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GlossarySuccess Chemistry Staff

Alve o le [von * alveoli -], pulmonary alveoli , gas-filled end chamber of the lungs , site of diffusion-based gas exchange ( alveolar air , blood gases ) with the blood(release of carbon dioxide [CO 2 ] to the respiratory air and absorption of oxygen [O 2 ] from the respiratory air [ respiratory gas transport ]). The typical alveolus of man has a diameter of approx. 0.2 mm. It is surrounded by a dense blood-perfused capillary network. The inner surface of the alveolus is lined with a surfactant layer (surfactant layer, surfactant factor ). This film, a secretion of the pneumocytes, consisting of characteristic proteins, phospholipids and carbohydrates, lowers the alveolar surface tension ( interfaces , capillarity ) between the lung epithelium and the gas-filled interior, preventing the alveoli from collapsing on exhalation and sticking together the epithelia. Venous blood reaches the capillaries of the alveolus from the right half of the heart ( heart) arising pulmonary artery (arteria pulmonalis) and their branches.

Alveoli in lungs - blood saturating by oxygen

The guest exchange in the lungs takes place via the pulmonary circulation in the approximately 300 million alveoli.

The oxygen volume fraction in the breathing air is 20.9 percent and the carbon dioxide content is 0.038 percent. The vast majority - 78.1 percent - is nitrogen, which is not usable for breathing. Humans need to breathe about 26 liters of air to extract one liter of oxygen.

Carbon dioxide-rich and oxygen-poor blood that comes from the cells of the body is pumped from the right ventricle to the lungs. Similar to the ever-finer air conduction system, the blood vessels leading to the lungs continue to ramify. Around the alveoli, a network of the finest blood vessels is formed, the so-called capillary network. Due to the strong branching of the blood vessels in the lungs, the blood becomes slower and the walls of the blood vessels become thinner and thinner.

The wall of the alveoli - the alveolar-capillary membrane - is also very thin (about one micrometer). The respiratory gases, oxygen (O 2)and carbon dioxide (CO 2), can therefore easily pass from one side to the other side of the air sac (diffusion).

Arrived at the alveoli, the carbon dioxide migrates from the blood into the air in the lungs and oxygen is taken from the breath into the blood. The now oxygen-rich blood is pumped back to the heart and distributed from the left ventricle in the rest of the body.

The area formed jointly by alveoli and capillaries is called the respiratory surface. In humans, this is about 100 to 140 square meters in size.

In physical rest, humans need 0.3 liters of oxygen per minute and exhale about 0.25 liters of carbon dioxide per minute. In order to achieve this, he transports about seven liters of air per minute through his lungs.

If the blood pressure in the pulmonary circulation, also known as the small circulation, is permanently increased, this is called pulmonary hypertension.

The typical partial pressures for oxygen are 5.3 kPa (= 40 mmHg) and carbon dioxide 6.1 kPa (= 46 mmHg). By breathing on the other hand (ventilation of the lungs) may be in the alveolar gas partial pressures of 13.3 kPa (= 100 mmHg, 14 vol.%) O 2 and 5.3 kPa (= 40 mmHg, 5.6 vol.%) CO 2 maintained. The difference of the partial pressure differences is the cause of the gas exchange by diffusion (Fick's law). During capillary passage, blood enters into close contact with the alveolar gas. As diffusion resistances must be overcome: the alveolar epithelium, the connective tissue, the capillary endothelium, the blood plasma and the erythrocyte membrane ( erythrocytes ). The mentioned partial structures of the alveolar-capillary membrane are not thicker than 0.5-1 μm. The capillary passage takes about 0.3 s.

This contact time is sufficient to virtually equalize the gas partial pressures in the blood with those of the alveolar gas. The oxygen-enriched blood leaves the capillaries via the vascular system of the pulmonary veins and then reaches the left half of the heart, which pumps it back into the body. The perfusion the lung is about the same as the heartbeat volume (5 l / min in a healthy adult). Normally, less than 2% of the blood reaches the left ventricle bypassing the alveoli.

