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90 Cards in this Set
- Front
- Back
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What is the purposeof the branching pattern of the respiratory tree?
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To allow for dramatic increase in cross-sectional area
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What type of epithelium lines the conducting zone:
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Ciliated, pseudostratified columnar epithelium
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At what point in the respiratory tree does gas exchange begin?
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Respiratory bronchioles
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What are the 4 barriers to gas exchange at the alveolar-capillary interface?
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Surfactant, Alveolar epithelium, Interstitial space, Capillary endothelium
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What 3 types of cells compose the alveolar surface?
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Type I pneumocytes: thin cells that constitute 90% of the surface area, even though less abundant than type II cells in number.
Type II pneumocytes: most abundant, but only constitute 10% of surface, and produce surfactant. Phagocytic alveolar macrophages: ingest and clears foreign, inhaled particles. |
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What are the two types of dead space?
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1. Anatomic dead space (respiratory tree with no alveoli present)
2. Alveolar dead space (alveoli with no perfusion) |
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What is the function of anatomic dead space?
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Warm and humidity inspired air
Removal of foreign particles |
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What is the mucociliary escalator?
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As foreign particles are trapped in the mucus that lines the epithelium of the respiratory tract, the cilia on the epithelium beat upwards, away form alveol and lower respiratory structures.
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Why do particles in venous blood not reach the arterial circulation?
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They are filtered out by the pulmonary circulation (these particles can vary, but can be clots, agglutinated RBCs, gas bubbles, etc).
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What does the pulmonary circulaiton 'filter' prevent?
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Thrombotic or occlusive events on the left side of circulation.
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Define the following lung volumes:
Tidal Volume (VT) Inspiratory reserve volume (IRV) Expiratory reserve volume (ERV) Residual volume (RV) |
VT: Volume of anormal breath at rest
IRV: Additional volume of gas that can be inspired above the VT ERV: Volume of gas that can be forcefully expired after a normal passive expiraton RV: Volume of gas that remains after maximal expiration |
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Define the following lung capacities:
Total lung capacity (TLC) Vital capacity (VC) Functional residual capacity (FRC) |
TLC: Volume of gas present after a maximal inspiration
VC: Maximal volume that can be expelled after a maximal inspiration. This is the maximal volume that can be exchanged in a single breath. FRC: Volume remaining at the end of a normal breath at rest. |
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What are the volumes that make up the following capacities:
Inspiratory capacity (IC) Funcitonal residual capacity (FRC) Vital Capacity (VC) Total lung capacity (TLC) |
IC = VT + IRV
FRC = RV + ERV VC = ERV + VT + IRV TLC = RV + ERV + VT + IRV |
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Which lung volumes and capacities cannot be measured using spirometry?
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Residual volume
Functional reserve capacity Total lung capacity |
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How can the above capacities be measured?
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Nitrogen washout
Helium dilution Body plethysmography |
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Define minute ventilation (VE)
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Volume of air inspired or expired per minute:
VE = VT x frequency |
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What are:
Forced vital capacity (FVC) Forced expiratory volume in 1 second (FEV1) |
FVC: Volume exhaled with maximal expiratory effort
FEV1: Volume that can be forcefully expired in 1 second |
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What is the normal ratio of FEV1 per FVC?
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80% (FEV1/FVC = 0.8)
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What is alveolar ventilation?
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The volume of air reaching the alveoli per minute
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Why is alveolar ventilation less than minute ventilation?
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The last part of inspired air only reaches the conduction zone and never reaches the respiratory zone
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How does shallow versus deep breathing affect alveolar ventilation?
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Rapid shallow breaths produces much less alveolar ventilation; most of each breath ventilates the conducting zone
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How is dead space calculate?
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Vd = Vt x ([PaCO2 x PeCO2]/PaCO2)
Vd: dead space volume Vt: total lung volume PaCO2: partial pressure of arterial CO2 PeCO2: partial pressure of expired CO2 |
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What are the muscles of inspiration?
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1. Diaphragm (majority of work at rest)
2. External intercostals (increase thoracic size and prevent retraction) 3. Accessory muslces of inspiration (not used during quiet breathign) |
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What are the accessory muscle of inspiration?
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Sternocleidomastoid
Scalenes Strap muscles of the neck |
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What is the innervation of the diaphragm?
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Phrenic nerve (C3,4,5 keep the diaphram alive)
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What action does the diaphragm perform?
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As it contracts it flattensinto the abdominal cavity, increasing the volume of the thoracic cavity
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Which muscles are involved in normal quiet expiration?
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None. It is a passive process due to the elastic recoil by the lungs.
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Which muscles are active in active expiration (e.g., exercise)?
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Abdominal muscles and internal intercostals
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Where is the intrapleural space?
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It is between the lung and the chest wall. It is actually only a "potential space" under normal conditions because the viceral and parietal plerual layers are usually closely apposed.
