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Copyright © 2011 Pearson Education, Inc.
BREATHING
Copyright © 2011 Pearson Education, Inc.
Mechanics of Breathing
Pulmonary ventilation has two phases:
1. Inspiration - gases flow into the lungs
2.Expiration - gases exit the lungs
Boyle’s LawP1V1 = P2V2
Pressure and volume are inversely proportional
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Pulmonary Ventilation
• Inspiration and expiration
• Depend on volume change
• Volume changes pressure changes
• Pressure changes gases flow
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Pressure in the Thorax
• Atmospheric pressure (Patm)
• Outside pressure
• = ~1 atm
• Negative respiratory pressure < Patm
• Positive respiratory pressure > Patm
• Zero respiratory pressure = Patm
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Alveolar Surface Tension
• Surfactant
• Detergent-like complex produced by alveolar cells
• Helps keep lungs from collapsing.
• Insufficient quantity in premature infants causes infant respiratory distress syndrome
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Pressure Problems
• Atelectasis (lung collapse):
• Plugged bronchioles collapse of alveoli
• pneumonia
• Chest wound
• Pneumothorax - air into pleural cavity
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Muscles of Breathing
• Diaphragm – main muscle
• Produces large changes in lung volume
• External intercostals – lift ribs
• Internal intercostals – forces exhalation
• Abdominals - expiration
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Inspiration
• An active process
• Inspiratory muscles contract
• Thoracic volume increases
• Pressure in the lungs decreases
• Air flows into the lungs, until Ppul = Patm
Copyright © 2011 Pearson Education, Inc. Figure 21.13 (1 of 2)
Sequence of events
Changes in anterior-posterior and superior-
inferior dimensions
Changes in lateraldimensions
(superior view)
Ribs are elevatedand sternum flares
as externalintercostals
contract.
Diaphragmmoves inferiorly
during contraction.
Externalintercostalscontract.
Inspiratory muscles contract (diaphragm descends; rib cage rises).
2
1
Thoracic cavity volume increases.
3 Lungs are stretched; intrapulmonary volume increases.
4 Intrapulmonary pressure drops (to –1 mm Hg).
5 Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is 0 (equal to atmospheric pressure).
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Expiration
• Expiration is a passive process
• Inspiratory muscles relax
• Thoracic cavity volume decreases
• Pressure increases
• Air flows out of the lungs until Ppul = 0
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Expiration
• Forced expiration is an active process
• abdominal and internal intercostal muscles contract
• Decreases in pulmonary volume
• Increase in pulmonary pressure
• Forces air out
Copyright © 2011 Pearson Education, Inc. Figure 21.13 (2 of 2)
Sequenceof events
Changes in anterior-posterior and superior-
inferior dimensions
Changes inlateral dimensions
(superior view)
Ribs and sternumare depressed
as externalintercostals
relax.
Externalintercostalsrelax.
Diaphragmmovessuperiorlyas it relaxes.
1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages).
2 Thoracic cavity volume decreases.
3 Elastic lungs recoil passively; intrapulmonary volume decreases.
4 Intrapulmonary pres-sure rises (to +1 mm Hg).
5 Air (gases) flows out of lungs down its pressure gradient until intra-pulmonary pressure is 0.
Copyright © 2011 Pearson Education, Inc. Figure 21.14
5 seconds elapsed
Volume of breath
Intrapulmonarypressure
Expiration
Intrapleuralpressure
Trans-pulmonarypressure
InspirationIntrapulmonary pressure. Pressure inside lung decreases as lung volume increases during inspiration; pressure increases during expiration.
Intrapleural pressure.Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils.
Volume of breath.During each breath, the pressure gradients move 0.5 liter of air into and out of the lungs.
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Respiratory Volumes
• Tidal volume (TV)
• Normal air exchange
• Inspiratory reserve volume (IRV)
• Forced air in
• Expiratory reserve volume (ERV)
• Forced exhale
• Residual volume (RV)
• Air needed to maintain lungs
Copyright © 2011 Pearson Education, Inc. Figure 21.16b
Respiratoryvolumes
Tidal volume (TV) Amount of air inhaled or exhaled with each breath under resting conditions
3100 ml Inspiratory reservevolume (IRV)
Expiratory reservevolume (ERV)
Residual volume (RV) Amount of air remaining in the lungs after a forced exhalation
500 ml
Amount of air that can be forcefully inhaled after a nor-mal tidal volume inhalationAmount of air that can beforcefully exhaled after a nor-mal tidal volume exhalation
1200 ml
1200 ml
Measurement DescriptionAdult maleaverage value
1900 ml
500 ml
700 ml
1100 ml
Adult femaleaverage value
Respiratory Volumes
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Respiratory Capacities
• Two or more volumes:
• Inspiratory capacity (IC)
• IRV + TV
• Functional residual capacity (FRC)
• ERV + RV
• Vital capacity (VC)
• IRV + TV + ERV
• Total lung capacity (TLC)
• IRV + TV + ERV + RV
Copyright © 2011 Pearson Education, Inc. Figure 21.16b
Respiratorycapacities
(b) Summary of respiratory volumes and capacities for males and females
Functional residualcapacity (FRC)
Volume of air remaining in the lungs after a normal tidal volume expiration: FRC = ERV + RV