The total oxygen intake of an adult at rest is about 300 ml / min and increases under load. The efficiency of alveolar gas exchange depends on: 1) the perfusion of the lung with blood, 2) the alveolar surface, 3) the diffusion path, and 4) the alveolar ventilation. Physiological regulatory mechanisms ( control ) set these variables so that the oxygen loading of the blood remains constant regardless of the load ( homeostasis ). All four parameters can be negatively affected by pathological processes in the lungs. respiratory system, Drilling effect , bronchi ; Respiratory system I . 2) Teeth , thecodont . 3) For belemnites a conical cavity in the front end of the rostrum, in which Phragmocone and Velamen triplex are stuck.



The respiratory organ of the human, the lung, sits in the thorax and is formed of two lungs. Due to the position of the heart on the left side of the body, the left lung is slightly smaller than the right one.

Each lung is divided into furrows by furrows. On the right side, there are three, on the left two lung lobes per lung. The individual lung lobes can be subdivided into functional areas, the so-called lung segments. Below the lungs sit the diaphragm, which separates the chest cavity from the abdomen.

Around both lungs is the so-called lung pleura (pleura visceral), a protective, thin skin. Together with the pleura (pleura parietalis) that sits opposite the inside of the thorax and the diaphragm, the lung pelt makes sure that the breathing works. The fluid-filled space between the pleura and lung is called the pleural cavity or pleural space.
For more on the function of breathing, see the chapter "Respiratory mechanics".

The general structure of the lungs is reminiscent of an inverted tree. Its trunk is formed by the trachea, which divides into the two main bronchi, which in turn enter the two lungs. The main bronchi, in turn, continue to bifurcate to bronchi and bronchioles, small branches that end in the alveoli.

Structure of the bronchi

Bronchi and bronchioles form a tube system in the lungs, which serves as a guidance system for the air. The trachea first divides into two main bronchi, which enter the two lungs. In the further course of the tube system, the main bronchi continue to bifurcate to bronchi and bronchioles, ever decreasing branches, which eventually end in the alveoli.

In contrast to the alveoli, there is no gas exchange in the tube system of the bronchi and bronchioles.

Bronchi are larger in diameter than bronchioles

This because their walls are reinforced by cartilage clasps.

Around the tubes of bronchi and bronchioles pull muscle strands of smooth muscle. These are controlled by parts of our autonomic nervous system, the sympathetic and the parasympathetic. During active phases, such as during sports, the sympathetic nerve ensures that the smooth muscles relax and the bronchi allow as much air as possible.

The parasympathetic nervous system, on the other hand, is responsible for allowing the body to enter a resting phase and to recover. It stimulates the contraction, that is, the contraction of the smooth muscles, thereby narrowing the diameter of the bronchi. Normally, this should help support breathing. But it can also lead to cramping of these muscles, such as in an asthma attack.

The inner walls of the bronchi and bronchioles are lined with a mucous-producing skin. Learn more about the function of mucus in the lungs.

Structure of the alveoli (alveoli)

The bronchioles end in humans in about 300 million small alveoli, where the gas exchange takes place. On the inner wall of the alveoli, there is a liquid film which tends to reduce its surface area. This surface tension is reduced by surface-active substances - so-called surfactants, especially lecithin derivatives.

The wall of the alveoli - the alveolar-capillary membrane - is very thin (about one micrometer) and provides little resistance to the oxygen (O 2 ) and carbon dioxide (CO 2) breathing gases, allowing the gases to pass easily from one side to the other (Diffusion).


Approximately 300 million alveoli, whose respiratory surface is approximately 100 to 140 square meters, provide for the oxygen supply of our body.

On the side of the alveoli, which is remote from the respiratory air, a network of finest blood vessels, a so-called capillary network, is deposited. The area formed by the alveoli and capillaries together is called the respiratory surface because only here does the gas exchange takes place in the lungs. In humans, about 300 million alveoli form a respiratory surface of about 100 to 140 square meters. So the body can be optimally supplied with oxygen. More in the chapter "Gas exchange".

