Respiratory system
Breathing
Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and removes carbon dioxide. Another important process involves the movement of blood by the circulatory system. Gas occurs in the pulmonary alveoli by passive diffusion of gases between the alveolar gas and the blood in lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system). The medical term for normal relaxed breathing is eupnoea. In addition to removing carbon dioxide, breathing results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.
Mechanics:
In mammals, breathing in, or inhaling, is usually a good movement, with the contraction of the diaphragm muscle. This is known as negative pressure breathing. Normally, the diaphragm's relaxed position recoils (decreasing the thoracic volume) whereas in the contracted position it is pulled downwards (increasing the thoracic volume). This process works in conjunction with the intercostals muscles connected to the rib cage. Contraction of these muscles lifts the rib cage, thus aiding in increasing the thoracic volume. Relaxation of the diaphragm compresses the lungs, effectively decreasing their volume while increasing the pressure inside them. The intercostals muscles simultaneously relax, further decreasing the volume of the lungs.
With a pathway to the mouth or nose clear, this increased pressure forces air out of the lungs. Conversely, contraction of the diaphragm increases the volume of the (partially empty) lungs, decreasing the pressure inside, which creates a partial vacuum. Environmental air then follows its pressure gradient down to fill the lungs.
In amphibians, the process used is positive pressure breathing. Muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils (which uses the same mechanics - pressure, volume, and diffusion - as a mammalian lung). With the nostrils and mouth closed, the floor of the oral cavity is forced up, which forces air down the trachea into the lungs.
At rest, breathing out, or exhaling, is a combination of passive and active processes powered by the elastic recoil of the alveoli, similar to a deflating balloon, and the contraction of the muscular body wall. The following organs are used in respiration: the mouth; the nose and nostrils; the pharynx; the larynx; the trachea; the bronchi and bronchioles; the lungs; the diaphragm; and the terminal branches of the respiratory tree, such as the alveoli.
Mechanics:
In mammals, breathing in, or inhaling, is usually a good movement, with the contraction of the diaphragm muscle. This is known as negative pressure breathing. Normally, the diaphragm's relaxed position recoils (decreasing the thoracic volume) whereas in the contracted position it is pulled downwards (increasing the thoracic volume). This process works in conjunction with the intercostals muscles connected to the rib cage. Contraction of these muscles lifts the rib cage, thus aiding in increasing the thoracic volume. Relaxation of the diaphragm compresses the lungs, effectively decreasing their volume while increasing the pressure inside them. The intercostals muscles simultaneously relax, further decreasing the volume of the lungs.
With a pathway to the mouth or nose clear, this increased pressure forces air out of the lungs. Conversely, contraction of the diaphragm increases the volume of the (partially empty) lungs, decreasing the pressure inside, which creates a partial vacuum. Environmental air then follows its pressure gradient down to fill the lungs.
In amphibians, the process used is positive pressure breathing. Muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils (which uses the same mechanics - pressure, volume, and diffusion - as a mammalian lung). With the nostrils and mouth closed, the floor of the oral cavity is forced up, which forces air down the trachea into the lungs.
At rest, breathing out, or exhaling, is a combination of passive and active processes powered by the elastic recoil of the alveoli, similar to a deflating balloon, and the contraction of the muscular body wall. The following organs are used in respiration: the mouth; the nose and nostrils; the pharynx; the larynx; the trachea; the bronchi and bronchioles; the lungs; the diaphragm; and the terminal branches of the respiratory tree, such as the alveoli.
Control of breathing:
Breathing is one of the few bodily functions which, within limits, can be controlled both consciously and unconsciously.
Conscious control:
Conscious control of breathing is common in many forms of meditation, specifically forms of yoga for example pranayama unlike anapana which is only awareness of breath. In swimming, cardio fitness, speech or vocal training, one learns to discipline one's breathing, initially consciously but later sub-consciously, for purposes other than life support. Human speech is also dependent on conscious breath control. Also breathing control is used in Buteyko method.
Unconscious control:
Unconsciously, breathing is controlled by specialized centers in the brainstem, which automatically regulate the rate and depth of breathing depending on the body’s needs at any time. When carbon dioxide levels increase in the blood, it reacts with the water in blood, producing carbonic acid. Lactic acid produced by anaerobic respiration during exercise also lowers pH. The drop in the blood's pH stimulates chemoreceptor’s in the carotid and aortic bodies in the blood system to send nerve impulses to the respiration centre in the medulla oblongata and pons in the brain. These, in turn send nerve impulses through the phrenicand thoracic nerves to the diaphragm.
Examples
For instance, while exercising, the level of carbon dioxide in the blood increases due to increased cellular respiration by the muscles, which activates carotid and aortic bodies and the respiration center, which ultimately cause a higher rate of respiration.
During rest, the level of carbon dioxide is lower, so breathing rate is lower. This ensures an appropriate amount of oxygen is delivered to the muscles and other organs. It is important to reiterate that it is the buildup of carbon dioxide making the blood acidic that elicits the desperation for a breath much more than lack of oxygen.
