Presentation of respiration and reflex associated with it
- 2. REGULATION OF RESPIRATION • The main function of respiratory system is to maintain Pco2 ,Po2 and pH of arterial blood constant by adjusting ventilation. • Spontaneous respiration is produced by rhythmic discharges from the brain to the motor neurons that innervate respiratory muscles.
- 3. • Respiration is regulated by two mechanisms: • Neural control • Chemical control Neural control :Voluntary Automatic Reflex control
- 4. Voluntary control • Respiration can be controlled voluntarily to some extent because all the muscles concerned with respiration are voluntary. • The center for voluntary control is motor cortex which send impulses through corticospinal tract to the respiratory motor neurons. • Voluntary hyperventilation and voluntary apnea are possible
- 5. • The point at which breathing can no longer be voluntarily inhibited is called breaking point. • Normally it is 40 seconds Reason : During apnea there is increase in Pco2,increase in H+ and decrease in Po2.
- 7. Automatic control • Automatic centre for control of respiration are located in the pons and medulla. • These centers are located bilaterally • Nerve fibers mediating inspiration converge on phrenic motor neurons(C3,4,5) and external intercostal neurons in spinal cord.
- 8. • The fibres concerned with expiration converge on spinal cord motor neuron that supply expiratory muscles mainly internal intercostal muscles. • The motor neurons to expiratory muscles are inhibited when those supplying the inspiratory muscles are activated through reciprocal innervation.
- 9. MEDULLARY CENTERS • Rhythmic respiration is initiated by small group of pacemaker cells in the pre-Bontziger complex on both sides of medulla oblangata. • These neurons can discharge spontaneously and are responsible for the rhythmicity of respiration. • Medulla also contain dorsal respiratory group and ventral respiratory group.
- 10. DORSAL RESPIRATORY GROUP(DRG) • DRG is located in and near the nucleus of tractus solitarius(NTS). • It is made up of inspiratory neurons which are controlled by pacemaker cells in the Pre-Botziger complex. • They are active during inspiration. • They receive impulses from lungs, chemoreceptors and baro-receptors through vagus.
- 11. VENTRAL RESPIRATORY GROUP • It is located in the ventrolateral part of medulla. • It extends through nucleus ambiguus and nucleus retro-ambiguus. • It contains inspiratory and expiratory neurons. • Expiratory neurons inhibit inspiratory neurons during expiration.
- 12. Inspiratory ramp signal • Pattern of action potential produced by the respiratory center is called inspiratory ramp signal • Initially there is a latent period then the intensity of action potential increases and then decreases followed by a latent period.
- 13. • The cycle is repeated and normally the duration of one cycle is 4-5 seconds. • The impulses pass to the inspiratory muscles and produce inspiration
- 14. PONTINE CENTERS • Rhythmic discharge of medullary neurons are modified by neurons of pons and afferents coming from the receptors in airways and lungs through vagus. • In the upper part of pons there is a pair of respiratory centres called pneumotaxic centre.
- 15. • Pneumotaxic centers has inhibitory effect on I neurons. • When this area is stimulated ,I neurons are inhibited and duration of IRS is reduced. • Rate of respiration is increased and filling volume will be decreased; respiration becomes shallow and rapid.
- 16. • Lower part of pons contain another set of neurons called apneustic center which is tonically active. • It has excitatory effect on I neurons . • Stimulation of these center increases duration of IRS producing sustained contraction of inspiratory muscles with expiratory gasps in between(apneusis).
- 17. Genesis of respiration Genesis of inspiration: • Apneustic center activates the inspiratory centre. • Inspiratory center discharges over pathways in the spinal cord to C3,4,5 and T1,2 and inspiration starts.
- 18. Genesis of expiration: • Inspiratory neurons in the medulla send excitatory impulses to pneumotaxic center which inturn inhibit the apneustic center. • Pulomonary stretch receptors in lungs get stimulated during inspiration also send inhibitory impulses via vagus nerve to the apneustic center.
