Lecture 20 Control of Breathing 2024 PDF

Lecture topic 20. Control of breathing  Learning objectives After today's lecture you should be able to describe: Local control of gas transport – O2 and CO2 Central control of ventilation – o central & peripheral chemoreceptors o Mechanore...

Lecture topic 20. Control of breathing  Learning objectives After today's lecture you should be able to describe: Local control of gas transport – O2 and CO2 Central control of ventilation – o central & peripheral chemoreceptors o Mechanoreceptors o respiratory centres in the pons and the medulla Part 1: Overview, local control of gas transport & introduction to sensors  How is breathing controlled? Unaware: until something goes wrong - dyspnea e.g. high altitude / disease Aware: scuba diving, partners to sleepy snorers Two key tasks: 1) establish automatic rhythm 2) adjust the rhythm to accommodate (i) metabolic [arterial blood gases + pH], (ii) mechanical [postural changes] (iii) episodic non-ventilatory behaviours e.g. speaking, sniffing, eating  Under normal conditions O2: rate of absorption is matched to delivery CO2: rate of generation is matched to removal alance achieved by: changes in blood flow and oxygen delivery → local changes in depth and rate of respiration → central Complexities no single pacemaker generating basic rhythm of breathing no single muscle devoted to the pumping of  Local Control of Gas O2 and PCO2 Transport In Active Tissue ↓PO2 ↑O2 ↑PCO2 ↑CO2 removal delivery vasodilatio n ↑ blood flow ung Perfusion ↓PO2 vasoconstricti ↓ blood flow on → direct blood to areas of higher PO2 lveolar ventilation ↑PCO2 bronchodilatio ↑ air flow n P direct airflow to areas of higher CO2 - improve efficiency of gas transport  Central Control of Ventilation CENTRAL CONTROLLER Respiratory Centres In the pons and medulla SENSORS EFFECTORS Central & Peripheral Muscles Chemoreceptors of ventilati Mechanorecepto on rs Aim is to keep arterial PCO2 and PO2 as constant as possible  Sensors Central chemoreceptors – medulla change in pH hypercapnia no effect of hypoxia Peripheral chemoreceptors – aortic and carotid body hypoxia hypercapnia change in pH Mechanoreceptors -Lung receptors Respond to stretch rapidly adapting receptors slowly adapting receptors C-fibres receptors  Factors influencing rate and depth of breathing Changing body demands, e.g. exercise Altitude – acute mountain sickness Disease Changing levels of – CO2 – H+ } – O2 in the arterial blood Only a problem when PO2 of alveolar gas and arterial blood falls below 60mmHg  Part 2: Central control of ventilation – central & peripheral chemoreceptor hear s t (Saladin,  Central Control of Ventilation CENTRAL CONTROLLER Respiratory Centres In the pons and medulla SENSORS EFFECTORS Central & peripheral Muscles chemoreceptors of ventilati Mechanorecepto on rs Aim is to keep arterial PCO2 and PO2 as constant as possible  Central Chemoreceptors just beneath the ventral surface of the medulla close to entry of VIII & XI cranial nerves stimulated by acidic or high PCO2 in the CSF PCO2 pH ↑ ventilation ↓ PCO2 CO2 crosses the Blood CSF blood-brain barrier CO2 pH – lipid soluble (CSF is only weakly gas buffered) has no effect on central chemoreceptors?  PO2  Peripheral Chemoreceptors Detect changes in PO2 PCO2 & pH CSN Vagu Outside brain s Carotid body at bifurcation caroti d of carotid arteries body Innervated by carotid sinus nerve (CSN) → glossopharyngeal aortic bodies aortic Aortic bodies above and below arch aortic arch hear Innervated by the vagus t (Saladin,  Stimuli PO2, PCO2, pH in arterial blood Discharge rate Normal 0 40 100 Arterial PO2 (mmHg) Function Peripheral chemoreceptors are vital for response to PO2  CO2 (and H+) are the most important If CO2 increases, e.g. limited gas exchange in emphysema → PCO2 ↑ (>43mmHg) CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- Equation pushed to the right ↑ H+ → pH drops (becomes more acidic) RESPIRATORY ACIDOSIS (pH