Respiratory Physiology

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Respiratory Physiology

• Sharron King

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Learning Objectives

• Describe the three processes of respiration
• Pulmonary ventilation
• External respiration
• Internal respiration
• Identify the various lung volumes and capacities
• Describe O2 and CO2 transport
• Identify the factors that control respiration
• Explain how smoking reduces respiratory
  efficiency

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Three Processes of Respiration (p. 830)

• Pulmonary ventilation (breathing)
• physical movement of air into and out of lungs
• inspiration - active
• expiration - usually passive
• Pulmonary (external) respiration
• gas exchange at lung
• Tissue (internal) respiration
• gas exchange at tissues

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Inhalation

• Inhalation
• Active process
• During quiet breathing contraction of diaphragm
  and external intercostals expands thoracic cavity
• Decreases pressure (Boyles law volume
  inversely related to pressure)
• air flows down pressure gradient

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Exhalation

• Exhalation during quiet breathing is passive
  process
• Elastic recoil of chest wall and lungs
• Due to
• Recoil of elastic fibres
• Inward pull of surface tension of alveolar fluid

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Deep Forceful Breathing

• Deep Inhalation
• During deep forceful inhalation accessory muscles
  of inhalation participate to increase size of
  thoracic cavity
• Sternocleidomastoid elevate sternum
• Scalenes elevate first two ribs
• Pectoralis minor elevate 3rd5th ribs
• Deep Exhalation
• Exhalation during forceful breathing is active
  process
• Muscles of exhalation increase pressure in
  abdomen and thorax
• Abdominals
• Internal intercostals

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Factors affecting pulmonary ventilation

• Surface tension of alveolar fluid
• surfactant
• Lung compliance
• Elasticity
• Surface tension
• Airway resistance

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Clinical Note Emphysema

• Enlargement of air spaces caused by destruction
  of alveolar walls
• Reduces surface area for gas exchange
• Increases work of breathing

R. Lower lobe full of air pockets Black deposits
from Cigarette residue
Emphysema Warnock (1999)
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Emphysema

• Emphysema causes air to becomes trapped in the
  lungs
• Results in barrel chest

Emphysema (n.d.)
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Respiratory rates and volumes(p. 837)

• Respiratory Minute Volume
• Total volume of air inhaled/exhaled per min
• Frequency x tidal volume
• Average healthy adult
• 12 breaths per min x 500 ml tidal volume
• 30 of tidal volume remains in anatomic dead
  space
• Alveolar ventilation rate
• Volume of air per min that reaches alveoli (i.e.
  70 of tidal volume)

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Lung volumes and capacities

• 4 lung volumes
• tidal (500 ml)
• inspiratory reserve (3100 ml)
• expiratory reserve (1200 ml)
• residual (1200 ml)
• 4 lung capacities
• inspiratory (3600 ml)
• functional residual (2400 ml)
• vital (4800 ml)
• total lung (6000 ml)

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Gas Exchange

• Exchange of O2 and CO2 between alveolar air and
  blood occurs via passive diffusion
• Governed by
• Daltons Law
• Each gas in a mixture exerts own pressure
• Partial pressure
• Henrys Law
• Quantity of gas that dissolves in liquid
  proportional to partial pressure and solubility
  coefficient
• Solubility of CO2 greater than O2 (24x)

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External and Internal Respiration

• External respiration
• Diffusion of
• O2 from alveoli to blood
• CO2 from blood to alveoli
• Blood leaving pulmonary capillaries mixes with
  blood draining lung tissue
• PO2 of blood in pulmonary veins lower than in
  pulmonary capillaries
• Internal respiration
• Diffusion of
• O2 from blood to tissues
• CO2 from tissues to blood

Jenkins, Kemmitz Tortora (2007 p. 861)
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Respiration

• Effective external and internal respiration
  depends on
• partial pressure differences
• gases move from high to low partial pressures
• surface area for gas exchange
• diffusion distance
• Molecular weight and solubility of gas
• O2 has lower molecular weight than CO2
• O2 would be expected to diffuse 1.2x faster
• CO2 24x more soluble than O2
• Net result CO2 diffusion approx 20x faster than
  O2 diffusion

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Oxygen transport in Blood(p. 842)

• Oxygen transport
• 1.5 dissolved in plasma
• 98.5 bound to hemoglobin (Hb)
• Oxyhemoglobin Saturation Curve
• higher PO2 results in greater Hb saturation

