The Body System Series: The Respiratory System and its Functions

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It is, in fact, a very forceful exhalatory effort against a tightly closed glottis , so that no air can escape from the lungs. The abdominal muscles contract very powerfully, causing the pressure inside the abdomen and thorax to rise to extremely high levels. The Valsalva maneuver can be carried out voluntarily, but is more generally a reflex elicited when attempting to empty the abdomen during, for instance, difficult defecation, or during childbirth.

Breathing ceases during this maneuver. The primary purpose of the respiratory system is the equilibration of the partial pressures of the respiratory gases in the alveolar air with those in the pulmonary capillary blood Fig. This process occurs by simple diffusion , [17] across a very thin membrane known as the blood—air barrier , which forms the walls of the pulmonary alveoli Fig.

It consisting of the alveolar epithelial cells , their basement membranes and the endothelial cells of the alveolar capillaries Fig. The air contained within the alveoli has a semi-permanent volume of about 2. This ensures that equilibration of the partial pressures of the gases in the two compartments is very efficient and occurs very quickly. This 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 fairly narrow and relatively long tubes the airways: nose , pharynx , larynx , trachea , bronchi and their branches down to the bronchioles , through which the air has to be breathed both in and out i.

This typical mammalian anatomy combined with the fact that the lungs are not emptied and re-inflated with each breath leaving a substantial volume of air, of about 2. Thus the animal is provided with a very special "portable atmosphere", whose composition differs significantly from the present-day ambient air.

The resulting arterial partial pressures of oxygen and carbon dioxide are homeostatically controlled. A rise in the arterial partial pressure of CO 2 and, to a lesser extent, a fall in the arterial partial pressure of O 2 , will reflexly cause deeper and faster breathing till the blood gas tensions in the lungs, and therefore the arterial blood, 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.

This is very tightly controlled by the monitoring of the arterial blood gases which accurately reflect composition of the alveolar air by the aortic and carotid bodies , as well as by 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.

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 partial pressure of carbon dioxide has returned to 5. If these homeostats are compromised, then a respiratory acidosis , or a respiratory alkalosis will occur. Oxygen has a very low solubility in water, and is therefore carried in the blood loosely combined with hemoglobin.

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The oxygen is held on the hemoglobin by four ferrous iron -containing heme groups per hemoglobin molecule. The reaction is therefore catalyzed by carbonic anhydrase , an enzyme inside the red blood cells. The total concentration of carbon dioxide in the form of bicarbonate ions, dissolved CO 2 , and carbamino groups in arterial blood i. Ventilation of the lungs in mammals occurs via the respiratory centers in the medulla oblongata and the pons of the brainstem. This information determines the average rate of ventilation of the alveoli of the lungs , to keep these pressures constant.

The respiratory center does so via motor nerves which activate the diaphragm and other muscles of respiration. The breathing rate increases when the partial pressure of carbon dioxide in the blood increases. This is detected by central blood gas chemoreceptors on the anterior surface of the medulla oblongata. Exercise increases the breathing rate due to the extra carbon dioxide produced by the enhanced metabolism of the exercising muscles.

Information received from stretch receptors in the lungs limits tidal volume the depth of inhalation and exhalation. The alveoli are open via the airways to the atmosphere, with the result that alveolar air pressure is exactly the same as the ambient air pressure at sea level, at altitude, or in any artificial atmosphere e. With expansion of the lungs through lowering of the diaphragm and expansion of the thoracic cage the alveolar air now occupies a larger volume, and its pressure falls proportionally , causing air to flow in from the surroundings, through the airways, till the pressure in the alveoli is once again at the ambient air pressure.

The reverse obviously happens during exhalation. This process of inhalation and exhalation is exactly the same at sea level, as on top of Mt. Everest , or in a diving chamber or decompression chamber. However, as one rises above sea level the density of the air decreases exponentially see Fig.

This is achieved by breathing deeper and faster i. There is, however, a complication that increases the volume of air that needs to be inhaled per minute respiratory minute volume to provide the same amount of oxygen to the lungs at altitude as at sea level. During inhalation the air is warmed and saturated with water vapor during its passage through the nose passages and pharynx.