Interaction
It is not possible for a healthy person to voluntarily stop breathing indefinitely. If one does not inhale, the level of carbon dioxide builds up in the blood, and one experiences overwhelming air hunger. This irrepressible reflex is not surprising given that without breathing, the body's internal oxygen levels drop dangerously low within minutes, leading to permanent brain damage followed eventually by death. However, there have been instances where people have survived for as long as two hours without air; this is only possible when submerged in cold water, as this triggers the mammalian diving reflex as well as putting the subject into a state of suspended animation.
If a healthy person were to voluntarily stop breathing (i.e. hold his or her breath) for a long enough amount of time, he or she would lose consciousness, and the body would resume breathing on its own. Because of this one cannot commit suicide with this method, unless one's breathing was also restricted by something else (e.g. water, see drowning).
Hyperventilating causes a drop in CO2 below normal levels, lowering blood and oxygen supply to vital organs due to CO2-induced vasoconstriction and suppressed Both effect. Voluntary hyperventilation can cause tissue oxygen levels to go to dangerously low levels leading to, for example, fainting due to brain hypoxia.
Conscious control:
Conscious control of breathing is common in many forms of meditation, specifically forms of yoga for example pranayama unlike anapana which is only awareness of breath. In swimming, cardio fitness, speech or vocal training, one learns to discipline one's breathing, initially consciously but later sub-consciously, for purposes other than life support. Human speech is also dependent on conscious breath control. Also breathing control is used in Buteyko method.
Unconscious control:
Unconsciously, breathing is controlled by specialized centers in the brainstem, which automatically regulate the rate and depth of breathing depending on the body’s needs at any time. When carbon dioxide levels increase in the blood, it reacts with the water in blood, producing carbonic acid. Lactic acid produced by anaerobic respiration during exercise also lowers pH. The drop in the blood's pH stimulates chemoreceptor’s in the carotid and aortic bodies in the blood system to send nerve impulses to the respiration centre in the medulla oblongata and pons in the brain. These, in turn send nerve impulses through the phrenicand thoracic nerves to the diaphragm.
Examples
For instance, while exercising, the level of carbon dioxide in the blood increases due to increased cellular respiration by the muscles, which activates carotid and aortic bodies and the respiration center, which ultimately cause a higher rate of respiration.
During rest, the level of carbon dioxide is lower, so breathing rate is lower. This ensures an appropriate amount of oxygen is delivered to the muscles and other organs. It is important to reiterate that it is the buildup of carbon dioxide making the blood acidic that elicits the desperation for a breath much more than lack of oxygen.
Interaction
It is not possible for a healthy person to voluntarily stop breathing indefinitely. If one does not inhale, the level of carbon dioxide builds up in the blood, and one experiences overwhelming air hunger. This irrepressible reflex is not surprising given that without breathing, the body's internal oxygen levels drop dangerously low within minutes, leading to permanent brain damage followed eventually by death. However, there have been instances where people have survived for as long as two hours without air; this is only possible when submerged in cold water, as this triggers the mammalian diving reflex as well as putting the subject into a state of suspended animation.
If a healthy person were to voluntarily stop breathing (i.e. hold his or her breath) for a long enough amount of time, he or she would lose consciousness, and the body would resume breathing on its own. Because of this one cannot commit suicide with this method, unless one's breathing was also restricted by something else (e.g. water, see drowning).
Hyperventilating causes a drop in CO2 below normal levels, lowering blood and oxygen supply to vital organs due to CO2-induced vasoconstriction and suppressed Both effect. Voluntary hyperventilation can cause tissue oxygen levels to go to dangerously low levels leading to, for example, fainting due to brain hypoxia.
The Muscles of Breathing
In order to breathe air into our lungs, we rely on several muscles. The diaphragm is the most important muscle. This is a large, dome-shaped muscle located between the chest and the abdomen. When we breathe in, the diaphragm moves down to let air into the lungs. When we breathe out, the diaphragm relaxes and lets air out of the lungs. There are other muscles that can be used in breathing, including the neck and shoulder muscles and the muscles between the ribs.
Cleaning of Air and Removal of Mucus
The air that we breathe contains many tiny particles that must be removed before the air reaches the air sacs deep in the lungs. The nose partially cleans the air by trapping dirt particles in its hairs. Located inside the airways are glands which produce a sticky fluid called mucus. Mucus coats the airways and traps dirt and germs found in the airways. Tiny broom-like structures (cilia) clear the dirty mucus from the airways. These sweep the mucus up toward the throat where it can be spit out or swallowed.
Moisturizing the Air We Breathe
If the air we breathe in is too dry, it can damage the tiny air sacs in our lungs. Therefore, the air must be made moist. This is done by absorbing water from the airways. The moisture in the airways comes from food and drink.
Cleaning of Air and Removal of Mucus
The air that we breathe contains many tiny particles that must be removed before the air reaches the air sacs deep in the lungs. The nose partially cleans the air by trapping dirt particles in its hairs. Located inside the airways are glands which produce a sticky fluid called mucus. Mucus coats the airways and traps dirt and germs found in the airways. Tiny broom-like structures (cilia) clear the dirty mucus from the airways. These sweep the mucus up toward the throat where it can be spit out or swallowed.
Moisturizing the Air We Breathe
If the air we breathe in is too dry, it can damage the tiny air sacs in our lungs. Therefore, the air must be made moist. This is done by absorbing water from the airways. The moisture in the airways comes from food and drink.