Gas exchange or respiration takes place at a respiratory surface—a boundary between the external environment and the interior of the body. For unicellular organisms the respiratory surface is simply the cell membrane, but for large organisms it usually is carried out in respiratory systems. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In living organisms a respiratory system functions to allow Gas exchange.
In biology, the word "respiration" can also refer to cellular respiration or metabolism (ATP generation inside cells). Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life.
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Process
Gasses cross the respiratory surface by diffusion, so from Fick's law we can predict that respiratory surfaces must have:
- a large surface area
- a thin permeable surface
- a moist exchange surface
Many also have a mechanism to maximise the diffusion gradient by replenishing the source and/or sink. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement Fick's laws of diffusion describe Diffusion and can be used to solve for the diffusion coefficient D.
Control of respiration is due to rhythmical breathing generated by the phrenic nerve to stimulate contraction and relaxation of the diaphragm during inspiration and expiration. Control of ventilation ( control of respiration) refers to the physiological mechanisms involved in the control of physiologic ventilation. The phrenic nerve arises from the third fourth and fifth cervical Spinal nerves (C3-C5 in Humans. For other types of diaphragm see Diaphragm. In the Anatomy of Mammals the thoracic diaphragm is a sheet of Muscle Ventilation is controlled by partial pressures of oxygen and carbon dioxide and the concentration of hydrogen ions. The control of respiration can vary in certain circumstances such as during exercise.
Gas exchange in humans and mammals
In humans and mammals, respiratory gas exchange or ventilation is carried out by mechanisms of the heart and lungs. The blood is subjected to a transient electric field (QRS waves of the EKG) in the heart which dissociates molecules of different charge. The blood, being a polar fluid, aligns dipoles with the electric field, is released, and then oscillates in a damped driven oscillation to form J or Osborn Waves, T, U, and V waves. The electric field exposure and subsequent damped driven oscillation dissociate gas from hemoglobin, primarily CO2, but more importantly BPG, which has a higher affinity for hemoglobin than does oxygen, due in part to its opposite charge. 23-Bisphosphoglycerate (23-BPG also known as 23-diphosphoglycerate or 23-DPG is a three carbon isomer of the glycolytic intermediate 13-bisphosphoglycerate. Completely dissociated hemoglobin (which will even effervesce if the electric field is too strong—the reason defibrillation joules are limited, to avoid bubble emboli that may clog vessels in the lung) enters the lung in RBC's ready to be oxygenated. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity
Convection occurs over the majority of the transport pathway. Convection in the most general terms refers to the movement of molecules within Fluids (i Diffusion occurs only over very short distances. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The primary force applied in the respiratory tract is supplied by atmospheric pressure. Total atmospheric pressure at sea level is 760 mmHg (101 kPa), with oxygen (O2) providing a partial pressure (pO2) of 160 mmHg, 21% by volume, at the entrance of the nares, a partial pressure of 150 mmHg in the trachea due to the effect of partial pressure of water vapor, and an estimated pO2 of 100 mmHg in the alveoli sac, pressure drop due to conduction loss as oxygen travels along the transport passageway. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Atmospheric pressure decreases as altitude increases making effective breathing more difficult at higher altitudes. Higher BPG levels in the blood are also seen at higher elevations, as well.
Similarly CO2 which is a result of tissue cellular respiration also exchange. The pCO2 changes from 45 mmHg to 40 mmHg in the alveoli. The concentration of this gas in the breath can be measured using a capnograph. A capnograph is an instrument used to measure the Carbon dioxide (CO2 concentration in an air sample As a secondary measurement, respiration rate can be derived from a CO2 breath waveform.
Gas exchange occurs only at pulmonary and systemic capillary beds, but anyone can perform simple experiments with electrodes in blood on the bench-top to observe electric field stimulated effervescence. lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive
Trace gases present in breath at levels lower than a part per million are ammonia, acetone, isoprene. These can be measured using selected ion flow tube mass spectrometry. Selected ion flow tube mass spectrometry is a sensitive and quantitative Mass spectrometry technique for trace gas analyses using chemical ionisation of sample trace gases by
Diffusion
Blood carries oxygen, carbon dioxide and hydrogen ions between tissues and the lungs. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge
The majority (70%) of CO2 transported in the blood is dissolved in plasma (primarily as dissolved bicarbonate; 60%). In Inorganic chemistry, bicarbonate ( IUPAC -recommended nomenclature hydrogencarbonate) is an intermediate form in the Deprotonation A smaller fraction (30%) is transported in red blood cells combined with the globin portion of hemoglobin as carbaminohaemoglobin. Hemoglobin ( also spelled haemoglobin and abbreviated Hb or Hgb) is the Iron -containing Oxygen -transport Metalloprotein
As CO2 diffuses into the blood stream 93% goes into RBCs and 7% is dissolved in plasma. 70% is converted into H2CO3 by carbonic anhydrase. The H2CO3 dissociates into H+ and HCO−3. The HCO−3 moves out of the RBC in exchange for CL− (chloride shift). The hydrogen is removed by buffers in the blood (Hb).
External links
- Human Physiology Respiration at eku.edu
- MeSH Pulmonary+Gas+Exchange
- RT Corner (Educational Site for RT's and Nurses) at rtcorner. Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books net
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