Human respiratory system

Saturated water vapor pressure is dependent only on temperature. In dry air the partial pressure of O 2 at sea level is At the summit of Mt. This reduces the partial pressure of oxygen entering the alveoli to 5. The reduction in the partial pressure of oxygen in the inhaled air is therefore substantially greater than the reduction of the total atmospheric pressure at altitude would suggest on Mt Everest: 5. A further minor complication exists at altitude. If the volume of the lungs were to be instantaneously doubled at the beginning of inhalation, the air pressure inside the lungs would be halved.

This happens regardless of altitude. The driving pressure forcing air into the lungs during inhalation is therefore halved at this altitude.

The design of the respiratory system

However, in reality, inhalation and exhalation occur far more gently and less abruptly than in the example given. All of the above influences of low atmospheric pressures on breathing are accommodated primarily by breathing deeper and faster hyperpnea. The exact degree of hyperpnea is determined by the blood gas homeostat , which regulates the partial pressures of oxygen and carbon dioxide in the arterial blood.

This homeostat prioritizes the regulation of the arterial partial pressure of carbon dioxide over that of oxygen at sea level.

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If this switch occurs relatively abruptly, the hyperpnea at high altitude will cause a severe fall in the arterial partial pressure of carbon dioxide, with a consequent rise in the pH of the arterial plasma. This is one contributor to high altitude sickness. On the other hand, if the switch to oxygen homeostasis is incomplete, then hypoxia may complicate the clinical picture with potentially fatal results. There are oxygen sensors in the smaller bronchi and bronchioles.

In response to low partial pressures of oxygen in the inhaled air these sensors reflexively cause the pulmonary arterioles to constrict. At altitude this causes the pulmonary arterial pressure to rise resulting in a much more even distribution of blood flow to the lungs than occurs at sea level. At sea level the pulmonary arterial pressure is very low, with the result that the tops of the lungs receive far less blood than the bases , which are relatively over-perfused with blood.

It is only in the middle of the lungs that the blood and air flow to the alveoli are ideally matched. This is a further important contributor to the acclimatatization to high altitudes and low oxygen pressures. When the oxygen content of the blood is chronically low, as at high altitude, the oxygen-sensitive kidney cells secrete erythropoietin often known only by its abbreviated form as EPO [28] into the blood.

In other words, at the same arterial partial pressure of O 2 , a person with a high hematocrit carries more oxygen per liter of blood than a person with a lower hematocrit does. High altitude dwellers therefore have higher hematocrits than sea-level residents. Irritation of nerve endings within the nasal passages or airways , can induce a cough reflex and sneezing. These responses cause air to be expelled forcefully from the trachea or nose , respectively.

In this manner, irritants caught in the mucus which lines the respiratory tract are expelled or moved to the mouth where they can be swallowed. This increases the expired airflow rate to dislodge and remove any irritant particle or mucus. Respiratory epithelium can secrete a variety of molecules that aid in the defense of the lungs. These include secretory immunoglobulins IgA , collectins , defensins and other peptides and proteases , reactive oxygen species , and reactive nitrogen species. These secretions can act directly as antimicrobials to help keep the airway free of infection.

A variety of chemokines and cytokines are also secreted that recruit the traditional immune cells and others to the site of infections. These proteins can bind to sugars on the surface of pathogens and thereby opsonize them for uptake by phagocytes. It also regulates inflammatory responses and interacts with the adaptive immune response. Surfactant degradation or inactivation may contribute to enhanced susceptibility to lung inflammation and infection. Most of the respiratory system is lined with mucous membranes that contain mucosa-associated lymphoid tissue , which produces white blood cells such as lymphocytes.

The lungs make a surfactant , a surface-active lipoprotein complex phospholipoprotein formed by type II alveolar cells. It floats on the surface of the thin watery layer which lines the insides of the alveoli, reducing the water's surface tension. The surface tension of a watery surface the water-air interface tends to make that surface shrink. The more acute the curvature of the water-air interface the greater the tendency for the alveolus to collapse.

