regulation of respiration prof. k. sivapalan. introduction 20132regulation of respiration
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Regulation of Respiration
Prof. K. Sivapalan
Regulation of Respiration 2
Introduction
• Respiration is altered by several factors.
• The usage of oxygen and production of carbon dioxide and acids vary depending on the metabolic needs.
• There is a good reserve of respiratory function- rate, depth and respiratory epithelium.
• The respiratory system is controlled to meet the needs.
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Median Sagital Section of Brain
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• All respiratory muscles are striated muscles under voluntary control.
• The nerves driving the respiratory muscles arise from the ventral horn of the spinal cord.
• The anterior horn cell is the final pathway.
• The voluntary efforts are controlled by cerebral cortex which activates the AHC.
• Autonomic control is effected by centers in the brain stem which also influences the AHC
Control of Respiratory Muscles
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Respiratory Centre
• Respiratory center is located bilaterally in Medulla and Pons.
• The dorsal group of cells are mainly expiratory and the ventral cells are bothe expiratory and inspiratory.
• Cells in pons inhibit medullary inspiratory cells.
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Rhythmic Activity of the Centers
• The inspiratory center, left alone on its own, discharges for about 2 seconds which results in inspiration.
• It then stops for about 3 seconds during which the recoil of the lungs results in expiration.
• The influence from the pons, pneumotaxic center, can reduce the inspiration to 0.5 second and absence can result in arrest in inspiration
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The Hering-BreuerInflation Reflex
• Afferents in the vagus inhibit inflation
• The afferents originate from the stretch receptors in the bronchi and broncheols.
• In human, they seem to be activated when the inflation is 1500 ml.
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Chemical Control of Respiration
• Respiration is modified changes in partial pressures of oxygen and carbon dioxide and pH of the blood.
• The receptors responsible are collectively called chemo receptors.
• The receptors located in Medulla are central chemo receptors and those in aorta and carotid arteries are peripheral chemo receptors
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Central Chemo-receptors• Cells in ventral Medulla respond
to changes in Hydrogen ions in CSF which is proportional to PCO2.
• Blood pH has no effect as H+ is not permeable through Blood brain barrier.
• The central chemo receptors activate respiratory centre when CO2 increases and inhibit when it decreases.
• The effect is potent immediately but after one day the HCO3
- diffuses into CSF and reduces the effect. [Renal compensation]
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Peripheral Chemo-receptors
• Most receptors- Carotid bodies near the bifurcation – glossopharingeal nerve.
• Some receptors in the arch of the aorta- vagus nerve
• A few receptors in abdominal and thoracic vessels.
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• Each body receives its own blood supply through an artery directly from the arterial trunk.
• The blood flow in each 2-mg carotid body is about 0.04 mL/min, or 2000 mL/100 g of tissue/min compared with a blood flow 54 mL or 420 mL per 100 g/min in the brain and kidneys.
• The blood flow is well above the need of the bodies: exposed to arterial blood.
• Type I cells have catecholamines which are released to stimulate the afferents.
• They increase discharge in response to reduction in PO2, increase in PCO2 and reduction of Hydrogen ion.
Receptors
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• There is normal discharge at the PO2 of 100 mm Hg.
• It decreases as partial pressure increases and increases when partial pressure decreases.
• The maximal change is between PO2 of 60-30 mmHg. The response is not affected by duration of hypoxia.
• Denervation of carotid bodies results abolishes response to changes in – Oxygen tension- totally
– pH- great extent
– Carbon dioxide by 30%
• Central for carbondioxide and peripheral for oxygen and hydrogen.
Response to Oxygen
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Factors that Affect Respiration
• Inherant activity of respiratory center and reflex inhibition by stretch.
• Changes in oxygen, carbon dioxide and hydrogen.
• Voluntary control of respiration, higher centers- pain and emotion.
• Motor cortical activity, proprioceptors: in exercise
• Deglutition center, vomiting centre , straining, hiccup, yawning.
• Changes in REM sleep, sleep apnoea.
• Baro-receptor – mild inhibition.
• Irritants in respiratory passage- cough and sneeze.
• Cerebral oedema- compression of vessels
• Anesthetics and narcotics.2013
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