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Regulation of the
respiration
Science Background
BIOLOGY
Human
Physiology
Respiration
People often think that the words breathing and respiration mean the same. However,
breathing is only part of the respiration. Respiration is the entire process through which a
body absorbs and uses oxygen, and produces carbon dioxide and water as waste
products.
The respiration consist of two parts:


Breathing, which involves inhaling and exhaling, and
Cellular respiration, which involves the chemical reactions that release energy from
organic compounds.
Breathing is enabled by the respiratory system, which consists of lungs, throat and
passageways that lead to the lungs.
Respiratory cycle
The exchange of gases between an organism and its environment is known as respiration.
The respiratory system provides oxygen for the cells and carbon dioxide, generated during
cellular respiration, is excreted into the environment. Breathing is the mechanical process
of moving air from the environment into the lungs and of expelling air from the lungs.
Inhalation or inspiration occurs when air flows into the lungs. Exhalation or expiration
occurs when air flows out of the lungs. A single breath, called a respiratory cycle, consists
of an inhalation followed by an exhalation.
Breathing is done by rib muscles and the diaphragm, a dome-shaped muscle underneath
the lungs. During inhalation, the volume of the thoracic cavity is increased by the
contraction of the diaphragm. When the diaphragm contracts and moves down, the chest
cavity volume increases. At the same time, some rib muscles contract and lift the rib cage,
also increasing the volume of the thoracic cavity.
This action reduces the pressure inside the lungs relative to the outside atmospheric air
pressure. As a consequence, a partial vacuum is created in the lungs and air rushes in
from the outside to fill them. The amount of air moved into and out of the lungs with each
normal resting breath is called the tidal volume.
The reverse occurs during exhalation. With healthy people, exhalation is mostly a passive
process that depends more on the elasticity of the lungs than on muscle contraction.
During exhalation, the diaphragm relaxes and it’s dome curves up into the chest cavity,
while the rib muscles relax and the ribs move back down and inward. As the chest cavity
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decreases in size, so do the lungs. The air in the lungs is forced more closely together and
it’s pressure increases. When that pressure rises to a point higher than the atmospheric
pressure, the air is expelled or forced out of the lungs until the two pressures are equal
again.
Breathing centers
The fact if and when a breath cycle starts is arranged in the central nervous system,
especially in the brain stem. From the respiratory center neurons regulate the ventilation.
These neurons are divided into three groups:
1. A dorsal respiration group (localized to the dorsum of the medulla oblongata),
mainly responsible for inhalation,
2. The pneumotaxic center located in the dorsal part of the pons where mainly the
respiratory rate is regulated,
3. A ventral respiration group (located in the ventrolateral part of the medulla
oblongata), which regulates both inspiration and expiration.
The dorsal respiration group
The group neurons that is localized in the dorsal portion of the medulla oblongata mainly
regulates the inhalation (= inspiration) and the regulation of respiration. These sensory
inputs include information of: baroreceptors and chemoreceptors in the lungs.
These receptors play a role in the control of breathing. The signal that is delivered to the
primary respiration muscles in the diaphragm changes gradually.
The inhalation movement can be influenced by an increase in signal strength, thereby the
ventilation is accelerating.
In addition, the respiration can be stopped abruptly. The faster the signal will stop, the
shorter the inspiration movement is, and the faster the breathing cycle.
The pneumotaxic center
This center is located in the nucleus parabrachialis of the upper portion of the pons. Here it
is determined where the respiratory signal is stopped, which can accelerate the breathing.
A strong pneumotaxic signal can cause an inhalation of just 0.5 sec. In this situation, the
lungs are only partially filled with air. When the pneumotaxic signals are weak, breathing
can take 5 seconds or longer.
Ventral respiration group
During regular breathing this center is inactive. When, however, great demands are made
on the respiration (for example during physical exercise), this area becomes active. This
area controls both inspiration and expiration during physical exercises.
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During a respiration, baroreceptors are activated in the lung tissue. These will give a signal
via the vagus nerve to the inspiratory part of the centers. These are then inhibited,
allowing the breath to flow seamless into an exhalation.
During a respiration, the concentration of oxygen, carbon dioxide and hydrogen ions are
again balanced in the tissues. The chemoreceptors are sensitive to changes in these
concentrations. A rise in pCO2 and pH in the veins ensures the stimulation of extra
ventilation. The same applies for a drop in arterial pO2.
In addition to the chemoreceptors and the baroreceptors, other factors influence the
breathing. There is a close correlation between the functioning of the cardiovascular
control center and the breathing centers. Even adrenaline or temperature triggers the
breathing centres.
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