REGULATION OF RESPIRATION

DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
REGULATION
OF
RESPIRATION.

OBJECTIVES
 Introduction.
 Neural Regulation.
 Automatic control.
 Afferent impulses to respiratory centre.
 Chemical regulation.
 Chemoreceptors.
 Effect of pO2, pCO2 & H+ ion conc on respiration.
 Applied aspects.
Friday, June 17, 2016

INTRODUCTION.
 The normal rate of respiration in
adults is 12-18/min,
 Tidal volume of approx. 500 ml.
 Adjusted to the requirements of
the body.
 Spontaneous respiration -
rhythmic discharge of motor
neurons that innervate the
respiratory muscles.

CONTROL MECHANISMS.
 Automatic control as
an involuntary
function.
 Located in medullary
& pontine centres.
 Functional
significance – breath
without conscious
effort as in sleep.

CONTROL MECHANISMS.
 Voluntary control.
 Located in cerebral
cortex.
 Functional
significance – facilitate
acts like talking, singing,
swimming, laughing,
breath holding &
hyperventilation.

FUNCTIONS OF RESPIRATORY
CENTRES.
 Genesis of normal
respiratory
spontaneous rhythm.
 Control rate & depth
of respiration.

REGULATION.
 Neural
 Automatic control.
 Afferent impulses to respiratory centre.
 Chemical.
 Chemoreceptors
 Effect of Po2, Pco2 &pH.

AUTOMATIC CONTROL.
 Medullary respiratory
centres.
 Pontine respiratory
centre.
 Reticular activating
system.

MEDULLARY RESPIRATORY
CENTRES.
 Dorsal respiratory
group of neurons.
 Ventral respiratory
group of neurons.

DORSAL RESPIRATORY GROUP OF
NEURONS..
 NTS (Nucleus of Tractus
Solitarius)
 I neurons – Discharge
during inspiration only.

CENTRAL INSPIRATORY
ACTIVITY NEURONS.(RΑ)
 Central inspiratory
activity neurons.(Rα)
 Inspiratory pump.
 Ramp signal.
 Inspiratory off-switch
(IOS) neurons.
 Terminate inspiratory
Ramp.
 Integrator neurons. (Rβ)
 Other neurons.(P cells)

INTEGRATOR NEURONS. (RΒ)
 Excitatory inputs.
 Cerebral cortex.
 Pneumotaxic
centre.
 Vagal afferents
from stretch
receptors.
 Inhibitory inputs.
 Apneustic centre.

VENTRAL RESPIRATORY GROUP
OF NEURONS.
 Caudal part or nucleus
Retroambigualis
(NRA)
 E neurons
 Bulbospinal expiratory
Premotor neurons.
 Intermediate part.
 I neurons.
 N. Parambigualis
 Most Rostral part.(NRF)
 Botzinger complex (E
neurons)

VENTRAL RESPIRATORY GROUP
OF NEURONS.
 Interactions of I & E
neurons.
 Role of VRG neurons.
 Totally inactive in
quiet breathing.
 Active during forceful
respiration.
 Example -- During
exercise
 Reciprocal
innervations.

PONTINE RESPIRATORY
CENTRE.
 Apneustic Centre (APN)
 Inhibitory neurons
bilaterally in pons.
 APN – Integrator – IOS
 Prevent switch off of ramp
from CIA
 Increases depth & duration
– Apneusis.
 Normally kept inhibited by
vagus & Pneumotaxic centre

PONTINE RESPIRATORY
CENTRE.
 Pneumotaxic centre.
(PNC)
 In N. Parabrachialis in
upper pons.
 Excite integrator N &
inhibits Apneustic C.
 Increases rate of breathing.
 So Rhythm by DRG, rate &
depth controlled by
APN,PNC.

RETICULAR ACTIVATING
SYSTEM.
 Increases respiratory
drive.
 During sleep – RAS
activity decreases –
respiratory drive
decreases – alveolar
ventilation decreases
– raise Pco2.

AFFERENT IMPULSES TO
RESPIRATORY CENTRE.
 From higher centre.
 From non-chemical receptors.
 From chemical receptors.

FROM HIGHER CENTRE.
 Voluntary control
system.
 Controlled by Neocortex
 Bypasses medullary
respiratory centres &
project directly to spinal
respiratory neurons.
 For talking, singing,
swimming & breath
holding.
 Limbic control
system.
 Limbic system –
pontomedullary
respiratory neurons.
 So alter during pain &
emotional stimuli.

FROM NON-CHEMICAL RECEPTORS.
 From Pulmonary stretch receptors (Hering-
Breuer Reflex)
 From J-Receptors.
 From Irritant receptors in the respiratory tract.
 From Proprioceptors..
 From Chest wall stretch receptors.
 From Baroceptors.
 From Thermoceptors.

