Respiratory System

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Respiratory System

• Anatomy of the Respiratory System
• Pulmonary Ventilation
• Gas Exchange and Transport
• Respiratory Disorders

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Organs of Respiratory System

• Nose
• Pharynx
• Larynx
• Trachea
• Bronchi
• Lungs

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General Aspects

• Airflow in lungs
• bronchi ? bronchioles ? alveoli
• Conducting division Passages for airflow
• Nostrils to bronchioles
• Respiratory division Gas exchange regions
• Alveoli
• Upper respiratory tract Parts in the head and
  neck
• Nose through larynx
• Lower respiratory tract Parts in the thorax
• Trachea through lungs

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Nose

• Functions
• warms, cleanses, humidifies inhaled air
• detects odors
• resonating chamber that amplifies the voice

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Upper Respiratory Tract
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Nasal Cavity - Conchae and Meatuses

• Superior, middle and inferior nasal conchae
• 3 folds of tissue on lateral wall of nasal fossa
• mucous membranes supported by thin scroll-like
  turbinate bones
• Meatuses
• narrow air passage beneath each conchae
• narrowness and turbulence ensures air contacts
  mucous membranes

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Nasal Cavity - Mucosa

• Olfactory mucosa
• lines roof of nasal fossa
• Respiratory mucosa
• lines rest of nasal cavity with ciliated
  pseudostratified epithelium
• Defensive role of mucosa
• mucus (from goblet cells) traps inhaled particles
• bacteria destroyed by lysozyme

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Nasal Cavity - Cilia and Erectile Tissue

• Function of cilia of respiratory epithelium
• sweep debris-laden mucus into pharynx to be
  swallowed
• Erectile tissue of inferior concha
• venous plexus that rhythmically engorges with
  blood and shifts flow of air from one side of
  fossa to the other once or twice an hour to
  prevent drying
• Spontaneous epistaxis (nosebleed)
• most common site is inferior concha

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• Nasopharynx
• pseudostratified epithelium
• posterior to choanae, dorsal to soft palate
• receives auditory tubes and contains pharyngeal
  tonsil
• 90? downward turn traps large particles (gt10?m)

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• Oropharynx
• stratifeid squamous epithelium
• space between soft palate and root of tongue,
  inferiorly as far as hyoid bone, contains
  palatine and lingual tonsils

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• Laryngopharynx
• stratified squamous
• hyoid bone to level of cricoid cartilage

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• Glottis vocal cords and opening between
• Epiglottis
• flap of tissue that guards glottis
• directs food and drink to esophagus

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• Epiglottic cartilage - most superior
• Thyroid cartilage largest laryngeal prominence
• Cricoid cartilage - connects larynx to trachea
• Arytenoid cartilages (2) - posterior to thyroid
  cartilage

• Corniculate cartilages (2) - attached to
  arytenoid cartilages like a pair of little horns
• Cuneiform cartilages (2) - support soft tissue
  between arytenoids and epiglottis

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Trachea

• Rigid tube 4.5 in. long and 2.5 in. diameter.
• Anterior to esophagus
• Supported by 16 to 20 C-shaped cartilaginous
  rings
• opening in rings faces posteriorly towards
  esophagus
• trachealis spans opening in rings, adjusts
  airflow by expanding or contracting
• Larynx and trachea lined with ciliated
  pseudostratified epithelium which functions as
  mucociliary escalator

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Mucociliary Escalator
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Lung Lobes

• Right lung has 3 lobes
• Superior
• Middle (smallest)
• Inferior
• Left Lung has 2 lobes
• Room for the heart
• Carina

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Bronchial Tree

• Primary bronchi (C-shaped rings)
• from trachea after 2-3 cm enter hilum of lungs
• right bronchus slightly wider and more vertical
  (aspiration)
• Secondary (lobar) bronchi (overlapping plates)
• one for each lobe of lung
• Tertiary (segmental) bronchi (overlapping plates)
• 10 right, 8 left

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Bronchial Tree

• Bronchioles (lack cartilage)
• layer of smooth muscle
• pulmonary lobule is the portion ventilated by one
  bronchiole
• divides into 50 - 80 terminal bronchioles
• Each divides into 2-10 alveolar ducts end in
  alveolar sacs
• Alveoli
• main site for gas exchange

