regulation of respiration inspirationexpiration.pptx

Respiration inspiration

1. Regulation of Respiration

2. The normal pulmonary ventilation can be adjusted to the requirements of the body by two mechanisms: Nervous and Chemical Nervous Regulation of Respiration A . Voluntary Control of Respiration 1 . Rate and/or depth of respiration can be modified at will only for a specific period . 2 . Examples: Voluntary hyperventilation; and breath holding . 3 . Pathway via corticospinal tract (bypasses the medullary respiratory neurons ).

3. B. Automatic Control of Respiration Medullary and Pontine respiratory centres Medullary respiratory centre : I and E-neurons 1 . Shows rhythmic discharge with varying frequencies from pacemaker cells in pre- Botzinger complex near nucleus ambiguous . 2 . I and E neurons show reciprocal innervation . 3 . Receives afferents from respiratory chemo- receptors.

4. Pontine respiratory centre : Apneustic and pneumotaxic 1 . Apneustic centre ( i) located in lower pons , ( ii) its neurons are tonically active → activates I-neurons , (iii) inhibited by afferents in the vagus nerve from the airways and lungs, therefore, if vagi are cut arrest of respiration in inspiration, called apneusis .

5. 2 . Pneumotaxic centre ( i) located in upper pons , ( ii) inhibits the neurons in lower pons → prevents apneusis . Note : All these respiratory centres are bilaterally represented in the brain stem with same sided control and freely communicate with each other .

6. Genesis of Respiration 1 . Genesis of inspiration. Apneustic centre → (+)I-neurons discharge over pathways in spinal cord to C3,4,5 and T1,2→ contraction of inspiratory muscles and inspiration starts . 2 . Genesis of expiration - begins with inhibition of inspiration (brought by ): ( i) I-neurons → (+) pneumotaxis centre → (-) apneustic centre . ( ii) Pulmonary stretch receptors → via vagus → (-) apneustic centre . ( iii) Pneumotaxic centre → (+) E-neurons → (-) I-neurons.

7. Factors affecting the respiratory centre 1 . Chemical stimuli (CO2, O2 and H +) 2 . Non-chemical stimuli ( i) Afferents from higher centres mediated by : ( a) Corticobulbar tracts ; ( b) Corticospinal tract → voluntary control of respiration ; ( c) Pain and emotional stimuli via hypothalamus and limbic system → stimulate respiration ; ( d) Fever via anterior hypothalamus → Tachypnoea (rapid, shallow respiration ).

8. (ii) Vagal afferents ( a) Hering -Breuer inflation reflex: Steady inflation of lungs → (+) pulmonary stretch receptor → (-) apneustic centre → (-) I-neurons → prolonged expiration . Significance : Threshold level is at 1-1.5 L, therefore, determines the pattern of breathing during exercise . ( b) Hering -Breuer deflation reflex: marked deflation of the lungs→↓ in duration of expiration . ( c) Hyperinflation of lungs → (+) juxta - pulmonary capillary receptors (or J-receptors) → reinforce action of pneumotaxis centre → apnoea, followed by tachypnoea ,↓ BP and↓ H.R. (d ) After cutting the vagi , respiration becomes deep and slow.

9. (iii) Proprioceptor afferents: Joint movement → (+) proprioceptors in muscle, joints and tendons (+) I-neurons→↑ rate and depth of respiration (thus helps increase ventilation during exercise ). ( iv) Afferent from pharynx, trachea and bronchi ( a) Vagal afferents endings in respiratory passage function as irritant receptors, stimulation of these receptors, in conducting zone → cough or sneezing reflex (i.e., deep inspiration followed by forced expiration); in respiratory zone → tachypnoea and bronchoconstriction (thereby limiting the irritants to reach the alveoli ).

10. ( b) Swallowing (deglutition) reflex: Swallowing movement inhibition of respiration (deglutition apnoea). Afferents in IX nerve inhibit the respiratory centre. v ) Afferents from baroreceptors Inj. of adrenaline ( Ep ) in high dose → ↑ BP which via baroreceptors → (-) respiratory centre apnoea (example: adrenaline apnoea). (Note: Adrenaline in small dose → stimulate respiration ) ( vi) Afferents from chemoreceptors ↓PO₂ or ↑ PCO₂ → (+) chemoreceptors → (+) respiratory centre →↑ rate and depth of respiration .

11. Chemical Regulation of Respiration : Chemical factors which affect the ventilation are; Hypoxia, Hypercapnea, increased hydrogen ion concentration (PO2, PCO2, H+ ion). Their effect is mediated via respiratory chemoreceptors Chemoreceptors :- There are 2 types of chemoreceptors - Peripherial chemoreceptors Central chemoreceptors Peripherial chemoreceptors Peripheral chemorceptors are Carotid bodies & Aortic bodies. Carotid body is present near the carotid artery bifurcation on each other. Carotid body contain cells which can sense the level of Po2, PCO2, H+ ion. Carotid body sends impulse to respiratory center in medulla via X cranial nerve (Vagus).

12. Central Chemoreceptors :- They are located in the medulla near the respiratory center. These central chemorceptors monitor the effect of PO2, PCO2 and H+ ion. This H+ ion is generated by CO2 in the extra cellular fluid of the brain which surronds the central chemoreceptors. When CO2 increases, we get: CO2 + H2O H + + HCO3- Increased H+ directly stimulates the central Chemoreceptors.

13. Effect of PO2, PCO2, H+ ion on Peripheral & Central Chemoreceptors : Effect on Peripheral Chemoreceptors :- Decreasd PO2 in the arterial blood - stimulates peripheral chemoreceptors when arterial PO2 falls below 60 mmHg Increased PCO2 in the arterial blood - weakly stimulates peripheral chemoreceptors. Increased H+ ion in the arterial blood - Stimulates Peripheral Chemoreceptors. Effect on Central Chemoreceptors :- Decreased PO2 in the arterial blood - Depresses the central chemoreceptors when arterial PO2 falls below 60mmHg. Increased PCO2 in the arterial blood - Strongly stimulates central chemoreceptors. It is dominant control of ventilation. PCO2 level more than 70-80 mmHg directly depresses the central chemoreceptors and respiratory center. Increased H+ ion in the arterial blood - Does not affect