Firstly the surface tension inside the alveoli resists expansion of the alveoli during inhalation i. Surfactant reduces the surface tension and therefore makes the lungs more compliant , or less stiff, than if it were not there. Secondly, the diameters of the alveoli increase and decrease during the breathing cycle. This means that the alveoli have a greater tendency to collapse i. Since surfactant floats on the watery surface, its molecules are more tightly packed together when the alveoli shrink during exhalation.

The tendency for the alveoli to collapse is therefore almost the same at the end of exhalation as at the end of inhalation. Thirdly, the surface tension of the curved watery layer lining the alveoli tends to draw water from the lung tissues into the alveoli. Surfactant reduces this danger to negligible levels, and keeps the alveoli dry.

Pre-term babies who are unable to manufacture surfactant have lungs that tend to collapse each time they breathe out. Unless treated, this condition, called respiratory distress syndrome , is fatal. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using steroids as a means of furthering development of type II alveolar cells. The lung vessels contain a fibrinolytic system that dissolves clots that may have arrived in the pulmonary circulation by embolism , often from the deep veins in the legs.

They also release a variety of substances that enter the systemic arterial blood, and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Some prostaglandins are removed from the circulation, while others are synthesized in the lungs and released into the blood when lung tissue is stretched.

The lungs activate one hormone. The physiologically inactive decapeptide angiotensin I is converted to the aldosterone -releasing octapeptide, angiotensin II , in the pulmonary circulation. The reaction occurs in other tissues as well, but it is particularly prominent in the lungs. Angiotensin II also has a direct effect on arteriolar walls , causing arteriolar vasoconstriction , and consequently a rise in arterial blood pressure. The converting enzyme also inactivates bradykinin. Four other peptidases have been identified on the surface of the pulmonary endothelial cells.

The movement of gas through the larynx , pharynx and mouth allows humans to speak , or phonate. Vocalization, or singing, in birds occurs via the syrinx , an organ located at the base of the trachea. The vibration of air flowing across the larynx vocal cords , in humans, and the syrinx, in birds, results in sound.

Because of this, gas movement is vital for communication purposes. Panting in dogs, cats, birds and some other animals provides a means of reducing body temperature, by evaporating saliva in the mouth instead of evaporating sweat on the skin. Disorders of the respiratory system can be classified into several general groups:.

Disorders of the respiratory system are usually treated by a pulmonologist and respiratory therapist. Where there is an inability to breathe or an insufficiency in breathing a medical ventilator may be used. Horses are obligate nasal breathers which means that they are different from many other mammals because they do not have the option of breathing through their mouths and must take in air through their noses. The elephant is the only mammal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue.

In the elephant the lungs are attached to the diaphragm and breathing relies mainly on the diaphragm rather than the expansion of the ribcage.

Gas Exchange

The respiratory system of birds differs significantly from that found in mammals. Firstly, they have rigid lungs which do not expand and contract during the breathing cycle. Instead an extensive system of air sacs Fig. Inhalation and exhalation are brought about by alternately increasing and decreasing the volume of the entire thoraco-abdominal cavity or coelom using both their abdominal and costal muscles. This pushes the sternal ribs, to which they are attached at almost right angles, downwards and forwards, taking the sternum with its prominent keel in the same direction Fig.

This increases both the vertical and transverse diameters of thoracic portion of the trunk. The forward and downward movement of, particularly, the posterior end of the sternum pulls the abdominal wall downwards, increasing the volume of that region of the trunk as well. During exhalation the external oblique muscle which is attached to the sternum and vertebral ribs anteriorly , and to the pelvis pubis and ilium in Fig.

Air is therefore expelled from the respiratory system in the act of exhalation. During inhalation air enters the trachea via the nostrils and mouth, and continues to just beyond the syrinx at which point the trachea branches into two primary bronchi , going to the two lungs Fig. The primary bronchi enter the lungs to become the intrapulmonary bronchi, which give off a set of parallel branches called ventrobronchi and, a little further on, an equivalent set of dorsobronchi Fig. Each pair of dorso-ventrobronchi is connected by a large number of parallel microscopic air capillaries or parabronchi where gas exchange occurs Fig.