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Pleurae and Pleural Fluid

• Similar to the pericardium except around the
  lungs
• Visceral (on lungs) and parietal (lines rib cage)
  pleurae
• Pleural cavity - space between pleurae,
  lubricated with fluid
• Functions
• reduce friction
• compartmentalization

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Pulmonary Ventilation

• Breathing (pulmonary ventilation) one cycle of
  inspiration and expiration
• quiet respiration at rest
• forced respiration during exercise
• Flow of air in and out of lung requires a
  pressure difference between air pressure within
  lungs and outside body

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Diaphragm
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Respiratory Muscles

• Diaphragm (dome shaped)
• contraction flattens diaphragm
• Scalenes
• hold first pair of ribs stationary
• External and internal intercostals
• stiffen thoracic cage increases diameter

• Pectoralis minor, sternocleidomastoid and erector
  spinae muscles
• used in forced inspiration
• Abdominals and latissimus dorsi
• forced expiration (to sing, cough, sneeze)

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Neural Control of Breathing

• Breathing depends on repetitive stimuli from
  brain
• Neurons in medulla oblongata and pons control
  unconscious breathing
• Voluntary control provided by motor cortex
• Inspiratory neurons fire during inspiration
• Expiratory neurons fire during forced expiration
• Fibers of phrenic nerve go to diaphragm
  intercostal nerves to intercostal muscles

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Respiratory Control Centers

• Respiratory nuclei in medulla
• The Dorsal Respiratory Group (formerly called the
  inspiratory center)
• The Ventral Respiratory Group (formerly called
  the expiratory center )
• Pons
• The Pontine Respiratory Center (formerly the
  pneumotaxic and apneustic centers)

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Input to Respiratory Centers

• From limbic system and hypothalamus
• respiratory effects of pain and emotion
• From airways and lungs
• irritant receptors in respiratory mucosa
• stimulate vagal afferents to medulla, results in
  bronchoconstriction or coughing
• stretch receptors in airways - inflation reflex
• excessive inflation triggers reflex
• stops inspiration
• From chemoreceptors
• monitor blood pH, CO2 and O2 levels

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Chemoreceptors (found near baroreceptors)

• Peripheral chemoreceptors
• found in major blood vessels
• aortic bodies
• signals medulla by vagus nerves
• carotid bodies
• signals medulla by glossopharyngeal nerves
• Central chemoreceptors
• in medulla
• primarily monitor pH of CSF

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Pressure and Flow

• Atmospheric pressure drives respiration
• 1 atmosphere (atm) 760 mmHg
• Intrapulmonary pressure and lung volume
• pressure is inversely proportional to volume
• for a given amount of gas, as volume ?, pressure
  ? and as volume ?, pressure ?
• Pressure gradients
• difference between atmospheric and intrapulmonary
  pressure
• created by changes in volume thoracic cavity

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Respiratory Cycle

• Atmospheric pressure drives respiration
• 1 atmosphere (atm) 760 mmHg
• ? intrapulmonary pressure
• lungs expand with visceral pleura
• 500 ml of air flows with a quiet breath

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Passive Expiration

• During quiet breathing, expiration achieved by
  elasticity of lungs and thoracic cage
• As volume of thoracic cavity ?, intrapulmonary
  pressure ? and air is expelled
• After inspiration, phrenic nerves continue to
  stimulate diaphragm to produce a braking action
  to elastic recoil

Forced Expiration

• Internal intercostal muscles depress the ribs
• Contract abdominal muscles
• ? intra-abdominal pressure forces diaphragm
  upward
• ? pressure on thoracic cavity

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Thats it for today
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Pneumothorax

• Presence of air in pleural cavity
• Collapse of lung (or part of lung) is called
  atelectasis

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Other causes of Atelectasis

• Atelectasis is the decrease or loss of air in all
  or part of the lung
• Tumors obstructing a bronchus
• Foreign body (an inhaled marble?)
• Serious pneumonia
• Lack of surfactant
• Smoke inhalation
• Post-operative complication

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Factors that affect resistance to airflow
Compliance is reduced by smoking and by fibrotic
conditions such as sarcoidosis or lupus

• Pulmonary compliance
• distensibility of lungs
• Bronchiolar diameter
• primary control over resistance to airflow
• bronchoconstriction
• triggered by airborne irritants, cold air,
  parasympathetic stimulation, histamine
• bronchodilation
• sympathetic nerves, epinephrine