Between the alveoli, there is connective tissue. If its cells proliferate excessively, pulmonary fibrosis develops.

The Basics on Lung health

UncategorizedSuccess Chemistry Staff

The Human Respiratory Organ

The lung - the human respiratory organ: built up out of thousands of air-filled bubbles, the lungs provide a surface about the size of a tennis court for oxygen uptake. But our respiratory system has even more tasks: it releases carbon dioxide, controls the pH of the blood and even has its own blood circulation. A healthy lung has enormous reserve capacity that can be mobilized during exercise.

The human lung anatomically consists of a left and a right lung . Together with the heart they fill the chest ( thorax ). Both the thorax and the lungs are covered by a sheet of the pleura ( pleura ). The name petticoat is misleading, as it is not a hairy coat, but two very thin but extremely firm layers of skin, between which a fine layer of fluid allows the mobility between the lungs and chest when breathing.

The left lung has to divide its thoracic half with the heart and is therefore slightly smaller than the right one. The lung tissue is very light and soft, it would float in the water. Under the microscope, the structure of the lung can be seen: three structures characterize their structure: alveoli , blood vessels and bronchi. 

The alveoli allow oxygen uptake

The alveoli are the place of gas exchange. They are air-filled bubbles with a diameter of one third of a millimeter, but together they offer a total surface of 50 to 100 square meters. This is covered by a stabilizing liquid, the surfactant, to German "humidifier". The surfactant maintains the wall tension of the alveoli comparable to a bubble, without it the bubbles would collapse and shrink the lungs into a small solid chunk. 

The wall of the alveoli is so thin that both oxygen, and carbon dioxide can pass through them. In some lung diseases, thickening of the alveolar walls and thus disorders of the oxygen supply occur. Smoking also leads to inflammatory damage to the alveoli. 

Vessels take in the oxygen

From the alveoli, the oxygen passes into the blood vessels of the pulmonary circulation. In turn, carbon dioxide migrates, it is produced by the consumption of oxygen in muscles and organs, back into the alveoli. The pulmonary circulation is also called "small circulation" and serves only the admission and release of the blood gases (oxygen and carbon dioxide) in the lung. The heart pumps "used up", oxygen-poor blood into the lungs.

There, the blood is enriched with oxygen and flows back to the heart, where it is ready to supply the body again. An interesting detail is that the lungs, in addition to small circuit for gas exchange, like any other organ also has vessels to their own supply. 

Bronchitis bring the air into the lungs

In order for the gas exchange to begin at all, about 8 liters of fresh air per minute must be inhaled and exhaled into the lungs at rest. The path of the air leads through the mouth or nose through the throat and larynx into the trachea. It divides into the two main bronchi that supply the left and right lungs and branch out into a framework of ever-smaller bronchi.

After 7 to 8 branches the air is at the target: the alveolus. The wall of the bronchi is also perfectly adapted to its tasks: it carries a so-called ciliated epithelium , which means that the lining cells carry tiny, movable brush hairs. The small brushes keep beating 'up', towards the larynx and mouth. 

Their task is to intercept inhaled dust particles in front of the alveoli and to transport them back to the larynx on a thin layer of mucus like a conveyor belt. If we clear our throat in the morning and some secretions cough up, the work of the flicker hair becomes recognizable. Many diseases, ranging from influenza infections, are associated with high mucus production. The cilia suffer especially from smoking: on the one hand more dirt particles in the bronchial tubes, which must be laboriously removed, on the other hand, the cimmering cells are gradually based on the poisons of tobacco smoke. Smokers know the problem: The lungs are chronically verschleimt, but a coughing will not succeed because the mucus can not solve. 

Arteries and veins carry different blood gases

All living things need oxygen, which is 'burned' during metabolic processes. The waste product carbon dioxide is produced. The cells of the human body depend on the supply of oxygen-rich blood through the arteries. The chemical binding of oxygen to the red blood cells changes the color of the blood: arterial blood is bright red. When blood is needed for laboratory testing, the doctor usually removes it from a vein. Venous blood is low in oxygen and dark red or bluish. The veins bring it back from consumers to the heart and lungs. It is important for the pulmonologist to determine the arterial oxygen concentration. For this purpose, he must take blood from an artery in the area of the wrist or the groin.

