Midnight sun.
Midnight sun seen from Fjellheisen Tromsø - 360 panorama
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v
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Parts of a day
Dawn–Twilight–Sunrise
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Daytime
Evening
Sunset–Twilight–Dusk
Night
Related articles:
Belt of Venus
Blue hour
Golden hour
Terminator
Daylight
Forenoon
Noon
Afternoon
Midnight
Midnight sun
Polar night
Zodiacal light
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Satya Nadella
From Wikipedia, the free encyclopedia
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Satya Nadella
Satya Nadella in 2017
Born
Bukkapuram Nadella Satyanarayana
(1967-08-19) 19 August 1967 (age 50)[1]
Hyderabad, Telangana, India
Citizenship
United States[2]
Alma mater
Manipal Institute of Technology (B.E. - Electrical Engineering)
University of Wisconsin–Milwaukee (M.S.)
University of Chicago (MBA)
Occupation
CEO of Microsoft Corp (2014–present)
Employer
Microsoft (1992–present)
Salary
$84.3 million (2018)
Net worth
$1.34 billion (January 2018) [3]
Board member of
Starbucks[4]
Fred Hutchinson Cancer Research Center[5]
Spouse(s)
Anupama Priya Nadella (m. 1992)
Children
3
Website
Satya Nadella - Microsoft.com
Satya Narayana Nadella (born 19 August 1967) is an Indian American business executive. He is the current Chief Executive Officer (CEO) of Microsoft, succeeding Steve Ballmer in 2014.[6][7] Before becoming CEO, he was Executive Vice President of Microsoft's cloud and enterprise group, responsible for building and running the company's computing platforms, developer tools and cloud computing services.
Contents
[hide]
1 Early life
2 Career
2.1 Sun Microsystems
2.2 Microsoft
3 Personal life
4 Publications
5 References
6 External links
Early life[edit]
Nadella was born in Hyderabad, Andhra Pradesh, India (now in the state of Telangana), to a brahmin family that is originally from Bukkapuram village in Rayalaseema.[8] His father, Bukkapuram Nadella Yugandher, was a civil servant who worked at the prestigious Indian Administrative Service within the Government of India.[9][10][11]
Nadella attended the Hyderabad Public School, Begumpet[12] before receiving a bachelor's in electrical engineering[13] from the Manipal Institute of Technology (then part of Mangalore University) in 1988.[14][15] Nadella subsequently traveled to the U.S. to study for a M.S. in computer science at the University of Wisconsin–Milwaukee,[16][17] receiving his degree in 1990.[18] Later, he received an MBA from the University of Chicago.[19]
Nadella said he "always wanted to build things"[20] and that electrical engineering "was a great way for [him] to go discover what turned out to become a passion," computer science.[21]
Career[edit]
Sun Microsystems[edit]
Nadella worked at Sun Microsystems as a member of its technology staff prior to joining Microsoft in 1992.[22]
Microsoft[edit]
At Microsoft, Nadella has led major projects that included the company's move to cloud computing and the development of one of the largest cloud infrastructures in the world.[23]
Nadella worked as the senior vice-president of Research and Development (R&D) for the Online Services Division and vice-president of the Microsoft Business Division. Later, he was made the president of Microsoft's $19 billion Server and Tools Business and led a transformation of the company's business and technology culture from client services to cloud infrastructure and services. He has been credited for helping bring Microsoft's database, Windows Server and developer tools to its Azure cloud.[19] The revenue from Cloud Services grew to $20.3 billion in June 2013 from $16.6 billion when he took over in 2011.[24] He received $18 million in 2016 pay.[25]
Nadella's 2013 base salary was nearly $700,000, for a total compensation, with stock bonuses, of $7.6 million.[26]
Previous positions held by Nadella include:[27]
President of the Server & Tools Division (9 February 2011 – February 2014)
Senior Vice-President of Research and Development for the Online Services Division (March 2007 – February 2011)[28]
Vice-President of the Business Division
Corporate Vice-President of Business Solutions and Search & Advertising Platform Group
Executive Vice-President of Cloud and Enterprise group[14]
On 4 February 2014, Nadella was announced as the new CEO of Microsoft,[6][7] the third chief executive in the company's history, following Bill Gates and Steve Ballmer.[29]
