Respiration is regulated by both nervous and chemical mechanisms. The nervous mechanism involves respiratory centers in the medulla oblongata and pons that collect sensory information and control respiratory muscles. There are four respiratory centers - the inspiratory and expiratory centers in the medulla, and the pneumotaxic and apneustic centers in the pons. The chemical mechanism involves central and peripheral chemoreceptors that detect changes in blood oxygen, carbon dioxide, and hydrogen ion levels and stimulate the respiratory centers.

1. REGULATION OF
RESPIRATION

2. Respiration is regulated by two
mechanisms:
• Nervous or neural mechanism
• Chemical mechanism
Nervous Mechanism:
• It involves respiratory centers, afferent and efferent nerves.
• Respiratory centers: The centres in the medulla oblongata and
pons that collects sensory information about the level of oxygen
and carbon dioxide in the blood and determines the signals to be
sent to the respiratory muscles.
• Stimulation of these respiratory muscles provide respiratory
movements which leads to alveolar ventilation.
• Respiratory centers are situated in the reticular formation of the
brainstem and depending upon the situation in brainstem, the
respiratory centers are classified into two groups:
1. Medullary centers
2. Pontine centers

3. There are two centers in each group:
• Medullary Centers:
A. Inspiratory center
B. Expiratory center
• Pontine Centers:
A. Pneumotaxic center
B. Apneustic center

4. Inspiratory center:
• Inspiratory center is situated in upper part of medulla
oblongata
• This center is also called dorsal group of respiratory neurons
• It is formed by nucleus of tractus solitarius
• Function: it is concerned with inspiration.
Expiratory center:
• It is situated in medulla oblongata anterior and lateral to the
inspiratory center
• It is also called ventral group of respiratory neurons
• It is formed by neurons of nucleus ambiguous and nucleus
retro ambiguous
• Function: this center is inactive during quiet breathing and
inspiratory center is the active center, but during forced
breathing or when the inspiratory center is inhibited it
becomes active.

5. Pneumotaxic center:
• It is situated in upper Pons.
• It is formed by nucleus parabrachialis.
• Function: it controls medullary respiratory centers,
particularly the inspiratory center through
apneustic center. It always controls the activity of
inspiratory center so that duration of inspiration is
controlled.
Apnuestic center:
• It is situated in lower Pons.
• Function: this center increases depth of inspiration
by acting directly on the inspiratory center.

6. Nervous connections of respiratory
centers:Afferent pathway:
• Respiratory center receive afferent impulses
from different parts of the body according to
movements of thoracic cage and lungs.
• From peripheral chemoreceptor and
baroreceptor impulses are carried by
glossopharyngeal and vagus nerves to
respiratory center.
Efferent pathway:
• Nerve fiber from respiratory center leaves the
brain and descend in anterior part of lateral
column of spinal cord.
• These nerve fibers terminate in the motor
neurons in the anterior horn cells of the cervical
and thoracic segments of spinal cord.
• From motor neurons two sets of nerve fiber
arise which supplies particular muscle:
1. Phrenic nerve fibers: supplies diaphragm
2. The intercostal nerve fibers: supplies
intercostal muscles.

7. Factors affecting respiratory centers:
1) Impulses from higher centers: impulses from
higher center can stimulate or inhibit respiratory
centers directly.
2) Impulses from stretch receptors of lung:

8. 3) Impulses from ‘J’ receptors of lungs:
• ‘J’ receptors are juxtacapillary receptors which are present in wall
of the alveoli and have close contact with the pulmonary
capillaries.
• These receptors get stimulated during conditions like pulmonary
edema, pulmonary congestion, pneumonia as well as due to
exposure of exogenous and endogenous chemicals like histamine,
serotonin.
• Stimulation of ‘J’ receptor produces a reflex response called apnea.
4) Impulses from irritant receptors of lungs:
• Irritant receptors are situated on the wall of bronchi and
bronchioles of lungs.
• They got stimulated by harmful chemicals like ammonia and sulfur
dioxide.
• Stimulation of irritant receptors produces reflex hyperventilation
along with bronchospasm which prevents entry of harmful
chemicals into the alveoli.

