Physiology Unit 4

RESPIRATORY PHYSIOLOGY

Respiraon

• External respiraon – venlaon – gas exchange • Internal respiraon – cellular respiraon – gas exchange • Respiratory Cycle – Inspiraon • Moving atmospheric air into the – Expiraon • Moving air out of the lungs Lungs vs. Balloons

• A is similar to a balloon in that it resists stretch, tending to collapse almost totally unless held inflated by a pressure difference between its inside and outside • Lungs and the chest have elasc properes Lung Compliance

• Compliance – Elascity – Tendency to recoil – Tendency of an elasc structure to oppose stretching or distoron * Resists distension • Surface tension * Resists distension - Surfactant • Reduces surface tension • Increases compliance (makes them easier to stretch) Airway Resistance F = ΔP/R • Same variables that affect resistance in blood vessels – Tube length, tube radius, fricon – Tube radius most important factor • Airway resistance is so small that small pressure differences produce large volumes of air flow – Average atmosphere-to-alveoli pressure difference is 1 mmHg, but 500 mL of air is moved (dal volume) – Low pressure and low resistance • Pulmonary 1/10th of systemic vascular resistance Venlaon

• Exchange of air between atmosphere and alveoli • Atmospheric air pressure is 760 mmHg at sea level • Air moves by bulk flow – F = ΔP/R

– F = (Palv – Patm)/R Boyle’s Law

• Boyle’s law = (P/V) • Pressure of a given quanty of gas is inversely proporonal to volume • An increase in the volume of the container (lungs) decreases the pressure of the gas (air) Venlaon Mechanics

• Lung volume depends on: 1. Transpulmonary pressure

(Ptp) • Inside to outside of the lung

• Ptp = Palv – Pip • The force that keeps the lungs inflated • Transmural pressure – Across the wall 2. How compliant the lungs are Transmural Pressures What Keeps the Lungs Inflated?

• Elasc recoil of the lungs * At rest natural tendency is to collapse

• Lungs are held open by the posive Ptp – At rest exactly opposes elasc recoil • Collapsing force of the lungs is 4 mmHg • Intrapleural pressure is -4 mmHg • Elasc recoil of the chest * At rest natural tendency is to expand Pneumothorax

• A pierce in the chest wall allows atmospheric

air to rush in causing Pip to go from -4 mmHg to 0 mmHg • Transpulmonary pressure acng to hold the lungs open is eliminated • Lung collapses • Chest wall expands Inspiraon/Expiraon

• In order for air to • In order for air to move into the lungs, move out of the the pressure in the lungs, the pressure lungs must drop in the lungs must below atmospheric exceed atmospheric pressure pressure

• Patm > Palv • Palv > Patm The Respiratory Cycle Paral Pressure of Gases

• Dalton’s Law – Pressure of each gas is independent of the pressure of other gases – Pressure of the gas is directly proporonal to its concentraon – Individual gas pressures in air is termed the paral pressure of a gas – Atmospheric air 760 mmHg at sea level • Air is 78% nitrogen – 0.78 ×760 mmHg = 593 mmHg

– PN2 = 593 mmHg • Air is 21% oxygen – 0.21 × 760 mmHg = 159 mmHg

– PO2 = 159 mmHg – Altude and Temperature also affect pressure Paral Pressure of O2 and CO2 in Blood Transport of O2 in the Blood

• 1 Liter of blood contains 200 mL of oxygen – Dissolved in plasma – Bound to (Hb)

• Solubility of O2 is relavely low

– Only 3 mL of O2 can dissolve in 1 L of blood at arterial PO2 of 100 mmHg (2%) – Remaining 197 mL of oxygen bound Hb (98%) Transport of O2 in the Blood

• Hemoglobin – Heme, globin – 280 million Hb per RBC x 4 = >1 billion molecules of oxygen per RBC • States of Hb – Hb • deoxyhemoglobin

– O2 + Hb <---> HbO2 • Oxyhemoglobin • Oxygen carrying-capacity of blood – a %

– Amount of HbO2 is 80 % of total Hb, the sample is 80% saturated

• Sigmoid curve Oxygen- – Each Hb molecule has 4 Hemoglobin sub-units – Binding cooperavity

Dissociaon Curve • Binding of first O2 increases the affinity for O2 at remaining three heme units • Significance of the shape of the curve – Steep slope between 20-60 mmHg • Increased unloading – Plateau • At 60 mmHg, 90% saturaon • Oxygen reserve Shis in the Oxygen-Hemoglobin Dissociaon Curve • Other factors influence the degree of Hb saturaon – 2,3-diphosphoglycerate (DPG) – Temperature – pH – PCO2

