Plasma

Chemistry

Physics

Plasma is defined differently depending on whether one is involved with chemistry or physics. In chemistry, it is the fluid part of blood; while in physics, it is ionized gas. Both descriptions will be discussed in more detail below.

Chemistry

Plasma is the liquid (fluid) portion of blood which is about 90% water and transports nutrients, wastes, antibodies, ions, hormones, and other molecules throughout the body. Humans typically have about 1.3 to 1.5 gal (5 to 6 l) of blood, which is about 55% plasma and 45% cells—red blood cells, white blood cells, and platelets. The plasma of humans and other vertebrates is nearly colorless, since the red color of hemoglobin is sequestered inside red blood cells. In contrast, many invertebrates have hemoglobin or hemocyanin carried directly in their plasma, so that their plasma is red, green, or blue.

Proteins make up about 8% by weight of human plasma. Humans have over 60 different proteins in their plasma, but the major ones are albumins, globulins, and fibrinogen. Albumins constitute about half (by weight) of all plasma protein and are important as carriers of ions, fatty acids, and other organic molecules. The most important class of globulins is the immunoglobulins, which are the antibodies that defend the body against attack by foreign organisms. Fibrinogen is a plasma protein important in the formation of blood clots following damage to a blood vessel. In clotting, fibrinogen is converted into fibrin and the fibrin molecules form an insoluble polymer, a blood clot. Additional plasma proteins serve as carriers for lipids, hormones, vitamins and other molecules.

Ions make up only about 1% by weight of human plasma. However, they are the major contributors to plasma molarity, since their molecular weights are much less than those of proteins. Thus, ions are important in preventing blood cells from bursting by taking up excess water in osmosis. Sodium chloride (NaCl) constitutes more than 65% of the plasma ions. Bicarbonate, potassium, calcium, phosphate, sulfate, and magnesium are other plasma ions. The kidneys regulate the levels of plasma ion concentrations.

Plasma is also a transport medium for nutrients and wastes. The nutrients include amino acids (used to synthesize proteins), glucose (an energy source), and fatty acids (an energy source). The plasma transorts waste products such as urea and uricacid to the kidneys, where they are excreted.

Cholesterol and cholesterol esters are also present in plasma. Cholesterol is used as an energy source, as a metabolic precursor for the synthesis of steroid hormones, and is incorporated in cell membranes. Excess cholesterol and saturated fatty acids in the plasma can be deposited in arteries and can lead to arteriosclerosis (hardening of the arteries) and to heart disease.

The plasma of vertebrates also contains dissolved gases. Most of the oxygen in blood is bound to hemoglobin inside the red blood cells but some oxygen is dissolved directly in the plasma. Additional plasma gases include carbon dioxide (which forms bicarbonate ions) and nitrogen (which is inert).

Physics

The term plasma refers to a condition of matter sufficiently different from solids, liquids, and gases to have earned its own description: the fourth state of matter. The state develops when a gas is heated to such a high temperature that all atoms in the gas are ionized. In this state, matter consists of positively charged ions and electrons in apparently random motion. The name plasma was given to this state by American chemist Irving Langmuir (1881–1957) in 1920. Langmuir was one of the first modern scientists to study ionized gases. He called them plasma because they looked similar to blood plasma.

The study of plasma-like materials actually goes as far back as the 1830s when English physicist Michael Faraday (1791–1867) passed electrical discharges through gases at low pressures. Faraday’s research was extended and expanded by English scientist Sir William Crookes (1832–1919) in the 1870s. Crookes was apparently the first scientist to suggest that the ionized gas within his glass tubes might be a fourth state of matter.

Plasma research during the 1920s and 1930s was largely a matter of interest to astronomers. It was apparent that, at temperatures present in stars, matter almost certainly exists as plasma. Understanding the composition and properties of stars, therefore, required some understanding of the nature of plasma.

Some of the earliest breakthroughs in plasma research were accomplished by Hannes Olof Gösta Alfvén (1808–1995), a Swedish astrophysicist. Alfvén developed a theory to explain the behavior of plasma in the presence of magnetic fields. His work forms the basis of the modern science known as magnetohydro-dynamics (MHD). For this research, Alfveń was awarded a share of the 1970 Nobel Prize for physics.

Research on nuclear fusion in the 1940s shifted the focus of plasma research from the stars to laboratories on the Earth. Nuclear fusion reactions—the combination of two small nuclei to produce one larger nucleus—occur only at very high temperatures, greater than 18 million^°F (10 million^°C). At such temperatures, similar to those present in the core of a star, matter exists as a plasma.

Scientists attempting to find ways to use fusion reactions as a practical source of energy discovered that trapping plasma inside magnetic fields was the best way to control such reactions. Finding the most practical method of achieving such controlled reactions, however, is an enormously difficult task, one that has still not been perfected after over a half century of research.

One of the earliest suggestions for solving the problem of plasma confinement was offered by Russian physicist Igor Evgenievich Tamm (1895–1971) in 1950. Tamm outlined a model by which the magnetic field surrounds the plasma and “pinches” it together. Another approach was proposed by American astro-physicist Lyman Spitzer, Jr. (1914–1997). Spitzer’s interest in controlled fusion grew out of his earlier research on fusion reactions in the stars. His model calls for a twisting magnetic field to be wrapped around the hot plasma in an arrangement that came to be known as a stellerator.