9. 5) Impulses from Proprioceptors:
• Proprioceptors are the receptors which give response to the
change in the position of different parts of the body.
• This receptors are situated in joints, muscles and tendons.
They get stimulated during exercise and sends impulses to the
cerebral cortex.
• Cerebral cortex in turn by activating medullary respiratory
centres causes hyperventilation.
6) Impulses from Thermoreceptors:
• Thermoreceptors give response to change in the body
temperature.
• They are cutaneous receptors namely cold and warmth
• When this receptors get stimulated they send signals to
cerebral cortex
• Cerebral cortex in turn stimulates respiratory centres and
causes hyperventilation.

10. 7) Impulses from pain receptors:
• Pain receptors give response to pain stimulus.
• Like other receptors this receptors also send impulses to the
cerebral cortex.
• Cerebral cortex in turn stimulates the respiratory centers ad
causes hyperventilation.
8) Cough reflex:
• This is a protective reflex caused by irritation of parts of the
respiratory tract beyond nose like larynx, trachea and bronchi.
• Irritation of any of this part causes stimulation of vagus nerve
and cough occurs.
• Cough begins with deep inspiration followed by forceful
expiration with closed glottis.
• So the intrapleural pressure rises above 100 mm Hg.
• Then, glottis is suddenly opened with explosive outflow of air
at a higher velocity. So the irritants may be expelled out of
the respiratory tract.

11. 9) Sneezing reflex:
• It is also a protective reflex which occurs due to the irritation
of nasal mucus membrane.
• During irritation of nasal mucus membrane, the olfactory
receptors and trigeminal nerve endings present in the nasal
mucosa are stimulated leading to sneezing.
• Sneezing starts with deep inspiration, followed by forceful
expiratory effort with opened glottis and the irritants are
expelled out of the respiratory tract.
10) Deglutition reflex:
• During swallowing of the food, the respiration is arrested for
a while.
• Temporary arrest of the respiration is called apnea and apnea
which occurs during swallowing called swallowing apnea or
deglutition apnea.
• This prevents entry of the food particles into the respiratory
tract.

12. Chemical Mechanism:
• The chemical mechanism of the respiration is operated
through the chemoreceptors.
Chemoreceptors:
• They are the receptors which give response to change
in the chemical constituents of blood like..
A. Hypoxia
B. Hypercapnea
C. Increased hydrogen ions concentration (decreased
blood pH)
• Chemoreceptors are classified into two groups:
1. Central chemoreceptors
2. Peripheral chemoreceptors

13. Central chemoreceptors
Situation:
• They are situated in deeper part
of medulla oblongata, close to
the dorsal group of neurons.
• This area is known as
chemosensitive area and neurons
are called as chemoreceptors.
• They are in close contact with
blood and CSF.
Action:
• They are very sensitive to increase in
hydrogen ion concentration.
• Hydrogen ion cannot cross the blood
brain barrier and blood cerebrospinal
fluid barrier.
• On the other hand if carbon dioxide
increases in the blood as it is a gas it
can cross both the barrier easily and
after entering the brain it combines
with water to form carbonic acid.
• As carbonic acid is unstable, it
immediately dissociates into hydrogen
and bicarbonate ions.
• The hydrogen ion now stimulates the
central cemoreceptors which
stimulates dorsal group of respiratory
center (inspiratory group) and
increase rate and force of breathing.
The chemoreceptors present in the brain are called central
chemoreceptors.

14. Peripheral chemoreceptors:
Situation: Action:
• They are very sensitive to
reduction in partial pressure
of oxygen.
• Whenever, the partial
pressure of oxygen decreases
these chemoreceptors
become activated and send
impulses to inspiratory
center and stimulate them.
• Thereby increases rate and
force of respiration and
rectifies the lack of oxygen.
The receptors are present in peripheral portions of the body
that’s why called as peripheral chemoreceptors.

15. Thank you