• A shi to the right decreases the affinity of Hb for O2 – increased unloading in the ssues

• A shi to the le increases the affinity of Hb for O2 – increased loading in the lungs Hb Saturaon Effects of DPG Concentraon • 2,3-diphosphoglycerate (DPG) – Always produced by RBCs – Increase in DPG causes a shi to the right • RBCs increase producon of DPG when there is a decrease

in PO2 – Higher altude – Anemia – Transfer from maternal blood to fetal Hb PO2 (mmHg) • Increased unloading in the

ssues to maintain O2 delivery Hb Saturaon Effects of Temperature • Higher temperature in ssue capillary blood than in arterial blood • The more metabolically acve the ssue is, the higher the temperature will be • Increased unloading in the ssue PO2 (mmHg) – Provides more metabolically acve cells

with more O2 Hb Saturaon Effects of pH • Higher [H+] in ssue capillary blood than in arterial blood

– Elevated PCO2 – Metabolically produced acids such as lacc acid • The more metabolically acve the ssue is, the greater the [H+] – Lower pH – Higher acidity • Increased unloading in the ssue – Provides more metabolically

acve cells with more O2 Transport of CO2 in Blood

• 200 mL CO2/min produced by metabolism • 10% dissolved in plasma

• 30% as carbaminohemoglobin (HbCO2)

– CO2 + Hb <---> HbCO2 - • 60% as (HCO3 ) - + – CO2 + H2O <---> H2CO3 <---> HCO3 + H – – Present in RBCs Chloride Shi Tissue Level • Bicarbonate reacon shis to the right...WHY?? - + – CO2 + H2O <---> H2CO3 <---> HCO3 + H • Steps:

– CO2 diffuses out of the ssue cells into the blood

– CO2 moved into the red blood cells

– CO2 combines with H2O to produce H2CO3 • Carbonic anhydrase makes this reacon fast + - – H2CO3 dissociates producing H + HCO3 + – H buffered by hemoglobin, facilitang the offloading of O2 • Forms HHb - - – Cl moves into the RBC in exchange for HCO3 moving into plasma – Bohr effect • Increased oxygen unloading in ssues

• Enhanced transport of CO2 Chloride Shi Tissue Level Reverse Chloride Shi Pulmonary Capillaries • Equaon shis to the le.....WHY?? - + – CO2 + H2O <---> H2CO3 <---> HCO3 + H • Steps: – Hb oxygenated – Hb decrease in affinity for H+ - - – Reverse chloride shi as Cl moves into plasma and HCO3 moves into the RBC

– H2CO3 dissociates to CO2 + H2O

– CO2 expired out • Remember: – H+ is buffered by Hb in RBC - + – HCO3 goes into the plasma and buffers incoming H Reverse Chloride Shi Pulmonary Capillaries Respiratory Control Centers Rhythmical • Medulla oblongata – Respiratory Rhythmicity Center • Controls the diaphragm and intercostals • Pons – Apneusc Center • Terminates inspiraon – Pneumotaxic Center – Modulates acvity of apneusc center – Smoothes the transion from inspiraon to expiraon • Cyclic inhibion • Pulmonary stretch receptors - Cut off signal for inspiraon to allow expiraon to occur Control of Venlaon + Monitoring PO2, PCO2, H • Respiratory rate and dal volume can be altered • Peripheral – Aorc and Carod bodies – Provides afferent input to the medulla via the Vagus Nerve

– Sensive to PO2 • Central chemoreceptors – In the Medulla

– Highly sensive to PCO2

Control of Venlaon + Monitoring PO2, PCO2, H • Peripheral chemoreceptors – Aorc and Carod Bodies – Sensive to:

• Decreased PO2 () • Increased H+ due to the build up of other acids (metabolic acidosis) + • Increased H due to CO2 retenon (respiratory acidosis) • Central chemoreceptors – Medulla – Sensive to • Increased H+ in brain extracellular fluid (CSF)

– CO2 crosses blood blain barrier to smulate receptors Protecve Reflexes

• Pulmonary irritant reflexes – Reflex constricon to prevent parculates from entering lungs – Receptors located between airway epithelial cells – Cough reflex – Sneeze reflex – Cessaon of breathing reflex – Triggered when noxious agents are inhaled – Chronic smoking causes loss of this reflex