The Mechanics of Respiration (Magill’s Medical Guide, Sixth Edition)
The primary function of respiration is performed by the lungs and their associated tissues. Air must be breathed in through the mouth and nose through the larynx (voice box) into the main airway, the trachea (windpipe). Inside the chest, the trachea branches into the two main airways called bronchi, which in turn successively branch many times into small bronchi called bronchioles. These airways end in very small sacs called alveoli. These alveoli have a very thin membrane separating the air space from the blood in the capillaries. Oxygen (O2) diffuses through the alveolar membrane across the capillary membrane and into the blood to be taken to all the tissues of the body. Tissues excrete carbon dioxide (CO2) into the blood that is carried back to the lungs. Carbon dioxide diffuses from the blood into the alveoli and is carried back through the airways and out of the lungs with the exhaled air. The mouth and nose humidify dry air to ensure that the linings of the lower airways do not dry out. The main airway divides to supply the left and right lungs. These large airways are cylindrical. Their circular shape is maintained by C-shaped cartilage in the walls. The stiff walls prevent collapse of the airways and the loss of gases through the walls of these “conducting” airways. The airways branch repeatedly into smaller airways. As the airways become smaller, they have less cartilage, until, in the very smallest...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
The major type of lung disease, which is called obstructive disease, has three subclasses. The first is general obstruction, a disease in which material is abnormally present in an airway. The second is disease in which the large airways are narrowed. The third is disease in which the small airways and alveoli are diseased.
The case of general airway obstruction is simple. The simplest form is one in which a foreign body such as food or part of a child’s toy is lodged in a large airway, such as the trachea or a main bronchus. The Heimlich maneuver (standing behind the affected individual, clasping the hands in a fist just below the rib cage, and thrusting up and in with the fist) is very effective in dislodging food caught in the trachea or larynx. An object that is small enough (such as a peanut), however, can get farther into the lung, in which case special instruments or surgery are necessary to remove the object. Tumors can also grow into the opening of an airway and obstruct it. Severe cases of tonsillitis are examples of this type of obstruction. Surgery is sometimes necessary to remove such a tumor if it limits airflow.
Large-airway narrowing is another type of related airway obstructive disease. Asthma and bronchitis are examples of this type of disease. The walls of the trachea and larger bronchi become thickened and thus make the passageway for air smaller. In addition, the specialized muscle (smooth...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Hippocrates (c. 460-c. 370 b.c.e.) recognized the breathing of air as an important function. He believed, however, that the function of breathing was to cool the generator of heat, the heart. Aristotle (384-322 b.c.e.) believed that air was breathed into the arteries, which carried it in the gaseous form to the rest of the body. Galen (129-c. 199 c.e.) transformed medicine from a hypothetical (philosophical) science into an experimental science by performing the first experiments on animals. He found that the arteries did not contain air, and he deduced that a quality of air (oxygen had not yet been discovered), not air itself, was important to life. In the seventeenth century, William Harvey discovered that blood circulated from arteries to veins in both the lung and the rest of the body, and oxygen was identified at the end of the eighteenth century by Joseph Priestly. Claude Bernard described the union of oxygen and hemoglobin at the end of the nineteenth century.
Many major technological advances have been made. Machines have been developed to assist and in some cases completely take over the function of respiration. Respirators can assist patients who have difficulty breathing on their own. Victims of poliomyelitis whose muscles for respiration are no longer functional, as well as paralyzed patients, have been greatly helped by respirators. Respirators maintain breathing during surgery when the patient receives...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Kittredge, Mary. The Respiratory System. Edited by Dale C. Garell. Philadelphia: Chelsea House, 2000. This text explains respiration in animals with and without lungs. Covers the historical development of respiratory knowledge and addresses many pathologies of the lung.
Levitzky, Michael G. Pulmonary Physiology. 7th ed. New York: McGraw-Hill Medical, 2007. A clinical text that describes the structure and function of the respiratory system. Covers topics such as the physical process of respiration from the interrelationship of basic lung mechanics, the microscopic changes at the alveolar level of gas exchange, the “nonrespiratory” functions of the lungs, and how the lungs respond to stress.
Mason, Robert J., et al., eds. Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed. Philadelphia: Saunders/Elsevier, 2010. Details basic anatomy, physiology, pharmacology, pathology, and immunology of the lungs.
Parker, Steve. The Lungs and Breathing. Rev. ed. New York: Franklin Watts, 1991. An excellent text on the anatomy of the lung and its elementary functions. The presentation of function is simple and understandable, and the excellent pictures and drawings are a very strong asset.
Ware, Lorraine B., and Michael A. Matthay. “The Acute Respiratory Distress Syndrome.” New England Journal of Medicine 342, no. 18 (May 4, 2000): 1334-1349. Acute...
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Respiration (Encyclopedia of Science)
The term respiration has two relatively distinct meanings in biology. First, respiration is the process by which an organism takes oxygen into its body and then releases carbon dioxide from its body. In this respect, respiration can be regarded as roughly equivalent to "breathing." In some cases, this meaning of the term is extended to mean the transfer of the oxygen from the lungs to the bloodstream and, eventually, into cells. On the other hand, it may refer to the release of carbon dioxide from cells into the bloodstream and, thence, to the lungs.
