The respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies depending on the size of the organism, the environment in which it lives and its evolutionary history. In land animals the respiratory surface is internalized as linings of the lungs. Gas exchange in the lungs occurs in millions of small air sacs called alveoli in mammals and reptiles, but atria in birds; these microscopic air sacs have a rich blood supply, thus bringing the air into close contact with the blood. These air sacs communicate with the external environment via a system of airways, or hollow tubes, of which the largest is the trachea, which branches in the middle of the chest into the two main bronchi; these enter the lungs where they branch into progressively narrower secondary and tertiary bronchi that branch into numerous smaller tubes, the bronchioles. In birds the bronchioles are termed parabronchi.
It is the bronchioles, or parabronchi that open into the microscopic alveoli in mammals and atria in birds. Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration. In most fish, a number of other aquatic animals the respiratory system consists of gills, which are either or external organs, bathed in the watery environment; this water flows over the gills by a variety of passive means. Gas exchange takes place in the gills which consist of thin or flat filaments and lammelae which expose a large surface area of vascularized tissue to the water. Other animals, such as insects, have respiratory systems with simple anatomical features, in amphibians the skin plays a vital role in gas exchange. Plants have respiratory systems but the directionality of gas exchange can be opposite to that in animals; the respiratory system in plants includes anatomical features such as stomata, that are found in various parts of the plant.
In humans and other mammals, the anatomy of a typical respiratory system is the respiratory tract. The tract is divided into a lower respiratory tract; the upper tract includes the nose, nasal cavities, sinuses and the part of the larynx above the vocal folds. The lower tract includes the lower part of the larynx, the trachea, bronchi and the alveoli; the branching airways of the lower tract are described as the respiratory tree or tracheobronchial tree. The intervals between successive branch points along the various branches of "tree" are referred to as branching "generations", of which there are, in the adult human about 23; the earlier generations, consisting of the trachea and the bronchi, as well as the larger bronchioles which act as air conduits, bringing air to the respiratory bronchioles, alveolar ducts and alveoli, where gas exchange takes place. Bronchioles are defined as the small airways lacking any cartilagenous support; the first bronchi to branch from the trachea are the right and left main bronchi.
Second only in diameter to the trachea, these bronchi enter the lungs at each hilum, where they branch into narrower secondary bronchi known as lobar bronchi, these branch into narrower tertiary bronchi known as segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, 6th order segmental bronchi, or grouped together as subsegmental bronchi. Compared to the, on average, 23 number of branchings of the respiratory tree in the adult human, the mouse has only about 13 such branchings; the alveoli are the dead end terminals of the "tree", meaning that any air that enters them has to exit via the same route. A system such as this creates dead space, a volume of air that fills the airways after exhalation and is breathed back into the alveoli before environmental air reaches them. At the end of inhalation the airways are filled with environmental air, exhaled without coming in contact with the gas exchanger; the lungs contract during the breathing cycle, drawing air in and out of the lungs.
The volume of air moved in or out of the lungs under normal resting circumstances, volumes moved during maximally forced inhalation and maximally forced exhalation are measured in humans by spirometry. A typical adult human spirogram with the names given to the various excursions in volume the lungs can undergo is illustrated below: Not all the air in the lungs can be expelled during maximally forced exhalation; this is the residual volume of about 1.0-1.5 liters. Volumes that include the residual volume can therefore not be measured by spirometry, their measurement requires special techniques. The rates at which air is breathed in or out, either through the mouth or nose, or into or out of the alveoli are tabulated below, together with how they are calculated; the number of breath cycles per minute is known as the respiratory rate. In mammals, inhalation at rest is due to the contraction of the diaphragm; this is an upwardly domed sheet of muscle that separates the thoracic cavity from the abdominal cavity.
