Control of Respiration PDF

6/29/20 Control of Respiration by Dr Lee Siew Keah Faculty of Medicine and Health Sciences, UTAR 3 Learning Outcomes 1. Describe the neural controls of respiration 2. Compare and...

6/29/20 Control of Respiration by Dr Lee Siew Keah Faculty of Medicine and Health Sciences, UTAR 3 Learning Outcomes 1. Describe the neural controls of respiration 2. Compare and contrast the influences of arterial pH, arterial partial pressures of oxygen and carbon dioxide, lung reflexes, volition, and emotions on respiratory rate and depth 4 4 1  6/29/20 Control of Respiration Involves higher brain centers, chemoreceptors, and other reflexes Neural controls (net like) ◦ Neurons in reticular formation of medulla and pons 1. Medullary respiratory centers ◦ Ventral respiratory group ◦ Dorsal respiratory group 2. Pontine respiratory centers 5 apneustic center: stimulates inhalation. promotes deep, prolonged inhalation by continuously stimulating the 5 neurons in the medulla that control the respiratory muscles. Pneumotaxic center: sends inhibitory signals to the apneustic center and the medullary respiratory centers to terminate inspiration, preventing over-inflation of the lungs. The DRG is primarily involved in controlling the basic rhythm of quiet breathing, particularly inspiration, while the VRG is m involved in controlling both inspiration and expiration during active breathing, such as during exercise or stress. Pons Medulla 6 6 2  6/29/20 Medullary Respiratory Centers 1. Ventral respiratory group (VRG) ◦ Rhythm-generating and integrative center ◦ Sets eupnea (12–15 breaths/minute) eu-good. pnea-breathing ◦ Normal respiratory rate and rhythm ◦ Its inspiratory neurons excite inspiratory muscles via phrenic (diaphragm) and intercostal nerves (external intercostals) ◦ Expiratory neurons inhibit inspiratory neurons 7 7 Medullary Respiratory Centers 2. Dorsal respiratory group (DRG) stretch receptors in lungs ◦ Integrates input from peripheral stretch and chemoreceptors; sends information à VRG how much lung stretch and how acidic blood is and carbon dioxide concentration in blood 8 8 3  6/29/20 Figure Locations of respiratory centers and their postulated connections. Pons Medulla smooths out breathing pattern Pontine respiratory centers and making transitions between interact with medullary breaths nice and steady respiratory centers to smooth the respiratory pattern. Ventral respiratory group (VRG) contains rhythm generators whose output drives respiration. Dorsal respiratory group (DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG. To inspiratory muscles External intercostal muscles Diaphragm 9 9 Medullary inspiratory neurons is very sensitive to inhibition by drugs such as barbiturates, morphine 10 10 4  6/29/20 Pontine Respiratory Centers 1 2 3 Influence and modify Smooth out transition Transmit impulses to VRG activity of VRG between inspiration and à modify and fine-tune expiration and vice versa breathing rhythms during vocalization, sleep, exercise 11 11 Apneustic Breathing damage Associated with pontine/upper medulla lesion Prolonged inspiratory phase followed by expiration apnea 1.5 breath/minute 12 12 5  6/29/20 Factors influencing Breathing Rate and Depth Depth determined by how actively respiratory center stimulates respiratory muscles stays Rate determined by how long inspiratory center active Both modified in response to changing body demands ◦ Chemical factors: Most important are changing levels of CO2, O2, and H+ ◦ Neural factors: Sensed by central and peripheral chemoreceptors 13 13 Chemical Factors - Control of Respiration 1. PCo2 2. PO2 3. pH 14 6  6/29/20 Chemical Factors - Pco2 Influence of Pco2 (most potent; most closely controlled) ◦ If blood Pco2 levels rise (hypercapnia), CO2 accumulates in brain à ◦ CO2 in brain hydrated à carbonic acid à dissociates, releasing H+ à pH drops ◦ H+ stimulates central chemoreceptors of brain stem ◦ Chemoreceptors synapse with respiratory regulatory centers à increased depth and rate of breathing à lower blood Pco2 à pH rises stimulates central chemoreceptors in the brainstem, which in turn signal the respiratory centers. This leads to an increase in both the depth and rate of breathing, which helps lower blood CO2 levels and raises pH back to normal. 