1. REGULATION OF RESPIRATION
1. Introduction
• Respiration is a reflex process.
• Voluntary control of respiration (voluntary
apnea) is possible for a short period of about 40
seconds.
• The pattern of respiration is regulated by two
mechanism:
 Nervous or neural mechanism
 Chemical mechanism

2. 2.Nervous Mechanism
• It involves respiratory centres, afferent
nerves and efferent nerves.
Respiratory Centres
• Adequate supply of oxygen to the tissues and
removal of carbon dioxide from the tissues is
achieved by continuous exchange of gases
between alveoli and blood.

3. • Alveoli ventilation is provided by respiratory
movements.
• Respiratory movements are in turn, controlled
and maintained by co-ordinated activity of some
groups of neurons in trainstem.
• These collections of these nueron are called
respiratory centres.
• Respiratory centres are situated in the reticular
formation of the trainstem and the respiratory

4. Centres are classified into two groups:
Medullar centres
Pontine centres
• There are two centres in each group
Medullar Centres
1. Inspiratory centre
2. Expiratory centre

5. Pontine Centres
1. Pneumotaxic centre
2. Apneustic centre
Inspiratory Centre
• Situated in upper part of medulla oblangata
• It is also called dorsal group of respiratory
neurons.
• It is formed by the nucleus of tractussolitarius
and some neurons surrounding this

6. Function
• Inspiratory centre is concerned with
inspiration.
• Nucleus solitarius receives sensory impulses
from peripheral baroreceptors,
chemoreceptors and pulmonary receptors
through vagus and glossopharyngeal nerves.

7. Effect of stimulation
• Electrical stimulation of inspiratory centre in
animals causes contraction of inspiratory
muscles and prolonged inspiration.
Expiratory Centre
• It is situated in the medulla oblangata anterior
and lateral to inspiratory centre, (is also called
the Ventral group of respiratory neurons).

8. • The neurons form nucleus ambiguus
anteriorly and nucleus retroambiguous
posteriorly.
Function
• This centre is inactive during quiet breathing
and the inspiratory centre is active.
• Expiratory centre becomes active during
forced breathing or when the inspiratory
centre is inhibited.

9. • But during quiet breathing expiration ia
passive process and is due to the recoiling
property of thoracic cage and lungs.
Effect of stimulation
• Electrical stimulation in animals causes
contraction of expiratory muscles and
expiration.

10. Pneumotaxic Centre
• Is situated in dorsalateral part of reticular
formation in upper pons.
Function
• To control the medullary respiratory centres
particularly the inspiratory centre through
apneustic centre.
• Pneumotaxic centre increases the respiratory
rate by reducing the duration of inspiration.

11. Effect of stimulation
• Stimulation does not produce any typical effect
Apneustic Centre
• Is situated in reticular formation of lower pons.
Function
• Accelerates the depth of inspiration by acting
directly on inspiratory centre

12. Effect of stimulation
• Stimulation increases the duration of
inspiration with short expiratory gasp.
• So, respiration is called gasping type of
respiration.

13. Nervous Connection of Respiratory
Centres
Efferent Pathway
• Nerve fibre from the respiratory centres leave
trainstem and descend in anterior part of
lateral columns of spinal cord.
• They terminate in motor neurons in the
anterior horn cells of cervical and thoracic
segments of spinal cord.
• From the motor neurons of spinal cord, two
sets of nerve fibres arise which:

14.  Phrenic nerve fibres which supply the diaphram
 Intercostal nerve fibres, which supply the
intercostal muscles.
 Vagus nerve also contains some afferent fibres
from respiratory centres.
Afferent Pathway
• Impulses from peripheral chemoreceptors and
baroreceptors are carried to respiratory centres

15. by fibres of glossopharyngeal and vagus nerves.
• Vagal nerve fibres also carry impulses from the
stretch receptors of lungs to the respiratory
centres.
• Therefore, respiratory centres receive afferent
impulses from different parts of the body and,
accordingly modulate the movements of thoracic
cage and lungs through afferent nerve fibres

16. Integration of Respiratory Centres
Role of Medullary Centres
• Inspiratory Ramp
Inspiratory centre,i.e. dorsal group of
respiratory neurons is responsible for normal
rhythm of respiration.
These neurons discharge impulses
intermittently at regular intervals and
impulses cause inspiration

17. This type of fire/discharge from inspiratory
centre is called inspiratory ramp signals.
The significance of inspiratory ramp signals is
that there is a slow and steady inspiration so
that, the filling of lungs with air is also steady.