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Respiration (World of Microbiology and Immunology)
Respiration is the physiological process that produces high-energy molecules such as adenosine triphosphate (ATP). The high-energy compounds become the fuel for the various manufacturing and growth processes of the cell. Respiration involves the transfer of electrons in a chemically linked series of reactions. The final electron acceptor in the respiration process is oxygen.
Respiration occurs in all types of organisms, including bacteria, protists, fungi, plants, and animals. In eukaryotes, respiration is often separated into three separate components. The first is known as external respiration, and is the exchange of oxygen and carbon dioxide between the environment and the organism (i.e., breathing). The second component of respiration is internal respiration. This is the exchange of oxygen and carbon dioxide between the internal body fluids, such as blood, and individual cells. Thirdly, there is cellular respiration, which is the biochemical oxidation of glucose and consequent synthesis of ATP.
Cellular respiration in prokaryotes and eukaryotes is similar. Cellular respiration is an intracellular process in which glucose is oxidized and the energy is used to make the high-energy ATP compound. ATP in turn drives energy-requiring processes such as biosynthesis, transport, growth, and movement.
In prokaryotes and eukaryotes, cellular respiration occurs in three sequential series of reactions; glycolysis, the citric acid cycle, and the electron transport chain. In prokaryotes such as bacteria, respiration involves components that are located in the cytoplasm of the cell as well as being membrane-bound.
Glycolysis is the controlled breakdown of sugar (predominantly, glucose, a 6-carbon carbohydrate) into pyruvate, a 3-carbon carbohydrate. Organisms frequently store complex carbohydrates, such as glycogen or starch, and break these down into glucose that can then enter into glycolysis. The process involves the controlled breakdown of the 6-carbon glucose into two molecules of the 3-carbon pyruvate. At least 10 enzymes are involved in glucose degradation. The oxidation of glucose is controlled so that the energy in this molecule can be used to manufacture other high-energy compounds. Each round of glycolysis generates only a small amount of ATP, in a process known as substrate-level phosphorylation. For each glucose molecule that is broken down by glycolysis, there is a net gain of two molecules of ATP. Glycolysis produces reduced nicotinamide adenine dinucleotide (NADH), a high-energy molecule that can subsequently used to make ATP in the electron transfer chain. For each glucose molecule that is broken down by glycolysis, there is a net gain of two molecules of NADH. Finally, glycolysis produces compounds that can be used to manufacture compounds that are called fatty acids. Fatty acids are the major constituents of lipids, and are important energy storage molecules.
Each pyruvate molecule is oxidized to form carbon dioxide (a 1-carbon molecule) and acetyl CoA (a two carbon molecule). Cells can also make acetyl CoA from fats and amino acids. Indeed, this is how cells often derive energy, in the form of ATP, from molecules other than glucose or complex carbohydrates. Acetyl CoA enters into a series of nine sequential enzyme-catalyzed reactions, known as the citric acid cycle. These reactions are so named because the first reaction makes one molecule of citric acid (a 6-carbon molecule) from one molecule of acetyl CoA (a 2-carbon molecule) and one molecule of oxaloacetic acid (a 4-carbon molecule). A complete round of the citric acid cycle expels two molecules of carbon dioxide and regenerates one molecule of oxaloacetic acid.
The citric acid cycle produces two high-energy compounds, NADH and reduced flavin adenine dinucleotide (FADH 2), that are used to make ATP in the electron transfer chain. One glucose molecule produces 6 molecules of NADH and 2 molecules of FADH 2. The citric acid cycle also produces guanosine triphosphate (GTP; a high-energy molecule that can be easily used by cells to make ATP) by a process known as substrate-level phosphorylation. Finally, some of the intermediates of the citric acid cycle reactions are used to make other important compounds, in particular amino acids (the building blocks of proteins), and nucleotides (the building blocks of DNA).
The electron transfer chain is the final series of biochemical reactions in respiration. The series of organic electron carriers are localized inside the mitochondrial membrane of eukaryotes and the single membrane of Gram-positive bacteria or the inner membrane of Gram-negative bacteria. Cytochromes are among the most important of these electron carriers. Like hemoglobin, cytochromes are colored proteins, which contain iron in a nitrogen-containing heme group. The final electron acceptor of the electron transfer chain is oxygen, which produces water as a final product of cellular respiration.
The main function of the electron transfer chain is the synthesis of 32 molecules of ATP from the controlled oxidation of the eight molecules of NADH and two molecules of FADH 2, made by the oxidation of one molecule of glucose in glycolysis and the citric acid cycle. The electron transfer chain slowly extracts the energy from NADH and FADH 2 by passing electrons from these high-energy molecules from one electron carrier to another, as if along a chain. As this occurs, protons (H+) are pumped across the membrane, creating a proton gradient that is subsequently used to make ATP by a process known as chemiosmosis.
Respiration is often referred to as aerobic respiration, because the electron transfer chain utilizes oxygen as the final electron acceptor. When oxygen is absent or in short supply, cells may rely upon glycolysis alone for their supply of ATP. Glycolysis presumably originated in primitive cells early in the Earth's history when very little oxygen was present in the atmosphere. The glycolysis process has been referred to as anaerobic respiration, although this term is little used today to avoid confusion.
See also Bacterial growth and division; Biochemistry