Control of Ventilation - Physiology and Anatomy - Lecture Slides, Slides for Physiology. Aliah University
santhanakrishnan
santhanakrishnan26 January 2013

Control of Ventilation - Physiology and Anatomy - Lecture Slides, Slides for Physiology. Aliah University

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This lecture is taken from slides of Physiology. Key important points are: Control of Ventilation, Brain Stem Respiratory Centers, Pons Respiratory Centers, Chemoreceptors, Effects of Blood, Brain Chemoreceptors, Pulmona...
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Control of Ventilation

Control of Ventilation

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Brain Stem Respiratory Centers

• Automatic breathing is generated by a rhythmicity center in medulla oblongata – Consists of inspiratory

neurons that drive inspiration & expiratory neurons that inhibit inspiratory neurons

• Their activity varies in a reciprocal way & may be due to pacemaker neurons

Insert fig. 16.25

Fig 16.25

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• Inspiratory neurons stimulate spinal motor neurons that innervate respiratory muscles

• Expiration is passive & occurs when inspiratories are inhibited

Brain Stem Respiratory Centers continued

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• Activities of medullary rhythmicity center is influenced by centers in pons – Apneustic center promotes inspiration by stimulating

inspiratories in medulla – Pneumotaxic center antagonizes apneustic center,

inhibiting inspiration

Pons Respiratory Centers

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Chemoreceptors

• Automatic breathing is influenced by activity of chemoreceptors that monitor blood PC02, P02, & pH – Central chemoreceptors

are in medulla • Peripheral chemoreceptors

are in large arteries near heart (aortic bodies) & in carotids (carotid bodies)

Fig 16.26

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Effects of Blood PC02 & pH on Ventilation

• Chemoreceptors modify ventilation to maintain normal CO2, O2, & pH levels – PCO2 is most crucial because of its effects on blood pH

• H20 + C02 ↔ H2C03 ↔ H+ + HC03-

• Hyperventilation causes low C02 (hypocapnia) • Hypoventilation causes high C02 (hypercapnia)

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Effects of Blood PC02 & pH on Ventilation continued

• Brain chemoreceptors are responsible for greatest effects on ventilation – H+ can't cross BBB but C02 can, which is why it is

monitored & has greatest effects – Rate and depth of ventilation adjusted to maintain

arterial PC02 of 40 mm Hg • Peripheral chemoreceptors do not respond to PC02,

only to H+ levels

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Effects of Blood P02 on Ventilation

• Low blood P02 (hypoxemia) has little affect on ventilation – Does influence chemoreceptor sensitivity to PC02 – P02 has to fall to about half normal before ventilation is

significantly affected – Emphysema blunts chemoreceptor response to PC02

• Oftentimes ventilation is stimulated by hypoxic drive rather than PC02

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Effects of Pulmonary Receptors on Ventilation

• Lungs have receptors that influence brain respiratory control centers via sensory fibers in vagus – Unmyelinated C fibers are stimulated by noxious substances such

as capsaicin • Causes apnea followed by rapid, shallow breathing

– Irritant receptors are rapidly adapting; respond to smoke, smog, & particulates

• Causes cough • Hering-Breuer reflex is mediated by stretch receptors activated

during inspiration – Inhibits respiratory centers to prevent overinflation of lungs

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