When it contracts the sheet flattens. The contracting diaphragm pushes, but because the pelvic floo
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal or human body. It has a small disc-shaped resonator, placed against the chest, two tubes connected to earpieces, it is used to listen to lung and heart sounds. It is used to listen to intestines and blood flow in arteries and veins. In combination with a sphygmomanometer, it is used for measurements of blood pressure. Less "mechanic's stethoscopes", equipped with rod shaped chestpieces, are used to listen to internal sounds made by machines, such as diagnosing a malfunctioning automobile engine by listening to the sounds of its internal parts. Stethoscopes can be used to check scientific vacuum chambers for leaks, for various other small-scale acoustic monitoring tasks. A stethoscope that intensifies auscultatory sounds is called phonendoscope; the stethoscope was invented in France in 1816 by René Laennec at the Necker-Enfants Malades Hospital in Paris. It was monaural. Laennec invented the stethoscope because he was uncomfortable placing his ear on women's chests to hear heart sounds.
He observed that a rolled piece of paper, placed between the patient's chest and his ear, could amplify heart sounds without requiring physical contact. Laennec's device was similar to a historical form of hearing aid. Laennec called his device the "stethoscope", he called its use "mediate auscultation", because it was auscultation with a tool intermediate between the patient's body and the physician's ear; the first flexible stethoscope of any sort may have been a binaural instrument with articulated joints not clearly described in 1829. In 1840, Golding Bird described a stethoscope. Bird was the first to publish a description of such a stethoscope but he noted in his paper the prior existence of an earlier design which he described as the snake ear trumpet. Bird's stethoscope had a single earpiece. In 1851, Irish physician Arthur Leared invented a binaural stethoscope and, in 1852, George Philip Cammann perfected the design of the stethoscope instrument for commercial production, which has become the standard since.
Cammann wrote a major treatise on diagnosis by auscultation, which the refined binaural stethoscope made possible. By 1873, there were descriptions of a differential stethoscope that could connect to different locations to create a slight stereo effect, though this did not become a standard tool in clinical practice. Somerville Scott Alison described his invention of the stethophone at the Royal Society in 1858; this was used to do definitive studies on binaural hearing and auditory processing that advanced knowledge of sound localization and lead to an understanding of binaural fusion. The medical historian Jacalyn Duffin has argued that the invention of the stethoscope marked a major step in the redefinition of disease from being a bundle of symptoms, to the current sense of a disease as a problem with an anatomical system if there are no noticeable symptoms; this re-conceptualization occurred in part, Duffin argues, because prior to stethoscopes, there were no non-lethal instruments for exploring internal anatomy.
Rappaport and Sprague designed a new stethoscope in the 1940s, which became the standard by which other stethoscopes are measured, consisting of two sides, one of, used for the respiratory system, the other for the cardiovascular system. The Rappaport-Sprague was made by Hewlett-Packard. HP's medical products division was spun off as part of Agilent Technologies, Inc. where it became Agilent Healthcare. Agilent Healthcare was purchased by Philips which became Philips Medical Systems, before the walnut-boxed, $300, original Rappaport-Sprague stethoscope was abandoned ca. 2004, along with Philips' brand electronic stethoscope model. The Rappaport-Sprague model stethoscope was heavy and short with an antiquated appearance recognizable by their two large independent latex rubber tubes connecting an exposed leaf-spring-joined pair of opposing F-shaped chrome-plated brass binaural ear tubes with a dual-head chest piece. Several other minor refinements were made to stethoscopes until, in the early 1960s, David Littmann, a Harvard Medical School professor, created a new stethoscope, lighter than previous models and had improved acoustics.
