Breathing - Wikipedia
Alveoli are the air sacs at the end of the respiratory tree of the lungs an are vital to respiration. Learn about their structure and common diseases. Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move Our respiratory system includes structures involved in our breathing. May 5, The Respiratory System - Structure And Function The structure of the lungs includes the bronchial tree – air tubes Source: Wikipedia.
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 lungsand 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 ATPsince 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. Lung Capacity[ edit ] 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. Stimulation of Breathing[ edit ] There are two pathways of motor neuron stimulation of the respiratory muscles.
The first is the control of voluntary breathing by the cerebral cortex.
Lung - Wikipedia
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 slowlybut to pH, which is dependent upon plasma carbon dioxide levels.
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: 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. 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: Problems Associated With the Respiratory Tract and Breathing[ edit ] 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. 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 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. 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.
Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death. Treatment, usually, is with anticoagulant medication. Upper Respiratory Tract Infections[ edit ] 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. Sinusitis An infection of the cranial sinuses is called sinusitis. This "sinus infection" develops when nasal congestion blocks off the tiny openings that lead to the sinuses.
Successful treatment depends on restoring the proper drainage of the sinuses. Taking a hot shower or sleeping upright can be very helpful. Otherwise, using a spray decongestant or sometimes a prescribed antibiotic will be necessary. Otitis Media Otitis media in an infection of the middle ear.
Even though the middle ear is not part of the respiratory tract, it is discussed here because it is often a complication seen in children who has a nasal infection. The infection can be spread by way of the 'auditory Eustachian tube that leads form the nasopharynx to the middle ear. The main symptom is usually pain.
Sometimes though, vertigo, hearing loss, and dizziness may be present. Antibiotics can be prescribed and tubes are placed in the eardrum to prevent the buildup of pressure in the middle ear and the possibility of hearing loss.
Tonsillitis Tonsillitis occurs when the tonsils become swollen and inflamed. The tonsils located in the posterior wall of the nasopharynx are often referred to as adenoids. If you suffer from tonsillitis frequently and breathing becomes difficult, they can be removed surgically in a procedure called a tonsillectomy.
Laryngitis An infection of the larynx is called laryngitis. It is accompanied by hoarseness and being unable to speak in an audible voice. Usually, laryngitis disappears with treatment of the URI. Persistent hoarseness without a URI is a warning sign of cancer, and should be checked into by your physician. Lower Respiratory Tract Disorders[ edit ] Lower respiratory tract disorders include infections, restrictive pulmonary disorders, obstructive pulmonary disorders, and lung cancer.
Lower Respiratory Infections[ edit ] Acute bronchitis An infection that is located in the primary and secondary bronchi is called bronchitis. Most of the time, it is preceded by a viral URI that led to a secondary bacterial infection. This ensures that equilibration of the partial pressures of the gases in the two compartments is very efficient and occurs very quickly. 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 CO2 and, to a lesser extent, a fall in the arterial partial pressure of O2, 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: 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 bodiesas 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 capillariesand 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 hyperventilationrespiration will be slowed down or halted until the alveolar partial pressure of carbon dioxide has returned to 5. The oxygen is held on the hemoglobin by four ferrous iron -containing heme groups per hemoglobin molecule. The reaction is therefore catalyzed by carbonic anhydrasean enzyme inside the red blood cells. The total concentration of carbon dioxide in the form of bicarbonate ions, dissolved CO2, and carbamino groups in arterial blood i.
This information determines the average rate of ventilation of the alveoli of the lungsto 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. Responses to low atmospheric pressures 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 proportionallycausing 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. Everestor 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.
Breathtaking Lungs: Their Function and Anatomy
Saturated water vapor pressure is dependent only on temperature. In dry air the partial pressure of O2 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: 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. 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 homeostatwhich 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. 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 baseswhich 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  into the blood.
In other words, at the same arterial partial pressure of O2, 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. These responses cause air to be expelled forcefully from the trachea or noserespectively. 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 IgAcollectinsdefensins and other peptides and proteasesreactive oxygen speciesand 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.
Surfactant immune function is primarily attributed to two proteins: 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.
Prevention of alveolar collapse Main article: Pulmonary surfactant The lungs make a surfactanta 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 compliantor 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.