This is due to the bronchial architecture which directs the inhaled air away from the openings of the ventrobronchi, into the continuation of the intrapulmonary bronchus towards the dorsobronchi and posterior air sacs. So, during inhalation, both the posterior and anterior air sacs expand, [41] the posterior air sacs filling with fresh inhaled air, while the anterior air sacs fill with "spent" oxygen-poor air that has just passed through the lungs.

During exhalation the pressure in the posterior air sacs which were filled with fresh air during inhalation increases due to the contraction of the oblique muscle described above. The aerodynamics of the interconnecting openings from the posterior air sacs to the dorsobronchi and intrapulmonary bronchi ensures that the air leaves these sacs in the direction of the lungs via the dorsobronchi , rather than returning down the intrapulmonary bronchi Fig.

The air passages connecting the ventrobronchi and anterior air sacs to the intrapulmonary bronchi direct the "spent", oxygen poor air from these two organs to the trachea from where it escapes to the exterior. The blood flow through the bird lung is at right angles to the flow of air through the parabronchi, forming a cross-current flow exchange system Fig. The blood capillaries leaving the exchanger near the entrance of airflow take up more O 2 than do the capillaries leaving near the exit end of the parabronchi.

When the contents of all capillaries mix, the final partial pressure of oxygen of the mixed pulmonary venous blood is higher than that of the exhaled air, [41] [44] but is nevertheless less than half that of the inhaled air, [41] thus achieving roughly the same systemic arterial blood partial pressure of oxygen as mammals do with their bellows-type lungs.

The trachea is an area of dead space : the oxygen-poor air it contains at the end of exhalation is the first air to re-enter the posterior air sacs and lungs. In comparison to the mammalian respiratory tract , the dead space volume in a bird is, on average, 4. In some birds e. The anatomical structure of the lungs is less complex in reptiles than in mammals , with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however.

Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inhalation and exhalation. Both the lungs and the skin serve as respiratory organs in amphibians. The ventilation of the lungs in amphibians relies on positive pressure ventilation.

Muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils into the oral cavity. With the nostrils and mouth closed, the floor of the oral cavity is then pushed up, which forces air down the trachea into the lungs. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialised cells, and is involved in cutaneous respiration. While the lungs are of primary organs for gas exchange between the blood and the environmental air when out of the water , the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.

Oxygen is poorly soluble in water. Fish have developed gills deal with these problems. Gills are specialized organs containing filaments , which further divide into lamellae. The lamellae contain a dense thin walled capillary network that exposes a large gas exchange surface area to the very large volumes of water passing over them.

Gills use a countercurrent exchange system that increases the efficiency of oxygen-uptake from the water. Water is drawn in through the mouth by closing the operculum gill cover , and enlarging the mouth cavity Fig. Simultaneously the gill chambers enlarge, producing a lower pressure there than in the mouth causing water to flow over the gills. Back-flow into the gill chamber during the inhalatory phase is prevented by a membrane along the ventroposterior border of the operculum diagram on the left in Fig.

Thus the mouth cavity and gill chambers act alternately as suction pump and pressure pump to maintain a steady flow of water over the gills in one direction. Oxygen is therefore able to continually diffuse down its gradient into the blood, and the carbon dioxide down its gradient into the water. In certain active pelagic sharks, water passes through the mouth and over the gills while they are moving, in a process known as "ram ventilation". But a small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move.

Obligate ram ventilation is also true of some pelagic bony fish species. There are a few fish that can obtain oxygen for brief periods of time from air swallowed from above the surface of the water. Thus Lungfish possess one or two lungs, and the labyrinth fish have developed a special "labyrinth organ", which characterizes this suborder of fish.

The labyrinth organ is a much-folded supra branchial accessory breathing organ. It is formed by a vascularized expansion of the epibranchial bone of the first gill arch, and is used for respiration in air. This organ allows labyrinth fish to take in oxygen directly from the air, instead of taking it from the water in which they reside through use of gills.

The labyrinth organ helps the oxygen in the inhaled air to be absorbed into the bloodstream. As a result, labyrinth fish can survive for a short period of time out of water, as they can inhale the air around them, provided they stay moist. Labyrinth fish are not born with functional labyrinth organs. The development of the organ is gradual and most juvenile labyrinth fish breathe entirely with their gills and develop the labyrinth organs when they grow older.

