Lecture 18: Introduction to Respiration PDF

Lecture 18: Introduction to Respiration Dr. Ann Revill [email protected] Office: Dr. Arthur G. Dobbelaere Science Hall 380E  Lecture Objectives By the end of this lecture, you will be able to: 1. Explain t...

Lecture 18: Introduction to Respiration Dr. Ann Revill [email protected] Office: Dr. Arthur G. Dobbelaere Science Hall 380E  Lecture Objectives By the end of this lecture, you will be able to: 1. Explain the steps of external respiration 2. Compare and contrast the components and role of the conducting zone and respiratory zones of the lung 3. Discuss the role of the autonomic nervous system in controlling airway resistance 4. Determine the factors that will influence diffusion of a gas (Fick’s Law) 5. Describe dead space and the parameters that contribute to dead space 6. Calculate tidal volume and alveolar ventilation volume 7. Define minute ventilation, alveolar minute ventilation 8. Calculate minute ventilation, alveolar minute ventilation 2  Why do humans need a respiratory system? Remember: – glucose + O2 → CO2 + H2O + ATP Efficient delivery of O2 from air to tissues and removal of CO2 from tissues to air 3 What else does the respiratory system do? Regulate pH Vocalization Defense against airborne pathogens – Removal of inhaled particles Lungs process certain blood-borne substances – angiotensin converting enzyme converts angiotensin I to angiotensin II – enzymes inactivate bradykinin and some prostaglandins – certain immunoglobulins (IgA) are released 4  Steps of external respiration Atmosphere 1. Ventilation between atmosphere and alveoli 2. Exchange of O2 and CO2 between air in alveoli and blood 3. Transport of O2 and CO2 between lungs and tissue 4. Exchange of O2 and CO2 between blood and tissue Sherwood 13-1 5. Internal respiration 5  Steps of external respiration Atmosphere 1. Ventilation Is ventilation rate constant? No – can be adjusted to meet body’s need for O2 uptake, CO2 removal 2. Gas exchange By which process is gas exchanged? diffusion 3. Transport of O2 and CO2 How is O2 transported? Primarily bound to hemoglobin How is CO2 transported? Primarily as bicarbonate 4. Gas exchange 5. Internal respiration Sherwood 13-1 Where does this occur? mitochondria 6  Organization of the respiratory system Respiratory system structures: Upper Airways – Nasal and oral cavities – Pharynx – Larynx (vocal cords) Trachea Lungs – Bronchi ➔ bronchioles ➔ alveoli – Smooth muscle & connective tissue – Pulmonary circulation Muscles of respiration Rib cage and pleura Parts of CNS that regulate respiration 7 Sherwood 13-2  Functional Anatomy Gen # Conducting zone (anatomical dead space, ~150 ml) Respiratory zone (exchange zone, alveolar ventilation volume) West 1-4 (c.f. Costanzo 5-1) 8  Conducting zone Role is to move air into/out of respiratory zone for gas exchange Functions: humidification and warming of air stream removal of dust – Cilia and mucous secreting cells decreases velocity of airflow 9 How does the ANS control conducting airway tone? Smooth muscle of bronchi and bronchioles is controlled by the ANS – SNS → adrenergic 2 receptor activation on bronchial smooth muscle airway dilation What happens to airway resistance? decreases – PNS → cholinergic M3 receptor activation on bronchial smooth muscle Airway constriction What happens to airway resistance? increases 10 Which disease is caused by inappropriate airway muscle tone? What are treatment options? Asthma Asthma attacks due to broncoconstriction Associated with chronic inflammatory condition commonly treated with albuterol (2 adrenergic receptor agonist) West 4-13 11  Pulmonary vasculature Pulmonary artery receives all of the right heart output – Pulmonary blood pressure is low (arterial pressure ~15 mmHg) – Since cardiac output is still 5- 6L/min, what does this mean for surface area of entire pulmonary circulation? Large surface area, low resistance Pulmonary blood flow not distributed evenly when we’re standing – Due to gravity – Lowest at top of lung and highest at bottom of lung 12  13 Sherwood 13-2  Respiratory zone = Respiratory bronchioles + alveoli Movement of gas mainly via diffusion – From high pressure to low pressure – CO2 into alveoli – O2 out of alveoli Design feature: increase surface area for diffusion 14 Sherwood 13-2  What makes up an alveolus? Type I alveolar cell – Alveolar epithelium Type II alveolar cell – Synthesize pulmonary surfactant Alveolar macrophages – Instead of cilia 300 million alveoli/lung Alveolar diameter ~200 μm Total alveolar surface area? ~50-100 m2 (aka tennis court!) 