Maximum amount of air contained in lungs after a maximum inspiratory effort: TLC = TV + IRV + ERV + RVMaximum amount of air that can be expired after a maxi-mum inspiratory effort: VC = TV + IRV + ERVMaximum amount of air that can be inspired after a normal expiration: IC = TV + IRV
Total lung capacity (TLC)
Vital capacity (VC)
Inspiratory capacity (IC)
6000 ml
4800 ml
3600 ml
2400 ml
4200 ml
3100 ml
2400 ml
1800 ml
Respiratory Capacities
Copyright © 2011 Pearson Education, Inc. Figure 21.16a
Inspiratoryreserve volume
3100 ml
Tidal volume 500 ml
(a) Spirographic record for a male
Expiratoryreserve volume
1200 ml
Residual volume1200 ml
Functionalresidualcapacity2400 ml
Inspiratorycapacity3600 ml Vital
capacity4800 ml
Total lungcapacity6000 ml
Respiratory Volumes and Capacities
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Nonrespiratory Air Movements
• Most result from reflex action
• Examples include: cough, sneeze, crying, laughing, hiccups, and yawns
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Gas Exchanges Between Blood, Lungs, and Tissues
• External respiration
• Internal respiration
• Depends on composition of gasses and fluid
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Composition of Alveolar Gas
• Alveoli contain more CO2 and water vapor than atmospheric air
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Gas Solubility
• Venous blood has much less oxygen than in alveoli
• Oxygen diffuses into the veins
• Carbon dioxide is transfused the same way
• In the opposite direction
Copyright © 2011 Pearson Education, Inc. Figure 21.17
Inspired air:P 160 mm HgP 0.3 mm Hg
Blood leavinglungs andentering tissuecapillaries:P 100 mm HgP 40 mm Hg
Alveoli of lungs:P 104 mm HgP 40 mm Hg
O2
Heart
Blood leavingtissues andentering lungs:P 40 mm HgP 45 mm Hg
Systemicveins
Systemicarteries
Tissues:P less than 40 mm HgP greater than 45 mm Hg
Internalrespiration
Externalrespiration
Pulmonaryveins (P100 mm Hg)
Pulmonaryarteries
CO2
O2
CO2
O2
CO2O2
CO2
O2
CO2
O2
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Ventilation-Perfusion Coupling
• Ventilation: amount of gas reaching the alveoli
• Perfusion: blood flow reaching the alveoli
• Ventilation and perfusion must be matched (coupled) for efficient gas exchange
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Internal Respiration
• Capillary gas exchange in body tissues
• Diffusion gradients are reversed compared to external respiration
• Oxygen is low in tissues, high in blood
• Carbon dioxide is high in tissues, low in blood
• Gas exchange occurs
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Transport of Respiratory Gases by Blood
• Oxygen (O2) transport
• 1.5% dissolved in plasma
• 98.5% loosely bound to Fe in hemoglobin (Hb)
• in RBCs
• 4 O2 per Hb
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Transport of Respiratory Gases by Blood
• Carbon dioxide (CO2) transport
• Combines with water in plasma
• Forms Bicarbonate (HCO3–)
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Transport and Exchange of CO2
• CO2 combines with water to form carbonic acid (H2CO3), which quickly dissociates:
• Important in pH balance of blood
• How acidic or basic blood is
• Measurement of H+ ions
CO2 + H2O H2CO3 H+ + HCO3–
Carbondioxide
Water Carbonic acid
Hydrogen ion Bicarbonate ion
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Influence of CO2 on Blood pH
• HCO3– in plasma is a buffer system
• Has the ability to add or remove H+ ions as needed
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Control of Respiration
• Main muscle is the diaphragm
• Innervated by the phrenic nerve
• Cervical nerve plexus
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Breathing Abnormalities
• Hyperventilation: increased rate of breathing
• exceeds need
• May cause cerebral vasoconstriction and cerebral ischemia
• Apnea: period of ceased breathing
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Pulmonary Irritant Reflexes
• Receptors in the bronchioles respond to irritants
• Promote constriction of air passages
• Receptors in the larger airways mediate the cough and sneeze reflexes
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Homeostatic Imbalances
• Chronic obstructive pulmonary disease (COPD)
• chronic bronchitis and emphysema
• Irreversible decrease in forced exhalation
• Increased risk when smoking
Copyright © 2011 Pearson Education, Inc. Figure 21.27
• Tobacco smoke• Air pollution
• Airway obstruction or air trapping• Dyspnea• Frequent infections
• Abnormal ventilation- perfusion ratio• Hypoxemia• Hypoventilation
-1 antitrypsindeficiency
Continual bronchialirritation and inflammation
Breakdown of elastin inconnective tissue of lungs
Chronic bronchitisBronchial edema,chronic productive cough,bronchospasm
EmphysemaDestruction of alveolarwalls, loss of lungelasticity, air trapping
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Homeostatic Imbalances
• Asthma
• Characterized by coughing, dyspnea, wheezing, and chest tightness
• Active inflammation of the airways
• Constriction of airways
• Immune response
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Homeostatic Imbalances
• Tuberculosis
• Infectious disease
• Mycobacterium tuberculosis
• Symptoms include spitting up blood
• Treatment entails a 12-month course of antibiotics
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Homeostatic Imbalances
• Lung cancer
• Leading cause of cancer deaths in North America
• 90% of cases result from smoking