REGULATION OF RESPIRATION physiology slides
- 1. REGULATION OF RESPIRATION DR. RUBAB AMJAD DEMONSTRATOR PHYSIOLOGY
- 2. INTRODUCTION • Respiration is a reflex process. • But it can be controlled voluntarily for a short period of about 40 seconds. However, by practice, breathing can be withheld for a long period. • At the end of that period, the person is forced to breathe. • Respiration is subjected to variation, even under normal physiological conditions. • For example, emotion and exercise increase the rate and force of respiration. • But the altered pattern of respiration is brought back to normal, within a short time by some regulatory mechanisms in the body. • Normally, quiet regular breathing occurs because of two regulatory mechanisms: 1. Nervous or neural mechanism 2. Chemical mechanism.
- 3. NERVOUS MECHANISM • Nervous mechanism that regulates the respiration includes: 1. Respiratory centers 2. Afferent nerves 3. Efferent nerves
- 5. RESPIRATORY CENTERS • Respiratory centers are group of neurons, which control the rate, rhythm and force of respiration. • These centers are bilaterally situated in reticular formation of the brainstem. • Depending upon the situation in brainstem, the respiratory centers are classified into two groups: A. Medullary centers consisting of i. Dorsal respiratory group of neurons ii. Ventral respiratory group of neurons B. Pontine centers i. Apneustic center ii. Pneumotaxic center
- 6. RESPIRATORY CENTERS (MEDULLARY CENTERS) DORSAL RESPIRATORY GROUP OF NEURONS Situation • Dorsal respiratory group of neurons are diffusely situated in the nucleus of tractus solitarius which is present in the upper part of the medulla oblongata. • Usually, these neurons are collectively called inspiratory center. • All the neurons of dorsal respiratory group are inspiratory neurons and generate inspiratory ramp by the virtue of their autorhythmic property. Function • Dorsal group of neurons are responsible for basic rhythm of respiration
- 7. RESPIRATORY CENTERS (MEDULLARY CENTERS) VENTRAL RESPIRATORY GROUP OF NEURONS Situation • Ventral respiratory group of neurons are present in nucleus ambiguous and nucleus retro ambiguous. • These two nuclei are situated in the medulla oblongata, anterior and lateral to the nucleus of tractus solitarius. • Earlier, the ventral group neurons were collectively called expiratory center. • Ventral respiratory group has both inspiratory and expiratory neurons. • Inspiratory neurons are found in the central area of the group. • Expiratory neurons are in the caudal and rostral areas of the group. Function • Normally, ventral group neurons are inactive during quiet breathing and become active during forced breathing. • During forced breathing, these neurons stimulate both inspiratory muscles and expiratory muscles.
- 8. RESPIRATORY CENTERS (PONTINE CENTERS) APNEUSTIC CENTER Situation • Apneustic center is situated in the reticular formation of lower pons. Function • Apneustic center increases depth of inspiration by acting directly on dorsal group neurons.
- 9. RESPIRATORY CENTERS (PONTINE CENTERS) PNEUMOTAXIC CENTER Situation • Pneumotaxic center is situated in the dorsolateral part of reticular formation in upper pons. It is formed by neurons of medial parabrachial and sub parabrachial nuclei. • Sub parabrachial nucleus is also called ventral parabrachial or Kölliker-Fuse nucleus. Function • Primary function of pneumotaxic center is to control the medullary respiratory centers, particularly the dorsal group neurons. It acts through apneustic center. • Pneumotaxic center inhibits the apneustic center so that the dorsal group neurons are inhibited. Because of this, inspiration stops and expiration starts. • Thus, pneumotaxic center influences the switching between inspiration and expiration. • Pneumotaxic center increases respiratory rate by reducing the duration of inspiration.
- 10. CONNECTIONS OF RESPIRATORY CENTERS Efferent Pathway • Nerve fibers from respiratory centers leave the brainstem and descend in anterior part of lateral columns of spinal cord. • These nerve fibers terminate on motor neurons in the anterior horn cells of cervical and thoracic segments of spinal cord. • From motor neurons of spinal cord, two sets of nerve fibers arise: 1. Phrenic nerve fibers (C3 to C5), which supply the diaphragm 2. Intercostal nerve fibers (T1 to T11), which supply the external intercostal muscles. Vagus nerve also contains some efferent fibers from the respiratory centers.
