Dr Archna Ghildiyal Associate Professor Department of Physiology KGMU Respiratory System

LECTURE:9 Contents Chemical control of Respiration Chemoreceptors-Central -Peripheral Effect of P CO2 and pH on Ventilation Lung receptors Cough Reflex

Learning Objectives Chemical Control of Respiration Chemoreceptors:Functional organization Ventilatory Responses: To changes in acid-base balance To CO 2 excess To Oxygen lack

Chemical control of respiration Chemoreceptors Central: Chemosensitive Area -Beneath ventral surface of medulla -Located bilaterally Peripheral: Aortic & Carotid Body

Functional Organization of Chemoreceptors A rise in PCO 2, a fall in pH or PO 2 of arterial blood increases respiratory neuron activity in the medulla. Stimulus: a change in blood chemistry Sensed by: receptors called chemoreceptors Response:  rate & depth of breathing (  minute ventilation)

Central chemoreceptors (medullary chemoreceptors) Location: brain stem, ventral surface of medulla, near I neurons Project to respiratory neurons Mainly sensitive to changes in PaCO2 A rise in PaCO2 effectively stimulates central chemoreceptors

H + is the Main Stimulus (in the CNS) In chemosensitive areas of the respiratory center, increased H + is the main stimulus Blood-brain barrier is not very permeable to H + CO 2 (lipid soluble) easily diffuses across the BBB CO 2 diffuses into the chemosensitive regions of the CNS, H + is formed and stimulates the dorsal respiratory group of neurones Increase in respiratory rate

Contd… Central respiratory response to elevated PCO 2 does not continue beyond few days Due to Renal readjustment of H+ ion conc in circulating blood

Effect of P CO2 and pH on Ventilation

Peripheral Chemoreceptors Located in carotid and aortic bodies 2 types of cells Type I or glomus cells contain oxygen sensitive K channels (Chemoreceptors) Sense arterial O 2 levels (P O2 ) Most sensitive at PO mmHg Blood flow rate: 2000 ml/100 g tissue/min

Peripheral Chemoreceptors

Contd.. Low P O2 levels stimulates the dorsal respiratory group  CO 2 & H + conc –Rapid stimulation(onset of exercise) The signal is sent to the respiratory center via the vagus or glossopharyngeal nerve Type II cells are supporting cells

Contd…  Arterial Pco2 &  H+(Peripheral chemoreceptor stimulation is 5 times as rapid as central stimulation,eg: during onset of exercise) Dopamine initiates action potentials in sensory nerve  arterial Po2 & high Pco2 is greater than the sum of their individual effects

Carotid body receptor and its response

Integrated effects Of PO 2,PCO 2 & pH on alveolar ventilation

Lung receptors Pulmonary stretch receptors (also called slowly-adapting pulmonary stretch receptors) Responsible for the Hering-Breuer reflex J receptors (juxta-capillary receptors) Irritant receptors (also called rapidly- adapting pulmonary stretch receptors)

Irritant receptors Location: Trachea,major airways,mostly in Larynx & Carina(point where trachea divides into bronchi) Stimulus: Cold air,Mucus,Dust Via Vagus to CNS Response: Bronchoconstriction,Hyperpnoea(deepr & rapid breathing than normal),Cough

Cough reflex Stimulus: noxious gas,foreign body Receptors: irritant (airway,larynx,carina) Mechanism:Sequence of events- Deep inspiration Closure of epiglottis & vocal chords Contraction of expiratory muscles including abdominal muscles

Contd… Steep rise in lung pressure( due to closed outlet) Sudden opening of epiglottis & VC Explosive release of air from lungs Particle blown out

References Guyton & Hall.Text book of Medical Physiology Ganong’s Review of Medical Physiology Berne & Levy Physiology phys/student_files.htmlhttp://meded.ucsd.edu/ifp/jwest/resp_ phys/student_files.html

Question:1 Raised alveolar Pco2 though a respiratory stimulant,can cause respiratory depression when the level(in mm Hg) exeeds: A) 10 B) 20 C) 40 D) 60

Question:2 Carotid bodies have: A) Glomus cells B) Innervated by vagus C) Blood flow of 200ml/g/min D) High A-V difference

Question:3 Type I or Glomus cells contain chemoreceptor as: A) O 2 sensitiveNa channels B) CO 2 sensitive K channels C) CO 2 sensitive Na channels D) O 2 sensitive K channels

Question:4 The peripheral Chemoreceptors: A) Have a nonlinear response to paO2 changes B) Respond to increase in PaO2 C) Respond to a fall in PaCO2 D) Are in the carotid sinus

Question:5 Highest density of Irritant receptors is present at A)Trachea B)Bronchioles C)Alveoli D)Larynx

Answers 1- D 2- A 3- D 4- A 5- D