Some species of crab use a respiratory organ called a branchiostegal lung. Some of the smallest spiders and mites can breathe simply by exchanging gas through the surface of the body. Larger spiders, scorpions and other arthropods use a primitive book lung. Most insects breath passively through their spiracles special openings in the exoskeleton and the air reaches every part of the body by means of a series of smaller and smaller tubes called 'trachaea' when their diameters are relatively large, and ' tracheoles ' when their diameters are very small.

The tracheoles make contact with individual cells throughout the body. Diffusion of gases is effective over small distances but not over larger ones, this is one of the reasons insects are all relatively small. Insects which do not have spiracles and trachaea, such as some Collembola, breathe directly through their skins, also by diffusion of gases.

The number of spiracles an insect has is variable between species, however they always come in pairs, one on each side of the body, and usually one pair per segment. Some of the Diplura have eleven, with four pairs on the thorax, but in most of the ancient forms of insects, such as Dragonflies and Grasshoppers there are two thoracic and eight abdominal spiracles. However, in most of the remaining insects there are fewer. It is at the level of the tracheoles that oxygen is delivered to the cells for respiration.

Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable.

Some small insects do not demonstrate continuous respiratory movements and may lack muscular control of the spiracles. Others, however, utilize muscular contraction of the abdomen along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns and to reduce water loss into the atmosphere. The most extreme form of these patterns is termed discontinuous gas exchange cycles. Molluscs generally possess gills that allow gas exchange between the aqueous environment and their circulatory systems.

These animals also possess a heart that pumps blood containing hemocyanin as its oxygen-capturing molecule. The respiratory system of gastropods can include either gills or a lung. Plants use carbon dioxide gas in the process of photosynthesis , and exhale oxygen gas as waste. The chemical equation of photosynthesis is 6 CO 2 carbon dioxide and 6 H 2 O water , which in the presence of sunlight makes C 6 H 12 O 6 glucose and 6 O 2 oxygen.

Photosynthesis uses electrons on the carbon atoms as the repository for the energy obtained from sunlight. It reclaims the energy to power chemical reactions in cells. In so doing the carbon atoms and their electrons are combined with oxygen forming CO 2 which is easily removed from both the cells and the organism. Plants use both processes, photosynthesis to capture the energy and oxidative metabolism to use it. Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes, known as stomata , that can open and close on the undersides of their leaves and sometimes other parts of their anatomy.

Most plants require some oxygen for catabolic processes break-down reactions that release energy. But the quantity of O 2 used per hour is small as they are not involved in activities that require high rates of aerobic metabolism. Their requirement for air, however, is very high as they need CO 2 for photosynthesis, which constitutes only 0. But inefficiencies in the photosynthetic process cause considerably greater volumes of air to be used.

From Wikipedia, the free encyclopedia. This article is about the biological system. For other uses, see Breathing system. A biological system of specific organs and structures for gas exchange in animals and plants. Main articles: Lung and Respiratory tract. Main articles: Breathing and Lung volumes. Play media. The "pump handle" and "bucket handle movements" of the ribs. The particular action illustrated here is called the pump handle movement of the rib cage. This exchange is a result of increased concentration of oxygen, and a decrease of C This process of exchange is done through diffusion.

External respiration is the exchange of gas between the air in the alveoli and the blood within the pulmonary capillaries. A normal rate of respiration is breaths per minute.

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  6. In external respiration, gases diffuse in either direction across the walls of the alveoli. Oxygen diffuses from the air into the blood and carbon dioxide diffuses out of the blood into the air. Most of the carbon dioxide is carried to the lungs in plasma as bicarbonate ions HCO When blood enters the pulmonary capillaries, the bicarbonate ions and hydrogen ions are converted to carbonic acid H2CO3 and then back into carbon dioxide CO2 and water.

