regulation of ventilation

1. REGULATION OF ventilation
DR. MADHU KIRAN

2. Breathing is regulated by two mechanisms:
• Nervous or neural mechanism
• Chemical mechanism

3. 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

4. There are two centers in each group:
• Medullary Centers:
A. Dorsal respiratory group
B. Ventral respiratory group
• Pontine Centers:
A. Pneumotaxic center
B. Apneustic center

5. Pre- Botzinger complex:
• Spontaneous automatic rhythmic respiration is initiated
by small group of synaptically coupled pace maker
cells in the pre-botzinger complex situated on either
side of medulla between nucleus ambiguous and lateral
reticular nucleus.
• Pre-BOTC neurons discharge rhythmically, producing
rhythmic discharge in phrenic motor neurons
• Pre-BOTC contact hypoglossal nuclei, and the tongue
is involved in the regulation of airway resistance.
• DRG & VRG involved in generation of respiratory
pattern project to pre-BOTC.

6. Dorsal respiratory group
• Center is situated in upper part of medulla oblongata
• This center is previously called inspiratory centre.
• It is formed by nucleus of tractus solitarius.
• DRG constitute the initial intra cranial processing station for
afferent inputs from 9th & 10th cranial nerves, which originate
from peripheral chemoreceptors, baroreceptors, and several
other receptors of airways and lungs.
• Function: it is concerned with inspiration and cause rhythmic
inspiratory discharge.
• Action potential in inspiratory neurons begin weakly and
increase steadily in a ramp like manner for about 2 sec. then it
ceases abruptly for 3 sec, which turns off inspiratory
muscles(diaphragm) and allows elastic recoil of lung and
chest wall to cause expiration.
.

7. Ventral respiratory group:
• It is situated in medulla oblongata anterior and
lateral to the DRG
• Contains both inspiratory and expiratory neurons.
• It is formed by neurons of nucleus retro fascialis,
nucleus paraambiguous 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

8. 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.
Stimulation leads to shallow and rapid breathing.
Apnuestic center:
• It is situated in lower Pons.
• Normally inhibited by pneumotaxic centre and vagus.
• Function: this center increases depth of inspiration by acting
directly on the inspiratory center.

9. 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.

10. Effect of lesion/ Transection
• Above pons: loss of voluntary control
Respiration remains normal
• At upper/mid pons:
 slow and deep breathing (vagi intact)
 Apneustic breathing (or prolonged respiratory spasm)
when vagi are also cut.
• At inferior border of pons & upper border of medulla:
spontaneous respiration continues some what irregular
and gasping occurs
• Below medulla: Respiration stops.

11. 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:

12. 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.

13. 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.

14. 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.

15. 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.

16. 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)

17. • Chemoreceptors are classified into two groups:
1. Central chemoreceptors
2. Peripheral chemoreceptors

18. 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.

19. 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.

20. Thank you