Asthma
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Alveolar Surface Tension

• Thin film of water needed for gas exchange
• creates surface tension that acts to collapse
  alveoli and distal bronchioles
• Pulmonary surfactant decreases surface tension
• Premature infants that lack surfactant suffer
  from respiratory distress syndrome

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Measurements of Ventilation

• Spirometer - measures ventilation
• Respiratory volumes
• tidal volume volume of air in one quiet breath
• inspiratory reserve volume
• air in excess of tidal inspiration that can be
  inhaled with maximum effort
• expiratory reserve volume
• air in excess of tidal expiration that can be
  exhaled with maximum effort
• residual volume (keeps alveoli inflated)
• air remaining in lungs after maximum expiration

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• Respiratory volumes
• tidal volume
• inspiratory reserve volume
• expiratory reserve volume
• residual volume

• Vital capacity
• total amount of air that can be exhaled with
  effort after maximum inspiration
• assesses strength of thoracic muscles and
  pulmonary function

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What influences lung volume and capacity?

• Age - ? lung compliance, respiratory muscles
  weaken
• Exercise - maintains strength of respiratory
  muscles
• Body size - proportional, big body/large lungs
• Restrictive disorders
• ? compliance and vital capacity
• Obstructive disorders
• interfere with airflow, expiration requires more
  effort or less complete

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Composition of Air

• Mixture of gases each contributes its partial
  pressure
• At sea level 1 atm. of pressure 760 mmHg
• Air is about 79 nitrogen 597 mmHg
• Air is only about 21 oxygen 159 mmHg
• Air has almost no carbon dioxide 0.3 mmHg
• In Denver (or Reno) atmospheric pressure 625
  (to 645) mmHg
• Air is about 79 nitrogen 494 (510) mmHg
• Air is only about 21 oxygen 131 (135) mmHg
• Air has almost no carbon dioxide 0.3 mmHg

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Alveolar Gas Exchange

• Important for gas exchange between air in lungs
  and blood in capillaries
• Gases diffuse down their concentration gradients
• Amount of gas that dissolves in water is
  determined by its solubility in water and its
  partial pressure in air

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Alveolar Gas Exchange

• Time required for gases to equilibrate 0.25 sec
• RBC transit time at rest 0.75 sec to pass
  through alveolar capillary
• RBC transit time with vigorous exercise 0.3 sec

What percentage of O2 loading at 0.75 sec transit
time is now possible?
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Factors Affecting Gas Exchange

• Membrane thickness - only 0.5 ?m thick
• Membrane surface area - 100 ml blood in alveolar
  capillaries, spread over 70 m2
• Ventilation-perfusion coupling
• areas of good ventilation need good perfusion
  (vasodilation)

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Oxygen Transport

• Concentration in arterial blood
• 20 ml/dl
• 98.5 bound to hemoglobin
• 1.5 dissolved
• Binding to hemoglobin
• each heme group of 4 globin chains may bind O2
• oxyhemoglobin (HbO2 )
• deoxyhemoglobin (HHb)

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Carbon Dioxide Transport

• As bicarbonate (and carbonic acid) - 90
• CO2 H2O ? H2CO3 ? HCO3- H
• As carbaminohemoglobin (HbCO2)- 5 binds to amino
  groups of Hb (and plasma proteins)
• As dissolved gas - 5

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Systemic Gas Exchange

• CO2 loading
• carbonic anhydrase in RBC catalyzes
• CO2 H2O ? H2CO3 ? HCO3- H
• chloride shift
• keeps reaction proceeding
• exchanges HCO3- for Cl-
• (H binds to hemoglobin)

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Systemic Gas Exchange

• O2 unloading
• H binding to HbO2 ? its affinity for O2
• Hb arrives 97 saturated
• Hb leaves 75 saturated
• venous reserve

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Reactions in the alveolus are the reverse of
systemic gas exchange
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Factors Affect O2 Unloading

• Active tissues need oxygen!
• ambient PO2 active tissue has ? PO2 O2 is
  released
• temperature active tissue has ? temp O2 is
  released

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Factors Affect O2 Unloading

• Active tissues need oxygen!
• Bohr effect active tissue has ? CO2, which
  lowers pH (muscle burn) O2 is released