In October 2014, Nadella courted controversy when he made a statement that women should not ask for a raise and should trust the system.[30] The statement was made while he was attending an event on Women in Computing in Phoenix, AZ. Nadella was roundly criticised for the statement and he apologised later on Twitter.[31] He later sent an email to Microsoft employees admitting he was "Completely wrong".[32]
Nadella changed the company’s direction after becoming CEO. His tenure has emphasized openness to working with companies and technologies with which Microsoft also competes, including Apple Inc.,[33] Salesforce,[34] IBM,[35] and Dropbox.[36] In contrast to previous Microsoft campaigns against the Linux operating system, Nadella proclaimed that "Microsoft ♥ Linux",[37] and in 2016, Microsoft joined the Linux Foundation as a Platinum member.[38]
Under Nadella Microsoft revised its mission statement to "empower every person and every organization on the planet to achieve more".[39] In comparison to founder Bill Gates's "a PC on every desk and in every home, running Microsoft software", Nadella says that it is an enduring mission, rather than a temporal goal.[40] His key goal has been transforming Microsoft’s corporate culture into one that values continual learning and growth.[41] He has cited the book Mindset: The New Psychology of Success by Carol Dweck as inspiration for this philosophy around a "growth mindset".[42]
Nadella's leadership of Microsoft included a series of high-profile acquisitions of other companies, to redirect Microsoft's focus. His first major acquisition was of Mojang, a Swedish game company best known for the popular freeform computer building game Minecraft, in late 2014, for $2.5 billion. Minecraft was notably a cross-platform game, with versions running on Apple's iOS mobile devices, and the Sony PlayStation dedicated gaming console, as well as Microsoft's Xbox.[43] He followed that in 2016 by purchasing Xamarin[44] and LinkedIn.[45]
In the years since becoming CEO, Nadella is viewed as having done well,[46] with Microsoft stock having risen more than 130% since he took over and achieving an all-time high.[47][48] During his leadership, stock in the company has grown at an annualized rate of 23%.
Personal life[edit]
In 1992, Nadella married Anupama, daughter of his father's Indian Administrative Service (IAS) batchmate, K.R. Venugopal.[49] The couple has three children, a son and two daughters, and lives in Bellevue, Washington.[50]
Nadella is an avid reader of business literature[51] and of American and Indian poetry. He also nurses a passion for cricket, having played on his school team.[52]
Nadella has authored a book titled Hit Refresh that explores his life, his career in Microsoft and how he believes technology will shape the future. It was announced that the profits from the book would go to Microsoft Philanthropies and through that to nonprofit organizations.[53]
Publications[edit]
Hit Refresh: The quest to rediscover Microsoft's soul and imagine a better future for everyone, 2017.[54][55]ISBN 9780062652508 (audiobook ISBN 9780062694805)
References[edit]
Jump up ^ "Happy Birthday Satya Nadella: 9 interesting facts about Microsoft CEO". Economic Times.
Jump up ^ Satya Nadella makes no mention of his Indian background Archived 27 September 2017 at the Wayback Machine.. Associated Press via hindustantimes.com. 6 February 2014
Jump up ^ {{|url=http://www1.salary.com/Satya-Nadella-Salary-Bonus-Stock-Options-for-MICROSOFT-CORP.html%7Ctitle=Compensation Information for Satya Nadella, Chief Executive Officer and Director of MICROSOFT CORP - Salary.com|first=Site built by:|last=Salary.com|website=Salary.com|accessdate=5 November 2017|deadurl=no|archiveurl=https://web.archive.org/web/20170824174320/http://www1.salary.com/Satya-Nadella-Salary-Bonus-Stock-Options-for-MICROSOFT-CORP.html%7Carchivedate=24 August 2017|df=dmy-all}}
Jump up ^ "Starbucks Corporation - Corporate Governance - Board of Directors". Starbucks. Archived from the original on 3 September 2017. Retrieved 28 September 2017.
Jump up ^ "Fred Hutchinson Cancer Research Center Board of Trustees". Fred Hutchinson Cancer Research Center. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
^ Jump up to: a b Ovide, Shira (5 February 2014). "Microsoft Board Names Satya Nadella as CEO". The Wall Street Journal. Archived from the original on 19 October 2014.
^ Jump up to: a b "Microsoft Board names Satya Nadella as CEO". Microsoft.com. 4 February 2014. Archived from the original on 26 April 2014.
Jump up ^ "'Studious, hardworking boy has achieved his goal,' says Satya Nadella's dad". DNA India. 2014. Archived from the original on 5 February 2014.
