Regulation of Respiration

Prepared by –
Dr Mythri G
Associate Professor
Department of Physiology
RajaRajeswari Medical College and Hospital

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 I. Neural Regulation of Respiration:
Neural
Regulation of
Respiration

Medullary Pontine
Respiratory Respiratory
Centres Centres

Dorsal Ventral
Pneumotaxic Apneustic
Respiratory respiratory
Centre Centre
Group Group

A. Medullary Respiratory Centres:

Generate basic respiratory rhythm

B.

1. Dorsal Respiratory Group:

• Located bilaterally
• Around NTS
• Inspiratory neurons- Inspiratory ramp

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2. Ventral Respiratory Group:
• Located bilaterally
• Around N. ambiguous & N. retrofacialis
• Inspiratory and expiratory neurons
• Remain inactive during quite breathing
• Role during forceful respiration-
exercise

B . Pontine Respiratory Centres:

1. Apneustic Centre:
Inhibitory neurons- B/L in lower pons
Prevents switch off of Inspiratory ramp signals
Increases TV and duration of inspiration
Stimulation -- apneusis
Normally, inhibited by Pneumotaxic centre and Vagus Nerves
Apneusis: Pause of breathing in deep inspiration

2. Pneumotaxic Centre:
Located in N. parabrachialis medialis upper pons
Inhibits Apneustic Centre
Shortens inspiration- shallow, rapid breathing

Experimental Evidence: The effects of

transections of different levels of the brainstem
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Applied Aspect:
Ondine's curse is one of the most enchanting mythical tales in the field of Medicine. The
nymph Ondine was an immortal water spirit who became human after falling in love for a
man, marrying him, and having a baby. In one of the versions of the tale, when she caught
her husband sleeping with another woman, she cursed him to remain awake in order to
control his own breathing. During the 19th century, the rare syndrome characterized by loss
of autonomic breath control, while voluntary respiration remains intact, was cleverly named
“Ondine's curse”. Nowadays, the term Ondine's curse is usually associated with congenital
central hypoventilation syndrome; however, in medical literature, it also designates several
respiratory disorders

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 II. Chemical Regulation of
Respiration:
The chemical factors regulating respiration include po2, pco2, and pH of blood. These
factors influence respiration in such a way that their own blood levels are maintained
constant.
The chemical mechanism of regulation operates through chemoreceptors – which are
sensory nerve endings highly sensitive to po2. pco2 and pH of blood

Central chemoreceptors:
th th
 Located ventral surface of medulla near exit of 9 & 10 cranial
nerves
+
 Stimulus : Increase in H ion concentration in CSF / Interstitial fluid of
brain
+
 Hypercapnia stimulates them via H ion 

+ -
(CO H O  H CO  H + HCO )
2+ 2 2 3 3
CSF separated from blood by BBB :
+ -
(impermeable to H &HCO ,
3

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 +
but CO crosses easily & liberates H  chemoreceptors)
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 Hypoxia & acidosis have no effect

Peripheral
chemoreceptors:
• Carotid & Aortic bodies
• 2 types of cells:
• Type I – Glomus cells
• Type II – Glial cells
• Type II (glial like supporting cells)
surround type I cells called Glomus
Stimulus - Increase CO ,
2
+
Decrease O & Increase H ions stimulate
2
them

Pulmonary & myocardial chemoreceptors stimulated by veratridine &

nicotine apnoea followed by tachypnoea (called pulmonary chemoreflex &
Bezold-Jarisch reflex)

Mechanism of action of pO2 on Ventilation :

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 Mechanism of action of pCO on Ventilation :
2

Mechanism of action of H+ on Ventilation

Applied Aspect:
Abnormal breathing patterns

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III. Respiratory Reflexes:
• Reflexes arising from the upper airways and lungs
• Provide feedback for fine tune breathing
• Protects the lungs from environmental insults
Receptors:
1. Slowly adapting receptors
2. Rapidly adapting receptors
3. C- fibre endings/ J receptors

HERING –BREUER REFLEX :

Also known as – “ Pulmonary Stretch Reflex”
When stimulated they inhibit Inspiration and prolong expiration.
Key points:
• Inhibitory protective reflex

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 • Strongest in rabbit
• Weakest in human
• Inactive during quite breathing
• Does not play any regulatory role in tidal respiration
• Only tries to limit Tidal volume ( when >1-1.5L) - exercise
• Bilateral vagotomyReflex
Hering-Breuer / Transient
(HBR)bilateral blockade of vagi by local
anaesthetic abolishes this reflex

Hering-Breuer Hering-Breuer
Inflation Reflex Deflation Reflex

a) Hering Breuer Inflation Reflex:

Significance of Hering Breuer:

• Protective Reflex ( Negative Feedback mechanism)
• Protects the lungs from overinflation while maintaining normal
alveolar ventilation
In Adults ( post natal habituation of HBR):
Tidal Volume > 1 litre ( >3* Normal Tidal Volume = 1.5L)

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J- Reflex

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