15 Sherwood 13-4 Blood gas diffusion across alveolar-capillary interface Red blood cells spend ~0.75 s in capillary, traversing 2-3 alveoli Diffusion distance is small (0.5 μm) – Three layers: alveolar epithelium, interstitial fluid, capillary endothelium 16 Sherwood 13-4  Diffusion of gases: Fick’s Law Vx = volume of gas diffused per unit time Vx = D x A x ΔP D = diffusion coefficient of the gas A = surface area ΔX ΔP = partial pressure difference of the gas ΔX = membrane thickness Diffusion directly proportional to: Diffusion coefficient Surface area Pressure gradient Diffusion inversely proportional to: Membrane thickness (diffusion distance) How does this relate to the alveolar- capillary barrier? Thin walls and huge surface area 17 Clinical connection: factors that affect gas diffusion rate What do you think would happen to the rate of gas diffusion for the following conditions and why? 1. Increased fibrotic tissue in the respiratory zone of the lung due to restrictive lung disease? Decreased, due to increased diffusion distance 2. A lung resection due to removal of a cancerous lung lobe? Decreased, due to decreased surface area 3. A person visits Cuzco, Peru? Decreased, due to decreased pressure gradient 4. Your friend goes for a run? Increased, due to increased surface area 18  Tidal volume Humans use tidal How do we adjust for ventilation increased metabolic demand – air moves bidirectionally into during exercise? and out of lungs by same We can adjust breathing rate, path or tidal volume Tidal volume = amount of air that moves in and out per breath during normal breathing What’s the challenge with tidal breathing? Dead space! Inspired breath (500 ml) Expired breath (500 ml) Airway (150 ml) Lung End-expiration Inspiration End-inspiration End-expiration 20  What is dead space? Volume of airways and lungs not involved in gas exchange Anatomical dead space Physiological dead space 21  Anatomical dead space What makes up anatomical dead space? Nasal cavity, trachea, bronchi, bronchioles (branches 0-16) In other words: volume of gas in conducting airways Typically estimate dead space as 1 ml per 1b weight – Therefore, ~150 ml for a 150 lb person 22  Physiological dead space Total volume of lungs not participating in gas exchange Physiological = Anatomical Alveolar dead space dead space + dead space Alveolar Dead Space – alveoli that are ventilated but not perfused – pulmonary capillaries are not all open at a given time – some pathologies increase alveolar dead space (e.g. pulmonary emboli) Normally: – physiological dead space ≈ anatomical dead space 23  Tidal volume (VT) and alveolar ventilation volume (VA) VT = VD + VA Dead space volume (VD): – amount of VT not available for gas exchange Alveolar ventilation volume (VA): VA = VT - VD – amount of VT available for gas exchange 24  Ventilation rates Minute ventilation (V) – Total volume moved into and out of lung per minute – V a poor estimate of gas exchange because of dead space (VD) V = VT x (breaths/min) Alveolar (functional) minute ventilation (VA): – Corrects for physiologic dead space – Provides a better estimate of gas exchange VA = VA x (breaths/min) 25  Example ventilation calculations During a routine medical exam, the following ventilation parameters were obtained for a pharmacy student: Respiratory rate: 12 breaths/min Tidal volume (VT): 500 ml Dead space volume (V D): 150 ml Calculate: minute ventilation alveolar minute ventilation V = VT x (breaths/min) VA = VT - VD VA = 500-150 ml = 350 ml Minute ventilation = 500 ml x 12 breaths/min V = 6000 ml/min VA = VA x (breaths/min) Alveolar minute ventilation: = 350 ml x 12 breaths/min VA = 4200 ml/min 26