FROM PULMONARY STRETCH RECEPTORS
(HERING-BREUER REFLEX)
 Lung inflation –
stimulation of
stretch receptors in
bronchi & bronchioles
– vagi –
pontomedullary
respiratory centers –
inhibit respiration.
 Only when TV > 1-1.5L

FROM J-RECEPTORS.
 Indian physiologist A.S
Paintal 1954.
 Juxtapulmonary capillary
receptors. (unmyelinated
vagal afferents)
 Sensitive to increase in
content of interstitial fluid
between capillary
endothelium & alveolar
epithelium.
 Stimulation causes
apnoea,
hyperventilation,
bradycardia ,
hypotension &
weakness of skeletal
muscles.

FROM IRRITANT RECEPTORS IN
THE RESPIRATORY TRACT.
 Cough reflex.
 Sneezing reflex.
 Hering-Breuer
deflation reflex.
 Reflex tachypnoea &
bronchoconstriction.
 Deglutition reflex.

FROM PROPRIOCEPTORS.
 Stimulate inspiratory neurons – increase rate &
depth of respiration.
 Increases ventilation during exercise.

FROM CHEST WALL STRETCH
RECEPTORS.
 In muscle spindles of
intercostal muscles
 Co-ordinate breathing
during change in posture
& during speech.
 Intercostal to intercostal
reflex.
 Intercostal to Phrenic
reflex.

FROM BAROCEPTORS.
 Raise BP – stimulate
Baroreceptors in
carotid sinus & aortic
arch.
 Inhibition of
respiration.

FROM THERMOCEPTORS.
 2 types, warm & cold.
 Warm receptors – via
somatic afferent
nerves – cerebral
cortex –
hyperventilation.
(Heat loss mechanism)
 E.g. Panting in Dogs.

FROM CHEMICAL RECEPTORS.
CHEMORECEPTORS.
 Peripheral
 Central.
 Pulmonary & Myocardial.

PERIPHERAL CHEMORECEPTORS.
 Location - carotid bodies &
aortic bodies.
 Structure.
 Capsule – surrounding
bodies.
 Sinusoidal large capillaries
below capsule
 Epithelial cells – type I
(Glomus cells) like
chromaffin cells contains
catecholamine.
 Type II (Glial cells).

PERIPHERAL CHEMORECEPTORS.
 Mechanism
 Less Po2 – decreases
activity of K channels –
decrease K efflux –
depolarization of glomus
cells – open L-type ca
channels – Ca influx –
release neurotransmitter
& stimulate afferent
nerve.

FACTORS STIMULATING
 O2 tension V o2
content.
 Elevated Pco2
 H+ conc.
 Hyperkalemia.
 Asphyxia.
 Functions
 Carotid bodies
increases both rate &
depth, aortic bodies
only rate of
respiration.

CENTRAL CHEMORECEPTORS.
 Location – beneath
ventral surface of
medulla.
 Innervations –
project directly to
respiratory centres
deeper to central
chemoreceptors.
 Mechanism.
 Co2 crosses BBB – in
CSF
 co2 + H2O – H2CO3
 H2CO3 ------H+ HCO3
 H+ ion stimulate
central
chemoreceptors.

PULMONARY & MYOCARDIAL
CHEMORECEPTORS.
 Location – pulmonary &
coronary blood vessels.
 Innervations – by Vagus
(X) nerve.
 Characteristics & effects.
 Caused by injection of
veratridine or nicotine
 Causes – bradycardia,
hypotension, apnoea
followed by tachypnoea.

EFFECT OF PO2, PCO2 & H+ ION
CONC ON RESPIRATION.

EFFECT OF HYPOXIA
 Normal arterial Po2 is
100 mm Hg. Decrease
in Po2 causes Hypoxic
Hypoxia.
 A decrease in arterial
Po2
 Po2 100-60mm Hg. –
breaking effect of CO2.
 Po2 below 60 mm Hg.

EFFECT OF HYPERCAPNIA.
 Normal pco2 – 40 mm Hg.
 Effect of Hypercapnia.
 Co2 Narcosis when PCO2 >
50 mmHg.
 Leads to depress CNS,
Respiratory centre,
headache, confusion,
convulsion, coma & Death.

EFFECT OF ARTERIAL pH
 Increase H+ ion conc.
(metabolic acidosis)-
leads to
hyperventilation. In
DKA, renal failure,
severe exercise.
 Decrease H+ ion conc.
(metabolic alkalosis)
 Primary pulmonary
hypoventilation
causes respiratory
acidosis.
 Primary pulmonary
Hyperventilation
causes respiratory
alkalosis.

EFFECT OF HYPERVENTILATION.
 Hypoventilation.
 Apnoea.
 Periodic breathing
(chynes-stokes
breathing)

EFFECT OF SLEEP ON
RESPIRATION.
 Apnoea for brief
period (10 sec)
 Sleep apnoea
syndrome.

REGULATION OF RESPIRATION

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