15 15 Figure Changes in PCO2 and blood pH regulate ventilation by a negative feedback mechanism. Arterial P CO2 P CO2 decreases pH in brain extracellular fluid (ECF) Central chemoreceptors in Peripheral chemoreceptors brain stem respond to H + in carotid and aortic bodies in brain ECF (mediate (mediate 30% of the CO 2 70% of the CO 2 response) response) Afferent impulses Medullary respiratory centers Efferent impulses Respiratory muscle Ventilation (more CO 2 exhaled) Arterial P CO2 and pH return to normal Initial stimulus Physiological response Result 16 16 7  6/29/20 Depth and Rate of Breathing hyperventilation-increased depth and rate of breathing that exceeds body's need to remove CO2 ◦ à decreased blood CO2 levels (hypocapnia) ◦ à cerebral vasoconstriction and cerebral ischemia à dizziness, fainting Apnea–breathing cessation from abnormally low Pco2 CO2 is a vasodilator: CO2 causes dilation of blood vessels, bringing about greater blood flow, increased O2 delivery 17 If You’re Hyperventilating, Breathe Into a Paper Bag CO2 Normalization: Hyperventilation often leads to decreased CO2 levels (hypocapnia) in the blood, which can cause symptoms like dizziness, tingling sensations, and anxiety. Breathing into a paper bag helps restore a more normal balance of CO2 in the blood by reintroducing some of the exhaled CO2. 18 8  6/29/20 A decrease in pH will have what effect on the respiration rate? 19 19 Apneustic breathing occurs as a result of damage to which respiratory center? apneustic center in the pons 20 9  6/29/20 Chemical Factors - Po2 Influence of Po2 ◦ Peripheral chemoreceptors in aortic and carotid bodies–arterial O2 level sensors ◦ When excited (by substantial decreased of PO2), cause respiratory centers to increase ventilation ◦ Declining Po2 normally slight effect on ventilation ◦ Huge O2 reservoir bound to Hb ◦ Requires substantial drop in arterial Po2 (to 60 mm Hg) to stimulate increased ventilation 21 21 Chemical Factors - Arterial pH Influence of arterial pH ◦ Can modify respiratory rate and rhythm even if CO2 and O2 levels normal ◦ Mediated by peripheral chemoreceptors diabetic ketoacidosis ◦ Decreased pH may reflect ◦ CO2 retention; accumulation of lactic acid; excess ketone bodies ◦ Respiratory system controls attempt to raise pH by increasing respiratory rate and depth 22 22 10  6/29/20 A drop in pH may reflect CO2 retention , but it may also result from metabolic causes – such as accumulation of lactic acid after vigorous exercise, fatty acid metabolites in poorly controlled DM patients 23 23 Influence of CO2 on Blood pH Slow, shallow breathing HCO3- remove causes CO2 accumulate in excess H+ by blood, carbonic acid level ↑, binding with it H+ ↑ ,blood pH ↓ Carbonic acid- à pH rises to bicarbonate normal buffer system resist shifts in blood pH H2CO3 dissociates to Low CO2 in blood, carbonic release H+ à acid levels ↓, H+ ↓ blood pH ↑ pH drops to normal 24 24 11  6/29/20 Hypothalamic controls: pain, strong emotions, Neural body temperature changes can alter respiration by acting through hypothalamic centers Influence: Cortical controls: respiration can be controlled Influence voluntarily for short periods of Higher Pulmonary irritant reflexes: initiated by dust, mucus, fume, pollutants à constriction of Brain bronchioles, sneezing, coughing etc Centers Inflation/Hering-Breuer reflex: a protective reflex initiated by extreme over-inflation of the lungs, acts to terminate inspiration 25 25 Drowning victims vs death before submersion 26 26 12  6/29/20 Figure Neural and chemical influences on brain stem respiratory centers. Higher brain centers (cerebral cortex—voluntary control over breathing) Other receptors (e.g., pain) + – and emotional stimuli acting through the hypothalamus + – Respiratory centers (medulla and pons) Peripheral chemoreceptors + – Stretch receptors + in lungs Central chemoreceptors – Irritant + receptors Receptors in muscles and joints 27 27 Summary Describe the neural controls of respiration ◦ Medullary respiratory centers ◦ Pontine respiratory centers Chemical factors in influencing breathing rate and depth Neural Influence: Influence of Higher Brain Centers 28 28 13