- 19. • Pneumotaxic center stimulates expiratory neuron in medulla which reciprocally inhibits the inspiratory center. • As a result inspiratory center stops discharging and expiration follows. • When the activity of inspiratory neurons are increased the rate and depth of inspiration is also increased.
- 22. Reflex control of respiration Receptors are classified into : • Receptors inside respiratory system • Receptors outside respiratory system Receptors inside respiratory centers: • Stretch receptors • Pulmonary irritant receptors
- 23. Stretch receptors Hering –Breuer Reflexes: Hering Breuer Inflation reflexes • When there is increase in the tidal volume greater than 1L,stretch receptors of lungs are stimulated .
- 24. • There is increased rate of afferent impulses passing through the vagus to the inspiratory centre and this leads to inhibition of inspiratory muscles • This reflex operates only when the tidal volume exceeds 1-1.5 L
- 25. Hering Breuer Deflation reflex • This reflex operates when there is excessive deflation of lungs. • Here there is stimulation of inspiration to bring back the lung volume to normal. Importance: • It functions as an important feedback mechanism and contribute to rhythmicity of respiration in NB babies.
- 26. Irritant receptors. • Pulmonary irritant receptors are found in airway epithelial cells. Stimulation of these receptors produce: • Bronchoconstriction • Hyperventilation • Cough, sneezing etc
- 27. Cough reflex: • This is a protective reflex . • Stimulation of irritant receptors of larynx, trachea and bigger bronchi produces cough. Sneezing reflex: • Stimulation of irritant receptors of nasal cavity and upper airways produces sneezing. • Sneezing is forced expiration against open glottis.
- 28. J reflex • ‘J’ receptors are juxta-capillary receptors which are present on the wall of the alveoli and have close contact with the pulmonary capillaries. • Stimulation of the ‘J’ receptors produces a reflex response, which is characterized by apnea, hyperventilation, bradycardia, hypotension and weakness of skeletal muscles.
- 29. • Conditions when ‘J’ receptors are stimulated : • i. Pulmonary congestion • ii. Pulmonary edema • iii. Pneumonia • iv. Over inflation of lungs
- 30. Receptors outside respiratory system Those which stimulate respiration: • Proprioceptors • Nociceptors • Thermoreceptors • Emotions Those which inhibit respiration: • Baroreceptors • Visceroceptors.
- 31. Proprioceptors • These are receptors in muscles, tendons and joints. • Stimulation of these receptors reflexly stimulates I neurons which will increase ventilation at the start of exercise . •Nociceptors: • These are pain receptors which when stimulated stimulate the respiratory center.
- 32. • CHEMORECEPTORS: • Acidosis and hypoxia stimulate chemoreceptors. • THERMORECEPTORS: • Thermoreceptors present in the hypothalamus are stimulated when there is increase in body temperature as in fever ,exercise. • EMOTIONAL STIMULI • Emotional stimuli produces impulses from hypothalamus ,limbic system which stimulate respiratory centre.
- 33. Those which inhibit Respiration: Baroreceptors: Increase in blood pressure stimulates baroreceptors leading to inhibition of respiration. Visceroceptors: In visceral reflexes like vomiting, swallowing, deglutition, there is reflex inhibition of respiration.
- 35. CHEMICAL REGULATION OF RESPIRATION • Changes in pO2,pCO2 and H+ concentration acts on the respiratory centers in the medulla through a set of receptors called as chemo receptors. • Chemoreceptors are classified into: Central chemoreceptors Peripheral chemoreceptors.
- 36. Central chemoreceptors • These are a set of neurons located on either side of medulla near the exit of IX and X cranial nerves • These can sense changes in H+ concentration in the brain interstitial fluid. • Central chemoreceptors are surrounded by brain extracellular fluid.