    This chemical reaction also uses up hydrogen ions. The removal of these ions gives the blood a more neutral pH, allowing hemoglobin to bind up more oxygen. De-oxygenated blood "blue blood" coming from the pulmonary arteries, generally has an oxygen partial pressure pp of 40 mmHg and CO2 pp of 45 mmHg. Oxygenated blood leaving the lungs via the pulmonary veins has an O2 pp of mmHg and CO2 pp of 40 mmHg. It should be noted that alveolar O2 pp is mmHg, and not mmHg. The reason why pulmonary venous return blood has a lower than expected O2 pp can be explained by "Ventilation Perfusion Mismatch".

    There is a point at the inferior portion of the trachea where it branches into two directions that form the right and left primary bronchus. This point is called the Carina which is the keel-like cartilage plate at the division point. We are now at the Bronchial Tree.

    Other Functions

    It is named so because it has a series of respiratory tubes that branch off into smaller and smaller tubes as they run throughout the lungs. The Right Primary Bronchus is the first portion we come to, it then branches off into the Lobar secondary Bronchi , Segmental tertiary Bronchi , then to the Bronchioles which have little cartilage and are lined by simple cuboidal epithelium See fig. The bronchi are lined by pseudostratified columnar epithelium. Objects will likely lodge here at the junction of the Carina and the Right Primary Bronchus because of the vertical structure.

    Items have a tendency to fall in it, where as the Left Primary Bronchus has more of a curve to it which would make it hard to have things lodge there. The Left Primary Bronchus has the same setup as the right with the lobar, segmental bronchi and the bronchioles. The lungs are attached to the heart and trachea through structures that are called the roots of the lungs. The roots of the lungs are the bronchi, pulmonary vessels, bronchial vessels, lymphatic vessels, and nerves. These structures enter and leave at the hilus of the lung which is "the depression in the medial surface of a lung that forms the opening through which the bronchus, blood vessels, and nerves pass" medlineplus.

    There are a number of terminal bronchioles connected to respiratory bronchioles which then advance into the alveolar ducts that then become alveolar sacs. Each bronchiole terminates in an elongated space enclosed by many air sacs called alveoli which are surrounded by blood capillaries. Present there as well, are Alveolar Macrophages , they ingest any microbes that reach the alveoli.

    The Pulmonary Alveoli are microscopic , which means they can only be seen through a microscope, membranous air sacs within the lungs. They are units of respiration and the site of gas exchange between the respiratory and circulatory systems. First the oxygen must diffuse from the alveolus into the capillaries.

    It is able to do this because the capillaries are permeable to oxygen. The other oxygen will bind to red blood cells. The red blood cells contain hemoglobin that carries oxygen. Blood with hemoglobin is able to transport 26 times more oxygen than plasma without hemoglobin. Our bodies would have to work much harder pumping more blood to supply our cells with oxygen without the help of hemoglobin. Once it diffuses by osmosis it combines with the hemoglobin to form oxyhemoglobin. Now the blood carrying oxygen is pumped through the heart to the rest of the body.

    Oxygen will travel in the blood into arteries, arterioles, and eventually capillaries where it will be very close to body cells. Now with different conditions in temperature and pH warmer and more acidic than in the lungs , and with pressure being exerted on the cells, the hemoglobin will give up the oxygen where it will diffuse to the cells to be used for cellular respiration, also called aerobic respiration. Cellular respiration is the process of moving energy from one chemical form glucose into another ATP , since all cells use ATP for all metabolic reactions. It is in the mitochondria of the cells where oxygen is actually consumed and carbon dioxide produced.

    Oxygen is produced as it combines with hydrogen ions to form water at the end of the electron transport chain see chapter on cells. As cells take apart the carbon molecules from glucose, these get released as carbon dioxide. Each body cell releases carbon dioxide into nearby capillaries by diffusion, because the level of carbon dioxide is higher in the body cells than in the blood. In the capillaries, some of the carbon dioxide is dissolved in plasma and some is taken by the hemoglobin, but most enters the red blood cells where it binds with water to form carbonic acid.

    It travels to the capillaries surrounding the lung where a water molecule leaves, causing it to turn back into carbon dioxide. It then enters the lungs where it is exhaled into the atmosphere. The normal volume moved in or out of the lungs during quiet breathing is called tidal volume. When we are in a relaxed state, only a small amount of air is brought in and out, about mL.