Carbon dioxide is produced in all burns, in the coal furnace, in the gasoline engine or in metabolism . But this gas is also an important part of the acidity of our body. Chemically, carbon dioxide is the anion of carbon dioxide, and the lung can control the pH of the blood, which is how acid or alkaline a liquid is by releasing or retaining carbon dioxide. If you breathe improperly strong and fast, you release too much carbon dioxide. The result is an increase in the pH in the blood, you become dizzy and sometimes unconscious. 

The lung volume is measured in spirometry.

With a strong breath, healthy people can inhale and exhale about five and a half liters of air. This value is called Vital capacity and is slightly higher in men than in women. Basically, there is a setpoint dependent on age, gender, height and weight for each person. Lung diseases can significantly reduce the vital capacity. It should be noted that never all air present in the lungs can be exhaled - a remainder of a little more than a liter always remains as a residual volume. 

Vital capacity and residual volume add up the total lung capacity . Not only the fixed volumes, but also the respiratory currents are important measurements in spirometry. Peak Flow and Forced Expiratory Volume ( FEV1) give the pulmonary doctor information about the ability of a person to breathe in and out of an efficient manner. The respiratory limit value describes the maximum ventilated air volume per minute, based on 30 breaths per minute men should reach 110 liters and women 100 liters. 

Datasheet of the lung

Men women Total capacity 7.0 liters 6.2 liters Vital capacity 5.6 liters 5.0 liters Residual 1.4 liters 1.2 liters FEV1 4.5 liters 4.0 liters

The respiratory muscles

Nobody has to think to breathe. Without our conscious perception, the respiratory muscles are in constant motion. A separate respiratory center in the brainstem controls the motor function of the muscles involved in breathing. At rest, the diaphragm , a flat muscle plate that also acts as a border between the rib cage and the abdominal cavity, provides the bulk of the work of breathing. As it contracts, the thoracic cavity becomes larger and air is inhaled into the lungs. The exhale takes place at rest without muscle work - the diaphragmatic tension decreases and the breathing air can escape.

The muscle fibers between the bony ribs are also involved in the respiratory movements. For greater effort, such as in sports, but also when illnesses make breathing difficult, the respiratory aid muscles are used. Muscles of the abdominal wall and neck are especially helpful in increased exhalation. Proper breathing technique is very important for lung patients. Many people breathe 'wrong', they lift the shoulders and chest excessively when inhaling deeply, thus reducing their lung capacity. Proper breathing involves the gut: a good example is the observation of opera and concert singers.

They achieve their often unbelievably long breath by skillful breathing technique, with each breath a strong movement of the belly can be recognized, while the shoulders remain calm. Respiratory training for the sick is offered by the physiotherapy , in some cases even with singing exercises that make the learning success for everyone recognizable and audible.

Oxygen means life

Oxygen, called by the chemist O2, is a colorless and odorless gas, it accounts for about 26% of our breathable air. Most of the remainder is nitrogen and the rare noble gases and is not involved in combustion processes. Only a very small proportion, which is growing due to the increase in industrial, household and traffic burns, is carbon dioxide. Pure one hundred percent oxygen is dangerous and harmful to living things.

Its presence causes otherwise moderate burns to explode. Many people with pulmonary disease, on the other hand, depend on a moderate accumulation of oxygen in their breathing air and carry their own breathing masks and gas bottles with them. All living beings, from unicellular organisms to humans and animals, depend on oxygen for their metabolism. Natural history, the ability to absorb oxygen very much limits the size and development of living things.

Only animals with specialized respiratory organs such as gills or lungs can become tall and competitive. Insects do not have powerful respiratory organs, they draw their oxygen through a network of cavities that grows through their bodies. That's one reason why these otherwise successful creatures always stay so small. If they had lungs like humans, we would have to reckon with man-sized ants like from a science-fiction movie.