Respiratory Physiology

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Respiratory Physiology

• Dr. Jena Hamra

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Respiratory Function

• Exchange of gases
• Regulation of body pH
• Protection
• Inhaled pathogens
• Irritating substances
• Vocalization

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Respiration

• Cellular
• Reaction of oxygen to yield ATP
• External
• Interchange of gases between environment and body
• 4 processes
• Ventilation
• Exchange of gases lungs and blood
• Transport of gases by blood
• Exchange of gases blood and cells

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Respiratory System

• Conducting system
• Airways
• Gas exchange surface
• Alveoli
• Ventilatory assistance
• Bones and muscle

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Bones and Muscles

• Thoracic cage
• Ribs and spine
• Diaphragm
• Intercostal muscles
• Sternocleidomastoids and scalenes
• Thorax
• Sealed cavity with 3 membranous bags
• Pericardial sac
• Pleural sacs

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Respiratory System

• Divided into upper and lower tracts
• Pleural sacs
• Contain lungs
• Double walled
• Pleural fluid
• Lungs
• Divided into lobes
• Right lung 3 lobes
• Left lung 2 lobes
• Rest on diaphragm

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Airways

• Air pathway
• Mouth, nose ? Pharynx ? Larynx ? Trachea ?
  Bronchi ?Bronchioles ? Respiratory bronchioles ?
  Alveoli
• Alveoli
• Site of gas exchange
• Single layer of thin exchange epithelium

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Alveoli

• Epithelial cells
• Type I
• Gas exchange
• Type II
• Secrete surfactant
• No muscle fibers
• Elastin fibers
• Covered by capillaries
• Gas exchange
• Diffusion

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Pulmonary Circulation

• Right ventricle ? Pulmonary trunk ? 2 pulmonary
  arteries ? Lungs ? Pulmonary veins ? Left atrium
• Blood flow
• Rate faster than other tissues
• Low pressure
• Low resistance
• Small volume ISF

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Gas Laws

• Daltons Law
• Total pressure is the sum of individual gas
  pressures
• Gases move from higher to lower pressure
• Boyles Law
• As volume decreases, pressure increases
• Change volume of chest cavity
• Change pressure in lungs

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Ventilation

• Upper airways
• Warm air
• Humidify
• Filter
• Trachea and bronchi
• Ciliated epithelium
• Mucus escalator
• Watery saline layer
• Cystic fibrosis

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Ventilation

• Air flow
• Pressure gradients
• Created by thoracic muscles
• Diaphragm, intercostals, scalenes
• Respiratory pressure
• Alveolar pressure
• Intrapleural pressure
• Flow due to difference in alveolar to atmospheric
  pressure

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Inspiration

• Somatic motor neurons fire
• Trigger contraction of
• Diaphragm
• External intercostals, scalene
• Increases thoracic cavity volume
• Decreases alveolar pressure
• Air flows in

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Expiration

• Somatic motor neurons cease firing
• Muscles relax
• Passive expiration
• Thoracic volume decreases
• Pressure increases
• Air flow reverses
• Active expiration
• Internal intercostals and abdominals
• Exercise

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Intrapleural Pressure

• Pleural fluid
• Adherence of lungs to thoracic cage
• Causes lung expansion and contraction
• Pneumothorax
• Puncture pleural cavity
• Loss of pressure gradient

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Compliance and Elastance

• Compliance
• Ability of lungs to stretch
• Elastance
• Elasticity
• Diseases that affect compliance and elastance
• Emphysema
• Lose elastin fibers
• High compliance, low elastance
• Restrictive lung diseases
• Reduced compliance

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Surfactant

• Surface tension
• Increases work in lungs
• Law of LaPlace
• Pressure depends on surface tension and radius
• Pressure is greater in smaller vessel if surface
  tension is the same
• Surfactants
• Disrupt cohesive forces between water molecules
• Secreted by Type II alveolar cells
• More in smaller alveoli

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Airway Resistance

• Airway diameter
• Decrease diameter, increase resistance
• Bronchiole diameter adjustable
• Controls resistance
• Control of bronchoconstriction
• CO2
• Histamine
• Parasympathetic neurons
• Beta-2 adrenergic receptors

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Lung Volumes

• Tidal volume (VT)
• Air volume moved in single normal inspiration or
  expiration
• Inspiratory reserve volume (IRV)
• Expiratory reserve volume (ERV)
• Residual volume (RV)
• Air in respiratory system after maximal exhalation

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Gas Exchange

• Simple diffusion
• Rate of diffusion
• Partial pressure gradient
• Higher to lower pressure
• Surface area
• Thickness of membrane
• Inversely proportional to distance

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Alveolar Membrane Changes

• Loss of alveolar surface
• Emphysema
• Fibrotic lung disease
• Slows diffusion
• Pulmonary edema
• Increase diffusion distance
• Asthma
• Decreased ventilation

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Movement of Gas into a Liquid

• Dependent on
• Pressure
• Moves from higher to lower
• Solubility
• More soluble, less pressure required
• Temperature
• Gases move until reach equilibrium
• Partial pressures the same

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Gas Exchange in Tissues

• Dependent on
• Pressure gradient
• Pressure of oxygen greater in blood
• Pressure of carbon dioxide greater in tissue
• Simple diffusion
• Rapid

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Gas Transport

• 2 methods
• Dissolved in blood
• By hemoglobin (RBCs)
• Oxygen transport
• Hemoglobin
• Dependent on
• Oxygen binding sites in RBCs
• Number of hemoglobin molecules in blood
• PO2 of plasma

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Hemoglobin

• Each hemoglobin molecule binds up to 4 oxygen
  molecules
• Oxyhemoglobin
• Determined by PO2
• Measured as percentage
• How much of hemoglobin is saturated
• Oxygen-hemoglobin dissociation curve

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Oxygen-Hemoglobin Binding

• Factors that affect the hemoglobin protein alter
  binding ability
• ? pH, ? PCO2, ? temperature
• Decreased affinity
• Exercise
• Decreased pH, decreased affinity
• Increased delivery of oxygen to tissues
• Right shift of curve

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Carbon Dioxide Transport

• 3 ways
• Dissolved in plasma
• Bound to hemoglobin
• Converted to bicarbonate ion
• Primarily transported dissolved in plasma
• Conversion to bicarbonate ion
• Carbonic anhydrase
• In RBCs
• CO2 H2O ? H HCO3-

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Chloride Shift

• Transport process
• HCO3- out of RBC for Cl-
• H bound to hemoglobin
• In lungs
• Reverse occurs
• CO2 out of lungs
• H leaves hemoglobin
• Chloride shift reverses

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Regulation of Ventilation

• Respiratory neurons in medulla
• Inspiration and expiration
• Neurons in pons
• Rate and depth of ventilation
• Spontaneously discharging neurons
• Rhythmic pattern of breathing
• Chemical factors
• Higher brain centers

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Medullary Control

• Central pattern generator
• Automatic
• Influenced by CO2, O2, and H levels
• 2 nuclei
• Dorsal respiratory group
• Inspiratory neurons
• Ventral respiratory group
• Active expiration or greater than normal
  inspiration

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Chemoreceptors

• Carbon dioxide chemoreceptors
• Primary stimulus
• Oxygen chemoreceptors
• Peripheral chemoreceptors
• Carotid and aortic bodies
• Sense change in O2, pH and PCO2
• Central chemoreceptors
• Ventral surface of medulla
• Sense CO2 in CSF

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