The control of ventilation refers to the

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...

mechanisms involved in the control of

breathing Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen. All aerobic creatures need oxygen for cell ...

, which is the movement of air into and out of the lungs. Ventilation facilitates respiration. Respiration refers to the utilization of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

and balancing of

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

by the body as a whole, or by individual cells in

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

. The most important function of breathing is the supplying of oxygen to the body and balancing of the carbon dioxide levels. Under most conditions, the

partial pressure of carbon dioxide ''p''CO2, pCO2, or P_\ceis the partial pressure of carbon dioxide (CO2), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO2 as a function of its ...

(PCO2), or concentration of carbon dioxide, controls the

respiratory rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is m ...

. The peripheral chemoreceptors that detect changes in the levels of oxygen and carbon dioxide are located in the arterial

aortic bodies The aortic bodies are one of several small clusters of peripheral chemoreceptors located along the aortic arch. They are important in measuring partial pressures of oxygen and carbon dioxide in the blood, and blood pH. Structure The aortic bodies ...

and the

carotid bodies The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. The carotid body is located in the adventitia, in the bifurcation (fork) of the common carotid artery, which runs along both sides of the neck. The ...

. Central chemoreceptors are primarily sensitive to changes in the pH of the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in th ...

, (resulting from changes in the levels of carbon dioxide) and they are located on the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

near to the medullar respiratory groups of the respiratory center. Information from the peripheral chemoreceptors is conveyed along nerves to the respiratory groups of the respiratory center. There are four respiratory groups, two in the medulla and two in the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

. The two groups in the pons are known as the pontine respiratory group. # Dorsal respiratory group – in the medulla # Ventral respiratory group – in the medulla # Pneumotaxic center – various nuclei of the pons # Apneustic center – nucleus of the pons From the respiratory center, the

muscles of respiration The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during ...

, in particular the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

,Tortora, G. J. and Derrickson, B. H., (2009). Principles of Anatomy and Physiology – Maintenance and continuity of the human body. 12th Edition. Danvers: Wiley are activated to cause air to move in and out of the lungs.

Control of respiratory rhythm

Ventilatory pattern

Breathing is normally an unconscious, involuntary, automatic process. The pattern of motor stimuli during breathing can be divided into an

inhalation Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

stage and an exhalation stage.

Inhalation Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

shows a sudden, ramped increase in motor discharge to the respiratory muscles (and the pharyngeal constrictor muscles). Before the end of inhalation, there is a decline in, and end of motor discharge. Exhalation is usually silent, except at high

s. The respiratory centre in the medulla and pons of the brainstem controls the rate and depth of respiration, (the

respiratory rhythm The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal res ...

), through various inputs. These include signals from the peripheral chemoreceptors and central chemoreceptors; from the vagus nerve and glossopharyngeal nerve carrying input from the pulmonary stretch receptors, and other mechanoreceptors in the lungs. as well as signals from the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

and

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...

. * Medulla ** ventral respiratory group (includes the pre-Bötzinger complex). The ventral respiratory group controls voluntary forced exhalation and acts to increase the force of inhalation. Regulates rhythm of inhalation and exhalation. ** dorsal respiratory group (

solitary nucleus In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, (SN or NTS) is a series of purely sensory nuclei (clusters of nerve cell bodies) forming a vertical column ...

). The dorsal respiratory group controls mostly movements of inhalation and their timing. * Pons ** pneumotaxic center. *** Coordinates speed of inhalation and exhalation *** Sends inhibitory impulses to the inspiratory area *** Involved in fine tuning of respiration rate. ** apneustic center *** Coordinates speed of inhalation and exhalation. *** Sends stimulatory impulses to the inspiratory area – activates and prolongs inhalations *** Overridden by pneumotaxic control from the apneustic area to end inhalation

Control of ventilatory pattern

Ventilation is normally unconscious and automatic, but can be overridden by conscious alternative patterns. Thus the emotions can cause yawning, laughing, sighing (etc.), social communication causes speech, song and whistling, while entirely voluntary overrides are used to blow out candles, and breath holding (for instance, to swim underwater).

Hyperventilation Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. ...

may be entirely voluntary or in response to emotional agitation or anxiety, when it can cause the distressing

hyperventilation syndrome Hyperventilation syndrome (HVS), also known as chronic hyperventilation syndrome (CHVS), dysfunctional breathing hyperventilation syndrome, cryptotetany, spasmophilia, latent tetany, and central neuronal hyper excitability syndrome (NHS), is a re ...

. The voluntary control can also influence other functions such as the

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and e ...

as in

yoga Yoga (; sa, योग, lit=yoke' or 'union ) is a group of physical, mental, and spiritual practices or disciplines which originated in ancient India and aim to control (yoke) and still the mind, recognizing a detached witness-conscio ...

practices and

meditation Meditation is a practice in which an individual uses a technique – such as mindfulness, or focusing the mind on a particular object, thought, or activity – to train attention and awareness, and achieve a mentally clear and emotionally calm ...