- 11. CONNECTIONS OF RESPIRATORY CENTERS Afferent Pathway • Respiratory centers receive afferent impulses from: 1. Peripheral chemoreceptors and baroreceptors via branches of glossopharyngeal and vagus nerves 2. Stretch receptors of lungs via vagus nerve. • By receiving afferent impulses from these receptors, respiratory centers modulate the movements of thoracic cage and lungs through efferent nerve fibers.
- 12. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from Higher Centers • Higher centers alter the respiration by sending impulses directly to dorsal group of neurons. • Impulses from anterior cingulate gyrus, genu of corpus callosum, olfactory tubercle and posterior orbital gyrus of cerebral cortex inhibit respiration. • Impulses from motor area and Sylvian area of cerebral cortex cause forced breathing.
- 13. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from Stretch Receptors of Lungs: Hering-Breuer Reflex • Hering Breuer reflex is a protective reflex that restricts inspiration and prevents overstretching of lung tissues. • It is initiated by the stimulation of stretch receptors of air passage. • Stretch receptors are the receptors which give response to stretch of the tissues. • These receptors are situated on the wall of the bronchi and bronchioles. • Expansion of lungs during inspiration stimulates the stretch receptors. • Impulses from stretch receptors reach the dorsal group neurons via vagal afferent fibers and inhibit them. • So, inspiration stops and expiration starts. • Thus, the overstretching of lung tissues is prevented. • However, HeringBreuer reflex does not operate during quiet breathing. • It operates, only when the tidal volume increases beyond 1,000 mL
- 14. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from ‘J’ Receptors of Lungs • ‘J’ receptors are juxtacapillary receptors which are present on the wall of the alveoli and have close contact with the pulmonary capillaries. • Nerve fibers from these receptors are nonmyelinated and belong to C type. • Few receptors are found on the wall of the bronchi. • Conditions when ‘J’ receptors are stimulated i. Pulmonary congestion ii. Pulmonary edema iii. Pneumonia iv. Over inflation of lungs v. Micro embolism in pulmonary capillaries vi. Stimulation by exogenous and endogenous chemical substances such as histamine, halo thane, bradykinin, serotonin and phenyldiguanide.
- 15. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from Irritant Receptors of Lungs • Besides stretch receptors, there is another type of receptors in the bronchi and bronchioles of lungs, called irritant receptors. • Irritant receptors are stimulated by irritant chemical agents such as ammonia and sulfur dioxide. • These receptors send afferent impulses to respiratory centers via vagal nerve fibers. • Stimulation of irritant receptors produces reflex hyperventilation along with bronchospasm. • Hyperventilation along with bronchospasm prevents further entry of harmful agents into the alveoli.
- 16. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from Baroreceptors • Baroreceptors or presso-receptors are the receptors which give response to change in blood pressure. Function • Baroreceptors in carotid sinus and arch of aorta give response to increase in blood pressure. • Whenever arterial blood pressure increases, baroreceptors are activated and send inhibitory impulses to vasomotor center in medulla oblongata. • This causes decrease in blood pressure and inhibition of respiration. • However, in physiological conditions, the role of baroreceptors in regulation of respiration is insignificant.
- 17. FACTORS AFFECTING RESPIRATORY CENTERS Impulses from Chemoreceptors • Chemoreceptors play an important role in the chemical regulation of respiration. Impulses from Proprioceptors • Proprioceptors are the receptors which give response to change in the position of body. • These receptors are situated in joints, tendons and muscles. • Proprioceptors are stimulated during the muscular exercise and send impulses to brain, particularly cerebral cortex, through somatic afferent nerves. • Cerebral cortex in turn causes hyperventilation by sending impulses to medullary respiratory centers
- 18. FACTORS AFFECTING RESPIRATORY CENTERS Impulses fromThermoreceptors • Thermoreceptors are cutaneous receptors, which give response to change in the environmental temperature. • Thermoreceptors are of two types, namely receptors for cold and receptors for warmth. • When body is exposed to cold or when cold water is applied over the body, cold receptors are stimulated and send impulses to cerebral cortex via somatic afferent nerves. • Cerebral cortex in turn, stimulates the respiratory centers and causes hyperventilation. Impulses from Pain Receptors • Pain receptors are those which give response to pain stimulus. • Whenever pain receptors are stimulated, the impulses are sent to cerebral cortex via somatic afferent nerves. • Cerebral cortex in turn, stimulates the respiratory centers and causes hyperventilation