In the late 1970s, 3M-Littmann introduced the tunable diaphragm: a hard glass-epoxy resin diaphragm member with an overmolded silicone flexible acoustic surround which permitted increased excursion of the diaphragm member in a Z-axis with respect to the plane of the sound collecting area. The left shift to a lower resonant frequency increases the volume of some low frequency sounds due to the longer waves propagated by the increased excursion of the hard diaphragm member suspended in the concentric accountic surround. Conversely, restricting excursion of the diaphragm by pressing the stethoscope diaphragm surface against the anatomical area overlying the physiological sounds of interest, the acoustic surround could be used to dampen excursion of the diaphragm in response to "z"-axis pressure against a concentric fret; this raises the freq
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
Stress, either physiological or biological, is an organism's response to a stressor such as an environmental condition. Stress is the body's method of reacting to a condition such as a threat, challenge or physical and psychological barrier. Stimuli that alter an organism's environment are responded to by multiple systems in the body; the autonomic nervous system and hypothalamic-pituitary-adrenal axis are two major systems that respond to stress. The sympathoadrenal medullary axis may activate the fight-or-flight response through the sympathetic nervous system, which dedicates energy to more relevant bodily systems to acute adaptation to stress, while the parasympathetic nervous system returns the body to homeostasis; the second major physiological stress, the HPA axis regulates the release of cortisol, which influences many bodily functions such as metabolic and immunological functions. The SAM and HPA axes are regulated by several brain regions, including the limbic system, prefrontal cortex, amygdala and stria terminalis.
Through these mechanisms, stress can alter memory functions, immune function and susceptibility to diseases. Definitions of stress differ. One system suggests there are five types of stress labeled "acute time-limited stressors", "brief naturalistic stressors", "stressful event sequences", "chronic stressors", "distant stressors". An acute time-limited stressor involves a short-term challenge, while a brief natural stressor involves an event, normal but challenging. A stressful event sequence is a stressor that occurs, continues to yield stress into the immediate future. A chronic stressor involves exposure to a long-term stressor, a distant stressor is a stressor, not immediate. Stress and illness may have intersecting components. Several studies indicate such a link, while theories of the stress–illness link suggest that both acute and chronic stress can cause illness, lead to changes in behavior and in physiology. Behavioral changes can include smoking, changes in eating habits and physical activity.
Physiological changes can include changes in sympathetic activation or HPA activity, immunological function. However, there is much variability in the link between illness; the HPA axis regulates many bodily functions, both behavioral and physiological, through the release of glucocorticoid hormones. The HPA axis activity varies with a spike in the morning; the axis involves the release of corticotropin releasing hormone and vasopressin from the hypothalamus which stimulates the pituitary to secrete ACTH. ACTH may stimulate the adrenal glands to secrete cortisol; the HPA axis is subject to negative feedback regulation as well. The release of CRH and VP are regulated by descending glutaminergic and GABAergic pathways from the amygdala, as well as noradrenergic projections. Increased cortisol acts to increase blood glucose, blood pressure, surpasses lysosomal, immunological activity. Under other circumstances the activity may differ. Increased cortisol favors habit based learning, by favoring memory consolidation of emotional memories.
Selye demonstrated that stress decreases adaptability of an organism and proposed to describe the adaptability as a special resource, adaptation energy. One study considered adaptation energy as an internal coordinate on the "dominant path" in the model of adaptation. Stress can make the individual more susceptible to physical illnesses like the common cold. Stressful events, such as job changes, may result in insomnia, impaired sleeping, physical and psychological health complaints. Research indicates the type of stressor and individual characteristics such as age and physical well-being before the onset of the stressor can combine to determine the effect of stress on an individual. An individual's personality characteristics and childhood experiences with major stressors and traumas may dictate their response to stressors. Chronic stress and a lack of coping resources available or used by an individual can lead to the development of psychological issues such as delusions and anxiety; this is true regarding chronic stressors.
These are stressors that may not be as intense as an acute stressor like a natural disaster or a major accident, but they persist over longer periods of time. These types of stressors tend to have a more negative effect on health because they are sustained and thus require the body's physiological response to occur daily; this depletes the body's energy more and occurs over long periods of time when these microstressors cannot be avoided. See allostatic load for further discussion of the biological process by which chronic stress may affect the body. For example, studies have found that caregivers those of dementia patients, have higher levels of depression and worse physical health than non-caregivers; when humans are under chronic stress, permanent changes in their physiological and behavioral responses may occur. Chronic stress can include events such as caring for a spouse with dementia, or may result from brief focal events that have long term effects, such as experiencing a sexual assault.
