PHYSIOLOGY OF CONTROL OF BREATHING

1
PHYSIOLOGY OF CONTROL OF BREATHING
Prof. Sultan Ayoub Meo MBBS, M.Phil, Ph.D (Pak),
M Med Ed (Dundee), FRCP (London), FRCP (Dublin),
FRCP (Glasgow), FRCP (Edinburgh) Professor and
Consultant, Department of Physiology, College of
Medicine, King Saud University, Riyadh, KSA
2
REGULATION OF RESPIRATION

• Respiration is regulated by three different
  mechanisms
• Nervous regulation
• Chemical regulation
• Peripheral chemoreceptor control system.

3
NERVOUS REGULATION

• Dorsal respiratory group
• Ventral respiratory group
• Pneumotaxic center
• Apneustic center

4
NERVOUS REGULATION
5
NERVOUS REGULATION
Controls automatic breathing. Consists of
interacting neurons that fire either during
inspiration (I neurons) or expiration
(E neurons).
6
NERVOUS REGULATION
I neurons Located primarily in dorsal
respiratory group (DRG) Regulate activity of
phrenic nerve. Project to and stimulate spinal
interneurons that innervate respiratory
muscles. E neurons Located in ventral
respiratory group (VRG) Passive
process. Controls motor neurons to the internal
intercostal muscles. E neurons inhibit the I
neurons. Rhythmicity of I and E neurons may be
due to pacemaker neurons.
7
NERVOUS REGULATION
Apneustic center Promote inspiration by
stimulating the I neurons in the medulla.
Pneumotaxic center Antagonizes the apneustic
center. Inhibits inspiration.
8
DORSAL RESPIRATORY GROUP OF NEURONS
Dorsal respiratory group of neurons are located
bilaterally in the dorsal portion of the medulla
oblongata in / close to the nucleus of the
tractus solitarius. Dorsal group of neuron is
made up of I neurons. They receive afferents
from the air ways and carotid and aortic bodies
which terminate in the nucleus of tractus
solitarius.
9
DORSAL RESPIRATORY GROUP OF NEURONS
Functions On stimulation initiate normal
inspiration Rhythmically discharges inspiratory
signals Inspiratory signals begin weekly and
increase in ramp fashion for 2 seconds, then
cease for next 3 seconds and then begin another
cycle.
10
VENTRAL RESPIRATORY GROUP OF NEURONS
Ventral respiratory group of neurons extend
through the nucleus ambigus and nucleus
retroambigus in the ventrolateral part of the
medulla oblongata. The ventral group has E
neurons at its caudal end I neurons in its mid
portion E neurons at its rostral ends. The
neurons in the rostral end of this group appear
to inhibit I neurons during expiration.
11
FUNCTIONS OF VENTRAL RESPIRATORY GROUP OF NEURONS

• Ventral respiratory group neurons are inactive
  during normal quiet respiration.
• Normal quiet breathing is caused by repetitive
  inspiratory signals from the dorsal respiratory
  group, transmitted mainly to the diaphragm.
  Expiration results from the elastic recoil of the
  lungs.
• These neurons provide active role / strong
  discharge during forceful expiration.

12
PNEUMOTAXIC CENTER

• Pneumotaxic center located dorsally in the
  nucleus parabrachialis of the upper pons,
  transmits impulses to the inspiratory area.
• Functions Transmit signals to the dorsal
  inspiratory areas to switch off the inspiratory
  ramp signals, controlling the duration of the
  filling phase of the lungs. When these signals
  are strong inspiration lasts for 0.5 sec. When
  weak, inspiration lasts as long as 5 seconds,
  filling the lungs with excess air.
•  Stimulation of the pneumotaxic center limits the
  period of inspiration,  It increases the rate of
  respiration

13
APNEUSTIC CENTER

• Apneustic center Situated in lower pons.
• Functions It send signals to the dorsal
  respiratory group of neurons to prevents the
  switch off of inspiratory ramp signals
• Stimulation of this centre prolongs the period of
  inspiration.
• An increase in the duration of inspiration result
  in a deeper and more prolonged inspiratory
  effort.
• The rate of respiration becomes slow because of
  the greater depth of inspiration

14
CHEMICAL REGULATION OF RESPIRATION
15
CHEMICAL REGULATION OF RESPIRATION

• Respiratory system maintain the concentration of
  CO2 and O2
• CO2 is most important stimulus for regulating
  respiratory rate.
• Effects of H and CO2 on the chemosensitive area
  Effects of blood H ions H ions that provide
  the important stimulus for regulating the rate of
  respiration, blood H ions cannot effect the
  chemosensitive area alone because it cannot cross
  the blood brain barrier and blood C.S.F barrier.
• Effects of blood CO2 Blood CO2 can cross the
  blood brain and blood C.S.F barriers, CO2 in
  blood combines with H2O to form carbonic acid.
  This CO2H2O form H2CO3

16
CHEMICAL REGULATION OF RESPIRATION
Carbonic acid rapidly dissociates into H ions
and bicarbonate (HCO3-) ions. Increase in CO2
will increase the H, but on the other hand a
decrease in CO2 will cause a decrease in H ions.
H ions stimulate the chemosensitive areas.
17
Chemoreceptors
2 groups of chemo-receptors that monitor changes
in blood PC02, P02, and pH. Central
Medulla. Peripheral Carotid and aortic bodies.
Control breathing indirectly via sensory nerve
fibers to the medulla (X, IX).
18
PERIPHERAL CHEMORECEPTORS
19
PERIPHERAL CHEMORECEPTORS
20
PERIPHERAL CHEMORECEPTORS
Effects of oxygen The peripheral chemoreceptors
detect changes in PO2. The arterial PO2 falls
from 104 mm Hg, impulses from these receptors are
carried to the brain via the vagus and
glossopharyngeal nerves, result in an increased
rate and depth of respiration. Effect of
decreased pH (increased H ions) Increased
alveolar ventilation lowers the PCO2 in the
arterial blood and reduces the amount of acid,
which tends to return the arterial pH to normal.
21
PERIPHERAL CHEMORECEPTORS

• Effects of CO2 CO2 stimulates the peripheral
  chemoreceptors.
• Peripheral chemoreceptors are stimulated by
  decreased or increased CO2, increased H ion
  concentration, and decreased pH and low O2. When
  peripheral chemoreceptors are stimulated, the
  impulses transmitted from these receptor sites to
  the dorsal inspiratory area causes the switch off
  of the inspiratory ramp signals. Since the period
  of inspiration becomes limited there is an
  increase in the rate of respiration.

22
CHEMORECEPTOR CONTROL
Central chemoreceptors More sensitive to changes
in arterial PC02. H20 C02 H cannot cross the
blood brain barrier. C02 can cross the blood
brain barrier and will form H2C03. Lowers pH of
CSF. Directly stimulates central chemoreceptors.
23
CHEMORECEPTOR CONTROL

• Peripheral chemoreceptors
• Are not stimulated directly by changes in
  arterial PC02.
• H20 C02 H2C03 H
• Stimulated by rise in H of arterial blood.
• Increased H stimulates peripheral
  chemoreceptors.

24
CHEMORECEPTOR CONTROL OF BREATHING
25
(No Transcript)
26
THANK YOU