Regulation of Respiration

https://nabeelbeeran.blogspot.com/
Regulation of Respiration

1. REGULATION OF RESPIRATION
Dr. NabeelBeeran
Department of Physiology
06/12/2019
1

2. Specific Learning Objectives
At the end of class students should be able to:
1.Describe the neural regulation of respiration.
2.Describe the chemical regulation of respiration.
2

3. Overall Control of Activity of Respiratory Centre
A) Involuntary (Automatic) Control:
I-Neurogenic Reflexes
II-Chemoreceptor Reflexes (Chemical control)
B) Voluntary Control
3

4. General organization of respiratory control mechanisms

5. NEURAL REGULATION OF
RESPIRATION
5

6. Medullary centers:
•Dorsal respiratory group of neurons
•Ventral respiratory group of neurons
Pontine centers:
•Apneusticcenter
•Pneumotaxiccenter
6

7. MEDULLARY CENTERS
1.Dorsal Respiratory Group of Neurons (DRG):
•Diffusely situated in the nucleus of tractus solitarius (NTS),
upper part of the medulla oblongata.
•Inspiratoryneurons.
-Autorhythmicproperty:generate inspiratory ramp.
Responsible for basic rhythm of respiration.
7

8. 2. Ventral Respiratory Group of Neurons (VRG):
•Situated in the medulla oblongata, anterior and lateral to the NTS.
•Ventral respiratory group has both inspiratory and expiratory
neurons.
•Normally, ventral group neurons are inactive during quiet
breathing and become active during forced breathing.
•During forced breathing, these neurons stimulate both inspiratory
and expiratory muscles.
8

9. 9
Respiratory centers in medulla

10. PONTINE CENTERS
ApneusticCenter:
•Apneusticcenter is situated in the reticular formation of lower
pons.
•Apneusticcenter increases depth of inspiration by acting
directly on dorsal group neurons.
10

11. PneumotaxicCenter:
•Situated in the dorsolateral part of reticular formation in upper
pons, and acts through apneusticcenter.
•Pneumotaxiccenter inhibits the apneusticcenter so that the
dorsal group neurons are inhibited. Because of this, inspiration
stops and expiration starts.
•Thus, pneumotaxiccenter influences the switching between
inspiration and expiration.
•Pneumotaxiccenter increases respiratory rate by reducing the
duration of inspiration.
11

12. 12
Respiratory centers in Pons

13. INTEGRATION OF RESPIRATORY CENTERS
Role of Medullary Centers:
•Dorsal respiratory group of neurons are responsible for the normal
rhythm of respiration by discharging impulses rhythmically.
•These impulses are transmitted to respiratory muscles by phrenic
and intercostal nerves.
•Ramp signals are not produced continuously but only for a period
of 2 seconds, during which inspiration occurs. After 2 seconds,
ramp signals stop abruptly and do not appear for another 3
seconds. Switching off the ramp signals causes expiration.
13

14. •Normally, during inspiration, dorsal respiratory group neurons
inhibit expiratory neurons of ventral group.
•During expiration, the expiratory neurons inhibit the dorsal
group neurons. Thus, the medullaryrespiratory centers
control each other.
Significance of inspiratory ramp signals:
•Steady increase in lung volume during inspiration rather than
respiratory gasps.
14

15. 15
Interaction between pontineand medullary
respiratory centers

16. Pre-BÖtzingercomplex (pre-BÖTC)
•Central pattern generator; ‘pace-maker cells’.
•Discharges rhythmically & responsible for initiation of rhythmic
respiration
•Located between nucleus ambigus& lateral reticular formation
on either side of the medulla.
•DRG & VRG respiratory neurons project to pre-BÖTC.
•It sends rhythmic impulses to phrenic motor neurons
16

17. Role of Pontine Centers:
•Pontine respiratory centers regulate the medullary centers.
•Apneusticcenter accelerates the activity of dorsal group of
neurons and the stimulation of this center causes prolonged
inspiration.
•Pneumotaxiccenter inhibits the apneusticcenter and restricts
the duration of inspiration.
17

18. Effects of transection of brainstem at various levels on
pattern, rate, and depth of respiration.

19. CHEMICAL REGULATION OF
RESPIRATION
19

20. Chemoreceptors:
•Chemoreceptors are the sensory nerve endings, which are
sensitive to changes in pCO
2, pO
2and pH of blood.
•Peripheral chemoreceptors
•Central chemoreceptors
20

21. Peripheral chemoreceptors:
•Carotid body is situated near bifurcation of common carotid
artery.
•Aortic body is located at arch of aorta.
•Chemoreceptors in the carotid body are supplied by Hering
nerve, branch of glossopharyngeal nerve.
•Chemoreceptors in the aortic body are supplied by aortic
nerve branch of vagus nerve.
21

22. Location of carotid bodyHistology of carotid body
22

23. Mechanisms of increased ventilation by hypoxia

24. Central chemoreceptors:
•Central chemoreceptors are situated in deeper part of
medulla oblongata, close to the dorsal respiratory group of
neurons.
•This area is known as chemosensitivearea and the neurons
are called chemoreceptors.
•Chemoreceptors are in close contact with blood and
cerebrospinal fluid.
•Responsible for 70% to 80% of increased ventilation through
chemical regulatory mechanism.
24

25. Location of central chemoreceptor areas on ventral
surface of medulla

26. Mechanism of action:
•Stimulant for central chemoreceptor-increased H
+
ion
concentration.
•If H
+
ion concentration increases in the blood, it cannot stimulate
the central chemoreceptors because, the H
+
ions from blood
cannot cross the blood-brain barrier.
•If CO
2increases in the blood, it can easily cross the blood-brain
barrier and enter the interstitial fluid of brain.
•After diffusion:
CO
2+ H
2O → H
2CO
3→ H
+
+ HCO
3
-
26

27. •H
+
ions stimulate the central chemoreceptors.
•The excitatory impulses reach dorsal respiratory group of
neurons, resulting in increased ventilation.
•Excess CO
2 is washed out and respiration is brought back to
normal.
27

28. 28

29. Summary
29

30. References
1.GuytonandHallTextbookofMedicalPhysiology.
2.Ganong’sReviewofMedicalPhysiology.
3.GKPal,ComprehensiveTextbookofPhysiology-Volume2.
4.InduKhuranaTextbookofMedicalPhysiology.
30

31. •PPT reviewed by review committee on 19/12/2019.
31

32. THANK YOU
32