Studies have shown that psychological stress may directly contribute to the disproportionately high rates of coronary heart disease morbidity and mortality and its etiologic risk factors. Acute and chronic stress have been shown to raise serum lipids and are associated with clinical coronary events. However, it is possible for individuals to exhibit hardiness—a term
The thoracic cavity is the chamber of the body of vertebrates, protected by the thoracic wall. The central compartment of the thoracic cavity is the mediastinum. There are two openings of the thoracic cavity, a superior thoracic aperture known as the thoracic inlet and a lower inferior thoracic aperture known as the thoracic outlet; the thoracic cavity includes the tendons as well as the cardiovascular system which could be damaged from injury to the back, spine or the neck. Structures within the thoracic cavity include: structures of the cardiovascular system, including the heart and great vessels, which include the thoracic aorta, the pulmonary artery and all its branches, the superior and inferior vena cava, the pulmonary veins, the azygos vein structures of the respiratory system, including the Diaphragm, trachea and lungs structures of the digestive system, including the esophagus, endocrine glands, including the thymus gland, structures of the nervous system including the paired vagus nerves, the paired sympathetic chains, lymphatics including the thoracic duct.
It contains three potential spaces lined with mesothelium: the paired pleural cavities and the pericardial cavity. The mediastinum comprises those organs; the cavity contains two openings one at the top, the superior thoracic aperture called the thoracic inlet, a lower inferior thoracic aperture, much larger than the inlet. If the pleural cavity is breached from the outside, as by a bullet wound or knife wound, a pneumothorax, or air in the cavity, may result. If the volume of air is significant, one or both lungs may collapse, which requires immediate medical attention. Thoraxlesson3 at The Anatomy Lesson by Wesley Norman
Oxygen saturation is a relative measure of the concentration of oxygen, dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media water; the standard unit of oxygen saturation is percent. Oxygen saturation can be measured noninvasively. Arterial oxygen saturation is measured using pulse oximetry. Tissue saturation at peripheral scale can be measured using NIRS; this technique can be applied on both brain. In medicine, oxygen saturation refers to oxygenation, or when oxygen molecules enter the tissues of the body. In this case blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygen saturation measure the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. Fish, invertebrates and aerobic bacteria all require oxygen for respiration. In aquatic environments, oxygen saturation is a ratio of the concentration of dissolved oxygen, to the maximum amount of oxygen that will dissolve in that water body, at the temperature and pressure which constitute stable equilibrium conditions.
Well-aerated water without oxygen producers or consumers is 100% saturated. It is possible for stagnant water to become somewhat supersaturated with oxygen either because of the presence of photosynthetic aquatic oxygen producers or because of a slow equilibration after a change of atmospheric conditions. Stagnant water in the presence of decaying matter will have an oxygen concentration much less than 100%, due to anaerobic bacteria being much less efficient at breaking down organic material. Similar to water, oxygen concentration plays a key role in the break down of organic matter in soils. Higher levels of oxygen saturation allow for aerobic bacteria to persist, which break down decaying organic material in soils much more efficiently than anaerobic bacteria, thus soils with high oxygen saturation will have less organic matter per volume than those with low oxygen saturation. Environmental oxygenation can be important to the sustainability of a particular ecosystem; the US Environmental Protection Agency has published a table of maximum equilibrium dissolved oxygen concentration versus temperature at atmospheric pressure.
The optimal levels in an estuary for dissolved oxygen is higher than 6 ppm. Insufficient oxygen caused by the decomposition of organic matter and/or nutrient pollution, may occur in bodies of water such as ponds and rivers, tending to suppress the presence of aerobic organisms such as fish. Deoxygenation increases the relative population of anaerobic organisms such as plants and some bacteria, resulting in fish kills and other adverse events; the net effect is to alter the balance of nature by increasing the concentration of anaerobic over aerobic species. Oxygen deficiency