Regulation of Ventilation and Gas Exchange


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Chemoreceptors detect changes in blood oxygen levels and change the acidity of the blood and brain. Mechanoreceptors monitor the expansion of the lung , the size of the airway, the force of respiratory muscle contraction, and the extent of muscle shortening. Although the diaphragm is the major muscle of breathing, its respiratory action is assisted and augmented by a complex assembly of other muscle groups. Intercostal muscles inserting on the ribs, the abdominal muscles, and muscles such as the scalene and sternocleidomastoid that attach both to the ribs and to the cervical spine at the base of the skull also play an important role in the exchange of air between the atmosphere and the lungs.

In addition, laryngeal muscles and muscles in the oral and nasal pharynx adjust the resistance of movement of gases through the upper airways during both inspiration and expiration. Although the use of these different muscle groups adds considerably to the flexibility of the breathing act, they also complicate the regulation of breathing. These same muscles are used to perform a number of other functions, such as speaking, chewing and swallowing, and maintaining posture. Input into the respiratory control system from higher brain centres may help optimize breathing so that not only are metabolic demands satisfied by breathing but ventilation also is accomplished with minimal use of energy.

The respiratory rhythm is generated within the pons and medulla oblongata.

Central chemoreceptors

Three main aggregations of neurons are involved: a group consisting mainly of inspiratory neurons in the dorsomedial medulla, a group made up of inspiratory and expiratory neurons in the ventrolateral medulla, and a group in the rostral pons consisting mostly of neurons that discharge in both inspiration and expiration. It is thought that the respiratory cycle of inspiration and expiration is generated by synaptic interactions within these groups of neurons. The inspiratory and expiratory medullary neurons are connected to projections from higher brain centres and from chemoreceptors and mechanoreceptors; in turn they drive cranial motor neurons , which govern the activity of muscles in the upper airways and the activity of spinal motor neurons, which supply the diaphragm and other thoracic and abdominal muscles.

The inspiratory and expiratory medullary neurons also receive input from nerve cells responsible for cardiovascular and temperature regulation, allowing the activity of these physiological systems to be coordinated with respiration. Neurally, inspiration is characterized by an augmenting discharge of medullary neurons that terminates abruptly. After a gap of a few milliseconds, inspiratory activity is restarted, but at a much lower level, and gradually declines until the onset of expiratory neuron activity.

Then the cycle begins again. The full development of this pattern depends on the interaction of several types of respiratory neurons: inspiratory, early inspiratory, off-switch, post-inspiratory, and expiratory. Early inspiratory neurons trigger the augmenting discharge of inspiratory neurons.

This increase in activity, which produces lung expansion, is caused by self-excitation of the inspiratory neurons and perhaps by the activity of an as yet undiscovered upstream pattern generator. Off-switch neurons in the medulla terminate inspiration, but pontine neurons and input from stretch receptors in the lung help control the length of inspiration. When the vagus nerves are sectioned or pontine centres are destroyed, breathing is characterized by prolonged inspiratory activity that may last for several minutes.

This type of breathing, which occasionally occurs in persons with diseases of the brain stem , is called apneustic breathing. Post-inspiratory neurons are responsible for the declining discharge of the inspiratory muscles that occurs at the beginning of expiration. Mechanically, this discharge aids in slowing expiratory flow rates and probably assists the efficiency of gas exchange.

As you inhale, you may feel the air pass down your throat and notice your chest expand. Now exhale and observe the opposite events occurring.

Anatomy and physiology of the respiratory system

Inhaling and exhaling may seem like simple actions, but they are just part of the complex process of respiration, which includes these four steps:. Respiration begins with ventilation. This is the process of moving air in and out of the lungs. The lungs are the organs in which gas exchange takes place between blood and air. Pulmonary gas exchange is the exchange of gases between inhaled air and the blood.

It occurs in the alveoli of the lungs.

Respiratory system - Revision 4 - GCSE Biology (Single Science) - BBC Bitesize

Alveoli singular, alveolus are grape-like clusters surrounded by networks of thin-walled pulmonary capillaries. After you inhale, there is a greater concentration of oxygen in the alveoli than in the blood of the pulmonary capillaries, so oxygen diffuses from the alveoli into the blood across the capillaries see Figure below.

Carbon dioxide, in contrast, is more concentrated in the blood of the pulmonary capillaries than in the alveoli, so it diffuses in the opposite direction. Alveoli are tiny sacs in the lungs where gas exchange takes place. After the blood in the pulmonary capillaries becomes saturated with oxygen, it leaves the lungs and travels to the heart. The heart pumps the oxygen-rich blood into arteries, which carry it throughout the body.

How Lungs Work

Eventually, the blood travels into capillaries that supply body tissues. These capillaries are called peripheral capillaries. The cells of the body have a much lower concentration of oxygen than does the oxygenated blood in the peripheral capillaries. Therefore, oxygen diffuses from the peripheral capillaries into body cells. Carbon dioxide is produced by cells as a byproduct of cellular respiration, so it is more concentrated in the cells than in the blood of the peripheral capillaries.


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As a result, carbon dioxide diffuses in the opposite direction. The carbon dioxide from body cells travels in the blood from the peripheral capillaries to veins and then to the heart. The heart pumps the blood to the lungs, where the carbon dioxide diffuses into the alveoli. Then, the carbon dioxide passes out of the body through the other structures of the respiratory system, bringing the process of respiration full circle.

Neural Control of Ventilation

Gas exchange is needed to provide cells with the oxygen they need for cellular respiration. Cells cannot survive for long without oxygen. Gas exchange is also needed to carry away carbon dioxide waste. Some of the carbon dioxide in the blood dissolves to form carbonic acid, which keeps blood pH within a normal range. Blood pH may become unbalanced if the rate of breathing is too fast or too slow. When breathing is too fast, blood contains too little carbon dioxide and becomes too basic. When breathing is too slow, blood contains too much carbon dioxide and becomes too acidic.

Neural Mechanisms (Respiratory Center)

Clearly, to maintain proper blood pH, the rate of breathing must be regulated. What do these have in common with a breath of air? Journey of a Breath of Air Take in a big breath of air through your nose. Inhaling and exhaling may seem like simple actions, but they are just part of the complex process of respiration, which includes these four steps: Ventilation Pulmonary gas exchange Gas transport Peripheral gas exchange Ventilation Respiration begins with ventilation.

Air enters the respiratory system through the nose.

Regulation of Ventilation and Gas Exchange Regulation of Ventilation and Gas Exchange
Regulation of Ventilation and Gas Exchange Regulation of Ventilation and Gas Exchange
Regulation of Ventilation and Gas Exchange Regulation of Ventilation and Gas Exchange
Regulation of Ventilation and Gas Exchange Regulation of Ventilation and Gas Exchange
Regulation of Ventilation and Gas Exchange Regulation of Ventilation and Gas Exchange

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