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What is the normal intraplerual pressure at rest?
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Slightly subatmospheric (-3 to -5 cm H2O)
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What is the normal six series of events during inspiration?
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1.Respiration initiated by central nervous system
2. Diaphragm contracts, along with other external intercostals 3. Thoracic volume increases 4. Decrease in intrapleural pressure 5. Alveolar pressure becomes subatmospheric 6. Air flows into the alveoli to equilibrate with atmospheric pressure |
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Define Compliance (C)
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An indcation of how easily the lungs and chest wall can be stretched or inflated. In general terms, it refers to the lungs abilit to accommodate incoming volume.
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What is the equation for compliance?
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C = change in volume / change in pressure
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What physiologic elements influence compliance?
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Most widely discussed are things like intrinsic recoil of pulmonary tissues, but remeber that lung volume and alveolar surface tension also contribute
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What processes can cause a decrease in compliance?
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Pulmonary congestion and various restrictive lung diseases
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What causes an increase in compliance?
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Destruction of lung tissue with concomitant loss of elastic tissues (e.g., emphysema)
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Compare the FEV1:FVC ratio of a normal lung to a lung with emphysema or chronic bronchitis
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Normal lung has an FEV1:FVC ratio of 80%, emphysematous lung has an FEV1:FVC ratio of <80% (usually 60-70% or less)
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What other obstructive lung disease cause a decrease in FEV1:FVC ratio?
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Asthma, bronchiectasis
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How does the FVC compare between a normal lung and one with restrictive disease?
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Total FVC is lower due to decreased lung compliance
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How does compliance change with lung volumes?
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Increases at low volumes, decreases at high volumes
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Define Elasticity
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The recoil force generated by distension of a structure
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How is compliance related to elasticigty?
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Inversely (C = 1/E)
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What contributes to the lungs' recoil properties:
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Lung parenchyma (elastin, collagen, etc)
Surface tesniison at air-liquid interface in alveoli |
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How does Laplace law relate to surface tension, and how does that affect the collapsibility of alveoli?
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P = 2T/r
P = collapsing pressure (dyne/cm2) T = surface tension (dyne/cm) r = alveolar radius (cm) |
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Which is easier to keep oen a large alveoli or a small one?
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Large alveoli (alveola radius is inversely proportional to collapsing pressure) P = 2T/r
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Which cells produce surfactant?
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Type II alveolar epithelia cells
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What are the 4 functions of pulmonary surfactant?
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1. Reduce surface tension at low lung volumes (prevent atelectasis)
2. Increase surface tension at high lung volumes (contribute to lung recoil) 3. INcrease alveolar radius 4. Reduce pulmonary capillary infiltration |
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What is the effect of surfactant on compliance and elasticity?
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Surfactant increases compliance and decreases elasticity
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What is surfactant composed of?
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1. Dipalmitoyl phosphatidycholine (aka lecithin) - major
2. Phosphatidylglycerol 3. Neutral lipids 4. Other lipids 5. Proteins |
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How may surfactant synthesis be reduced:
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Developmental deficiency (e.g., prematruity)
Hypovolemia Hypothermia Acidosis Hypoxemia Rare genetic disorders of surfactant synthesis |
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Under normal conditions,what structural feature of infidividual alveoli helps to prevent the from collapsing?
What is this theory called? |
Alveolar interdependence: Alveolar walls and airway walls are structurally connected so that tension on alveolar walls created by one collapsing alveolus helps to hold adjacent alveoli open
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What two types of resistance make up pulmonary resistance?
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1. Airway resistance (~80%)
2. Pulmonary tissue resistance (~20%) |
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What factors determine airway resistance?
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Gas viscosity, Diameter of the airway, Length of the airway
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What law describes airway resistance?
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Poiseuille law:
R = 8nl/3.14r^4 R = resistance n = viscosity of inspired gas l = length of airway r = radius of airway |
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How are airway resistance and airflow related?
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Much life flow through the cardiovascular system, they are inversely related:
Q = change P/R Q = airflow (L/min) Change P = pressure gradient (cm H2O) R = airway resistance (cm/H2O/L/min) |
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Which part of the respiratory system is the major site of airway resistance?
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Medium-sized bronchi
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Which part of the respiratory system has the hightest individual resistance?
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Small terminal airways; they are not the major site of airway resistance because they are far mor numerous and are arranged in parallel
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What 3 factors can change airway resistance?
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Altering the radius of the airways
Changes in lung volume Viscosity/density of the inspired gas |
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What is bronchoconstriction/dilation?
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Changes in the diameter of conducting airways
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What causes bronchoconstriction?
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Parasympathetic discharge
Substance P Adenosine Hypersensitivity response (e.g., histamines) Arachidonic acid metabolites (e.g., prostaglandins and leukotrienes) |
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How does bronchoconstriction affect airways?
