Everything about Respiratory totally explained
In
humans and other
mammals, the
respiratory system consists of the airways, the
lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the
alveolar system of the lungs, molecules of
oxygen and
carbon dioxide are passively exchanged, by
diffusion, between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation.
The system also helps to maintain the acid-base balance of the body through the efficient removal of
carbon dioxide from the blood.
Anatomy
In humans and other animals, the respiratory system can be conveniently subdivided into an
upper respiratory tract and
lower respiratory tract, trachea and lungs, or into the conducting zone (for gas transport, anywhere from atmosphere to alveoli) and the respiratory zone (the alveolated region where gas exchange occurs). The respiratory zone also contains the transitional zone.
Air moves through the body in the following order
Upper respiratory tract/conducting zone
The conducting zone begins with the
nares (nostrils) of the
nose, which open into the
nasopharynx (nasal cavity). The primary functions of the nasal passages are to: 1) filter, 2) warm, 3) moisten, and 4) provide resonance in speech. The nasopharynx opens into the
oropharynx (behind the oral cavity). The oropharynx leads to the
laryngopharynx, and empties into the
larynx (voicebox), which contains the
vocal cords, passing through the
glottis, connecting to the
trachea (wind pipe).
Ventilation
Ventilation of the lungs is carried out by the muscles of respiration.
Control
Ventilation occurs under the control of the autonomic nervous system from parts of the
brain stem, the
medulla oblongata and the
pons. This area of the brain forms the respiration regulatory center, a series of interconnected brain cells within the lower and middle brain stem which coordinate respiratory movements. The sections are the
pneumotaxic center, the
apneustic center, and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped and/or shaken violently. The result can be death due to "
shaken baby syndrome."
Inhalation is initiated by the
diaphragm and supported by the
external intercostal muscles. Normal resting respirations are 10 to 18 breaths per minute. Its time period is 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure,
accessory muscles of respiration are recruited for support. These consist of
sternocleidomastoid,
platysma, and the
strap muscles of the neck.
Inhalation is driven primarily by the
diaphragm. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume, which in turn causes a decrease in intrathoracic pressure. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
During forced inhalation, as when taking a deep breath, the
external intercostal muscles and accessory muscles further expand the thoracic cavity.
Exhalation
Exhalation is generally a passive process, however active or
forced exhalation is achieved by the
abdominal and the
internal intercostal muscles. During this process air is forced or
exhaled out.
The lungs have a natural elasticity; as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.
During forced exhalation, as when blowing out a candle, expiratory muscles including the
abdominal muscles and
internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.
Circulation
The right side of the heart pumps blood from the
right ventricle through the
pulmonary semilunar valve into the
pulmonary trunk. The trunk branches into right and left
pulmonary arteries to the
pulmonary blood vessels. The vessels generally accompany the
airways and also undergo numerous branchings. Once the gas exchange process is complete in the pulmonary capillaries, blood is returned to the left side of the heart through four
pulmonary veins, two from each side. The
pulmonary circulation has a very low resistance, due to the short distance within the lungs, compared to the
systemic circulation, and for this reason,
all the pressures within the pulmonary blood vessels are normally low as compared to the pressure of the systemic circulation loop.
Virtually all the body's blood travels through the lungs every minute. The lungs add and remove many chemical messengers from the blood as it flows through pulmonary capillary bed . The fine capillaries also trap blood clots that have formed in systemic veins.
Gas exchange
The major function of the respiratory system is
gas exchange. As gas exchange occurs, the acid-base balance of the body is maintained as part of
homeostasis. If proper ventilation isn't maintained two opposing conditions could occur: 1)
respiratory acidosis, a life threatening condition, and 2)
respiratory alkalosis.
Upon inhalation, gas exchange occurs at the
alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres), and are permeable to gases. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange.
Development
The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system is to the under-developed lungs. This is due to the incomplete development of the
alveoli type II cells in the lungs, necessary for the production of
surfactant. The infant lungs don't function due to collapse of alveoli caused by surface tension of water remaining in the lungs, which in normal cases would be prohibited by the presence of surfactant. This condition may be avoided by giving the mother a series of steroid shots in the final week prior to delivery, which will have weard the development of type II alveolar cells.
Role in communication
The movement of gas through the larynx, pharynx and mouth allows
humans to speak, or
phonate. Because of this, gas movement is extremely vital for communication purposes.
Conditions of the respiratory system
Disorders of the respiratory system can be classified into four general areas:
Obstructive conditions (for example, emphysema, bronchitis, asthma attacks)
Restrictive conditions (for example, fibrosis, sarcoidosis, alveolar damage, pleural effusion)
Vascular diseases (for example, pulmonary edema, pulmonary embolism, pulmonary hypertension)
Infectious, environmental and other "diseases" (for example, pneumonia, tuberculosis, asbestosis, particulate pollutants) coughing is of major importance, as it's the body's main method to remove dust, mucus, saliva, and other debris from the lungs. Inability to cough can lead to infection. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.
The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechani to defend itself and prevent pathogens from entering the body.
Disorders of the respiratory system are usually treated internally by a pulmonologist or Respiratory Physician.
Gas exchange in plants
Plants use carbon dioxide gas in the process of photosynthesis, and then exhale oxygen gas, a waste product of photosynthesis. However, plants also sometimes respire as humans do, using oxygen and producing carbon dioxide.
Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes on the undersides of their leaves known as stomata(sing:stoma). However, most plants require little air. Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly aerobic activities, and thus have no need of these living cells.
Further Information
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