Respiratory Drive

1. HypoxicRespiratoryDrive
O2, CO2 and H+ ??!!

2. ● John Scott Haldane discovered that the respiratory reflex
is triggered by an excess of CO2 in the blood, rather than a
lack of O2.
● He described in details of regulation of respiratory drive by
CO2 and its effects on blood H+.
● And the Effect of ‘loading of oxygen in the lung facilitating
unloading of carbon dioxide’ is named after him and
popularly known as Haldane effect.
● Father of Oxygen Therapy
Background

3. OVERVIEW
RESPIRATORY
CONTROL
Control of breathing is broadly divided into
three categories:
• Neural control (voluntary and automatic
control)
• Chemical control (PO2, PCO2 and pH)
• Nonchemical (reflexes from lungs and
chest wall) control

4. RESPIRATOR
Y CENTER
• Composed of several groups of neurons
located bilaterally in the medulla oblongata
and pons of the brain stem, as shown in
Figure 42-1.
(1) A dorsal respiratory group, located in the
dorsal portion of the medulla (INSPIRATION)
(2) a ventral respiratory group, located in the
ventrolateral part of the medulla (EXPIRATION);
and (3) the pneumotaxic center, located dorsally
in the superior portion of the pons, which mainly
controls rate and depth of breathing

5. ● The ultimate goal of respiration is to maintain
proper concentrations of O2, CO2, and H+ in
the tissues.
● Excess CO2 or excess H+ in the blood
mainly act directly on the respiratory
center→ greatly ↑ strength of both the
inspiratory and the expiratory motor signals to
the respiratory muscles.
● Oxygen, does NOT have a major direct
effect on the respiratory center of the brain in
controlling respiration.
● Instead, it acts almost entirely on peripheral
chemoreceptors located in the carotid and
aortic bodies, → respiratory center for control
of respiration.
CHEMICAL CONTROL
OF RESPIRATION

6. Chemosensitive Area of the
Respiratory Center Beneath the
Medulla’s Ventral Surface.
● An additional neuronal area, a
chemosensitive area.
● Located bilaterally, lying only 0.2
millimeter beneath the ventral surface
of the medulla.
● This area is highly sensitive to
changes in either blood Pco2 or H+
concentration → excites the other
portions of the respiratory center.
DIRECT CONTROL OF RESPIRATORY CENTER
ACTIVITY BY CO2 AND H+

7. Excitation of the Chemosensitive Neurons by H+
Is Likely the Primary Stimulus.
● Chemosensitive area are especially excited by
H+; may be the only important direct stimulus for
these neurons.
● However, H+ ions do not easily cross the blood–
brain barrier.
● Changes in H+ concentration in the blood have
considerably less effect in stimulating the
chemosensitive neurons than changes in blood
CO2, even though CO2 is believed to stimulate
these neurons secondarily

8. CO2 Indirectly Stimulates the
Chemosensitive Neurons.
● Although CO2 has little direct effect in
stimulating the neurons in the
chemosensitive area, it does have a potent
indirect effect.
● CO2 + water of the tissues → carbonic acid,
which dissociates into H+ and HCO3−; the
H+ then have a potent direct stimulatory
effect on respiration.

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