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Factors Affecting CO2 Loading

• Haldane effect
• HbO2 does not bind CO2 as well as
  deoxyhemoglobin
• low level of HbO2 (as in active tissue) enables
  blood to transport more CO2

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Blood Chemistry and Respiratory Rhythm

• Rate and depth of breathing adjusted to maintain
  levels of
• pH
• PCO2
• PO2
• Lets look at their effects on respiration

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Effects of Hydrogen Ions

• pH of CSF (most powerful respiratory stimulus)
• Respiratory acidosis (pH lt 7.35) caused by
  failure of pulmonary ventilation
• hypercapnia PCO2 gt 43 mmHg
• CO2 easily crosses blood-brain barrier
• in CSF the CO2 reacts with water and releases H
• central chemoreceptors strongly stimulate
  inspiratory center
• blowing off CO2 pushes reaction to the left
  CO2 (expired) H2O ? H2CO3 ? HCO3- H
• The induction of hyperventilation reduces H
  (reduces acid)

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Effects of Hydrogen Ions

• Respiratory alkalosis (pH gt 7.45) caused by
  hyperventilation
• hypocapnia PCO2 lt 37 mmHg
• The induction of hypoventilation (? CO2), pushes
  reaction to the right ? CO2 H2O ? H2CO3 ?
  HCO3- H
• ? H (increases acid), lowers pH to normal
• pH imbalances can have metabolic causes
• eg - uncontrolled diabetes mellitus can cause
  acidosis
• fat oxidation causes ketoacidosis, may be
  compensated for by Kussmaul respiration (deep
  rapid breathing)

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Hypoxia and dyspnea

• Hypoxia is a deficiency in the amount of oxygen
  reaching the tissues
• Dyspnea is difficult or labored breathing, air
  hunger
• Cyanosis is a blueish color of the skin and
  mucous membranes
• Causes of hypoxia
• hypoxemic hypoxia - usually due to inadequate
  pulmonary gas exchange
• high altitudes, drowning, aspiration, respiratory
  arrest, degenerative lung diseases, CO poisoning
• ischemic hypoxia - inadequate circulation
• anemic hypoxia - anemia
• histotoxic hypoxia - metabolic poison (cyanide)
• Primary effect of hypoxia
• tissue necrosis, organs with high metabolic
  demands affected first

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Oxygen Excess

• Oxygen toxicity pure O2 breathed at 2.5 atm or
  greater
• generates free radicals and H2O2 which destroys
  enzymes
• damages
• CNS seizures, coma death
• Eyes blindness
• Lungs painful breathing
• Hyperbaric oxygen (high O2 under increased
  atmospheric pressures)
• formerly used to treat premature infants

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Chronic Obstructive Pulmonary Disease

• Asthma (if it is poorly controlled)
• allergen triggers histamine release
• intense bronchoconstriction (blocks air flow)
• COPD is most often associated with smoking
• chronic bronchitis
• leads to emphysema

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Chronic Obstructive Pulmonary Disease

• Chronic bronchitis
• cilia immobilized and ? in number
• goblet cells enlarge and produce excess mucus
• sputum formed (mucus and cellular debris)
• ideal growth media for bacteria
• leads to chronic infection and bronchial
  inflammation

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Chronic Obstructive Pulmonary Disease

• Emphysema
• alveolar walls break down
• much less respiratory membrane for gas exchange
• lungs fibrotic and less elastic
• air passages collapse
• obstruct outflow of air
• air trapped in lungs

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Effects of COPD

• ? pulmonary compliance and vital capacity
• Hypoxemia, hypercapnia, respiratory acidosis
• hypoxemia stimulates erythropoietin release and
  leads to polycythemia
• Cor pulmonale
• hypertrophy and potential failure of right heart
  due to obstruction of pulmonary circulation

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Progression of Lung Cancer

• Lung cancer accounts for more deaths than any
  other form of cancer
• most important cause is smoking (15 carcinogens)
• 90 originate in primary bronchi
• Tumor invades bronchial wall, compresses airway
  may cause atelectasis
• Often first sign is coughing up blood
• Metastasis is rapid usually occurs by time of
  diagnosis
• common sites pericardium, heart, bones, liver,
  lymph nodes and brain
• Prognosis poor after diagnosis
• only 7 of patients survive 5 years