- 37. • Blood brain barrier and blood CSF barrier are easily crossed by carbondioxide. • Whenever there is hypercapnia CO2 enters brain tissue and CSF, where it is hydrated to form H2CO3. • This splits to form H+ and HCO3-.
- 38. • Increase in H+ concentration is only the direct stimulant for central chemoreceptors. • CO2 has only indirect action. • Lack of oxygen does not have significant effect on the central chemoreceptors
- 39. • Stimulation from central chemoreceptors go to the inspiratory center(DRG) and stimulate respiration. • Central chemoreceptors are inhibited by anaesthesia, cyanosis ,during sleep etc.
- 41. Peripheral chemoreceptors • These are carotid body and aortic body. • These are neurovascular structures Location: • Carotid body is located at the bifurcation of common carotid artery. • Aortic bodies are located in the arch of aorta.
- 43. Innervation of peripheral chemoreceptors. • Carotid body is supplied by a branch of ninth cranial nerve(sinus nerve). • Sensory impulses from carotid body are carried through this nerve. • Aortic body is supplied by a branch of vagus nerve.(aortic nerve)
- 44. • Sinus nerve and aortic nerve together referred as sino-aortic nerve. • PCR contains two types of cells surrounded by fenestrated sinusoidal capillaries. • Type I cell/glomus cells • Type II cells/Glial cells / supporting cells.
- 45. Type I cell or glomus cells. • They contain dense granules with dopamine. • They are in close association with afferent nerve fibres of ninth cranial nerves. Type II cells/glial cells or supporting cells. • These cells surround 4-6 glomus cells . • Function : Protection and support of glomus cells.
- 46. Mechanism of action of PCR • Reduction in partial pressure of oxygen is the most potent stimulus for PCR. • If the arterial pO2 falls below 60 mm of Hg, the peripheral chemoreceptors are strongly stimulated which inturn will stimulate the respiratory center .
- 47. • This leads to increase in rate and depth of respiration which brings blood pO2 to normal • In the absence of PCR, severe hypoxia depress respiration by a direct inhibitory action on respiratory centres.
- 48. Factors affecting PCR Decrease in arterial pO2. • Vascular stasis as in circulatory shock(stagnant hypoxia). • The PCR responds only to reduction in dissolved oxygen in the blood. • In anemic hypoxia and carbon-monoxide poisoning there is no stimulation of respiration through PCR
- 49. Decrease in pCO2 • Peripheral chemoreceptors are also sensitive to increased pCO2. • Increased pCO2 stimulates peripheral chemo receptors which inturn stimulates resp centre • Increase in carbon dioxide washout until arterial pCO2 becomes normal.
- 50. Effect of H+ concentration Acidosis stimulates respiratory center and causes hyperventilation Alkalosis depress respiratory center and causes hypoventilation. Mediated by peripheral chemoreceptors. NOTE : Action of CO2 on respiration is increased by Hypoxia . • Decreased by sleep, hypothermia and anaesthesia.
- 52. ABNORMALITIES Respiratory center depression: • Causes : Old age • Anesthetics. Periodic breathing : Consists of alternating waxing and waning of respiration or alternate hyperpnea and apnea. • It may be normal or abnormal.
- 53. Types of periodic breathing • 1.Voluntary hyperventilation • Hyperventilation in normal subject is followed by a period of apnea which in turn is followed by a few shallow breaths and then another period of apnea followed again by few breaths. • This cycles lasts for some time before normal breathing is resumed.
- 54. 2.Cheyne-stokes respiration • Seen in both physiological and pathological conditions • Regular alternating period of hyperventilation and apnea are seen. Physiological causes: • Deep sleep • Infants • High altitude Pathological causes: • Congestive cardiac failure • Raised ICT, Uremia and morphine poisoning.
- 55. 3.Biot’s breathing • This type of breathing is always pathological. • Irregular periods of apnea and hyperventilation. • Changes are abrupt. Causes : Meningitis Medullary lesions.