Jump up ^ ‘Studious, hardworking boy has achieved his goal,’ says Satya Nadella's dad Archived 5 February 2014 at the Wayback Machine.. Daily News and Analysis. (5 February 2014). Retrieved 16 February 2014.
Jump up ^ Satya, Nadella (5 February 2014). "Well done Satya". Eenadu. Archived from the original on 22 February 2014. Retrieved 5 February 2014.
Jump up ^ Anisha Dhiman (25 August 2015). "'Satya Nadella on the Meaning of Work': Satya Nadella". Oxy. Archived from the original on 13 September 2017.
Jump up ^ Anisha Dhiman (29 July 2013). "'Never, ever stop learning': Satya Nadella". Decan Chronicle. Archived from the original on 2 February 2014.
Jump up ^ Satya Nadella Archived 24 April 2017 at the Wayback Machine.. news.microsoft.com
^ Jump up to: a b Satya Nadella, President, Server & Tools Business, archived from the original on 2014-02-09, retrieved 2017-06-26
Jump up ^ "MIT thrilled over Nadella being in race to head Microsoft". DNA India. Archived from the original on 29 August 2013.
Jump up ^ "I went to the United States right when Sachin Tendulkar started to play for India so I look at it and say, wow, I missed the entire Sachin era of Indian cricket". Espncricinfo.com. Archived from the original on 11 October 2017.
Jump up ^ "UWMilwaukee alum named Microsoft CEO | UWM News". 5.uwm.edu. 4 February 2014. Archived from the original on 29 July 2014.
Jump up ^ "Satya Nadella education". 5.uwm.edu. Archived from the original on 14 October 2016. Retrieved 5 November 2017.
^ Jump up to: a b McCracken, Harry (15 December 2010). "Microsoft's New CEO Satya Nadella: 10 Things to Know". Time. Archived from the original on 4 February 2014.
Jump up ^ "Meet Satya Nadella, the new Microsoft CEO | NDTV Gadgets". Gadgets.ndtv.com. Archived from the original on 5 February 2014.
Jump up ^ "Satya Nadella – Microsoft's CEO". Microsoft. Archived from the original on 8 November 2015. Retrieved 10 November 2015. 'I think playing cricket taught me more about working in teams and leadership that has stayed with me throughout my career.'
Jump up ^ "IAS officer's son tipped to become Microsoft CEO". The Times of India. 1 February 2014. Archived from the original on 1 March 2014.
Jump up ^ Satya, Nadella (4 February 2014). "Satya Nadella CEO". Hindustan Times. Archived from the original on 7 February 2014. Retrieved 7 February 2014.
Jump up ^ "Indo-American Satya Nadella in race to be Microsoft's new CEO". Biharprabha News. Indo-Asian News Service. Archived from the original on 1 February 2014. Retrieved 30 January 2014.
Jump up ^ "Microsoft CEO Nadella Received $18 Million in 2016 Pay". Bloomberg.com. 3 October 2016. Archived from the original on 20 August 2017. Retrieved 5 November 2017.
Jump up ^ Kyle Nazario (27 January 2014). "Satya Nadella biography: Everything you need to know about Microsoft's new CEO". IT PRO.
Jump up ^ "Satya Nadella: Executive Profile & Biography". Bloomberg BusinessWeek. Archived from the original on 1 March 2014.
Jump up ^ "Equilar Atlas". Archived from the original on 28 February 2014. Retrieved 4 February 2014.
Jump up ^ "Microsoft names Satya Nadella new CEO". News.cnet.com. 4 February 2014. Archived from the original on 6 February 2014. Retrieved 4 February 2014.
Jump up ^ Staff; agencies (10 October 2014). "Microsoft CEO Satya Nadella: women, don't ask for a raise". Theguardian.com. Archived from the original on 17 September 2017. Retrieved 5 November 2017.
Jump up ^ Satya Nadella [@satyanadella] (9 October 2014). "Was inarticulate re how women should ask for raise. Our industry must close gender pay gap so a raise is not needed because of a bias #GHC14" (Tweet) – via Twitter.
Jump up ^ "Satya Nadella email to employees: RE: Grace Hopper Conference - News Center". News.microsoft.com. 9 October 2014. Archived from the original on 8 November 2017. Retrieved 5 November 2017.