    You can increase both the amount you inhale, and the amount you exhale, by breathing deeply. Breathing in very deeply is Inspiratory Reserve Volume and can increase lung volume by mL, which is quite a bit more than the tidal volume of mL. We can also increase expiration by contracting our thoracic and abdominal muscles. This is called expiratory reserve volume and is about ml of air. Vital capacity is the total of tidal, inspiratory reserve and expiratory reserve volumes; it is called vital capacity because it is vital for life, and the more air you can move, the better off you are.

    There are a number of illnesses that we will discuss later in the chapter that decrease vital capacity. Vital Capacity can vary a little depending on how much we can increase inspiration by expanding our chest and lungs. Some air that we breathe never even reaches the lungs! Instead it fills our nasal cavities, trachea, bronchi, and bronchioles. These passages aren't used in gas exchange so they are considered to be dead air space. To make sure that the inhaled air gets to the lungs, we need to breathe slowly and deeply.

    Even when we exhale deeply some air is still in the lungs, about ml and is called residual volume. This air isn't useful for gas exchange. There are certain types of diseases of the lung where residual volume builds up because the person cannot fully empty the lungs. This means that the vital capacity is also reduced because their lungs are filled with useless air.

    There are two pathways of motor neuron stimulation of the respiratory muscles. The first is the control of voluntary breathing by the cerebral cortex. The second is involuntary breathing controlled by the medulla oblongata. There are chemoreceptors in the aorta, the carotid body of carotid arteries, and in the medulla oblongata of the brainstem that are sensitive to pH.

    As carbon dioxide levels increase there is a buildup of carbonic acid, which releases hydrogen ions and lowers pH. Thus, the chemoreceptors do not respond to changes in oxygen levels which actually change much more slowly , but to pH, which is dependent upon plasma carbon dioxide levels.

    Anatomy and Physiology of Respiratory System

    In other words, CO2 is the driving force for breathing. The receptors in the aorta and the carotid sinus initiate a reflex that immediately stimulates breathing rate and the receptors in the medulla stimulate a sustained increase in breathing until blood pH returns to normal. This response can be experienced by running a meter dash. During this exertion or any other sustained exercise your muscle cells must metabolize ATP at a much faster rate than usual, and thus will produce much higher quantities of CO2. The blood pH drops as CO2 levels increase, and you will involuntarily increase breathing rate very soon after beginning the sprint.

    You will continue to breathe heavily after the race, thus expelling more carbon dioxide, until pH has returned to normal. Metabolic acidosis therefore is acutely corrected by respiratory compensation hyperventilation. It is vital to our survival. Normal blood pH is set at 7. If the pH of our blood drops below 7. Blood pH levels below 6. Another wonder of our amazing bodies is the ability to cope with every pH change — large or small. There are three factors in this process: the lungs, the kidneys and buffers. So what exactly is pH? The most important buffer we have in our bodies is a mixture of carbon dioxide CO2 and bicarbonate ion HCO3.

    In a nutshell, blood pH is determined by a balance between bicarbonate and carbon dioxide. Bicarbonate Buffer System. With this important system our bodies maintain homeostasis. The CO2 level is increased when hypoventilation or slow breathing occurs, such as if you have emphysema or pneumonia. Bicarbonate will be lowered by ketoacidosis, a condition caused by excess fat metabolism diabetes mellitus. This condition is less common than acidosis. CO2 can be lowered by hyperventilation. So, in summary, if you are going into respiratory acidosis the above equation will move to the right.

    In contrast, if you are going into respiratory alkalosis the equation will move to the left. So the body will try to breathe less to release HCO3. You can think of it like a leak in a pipe: where ever there is a leak, the body will "fill the hole". The environment of the lung is very moist, which makes it a hospitable environment for bacteria.