18. Role of Pontine Centres
• The medullary respiratory centres are under
the influence of pontine centres.
• The apneustic centre always accelerates the
activity of inspiratory centre, cause prolonged
inspiration.
• The pneumotaxic centre inhibits the apneustic
centre and restricts the duration of
inspiration.

19. Factors affecting Respiratory Centres
Respiratory centres regulate the respiratory
movements by receiving impulses from
various sources:
1. Impulses from anterior cingulate gyrus genu
of corpus collusum, olfactory tubercle and
posterior orbital gyrus of cerebral cortex
inhibit respiration.
2. Impulses from stretch receptors of lungs –
Hering Breuer reflex.

20. • Impulses from lungs bring about a respiratory
reflex called Hering – Breuer reflex.
• There are some stretch receptors on the wall
of bronchi and bronchioles of lungs.
• Stretch receptors give response to stretch of
the lung tissues.
• This reflex is a protective reflex because, it
restricts inspiration and limits overstretch of
lung tissues.

21. 3. Impulses from J receptors of lungs
• ‘J’ receptors are juxta capillary receptors.
• They are the nerve endings of the vagus.
• They are present on the wall of alveoli and
have close contact with pulmonary
capillaries.
• They are stimulated during the following:
 Pulmonary congestion

22.  Pulmonary edema
Pneumonia
Hyperinflation of lungs
Microembolism in pulmonary capillaries
• Some exogenous and endogenous chemical
substances like histamine,
halothane,bradykinin, serotonin also stimulate
‘J’ receptors.

23. 4.Impulses from Irritant Receptors of Lungs
• Are situated on the wall of bronchi and
bronchioles of lungs.
• They also send afferent impulses to respiratory
centres via vagal nerve fibres
• Are stimulated by harmful chemical agents like
ammonia and sulfur dioxide.
• Stimulation of irritant receptors produce reflex
hyperventilation along with bronchospasm.

24. • Hyperventilation along with bronchospasm
prevent the entry of harmful agents into
alveoli.
5. Impulses from Baroreceptors
• These are situated in carotid sinus and arch of
aorta.
• Are endings of Hering’s nerve (sinus nerve)
which is branch of glossopharyngeal nerve.

25. • Aortic baroreceptors are supplied by vagal
nerve fibres.
• They give response to increase in BP.
• Whenever BP is increased, they are activated,
in turn send impulses to medullar oblangata
and causes inhibition of respiration.
6. Impulses from Chemoreceptors
• Chemoreceptors play important role in the
regulation of respiration (later).

26. 7. Impules from proprioceptors
• These receptors give response to change in
position of different parts of the body.
• They are situated in joints, tendons and
muscles.
• They stimulated during muscular exercises,
send impulses to cerebral cortex in turn cause
hyperventilation by sending impulses to
medullary respiratory centres.

27. 8.Impulses from Thermoreceptors
• These respond to change in body
temperature.
• Are cutanervous receptors.
• When body is exposed to cold or when cold
water is applied over the body, the cold
receptors are stimulated and , send impulses
to cerebral cortex via somatic afferent nerves.

28. • Cerebral cortex in turn stimulates the respiratory
centres and cause hyperventilation
9. Impulses from Pain Receptors
• These give response to pain stimulus.
• When stimulated, impulses are send from hem to
cerebral cortex via somatic afferent nerves
• Somatic cortex in turn stimulates the respiratory
centres and causes hyperventilation.

29. 10. Cough Reflex
• Is a protective reflex caused by irritation of
parts of respiratory tract beyond nose, i.e.
larynx, trachea and bronchi
• Irritation in any of these parts causes
stimulation of vagal nerve endings and cough
occurs.
• This temporary arrest of respiration is called
apnea.

30. 11. Sneezing Reflex
• Is also a protective reflex
• This occurs due to the irritation of the nasal
mucus membrane
• During the irritation of nasal mucous
membrane, the olfactory receptors and
trigeminal nerve endings in nasal mucosa are
stimulated leading to sneezing.

31. • Sneezing starts with deep inspiration, followed
by forceful expiratory effort with opened
glottis and the irritants are expelled out of
respiratory tract.
12. Deglutition Reflex
• During swallowing of food, respiration is
arrested for a while.
• The temporary arrest is called apnea.