Jump up ^ O'Brien, Chris (27 March 2014). "Microsoft CEO Satya Nadella publicly debuts himself, Office for iPad". Los Angeles Times. Archived from the original on 19 May 2016. Retrieved 28 September 2017.
Jump up ^ Hempel, Jesse (February 2015). "Satya Nadella's Got a Plan to Make You Care About Microsoft. The First Step? Holograms". Wired. Archived from the original on 25 September 2017. Retrieved 28 September 2017.
Jump up ^ Clarke, Gavin (22 October 2014). "Big Azure? Microsoft and IBM ink deal on business cloud". The Register. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Bort, Julie (4 November 2014). "Microsoft Partners With Dropbox". Business Insider. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Jackson, Joab (20 October 2014). "Microsoft (hearts) Linux, for Azure's sake". PC World. Archived from the original on 22 October 2016. Retrieved 28 September 2017.
Jump up ^ Frank, Blair Hanley (16 November 2016). "Microsoft doubles down on Linux love, joins foundation". Computerworld. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Statt, Nick (25 June 2015). "Microsoft CEO Nadella wants to help the world 'to achieve more'". CNET. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ McCracken, Harry (18 September 2017). "Satya Nadella Rewrites Microsoft's Code - The future of business". Fast Company. Archived from the original on 28 September 2017. Retrieved 28 September 2017.
Jump up ^ della Cava, Marco (20 February 2017). "Microsoft's Satya Nadella is counting on culture shock to drive growth". USA Today. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Bass, Dina (4 August 2016). "Satya Nadella on a Middle-Aged Microsoft". Bloomberg L.P. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Molina, Brett. "Microsoft to acquire 'Minecraft' maker Mojang for $2.5B". USA Today. Archived from the original on 7 September 2017. Retrieved 20 September 2017.
Jump up ^ Weinberger, Matt (24 February 2016). "Microsoft acquires Xamarin". Business Insider. Archived from the original on 4 July 2017. Retrieved 20 September 2017.
Jump up ^ Wingfield, Nick (13 June 2016). "Microsoft Buys LinkedIn for $26.2 Billion, Reasserting Its Muscle". The New York Times. Archived from the original on 14 September 2017. Retrieved 20 September 2017.
Jump up ^ Lynley, Matthew (29 December 2016). "The new Microsoft under Satya Nadella is still looking good on Wall Street". TechCrunch. Archived from the original on 16 September 2017. Retrieved 28 September 2017.
Jump up ^ La Monica, Paul R. (1 December 2015). "Is Satya Nadella a better Microsoft CEO than Bill Gates?". CNN. Archived from the original on 9 August 2017. Retrieved 28 September 2017.
Jump up ^ Fiegerman, Seth (21 October 2016). "Microsoft stock hits a new all-time high. Here's why". CNN. Archived from the original on 29 September 2017. Retrieved 28 September 2017.
Jump up ^ Nikhila Henry & Rohit P S, TNN. "Nadella's other passions: Cricket, running and pastries". The Times of India.
Jump up ^ Drusch, Andrea (2 April 2014). "10 things to know: Satya Nadella". Politico.com. Archived from the original on 2 March 2014.
Jump up ^ https://www.fastcompany.com/40457479/the-7-books-microsoft-ceo-satya-nadella-says-you-need-to-lead-smarter
Jump up ^ "All for love: When Microsoft CEO Satya Nadella surrendered his Green Card for wife Anu". Firstpost.com. Archived from the original on 3 November 2017. Retrieved 5 November 2017.
Jump up ^ "Microsoft CEO Satya Nadella is writing a book called Hit Refresh". The Verge. 29 June 2016. Archived from the original on 25 April 2017. Retrieved 24 April 2017.
Jump up ^ "Microsoft CEO Satya Nadella Offers A Business-Like Memoir | Star2.com". Star2.com. 2 February 2018. Retrieved 11 February 2018.
Jump up ^ MacLellan, Lila. "With his new book, Satya Nadella takes control of the Microsoft narrative". Quartz. Retrieved 11 February 2018.
External links[edit]
Wikimedia Commons has media related to Satya Nadella.
Microsoft bio
Satya Nadella's theCUBE Interview from Accel Stanford Symposium 2013
Appearances on C-SPAN
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VIAF: 317106370
LCCN: nb2015015253
Retrieved from "https://en.wikipedia.org/w/index.php?title=Satya_Nadella&oldid=838497973"
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