    Many respiratory illnesses are the result of bacterial or viral infection of the lungs. Because we are constantly being exposed to harmful bacteria and viruses in our environment, our respiratory health can be adversely affected.

    human respiratory system | Description, Parts, Function, & Facts |

    There are a number of illnesses and diseases that can cause problems with breathing. Some are simple infections, and others are disorders that can be quite serious. Carbon Monoxide Poisoning : caused when carbon monoxide binds to hemoglobin in place of oxygen. Carbon monoxide binds much tighter, without releasing, causing the hemoglobin to become unavailable to oxygen. The result can be fatal in a very short amount of time. Pulmonary Embolism: blockage of the pulmonary artery or one of its branches by a blood clot, fat, air or clumped tumor cells.

    By far the most common form of pulmonary embolism is a thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. The upper respiratory tract consists of our nasal cavities, pharynx, and larynx. Upper respiratory infections URI can spread from our nasal cavities to our sinuses, ears, and larynx. Sometimes a viral infection can lead to what is called a secondary bacterial infection.

    Antibiotics aren't used to treat viral infections, but are successful in treating most bacterial infections, including strep throat. The symptoms of strep throat can be a high fever, severe sore throat, white patches on a dark red throat, and stomach ache. Lower respiratory tract disorders include infections, restrictive pulmonary disorders, obstructive pulmonary disorders, and lung cancer.

    At birth the pressure needed to expand the lungs requires high inspiratory pressure. In the case of deficiency of surfactant the lungs will collapse between breaths, this makes the infant work hard and each breath is as hard as the first breath. If this goes on further the pulmonary capillary membranes become more permeable, letting in fibrin rich fluids between the alveolar spaces and in turn forms a hyaline membrane. The hyaline membrane is a barrier to gas exchange, this hyaline membrane then causes hypoxemia and carbon dioxide retention that in turn will further impair surfactant production.

    Type two alveolar cells produce surfactant and do not develop until the 25th to the 28th week of gestation, in this, respiratory distress syndrome is one of the most common respiratory disease in premature infants. Furthermore, surfactant deficiency and pulmonary immaturity together leads to alveolar collapse. Predisposing factors that contribute to poorly functioning type II alveolar cells in a premature baby are if the child is a preterm male, white infants, infants of mothers with diabetes, precipitous deliveries, cesarean section performed before the 38th week of gestation.

    Surfactant synthesis is influenced by hormones, this ranges form insulin and cortisol. Insulin inhibits surfactant production, explaining why infants of mothers with diabetes type 1 are at risk of development of respiratory distress syndrome. Cortisol can speed up maturation of type II cells and therefore production of surfactant. Finally, in the baby delivered by cesarean section are at greater risk of developing respiratory distress syndrome because the reduction of cortisol produced because the lack of stress that happens during vaginal delivery, hence cortisol increases in high stress and helps in the maturation of type II cells of the alveoli that cause surfactant.

    Today to prevent respiratory distress syndrome are animal sources and synthetic surfactants, and administrated through the airways by an endotracheal tube and the surfactant is suspended in a saline solution. Treatment is initiated post birth and in infants who are at high risk for respiratory distress syndrome. Sleep apnea or sleep apnoea is a sleep disorder characterized by pauses in breathing during sleep. These episodes, called apneas literally, "without breath" , each last long enough so one or more breaths are missed, and occur repeatedly throughout sleep.

    The standard definition of any apneic event includes a minimum 10 second interval between breaths, with either a neurological arousal 3-second or greater shift in EEG frequency, measured at C3, C4, O1, or O2 , or a blood oxygen desaturation of percent or greater, or both arousal and desaturation. Sleep apnea is diagnosed with an overnight sleep test called polysomnogram. This machine forces the wearer to breathe a constant number of breaths per minute.

    CPAP , or continuous positive airway pressure, in which a controlled air compressor generates an airstream at a constant pressure.


    This pressure is prescribed by the patient's physician, based on an overnight test or titration. Nutrition is particularly important for ventilator-dependent patient. When metabolizing macronutrients carbon dioxide and water are produced. The respiratory quotient RQ is a ratio of produced carbon dioxide to amount consumed. Carbohydrates metabolism produces the most amount of carbon dioxide so they have the highest RQ.

    Fats produce the least amount of carbon dioxide along with proteins. Protein has a slightly higher RQ ratio. It is recommended that this kind of patient not exceed a 1.