1. Regulation of respiration
Breathing is controlled by the central neuronal network to meet the metabolic demands of the body
Neural regulation
Chemical regulation

2. Respiratory center Definition:
A collection of functionally similar neurons that help to regulate the respiratory movement

3. Respiratory center Spinal cord: Medulla Pons
respiratory motor neurons
Medulla
Pons
Higher respiratory center:
cerebral cortex, hypothalamus & limbic system
Basic respiratory center: produce and control the respiratory rhythm

4. Neural regulation of respiration
Voluntary breathing center
Cerebral cortex
Automatic (involuntary) breathing center
Medulla
Pons

6. Neural generation of rhythmical breathing
1. The discharge of medullary inspiratory neurons provides rhythmic input to the motor neurons innervating the inspiratory muscles.
2. Then the action potential cease, the inspiratory muscles relax, and expiration occurs as the elastic lungs recoil.

7. Inspiratory neurons
Expiratory neurons

8. Respiratory center
Dorsal respiratory group (medulla) – mainly causes inspiration
Ventral respiratory group (medulla) – causes either expiration or inspiration
Pneumotaxic center (upper pons) – inhibits apneustic center & inhibits inspiration,helps control the rate and pattern of breathing
Apneustic center (lower pons) – to promote inspiration

10. Hering-Breuer inflation reflex (Pulmonary stretch reflex)
The reflex is originated in the lungs and mediated by the fibers of the vagus nerve:
Pulmonary inflation reflex:
inflation of the lungs, eliciting expiration.
Pulmonary deflation reflex:
deflation, stimulating inspiration.

11. Pulmonary inflation reflex
Inflation of the lungs  +pulmonary stretch receptor +vagus nerve  -medually inspiratory neurons  +eliciting expiration

12. Pulmonary inflation reflex
Role:
Feedback from the lungs helps terminate inspiration and enhance inspiration/expiration transition, thus increasing respiratory rate.

14. Chemical control of respiration
Chemoreceptors
Central chemoreceptors: medulla
Stimulated by [H+] in the CSF
Peripheral chemoreceptors
Carotid body
Stimulated by arterial PO2 or [H+]
Aortic body

15. Central chemoreceptors

16. Peripheral chemoreceptors
Chemosensory neurons
that respond to changes
in blood pH and gas
content are located in
the aorta and in the
carotid sinuses; these
sensory afferent
neurons alter CNS
regulation of
the rate of ventilation.

17. Peripheral chemoreceptors and their afferent nerves

19. Effect of carbon dioxide on pulmonary ventilation
Small changes in the
carbon dioxide content
of the blood quickly
trigger changes in
ventilation rate.
CO2    respiratory activity

20. BBB
CO2 H+

21. Central and peripheral
chemosensory neurons that respond to increased carbon dioxide levels in the blood are also stimulated by the acidity from carbonic acid, so they “inform” the ventilation control center in the medulla to increase the rate of ventilation.
CO2+H2O  H2CO3  H++HCO3-

22. Effect of carbon dioxide on pulmonary ventilation
Very high levels of CO2 actually inhibits ventilation and may be lethal.
This is because high concentration of CO2 act directly on the medulla to inhibit the respiratory neurons by an anesthesia-like effect.

23. Effect of hydrogen ion on pulmonary ventilation
[H+]    respiratory activity
Regardless
of the source,
increases in
the acidity of
the blood cause
hyperventilation.

24. Regardless of the source, increases in the acidity of the blood cause hyperventilation, even if carbon dioxide levels are driven to abnormally low levels.

25. Effect of low arterial PO2 on pulmonary ventilation
PO2    respiratory activity
A severe reduction in the arterial concentration of
oxygen in the blood can stimulate hyperventilation.

26. Chemosensory neurons
that respond to decreased
oxygen levels in the blood
“inform” the ventilation
control center in the
medulla to increase the rate of ventilation.

27. In summary:
The levels of
oxygen, carbon
dioxide, and
hydrogen ions
in blood and CSF
provide information
that alters the
rate of ventilation.

28. Regulation of respiration

29. Questions
1. Why is increased depth of breathing far more effective in evaluating alveolar ventilation than is an equivalent increase in breathing rate?

30. Questions
2. Describes the effects of PCO2, [H+] and PO2 on alveolar ventilation and their mechanisms.
CO2 ­-­  respiratory activity; Peripheral mechanism and central mechanism, the latter is the main one.
[H+]  ­-­  respiratory activity; Peripheral mechanism and central mechanism, the former is the main one.
PO2  ­-­  respiratory activity; Peripheral mechanism is excitatory.

31. Questions
3. What is the major result of the ventilation-perfusion inequalities throughout the lungs?
1) An increase of the ventilation-perfusion ratio will result in an increase of alveolar dead space.
2) A decrease of the ventilation-perfusion ratio will result in the functional A-V shunt.
3) The major result of the ventilation-perfusion inequality is to decrease the PO2 of systemic arterial blood. Because the diffusion coeffient for CO2 is about 20 times that for O2.

32. Questions
4. Describe the factors that influence gas exchange in the lungs.

33. Questions
5. If an experimental rabbit’s vagi were obstructed to prevent them from sending action potential, what will happen to respiration?
1) Pulmonary stretch reflex: Inflation of the lungs  +pulmonary stretch receptor +vagus nerve  -medually inspiratory neurons  +eliciting expiration.
2) The feedback from the lungs helps terminate inspiration and enhance inspiration/expiration transition, thus increasing respiratory rate.
3) In the animal experiment, if the vagi were destrcted, prolonged inspiration and deep slow breathing could be observed.