32. • Apnea during swallowing is called swallowing
apnea or deglutition apnea.
• It occurs during pharyngeal stage, i.e. 2 stage
of deglutition.
• It prevents entry food particles into
respiratory tract.
• The nerve involved in this reflex is
glossopharyngneal.

33. 3. CHEMICAL MECHANISM
• The chemical mechanism of regulation of
respiration is opperated through
chemoreceptors.
Chemoreceptors
• These are receptor which give response to
change in chemical constituents of blood.
• The chemoreceptors give response to the
following changes in the chemical constituents
of blood:

34.  Hypoxia
 Hyperoapnea and
 Increased hydrogen ion concentration
• Chemoreceptors are classified into two groups:
 Central chemoreceptors
 Peripheral chemoreceptors
Central Chemoreceptors
• These are present in the brain

35. • They are situiated in deep part of medullar oblangata,
close to dorsal group of neurons.
• These chemoreceptors are in close contact with blood
and ceretrospinal fluid.
Mechanism of action
• Main stimulant for central chemoreceptors is the
increased hydrogen ion concentration
• If hydrogen ion concentration increases in blood, it
cannot stimulate the central chemoreceptors because,
the hydrogen ions from blood cannot cross the blood
brain barrier and blood cerebrospinal fluid barrier.

36. • On the other hand, if carbon dioxide increases in
the blood, it can easily cross the blood brain
barrier and blood cerebrospinal barrier and entre
the interstitial fluid of brain or cerebrospinal
fluid.
• There, the carbon dioxide molecules combine
with water to form carbonic acid.
• Since carbonic acid is unstable, it immediately
dissociates into hydrogen ion and bicarbonate
ion.

37. • The hydrogen ions now stimulate the central
chemoreceptors
• The chemoreceptors send inhibitory impulses to
inspiratory centre causing increased rate and
force of breathing.
• Because of this excess carbon dioxide is washed
out and the respiration is brought back to
normal.
• Lack of oxygen does not have any significant
effect on the central chemoreceptors except that

38. it generally depresses the overall function of
the brain
Peripheral Chemoreceptors
• They are situated in the carotid body and
aortic body.
• Carotid body is present over the internal
carotid artery near the bifurcation of common
carotid artery into internal and external
carotid arteries.

39. Nerve Supply
• Chemoreceptors in the carotid body are
supplied by sinus nerve, which is a branch of
glossopharyngeal nerve.
• The sinus nerve is also called Hering ‘s nerve.
• The chemoreceptors in aortic body are
supplied by the aortic nerve, which is branch
of the vagus nerve.
•

40. Mechanism of Action
• Reduction in partial pressure of oxygen is the
most potent stimulant for peripheral
chemoreceptors.
• Whenever, the partial pressure of oxygen
decreases, these chemoreceptors are
activated and send impulses through the
aortic and sinus nerves.
• These impulse reach the respiratory centres

41. particularly the inspiratory centre and
stimulate them.
• So, rate and force of respiration is increased.
• This provides enough oxygen and rectifies the
lack of oxygen.

42. Disturbances of Respiration
Introduction
Eupnea refers to normal respiration. Following
are the forms used for some of the altered
patterns of respiration:
• Tachypnea: The increase in rate of respiration
is called tachypnea.
• Bradypnea: The decrease in rate of respiration
is called bradypnea.

43. • Polypnea: Polypnea means rapid, shallow
breathing resembling panting dogs. In this,
only the rate of inspiration is increased but
the force does not increase significantly.
• Hyperpnea: hyperpnea refers to a highly
significant in pulmonary ventilation due to
increase in rate or force of respiration or
sometimes due to both with more change in
rate.

44. • Apnea: Apnea means temporary arrest of
breathing.
• Hyperventilation: increase in rate and force of
respiration is called hyperventilation.
• Dyspnea: Dyspnea means difficult breathing.
• Periodic breathing: The abnormal breathing is
called periodic breathing.
• Tachypnea: Increased ventilation frequency,
usually with a decrease in ventilatory volume.

45. • Hypoxia: Reduced availability of oxygen to
cells. The word anoxia refers to absence of
oxygen. Since, there is no possibility for total
absence of oxygen in living conditions, the use
of this term has been abandoned.