Respiratory Physiology. Moving air to the exchange surface of the lungs Gas exchange between air and...
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Transcript of Respiratory Physiology. Moving air to the exchange surface of the lungs Gas exchange between air and...
![Page 1: Respiratory Physiology. Moving air to the exchange surface of the lungs Gas exchange between air and circulating blood Protection of respiratory surfaces.](https://reader031.fdocuments.in/reader031/viewer/2022020320/56649e915503460f94b95f44/html5/thumbnails/1.jpg)
Respiratory Physiology
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• Moving air to the exchange surface of the lungs
• Gas exchange between air and circulating blood
• Protection of respiratory surfaces (from dehydration, temperature changes, and defending the RS from invading pathogens)
• Production of sound
• Provision for olfactory sensations
Functions of the respiratory system
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The Components of the Respiratory System
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The Components of the Respiratory System
• Conducting Zone.
• Respiratory Zone
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• All the structures air passes through before reaching the respiratory zone.
• Function:
• Warms and humidifies inspired air.
• Filters and cleans:
• Mucus secreted to trap particles in the inspired air.
• Mucus moved by cilia to be expectorated.
Insert fig. 16.5
Conducting Zone
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• Region of gas exchange between air and blood.
• Includes respiratory bronchioles and alveolar sacs.
Respiratory Zone
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The Bronchi and Lobules of the Lung
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Respiratory Membrane
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Respiratory Membrane
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Respiratory Membrane
• This air-blood barrier is composed of:
• Alveolar and capillary walls
• Their fused basal laminas
• Alveolar walls:
• Are a single layer of type I epithelial cells
• Permit gas exchange by simple diffusion
• Type II cells secrete surfactant
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Respiratory Volumes
• Tidal volume (TV) – air that moves into and out of the lungs with each breath (approximately 500 ml)
• Inspiratory reserve volume (IRV) – air that can be inspired forcibly beyond the tidal volume (2100–3200 ml)
• Expiratory reserve volume (ERV) – air that can be evacuated from the lungs after a tidal expiration (1000–1200 ml)
• Residual volume (RV) – air left in the lungs after maximal forced expiration (1200 ml)
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Respiratory Capacities
• Inspiratory capacity (IC) – total amount of air that can be inspired after a tidal expiration (IRV + TV)
• Functional residual capacity (FRC) – amount of air remaining in the lungs after a tidal expiration (RV + ERV)
• Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV)
• Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in males)
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Respiratory Volumes and Capacities
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Dead Space
• The volume of the airways that does not participate in gas exchange
• Anatomical dead space – volume of the conducting respiratory passages (150 ml)
• Functional dead space – alveoli that cease to act in gas exchange due to collapse or obstruction
• Physiological dead space – sum of alveolar and anatomical dead spaces
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Mechanics of Breathing
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• The physical movement of air into and out of the lungs
Pulmonary Ventilation
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• Movement of air depends upon
• Boyle’s Law
• Pressure and volume inverse relationship
• Volume depends on movement of diaphragm and ribs
Air movement
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Inspiration• Inspiration
• Diaphragm contracts -> increased thoracic volume vertically.
• Intercostals contract, expanding rib cage -> increased thoracic volume laterally.
• Active
• More volume -> lowered pressure -> air in.
• (Negative pressure breathing.)
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Expiration
• Expiration
• Due to recoil of elastic lungs.
• Passive.
• Less volume -> pressure within alveoli is above atmospheric pressure -> air leaves lungs.
• Note: Residual volume of air is always left behind, so alveoli do not collapse.
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Mechanisms of Pulmonary Ventilation
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Gas Exchange
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• Daltons Law and partial pressure
• Individual gases in a mixture exert pressure proportional to their abundance
• Diffusion between liquid and gases (Henry’s law)
• The amount of gas in solution is directly proportional to their partial pressure
The gas laws
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Henry’s Law and the Relationship between Solubility and Pressure
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• Gas exchange across respiratory membrane is efficient due to:
• Differences in partial pressure
• Small diffusion distance
• Lipid-soluble gases
• Large surface area of all alveoli
• Coordination of blood flow and airflow
Diffusion and respiratory function
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Gas Pickup and Delivery
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An Overview of Respiratory Processes and Partial Pressures in Respiration
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Gas Exchange in the Lungs and Tissues: Oxygen
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Gas Transport in the Blood: Oxygen
• 2% in plasma
• 98% in hemoglobin (Hb)
• Blood holds O2 reserve
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• Carried mainly by RBCs, bound to hemoglobin
• The amount of oxygen hemoglobin can carried is dependent upon:
• PO2
• pH
• temperature
• DPG
• Fetal hemoglobin has a higher O2 affinity than adult hemoglobin
Oxygen transport
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Hemoglobin Transport of Oxygen
• 4 binding sites per Hb molecule
• 98% saturated in alveolar arteries
• Resting cell PO2 = 40 mmHg
• Working cell PO2 = 20 mmHg
• More unloaded with more need
• 75% in reserve at normal activity
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Hemoglobin Saturation Curve
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• Temperature, pH, PCO2, and DPG
• Increase of temperature, PCO2, and DPG and decrease of pH :• Decrease hemoglobin’s affinity for oxygen• Enhance oxygen unloading from the blood
• Decreases of temperature, PCO2, and DPG and the increase of pH act in the opposite manner
• These parameters are all high in systemic capillaries where oxygen unloading is the goal
Factors Influencing Hemoglobin Saturation
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The Effect of pH and Temperature on Hemoglobin Saturation
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A Functional Comparison of Fetal and Adult Hemoglobin
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• 7% dissolved in plasma
• 70% carried as carbonic acid
• buffer system
• 23% bound to hemoglobin
• carbaminohemoglobin
• Plasma transport
Carbon dioxide transport
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Carbon Dioxide Transport in Blood
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• Driven by differences in partial pressure
• Oxygen enters blood at lungs and leaves at tissues
• Carbon dioxide enters at tissues and leaves at lungs
Summary of gas transport
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A Summary of the Primary Gas Transport Mechanisms
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Control of Respiration
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• Medullary centers
• Respiratory rhythmicity centers set pace
• Dorsal respiratory group (DRG)– inspiration
• Ventral respiratory group (VRG)– forced breathing
Respiratory centers of the brain
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• Pons
• Apneustic and pneumotaxic centers:
● regulate the respiratory rate and the depth of respiration in response to sensory stimuli or input from other centers in the brain
Respiratory centers of the brain
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Respiratory Centers and Reflex Controls
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Chemoreceptors
• Chemoreceptors are located throughout the body (in brain and arteries).
• chemoreceptors are more sensitive to changes in PCO2
(as sensed through changes in pH).
• Ventilation is adjusted to maintain arterial PC02 of 40 mm Hg.
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Medullary Respiratory Centers