Breathing, called ventilation consists of two phases, inspiration and expiration. During inspiration the diaphragm and the external intercostal muscles contract. The diaphragm moves downward increasing the volume of the thoracic (chest) cavity, and the external intercostal muscles pull the ribs up and outward, expanding the rib cage, further increasing this chest volume. This increase of volume lowers the air pressure in the lungs as compared to atmospheric air. Because air always flows from a region of high pressure to an area of lower pressure, it travels in through the body’s conducting airway (nostrils, throat, larynx and trachea) into the alveoli of the lungs. During a resting expiration the diaphragm and external intercostal muscles relax, restoring the thoracic cavity to its original (smaller) volume, and forcing air out of the lungs into the atmosphere. Whereas breathing is involved with the movement of air into and out of the thoracic cavity, respiration involves the exchange of gases in the lungs.
With each breath, air passes through its conducting zone into the microscopic air sacs in the lunges called alveoli. It is here that external (referring to the lungs) respiration occurs. External respiration is the exchange of oxygen and carbon dioxide between the air and the blood in the lungs. Blood enters the lungs via the pulmonary arteries. It then proceeds through arterioles and into the very tiny alveolar capillaries. Oxygen and carbon dioxide are exchanged between the blood and the air; oxygen is loaded onto the red blood cells while carbon dioxide is unloaded from them into the air. The oxygenated blood then flows out of the alveolar capillaries, through venules, and back to the heart via the pulmonary veins. The heart then pumps the blood throughout the systemic arteries to deliver oxygen throughout the body.
How Does Body Control Breathing? Introducing the Metabolic Control:
The respiratory centre in the brainstem is responsible for controlling a person’s breathing rate. It sends a message to the respiratory muscles telling them when to breathe. The medulla, located nearest the spinal cord, directs the spinal cord to maintain breathing, and the pons, a part of the brain very near the medulla, provides further smoothing of the respiration pattern. This control is automatic, involuntary and continuous. You do not have to consciously think about it.
The respiratory centre knows how to control the breathing rate and depth by the amount (or percent) of carbon dioxide, oxygen and acidosis in the arterial blood. There are receptors, called chemoreceptors, in the arch of the aorta and throughout the arteries that send signals and feedback (to the respiratory centre) to increase or decrease the ventilatory output depending on the condition of these metabolic variables. For example, when you exercise, carbon dioxide levels increase significantly which alert the chemoreceptors, which subsequently notify the brain’s respiratory centre to increase the speed and depth of breathing. This elevated respiration rids the body of excess carbon dioxide and supplies the body with more oxygen, which are needed during aerobic exercise. Upon cessation of the exercise, breathing rate and depth gradually declines until carbon dioxide in the arterial blood returns to normal levels; the respiratory centre will no longer be activated, and breathing rate is restored to a pre-exercise pattern. This arterial pressure regulation feedback system that carbons dioxide, oxygen and blood acid levels provide is referred to as the metabolic control of breathing.
How Does Body Control Breathing? Introducing the Behavioural Control:
Breathing is most unique as compared to other visceral (e.g., digestion, endocrine cardiovascular) functions in that it can also be regulated voluntarily. The behavioural, or voluntary control of breathing is located in the cortex of the brain and describes that aspect of breathing with conscious control, such as a self-initiated change in breathing before a vigorous exertion or effort. Speaking, singing and playing some instruments (e.g., clarinet, flute, saxophone, trumpet, etc.) are good examples of the behavioural control of breathing and are short-lived interventions. As well, the behavioural control of breathing encompasses accommodating changes in breathing such as those changes from stress and emotional stimuli. The differentiation between voluntary and automatic (metabolic) breathing is that automatic breathing requires no attention to maintain, whereas voluntary breathing involves a given amount of focus.
It is not fully understood how the behavioral and metabolic controls of respiration are linked.
The meaning of pranayama: Joining of two words prana (life’s energy) and yama (we all know). When prana vayu scatters yama takes over and in pranayama process you add them together —thus dislodging yama of its functions