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1. Reduces airway radius
2. Increases resistance 3. Via the above 2 changes, limits airfow during inspiration or expiration |
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What causes bronchodilation?
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Sympathetic discharge and sympathetic agonists via Beta-2 receptors
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How do obstrctive diseases affect respiratory mechanisms?
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Increase airway resistance; it creates air trapping which increases lung volumes
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How do restrictive diseases affect respiratory mechanics?
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Decrease compliance, affecting inspiration mechanics
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How are partial prssures determined?
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Dalton law: Pp = Pt x fractional (gas)
Pp = partial pressure Pt = total pressure fractional [gas] = gas concentration |
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What is the fraction of oxygen and carbon dioxide in ambient air?
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O2 = 21%
CO2 = 0.04% (can assume atomospheric CO2 is equal to zero) |
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What are the partial pressures of O2 and CO2 in the following locations?
Atomspheric air Air in the trachea Alveolar air Arterial blood Mixed venous blood |
Atomspheric air O2: 160mmHg; CO2 0mmHg
Air in the trachea: O2 150mmHg; CO2 0mmHg Alveolar air: O2 100mmHg; CO2 40mmHg Arterial blood: O2 slightly <100mmHg; CO2 40mmHg Mixed venous blood: O2 40mmHg; CO2 46mmHg |
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Why is the PO2 in the trachea less than that of the atmosphere?
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The air in the trachea is humidified (addition of H2O, which decreases PO2)
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Why is the PO2 in arterial blood slightly less than 100mmHg?
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Regional V/Q mismatching and normal physiologic shunt
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What is a physiologic shunt?
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The ~2% of systemic cardiac output that bypasses the pulmonary circulation (bronchial circulation)
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Why does alveolar gas composition remain constant at rest?
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Because the FRC is much larger than the tidal volume, creating a steady state environment for PAO2 and PACO2.
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Define gas exchange:
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Transport of gas from alveoli to hemoglobin in the blood across the respiratory membrane.
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Where in the resiratory system does gas exchange occur?
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In the terminal portions of the airways (respiratory bronchioles, alveolar ducts, and alveoli)
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At rest, how long does it take for the blood to transverse the pulmonary capillaries?
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It takes only 0.75 s for blood to move thorugh the portion of the capillary where gas exhange occurs.
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What happens to the time for the blood to transverse the pulmonary capillaries during excercise?
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Decreases (down to 0.25 s under strenous exercise).
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What factors determine pulmonary gas diffusion?
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1. Surface area for diffusion
2. Partial pressure difference across membrane 3. Thickness of barrier 4. Diffusivity of gas |
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What equation governs pulmonary gas diffusion?
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Fick equation:
Vgas ~ (A/Th) x D x (Pc - PA) Vgas = flow of gas across an area A = area of barrier Th = thickness of barrier D = diffusion coefficient Pc = partial pressure of gas in the pulmonary capillary PA = partial pressure of gas in the alveoli |
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Explain flow limitation
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Gases enter the blood more quickly than the blood transverses the pulmonary capillaries. Therefore, the limiting factor in the amount of gas into the blood is not the diffusion through the membrane but the flow of blood through the capillaries.
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What is another name for flow limitation?
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Perfusion limitation
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How can flow limitation be overcome?
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By increasing blood flow (e.g., increasing cardiac output during exercise)
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Which gases are subject to flow limitation?
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N2O, O2
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Explain diffusion limitation
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Gases diffuse into the blood more slowly than blood flows through pulmonary capillaries. Therefore, the limiting factor is the rate of diffusion into the blood, not the amount of blood flowing through the capillaries.
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What is an example of a gas that is subject to diffusion limitation?
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Carbon monoxide (Quickly binds Hb, but does not dissovle well in blood)
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Wha is the significance of diffusing capacity (DL)
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Its measurement permits evaluation of the diffusion properties of alveolar capillary membrane by measuring the rate of gas transfer (conductance) by the respiratory system)
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Can oxygen be subject to diffusion limitation?
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Yes, in pathologic states
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How is O2 transported in blood?
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Inarterial blood at PO2 100 mm Hg, PCO2 40 mm Hg, and Hb 97% saturated
Major: chemical combination with Hb (19.5 mL O2/100mL blood) Minor: dissolved in plasma (0.29 mL O2/100ml blood) |
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What is the partial pressure (oxygen tension) of normal O2 arterial blood?
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85 to 100 mm Hg
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In normal adults, what are hemoglobin molecules (HbA) composed of?
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Two alpha and two beta chains. there are exceptions: fetal hemoglobin and disease states
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What are the funcitons of hemoglobin?
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1. Facilitates O2 transport
2. Facilitates CO2 transport 3. Buffers pH of the blood 4. Facilitates NO transport |
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What is heme?
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Complex made up of a porphyrin ring and one atom of ferrous iron (there is one heme group per chain)
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