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CO2 Transport

• Carbon dioxide transport
• 9 dissolved in plasma
• 13 as carbamino compounds
• Most combined with Hb
• 78 converted to HC03-
• CO2 H2O ? H2CO3 ? H HCO3-
• Haldane effect
• Inverse relationship between amount of Hb-O2 and
  CO2 carrying capacity of blood
• Hb binds and transports more CO2 than O2
• Hb buffers more H than Hb-O2
• Promotes conversion of CO2 to HCO3- via carbonic
  anhydrase reaction

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Key Concepts

• O2 mostly transported in blood bound to
  hemoglobin
• If the PO2 increases Hb binds O2
• If PO2 decreases Hb releases O2
• CO2 mostly transported in blood as HCO3-
• Lesser amounts of CO2 are bound to Hb or
  dissolved in plasma

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Respiratory centers (p. 848)

• Basic rhythm of ventilation controlled by
  medullary rhythmicity area (medulla oblongata)
• Inspiratory area (Dorsal Resp.Group)
• determines basic rhythm of breathing
• causes contraction of diaphragm and external
  intercostals
• Expiratory area (Ventral Resp. Group)
• Inactive during normal quiet breathing
• Activated by inspiratory area during forceful
  breathing
• Causes contraction of internal intercostals and
  abdominal muscles

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Respiratory centers

• Transition between inhalation and exhalation
  controlled by
• Pneumotaxic area
• located in pons
• inhibits inspiratory area of medulla to stop
  inhalation
• Breathing more rapid when pneumotaxic area active
• Apneustic area
• located in pons
• stimulates inspiratory area of medulla to prolong
  inhalation

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Regulation of Respiratory centers

• Basic rhythm of ventilation coordinated by
  inspiratory area of respiratory centre, but
  modified by
• Cortical influences
• Voluntary control over breathing
• Hypothalamus and limbic system
• Emotional stimuli
• Proprioceptors
• Upper motor neurons of primary motor cortex also
  stimulate inspiratory area
• Inflation (Hering-Breuer) reflex
• Stretch receptors in walls of bronchi and
  bronchioles
• Inhibit inspiratory and apneustic areas
• causes exhalation to begin to protect against
  overinflation
• Chemoreceptors
• Increased PCO2, or reduced pH or PO2 causes
  chemoreceptors to stimulate inspiratory area of
  respiratory centre

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Problem solving

• Josh hyperventilates for several minutes before
  diving into a pool. Shortly after he enters the
  water he blacks out and almost drowns. What
  caused this to happen?

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Regulation of Respiratory centers

• Rhythm of ventilation also modified by
• Temperature
• ? temp ? ventilation (and vice versa)
• sudden cold stimulus may cause apnea
• Pain
• Sudden severe pain can cause apnea
• Prolonged somatic pain increases respiratory rate
• Visceral pain may slow respiratory rate
• Irritation of airways
• Blood pressure
• ?BP ?ventilation (and vice versa)
• Attempt to reduce venous return via respiratory
  pump?

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Effects of smoking

• Smoking reduces respiratory efficiency
• Deposits tar other chemicals
• swelling of mucosal lining and increased
  production of mucus
• Impedes airflow
• destroys cilia and inhibits their movement
• Reduces removal of excess mucus and debris

Smokers lungs Bodies The exhibition March 2006
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Smoking

• Nicotine constricts terminal bronchioles
• Reduces airflow into and out of lung
• CO binds irreversibly to Hb
• Reduces blood oxygen carrying capacity
• Destruction of elastic fibers (prime cause of
  emphysema)
• Reduced lung compliance
• Collapse of small bronchioles during exhalation
• traps air in alveoli during exhalation
• Reduces efficiency of gas exchange

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References

• Bodies The exhibition 2006, updated 29 March
  2006, MOSI, viewed 20 May 2006,
  lthttp//www.bodiestheexhibition.com/bodies.htmlgt.
• Emphysema (n.d.) Viewed 14 August 2006,
  lthttp//www.physicaltherapy.ca/cardio/Emphysema1.h
  tmlgt
• Jenkins, GW, Kemmitz, CP Tortora, GJ 2007,
  Anatomy and Physiology From Science to Life,
  John Wiley Sons Inc, New Jersey.
• Martini, FH 2006, Fundamentals of Anatomy and
  Physiology, 7th edn, Pearson Benjamin Cummings,
  San Francisco.
• Small Cell Lung Cancer 2005, updated 10 April,
  AstraZeneca, viewed 12 July 2006,
  lthttp//www.astrazeneca.no/sykdommer/lungekreft/fo
  r_helsepersonell/typer_lungekreft.htmlgt.
• Warnock, ML 1999, Overview of Pulmonary
  Pathology, updated 5 Feb 2006, viewed 20 May
  2006, lthttp//pathhsw5m54.ucsf.edu/overview/emphys
  ema.htmlgt.