Regulation of Respiration Prof K Sivapalan Introduction Respiration

Regulation of Respiration Prof. K. Sivapalan

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. 2013 Regulation of Respiration 2

Median Sagital Section of Brain 2013 Regulation of Respiration 3

Control of Respiratory Muscles • 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 2013 Regulation of Respiration 4

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. 2013 Regulation of Respiration 5

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 absence can result in arrest in inspiration 2013 Regulation of Respiration 6

The Hering-Breuer Inflation 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. 2013 Regulation of Respiration 7

Chemical Control of Respiration • Respiration is modified changes in partial pressures of oxygen and carbon dioxide and p. H 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 2013 Regulation of Respiration 8

Central Chemo-receptors • Cells in ventral Medulla respond to changes in Hydrogen ions in CSF which is proportional to PCO 2. • Blood p. H has no effect as H+ is not permeable through Blood brain barrier. • The central chemo receptors activate respiratory centre when CO 2 increases and inhibit when it decreases. • The effect is potent immediately but after one day the HCO 3 diffuses into CSF and reduces the effect. [Renal compensation] 2013 Regulation of Respiration 9

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. 2013 Regulation of Respiration 10

Receptors • 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 m. L/min, or 2000 m. L/100 g of tissue/min compared with a blood flow 54 m. L or 420 m. L 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 PO 2, increase in PCO 2 and reduction of Hydrogen ion. 2013 Regulation of Respiration 11

Response to Oxygen • There is normal discharge at the PO 2 of 100 mm Hg. • It decreases as partial pressure increases and increases when partial pressure decreases. • The maximal change is between PO 2 of 60 -30 mm. Hg. The response is not affected by duration of hypoxia. • Denervation of carotid bodies results abolishes response to changes in – Oxygen tension- totally – p. H- great extent – Carbon dioxide by 30% • Central for carbondioxide and peripheral for oxygen and hydrogen. 2013 Regulation of Respiration 12

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 Regulation of Respiration 13