Regulatory Mechanisms

REGULATORY MECHANISMS Spontaneous respiration is produced by rhythmic discharge of motor neurons that innervate the respiratory muscles. Discharge is from nerve impulse the brain.

NERVOUS REGULATORY CENTER CHEMICAL REGULATORY CENTRE NERVOUS REGULATORY CENTRE DIVIDED INTO AUTONOMOUS CONTORL VOLUNTARY CONTROL

AUTONOMOUS CONTROL Two centre MEDULLARY RESPIRATORY CENTRE PONTINE RESPIRATORY CENTRE MEDULLARY RESPIRATORY CENTRE LOCATION - ventro lateral medulla Respiratory neurons of two types I ) I neurons-inspiratory neurons- discharge during inspiration II ) E neurons – expiratory neurons- discharge during expiration NOTE- I and E neurons have inhibitory relation to each other. LOCATION -TWO groups in medulla. DORSAL - located in tractus solitarius. Consists mainly of I neurons

AFFERENTS- Airways and aortic and carotid bodies. VENTRAL Location – nucleus ambiguous Divided into c c

cranial division innervates accessory muscles of respiration caudal division innervates the intercostal muscles.

PONTINE RESPIRATORY CENTRE DIVIDE ANTO 1. APNEUSTIC CENTRE Location – LOWER PONS ROLE- activates the I neurons in medulla. Inhibited by vagus nerve afferents from airways and lung.

2. PNEUMOTAXIC CENTRE Location - UPPER PONS Contains both I and E neurons Inhibits the neurons in lower pons, preventing apneusis.

APPLIED

IF VAGUS CUT THEN EFFECT ON MEDULLA

VOLUNTARY CONTROL OF RESPIRATION Pathway – corticospinal tract Origin – cerebral cortex Ends - spinal motor neurons Action – innervate respiratory muscles. Voluntary inspiration Activated by apneustic centre in lower pons Expiration

c

c

c

pneumotaxic centre in upper pons sends inhibitory impulses to apneustic centre. pulmonary stretch receptors on stimulation during inspiration send inhibitory impulses to apneustic centre pneumotaxic centre send impulses to expiratory centre

FACTORS AFFECTING RESPIRATORY CENTRE 1. AFFERENTS FROM HIGHER CENTRES Cerebral cortex Mediated by- I . corticospinal tracts Hypothalamus Pain , anxiety,fear 2. PULMONARY STRETCH RECEPTORS Location- smooth muscles of the airway Inflation of the lungs stimulates stretch receptors in lungs

Leading to inhibition of apneustic centre by vagus nerve HERING BREUR INFLATION REFLEX. HERING BREUR DEFLATION REFLEX During deflation of lung, decrease in expiration J RECEPTORS Location - alveolar wall Hyperinflation of lungs stimulates J receptors. Stimulates pneumotaxic centre, inhibiting inspiration. J RECEPTORS sensitive to pulmonary congestion, Pulmonary edema Irritants of lung APPLIED

AFFERENTS FROM PROPRIOCEPTORS Movements of joints stimulates inspiratory neurons Increase ventilation during exercise

AFFERENTS FROM AIRWAYS STIMULATION of receptors in airways causes sneezing, coughing, tachypnea and bronchoconstriction AFFERENTS FROM BARORECPTORS Location - Aortic arch and carotid sinus Stimulated by high blood pressure ACTION- Inhibition of respiration CHEMORECEPTORS Location – Carotid and aortic bodies Stimulated by chemical changes in blood ACTION – Increase the rate and depth of respiration.

CHEMICAL REGULATION OF RESPIRATION CHEMORECEPTORS c c c

PERIPHERAL CHEMORECEPTORS CENTRAL CHEMORECEPRTOS PULMONARY AND CARDIAL CHEMORECEPTOS

1. PERIPHERAL CHEMORECEPTOR CAROTID AND AORTIC BODIES Located near common carotid artery bifurcation and arch of aorta respectively STIMULATING FACTORS 1. 2. 3. 4.

Hypoxia Decreased blood flow Asphyxia Cyanide poisoning

ACTION On stimulation, increase rate as well as depth of respiration.

3. CENTRAL CHEMORECEPTORS (MEDULLARY) LOCATION- Ventral part of medulla NOTE - Separate from respiratory centre ACTION – stimulates respiration by impulses acting on apneustic centre STIMULATING FACTORS H+ concentration of CSF Directly proportional increase with H+ increase. NOTE - NOT Stimulated by hypoxia H+ increase with increase in CO2 concentration Mechanism CO2 + H2O

H2CO3

H + HCO3

CO2 passes blood brain barrier where as H passes slowly Effect of CO2 on respiration is mainly due its movement into CSF where it increase concentration of H+and stimulates central chemoreceptors.

1. PULMONARY AND CARDIAL CHEMORECEPTORS

FACTORS AFFECTING RESPIRATION HYPOXIA Decrease in pO2 stimulates respiratory centre leading to increased respiration MECHANISM Stimulates peripheral chemoreceptors causing increased respiration Above pO2 60 mm Hg, slight fall change in respiration Below 60mmHg, marked increased respiration

EFFECT OF CO2 Rise in pCO2 stimulates mainly CENTRAL chemoreceptors leading to increased respiration Also stimulates peripheral chemoreceptors. EFFECT OF H+ Stimulates peripheral chemoreceptors H cannot enter CSF therefore unable to stimulate central chemoreceptors.

EFFECT OF INTERACTION OF VARIOUS CHEMICAL FACTORS