The most common mechanism for controlling plasma reactions today is called a tokamak, originally designed by Russian physicist Lev Andreevich Artsimovich (1909–1973) in the late 1950s. A tokamak consists of a toroidal (hollow, doughnut-shaped) tube in which the hot plasma is contained by a strong magnetic field. Two tokamaks were built in the 1980s at Princeton University in the United States and another one in the U.S.S.R. (now called Russia). When these tokamaks release their energy, the temperature within its confinement chamber reaches three times the temperature of the Sun’s core. Two other more recently built tokamaks is the HT-7 (Hefei Tokamak-7) in Hefei, China (completed in 1994), and the MAST (Mega Ampere Spherical Tokamak) in Culham, Oxfordshire, England (in operation since December 1999).

Plasma

Plasma is the liquid portion of blood which is about 90% water and transports nutrients , wastes, antibodies, ions, hormones , and other molecules throughout the body. Humans typically have about 1.3-1.5 gal (5-6 l) of blood, which is about 55% plasma and 45% cells-red blood cells, white blood cells, and platelets. The plasma of humans and other vertebrates is nearly colorless, since the red color of hemoglobin is sequestered inside red blood cells. In contrast, many invertebrates have hemoglobin or hemocyanin carried directly in their plasma, so that their plasma is red, green, or blue.

Proteins make up about 8% by weight of human plasma. Humans have over 60 different proteins in their plasma, but the major ones are albumins, globulins, and fibrinogen. Albumins constitute about half (by weight) of all plasma protein and are important as carriers of ions, fatty acids , and other organic molecules. The most important class of globulins is the immunoglobulins, which are the antibodies that defend the body against attack by foreign organisms. Fibrinogen is a plasma protein important in the formation of blood clots following damage to a blood vessel. In clotting, fibrinogen is converted into fibrin and the fibrin molecules form an insoluble polymer , a blood clot. Additional plasma proteins serve as carriers for lipids, hormones, vitamins and other molecules.

Ions make up only about 1% by weight of human plasma. However, they are the major contributors to plasma molarity, since their molecular weights are much less than those of proteins. Thus, ions are important in preventing blood cells from bursting by taking up excess water in osmosis . Sodium chloride (NaCl) constitutes more than 65% of the plasma ions. Bicarbonate, potassium, calcium , phosphate, sulfate, and magnesium are other plasma ions. The kidneys regulate the levels of plasma ion concentrations.

Plasma is also a transport medium for nutrients and wastes. The nutrients include amino acids (used to synthesize proteins), glucose (an energy source), and fatty acids (an energy source). The plasma transorts waste products such as urea and uricacid to the kidneys, where they are excreted.

Cholesterol and cholesterol esters are also present in plasma. Cholesterol is used as an energy source, as a metabolic precursor for the synthesis of steroid hormones, and is incorporated in cell membranes. Excess cholesterol and saturated fatty acids in the plasma can be deposited in arteries and can lead to arteriosclerosis (hardening of the arteries) and to heart disease .

The plasma of vertebrates also contains dissolved gases. Most of the oxygen in blood is bound to hemoglobin inside the red blood cells but some oxygen is dissolved directly in the plasma. Additional plasma gases include carbon dioxide (which forms bicarbonate ions) and nitrogen (which is inert).

plas·ma / ˈplazmə/ (also plasm / ˈplazəm/ ) • n. 1. the colorless fluid part of blood, lymph, or milk, in which corpuscles or fat globules are suspended. ∎  this substance taken from donors or donated blood for administering in transfusions. 2. an ionized gas consisting of positive ions and free electrons in proportions resulting in more or less no overall electric charge, typically at low pressures (as in the upper atmosphere and in fluorescent lamps) or at very high temperatures (as in stars and nuclear fusion reactors). ∎  an analogous substance consisting of mobile charged particles (such as a molten salt or the electrons within a metal). 3. a dark green, translucent variety of quartz used in mosaic and for other decorative purposes. 4. another term for cytoplasm or protoplasm. DERIVATIVES: plas·mat·ic / plazˈmatik/ adj. plas·mic / -mik/ adj. ORIGIN: early 18th cent. (in the sense ‘mold, shape’): from late Latin, literally ‘mold,’ from Greek plasma, from plassein ‘to shape.’

plasma is the liquid component that accounts for about 55% of the volume of blood and in which are suspended the 45% taken up by cellular elements. When the two components are separated by centrifuge, using a test tube sample of blood treated to prevent clotting, the plasma separates as a yellowish layer. Plasma is different from serum — the fluid which is extruded when blood is allowed to clot — because some plasma constituents take part in clot formation. Plasma is about 95% water, with dissolved or suspended substances ranging from simple chemicals to complex protein molecules and fat particles. Its osmolarity (close to 300 milliosmoles/litre) and pH (close to 7.4) are closely controlled; likewise the main anions (chloride, bicarbonate) and cations (sodium, potassium, calcium, magnesium) and the major proteins (albumin and globulins). Nutrients (glucose, fatty acids, amino acids) and the nitrogenous waste product urea, vary more in their concentration, along with meals and metabolic activity. Other substances in much smaller concentration are equally important, such as the hormones, factors required for coagulation, and trace elements. Plasma is continually exchanging its constituents, apart from the large proteins, with all tissue fluids across capillary walls; it is also continually ‘sampled’ and its composition corrected by the kidneys, which partially filter it off from the blood at a rate of 2–3 times the whole 2–3 litres of circulating plasma every hour, process it, and restore it to the circulation — except for about 1% which forms the urine.

Stuart Judge

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