Regulation of respirationRegulation of respiration

Lecture by Lecture by Dr SandeepDr Sandeep

28-04-0828-04-088:30-9:30am8:30-9:30am

Nervous system normally adjusts the rate of alveolar ventilation Nervous system normally adjusts the rate of alveolar ventilation almost exactly to the demands of the bodyalmost exactly to the demands of the body

The respiratory center is composed of several groups of The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons neurons located bilaterally in the medulla oblongata and pons of the brainstemof the brainstem

It is divided into 3 major collection of neurons It is divided into 3 major collection of neurons

1)1) dorsal respiratory group, located in the dorsal portion of dorsal respiratory group, located in the dorsal portion of medulla medulla

2)2) ventral respiratory group, located in the ventrolateral part of ventral respiratory group, located in the ventrolateral part of medulla, and medulla, and

3)3) the pneumotaxic center, located in the superior portion of the the pneumotaxic center, located in the superior portion of the pons pons

The basic rhythm of respiration is generated mainly in The basic rhythm of respiration is generated mainly in the dorsal respiratory group of neurons and is the dorsal respiratory group of neurons and is conveyed to inspiratory muscle, diaphragmconveyed to inspiratory muscle, diaphragm

Inspiratory “ramp” signalsInspiratory “ramp” signals begins weakly and begins weakly and increases steadily in a ramp manner for about 2 sec, increases steadily in a ramp manner for about 2 sec, then it ceases abruptly for 3 secthen it ceases abruptly for 3 sec

The advantage of ramp is that it causes a steady The advantage of ramp is that it causes a steady increase in the volume of the lungs during inspirationincrease in the volume of the lungs during inspiration

A pneumotaxic center, located dorsally in the nucleus A pneumotaxic center, located dorsally in the nucleus parabrachialis of the upper pons, transmits signals to the parabrachialis of the upper pons, transmits signals to the inspiratory areainspiratory area

The primary effect of this center is to control the “switch-The primary effect of this center is to control the “switch-off” point of the inspiratory ramp, thus controling the off” point of the inspiratory ramp, thus controling the filling phase of the lung cyclefilling phase of the lung cycle

The function of the pneumotaxic center is primarily to The function of the pneumotaxic center is primarily to limit inspiration limit inspiration

Ventral respiratory group of neuronsVentral respiratory group of neurons

Located in each side of the medulla, about 5 mm anterior and Located in each side of the medulla, about 5 mm anterior and lateral to dorsal respiratory group of neuronslateral to dorsal respiratory group of neurons

These neurons remain totally inactive during normal respirationThese neurons remain totally inactive during normal respiration

During increased pulmonary ventilation, these neurons During increased pulmonary ventilation, these neurons contributes to extra respiratory drivecontributes to extra respiratory drive

These neurons contributes in both inspiration and in expiration, These neurons contributes in both inspiration and in expiration, signals to abdominal muscles during expirationsignals to abdominal muscles during expiration

In addition to the central nervous system, sensory In addition to the central nervous system, sensory nervous system from lungs also help control nervous system from lungs also help control respiration respiration

Most imp are located in the walls of bronchi and Most imp are located in the walls of bronchi and bronchioles as stretch receptorsbronchioles as stretch receptors

When lungs are over stretched, stretch receptors are When lungs are over stretched, stretch receptors are stimulated send inhibitory signals and inspiratory stimulated send inhibitory signals and inspiratory ramps are switched offramps are switched off

This is called the This is called the Hering-Breuer inflation reflex.Hering-Breuer inflation reflex.

Function is to prevent overstretching of lungs Function is to prevent overstretching of lungs

Chemical control of respirationChemical control of respiration

The ultimate goal is to maintain proper concentration of The ultimate goal is to maintain proper concentration of OO2 2 and COand CO22 in the body in the body

Excess of COExcess of CO22 or excess of hydrogen ions in the blood or excess of hydrogen ions in the blood

mainly act directly on the respiratory center itself, mainly act directly on the respiratory center itself, causing increasing in the strength of both inspiratory causing increasing in the strength of both inspiratory and expiratory signalsand expiratory signals

OO22 does not have significant direct effect on respiratory does not have significant direct effect on respiratory

centercenter

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Peripheral chemoreceptor systemPeripheral chemoreceptor system

This is special nervous chemical receptors, called This is special nervous chemical receptors, called chemoreceptors mainly located outside brainchemoreceptors mainly located outside brain

They are important in detecting change in OThey are important in detecting change in O22 in the in the

blood rather than COblood rather than CO22

They are called “They are called “carotid bodies”carotid bodies” located in the located in the bifurcation of the common carotid arteries and in bifurcation of the common carotid arteries and in arch of aorta arch of aorta

Basic mechanism of stimulationBasic mechanism of stimulation

The exact mechanism is still unknown. However, The exact mechanism is still unknown. However, these bodies have multiple highly characteristic these bodies have multiple highly characteristic glandular-like cells called glandular-like cells called glomus cellsglomus cells

That synapses directly or indirectly on the nerve That synapses directly or indirectly on the nerve endingsendings

When there is low OWhen there is low O22 level in the blood these cells level in the blood these cells

are stimulated and stimulates afferent nerve fibersare stimulated and stimulates afferent nerve fibers

there by stimulating inspiratory centerthere by stimulating inspiratory center

Regulation of respiration during exerciseRegulation of respiration during exercise

In strenuous exercise, OIn strenuous exercise, O22 consumption and carbon consumption and carbon dioxide formation can increase as much as 20 folddioxide formation can increase as much as 20 fold

What causes intense ventilation during exercise?What causes intense ventilation during exercise?

When a person begins to exercise, a large share of When a person begins to exercise, a large share of the total increase in ventilation begins immediately on the total increase in ventilation begins immediately on initiation of the exercise, even before blood chemical initiation of the exercise, even before blood chemical changechange

Most of this increase is from neurogenic signalsMost of this increase is from neurogenic signals

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