. The ventilatory pattern is also temporarily modified by complex reflexes such as sneezing, straining, burping, coughing and vomiting.

Determinants of ventilatory rate

Ventilatory rate ( respiratory minute volume) is tightly controlled and determined primarily by blood levels of

as determined by

metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...

. Blood levels of

become important in hypoxia. These levels are sensed by central chemoreceptors on the surface of the

for decreased pH (indirectly from the increase of carbon dioxide in

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...

), and the peripheral chemoreceptors in the arterial blood for oxygen and carbon dioxide. Afferent neurons from the peripheral chemoreceptors are via the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. Be ...

(CN IX) and the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and rig ...

(CN X). The concentration of CO₂ rises in the blood when the metabolic use of O₂, and the production of CO₂ is increased during, for example, exercise. The CO₂ in the blood is transported largely as bicarbonate (HCO₃⁻) ions, by conversion first to carbonic acid (H₂CO₃), by the enzyme carbonic anhydrase, and then by disassociation of this acid to H⁺ and HCO₃⁻. Build-up of CO₂ therefore causes an equivalent build-up of the disassociated hydrogen ions, which, by definition, decreases the pH of the blood. The pH sensors on the brain stem immediately respond to this fall in pH, causing the respiratory center to increase the rate and depth of

. The consequence is that the partial pressure of CO (PCO2) does not change from rest going into exercise. During very short-term bouts of intense exercise the release of lactic acid into the blood by the exercising muscles causes a fall in the blood plasma pH, independently of the rise in the PCO2, and this will stimulate pulmonary ventilation sufficiently to keep the blood pH constant at the expense of a lowered PCO2. Mechanical stimulation of the lungs can trigger certain reflexes as discovered in animal studies. In humans, these seem to be more important in neonates and ventilated patients, but of little relevance in health. The tone of respiratory muscle is believed to be modulated by muscle spindles via a reflex arc involving the spinal cord. Drugs can greatly influence the rate of respiration.

Opioids Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...

and

anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into tw ...

s tend to depress ventilation, by decreasing the normal response to raised

levels in the arterial blood. Stimulants such as

amphetamines Substituted amphetamines are a class of compounds based upon the amphetamine structure; it includes all derivative compounds which are formed by replacing, or substituting, one or more hydrogen atoms in the amphetamine core structure with su ...

can cause

hyperventilation Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. ...

Pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...

tends to increase ventilation (lowering plasma carbon dioxide tension below normal values). This is due to increased

progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

levels and results in enhanced gas exchange in the

placenta The placenta is a temporary embryonic and later fetal organ (anatomy), organ that begins embryonic development, developing from the blastocyst shortly after implantation (embryology), implantation. It plays critical roles in facilitating nutrien ...

Feedback control

Receptors play important roles in the regulation of respiration and include the central and peripheral chemoreceptors, and pulmonary stretch receptors, a type of

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

. * Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface, are sensitive to the pH of their environment.Coates EL, Li A, Nattie EE. Widespread sites of brain stem ventilatory chemoreceptors. J Appl Physiol. 75(1):5–14, 1984.Cordovez JM, Clausen C, Moore LC, Solomon, IC. A mathematical model of pH(i) regulation in central CO₂ chemoreception. Adv Exp Med Biol. 605:306–311, 2008. * Peripheral chemoreceptors act most importantly to detect variation of the PO2 in the arterial blood, in addition to detecting arterial PCO2 and pH. * Mechanoreceptors are located in the

airway The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to ...

s and

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

, and are responsible for a variety of reflex responses. These include: ** The Hering-Breuer reflex that terminates inhalation to prevent over inflation of the lungs, and the reflex responses of

coughing A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...

, airway constriction, and

. ** The upper airway receptors are responsible for reflex responses such as,

sneezing A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth and ...

, coughing, closure of

glottis The glottis is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing vowels and voiced consonants. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γλῶττα'' (glôtta), ...

, and hiccups. ** The

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...

reflex responses include the activation of additional respiratory muscles as compensation, gasping response, hypoventilation, and an increase in breathing frequency and volume. ** The nasopulmonary and nasothoracic

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

es regulate the mechanism of breathing through deepening the inhale. Triggered by the flow of the air, the pressure of the air in the

nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next pass ...

, and the quality of the air, impulses from the nasal mucosa are transmitted by the trigeminal nerve to the respiratory center in the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

, and the generated response is transmitted to the

bronchi A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronch ...

, the

intercostal muscles Intercostal muscles are many different groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing by helping expand and shrink the size of ...

and the

. ** Head's paradoxical reflex where sudden inflation of the lung causes a transient respiratory effort or gasp.

References

External links

* * Rabbany, Sina Y., "Breathing Coordination", Hofstra Universit

* Webber, Charles L., Jr., Ph.D., Pulmonary Curriculum Function:"Neural Control of Breathing", Stritch School of Medicine, Loyola University-Chicag

{{DEFAULTSORT:Control Of Respiration Respiratory physiology