Process of respiration
- Pulmonary ventilation (breathing)-movement of air into and out of lungs
- External respiration-O2 and CO2 exchange between lungs and blood
- Transport-O2 and CO2 in blood
- Internal respiration-O2 and CO2exchange between systemic blood vessels and tissues
Site of gas exchange
Respiratory zone
–Microscopic structures-respiratory bronchioles, alveolar ducts, and alveoli
Conduits to gas exchange sites
Conducting zone
–Includes all other respiratory structures; cleanses, warms, humidifies air
Primary respiratory muscles
Diaphragm and intercostal muscles that promote ventilation
Functions of the nose
- Provides an airway for respiration
- Moistens and warms entering air
- Filters and cleans inspired air
- Serves as resonating chamber for speech
- Houses olfactory receptors
Contains olfactory epithelium
Olfactory mucosa
–Mucous and serous secretions contain lysozyme and defensins
–Cilia move contaminated mucus posteriorly to throat
–Sensory nerve endings trigger sneezing
Respiratory mucosa
–During inhalation filter, heat, and moisten air
–During exhalation reclaim heat and moisture
Nasal conchae - superior, middle, inferior
Groove inferior to each conchae
Nasal meatus
Sinuses in bone that surround the nasal cavity
–Frontal
–Sphenoid
–Ethmoid
–Maxillary
*Mnemonic: Fast snakes eat mice
Function of sinuses
Lighten skull; secrete mucus; help to warm and moisten air
Sinusitis
Inflamed sinuses
Rhinitis
–Inflammation of nasal mucosa
–Nasal mucosa continuous with mucosa of respiratory tract –> spreads from nose to throat to chest
–Spreads to tear ducts and paranasal sinuses causing blocked sinus passageways –> sinus headache
Pharynx
Muscular tube from base of skull to C6
–Connects nasal cavity and mouth to larynx and esophagus
–Composed of skeletal muscle
Three regions of the pharynx
- Nasopharynx
- Oropharynx
- Laryngopharynx
Nasopharynx
- Air passageway posterior to nasal cavity
- Soft palate and uvula close nasopharynx during swallowing
- Pharyngeal tonsil (adenoids) on posterior wall •Pharyngotympanic (auditory) tubes drain and equalize pressure in middle ear; open into lateral walls
Oropharynx
- Passageway for food and air from level of soft palate to epiglottis
- Palatine tonsils-in lateral walls of fauces (latin for throat)
- Lingual tonsil-on posterior surface of tongue
Laryngopharynx
- Passageway for food and air
- Posterior to upright epiglottis
- Extends to larynx, where continuous with esophagus
Larynx
•Attaches to hyoid bone; opens into laryngopharynx; continuous with trachea
Functions of the larynx
- Provides patent airway
- Routes air and food into proper channels
- Voice production - houses vocal folds
Epiglottis
Elastic cartilage; covers laryngeal inlet during swallowing; covered in taste bud-containing mucosa
True vocal cords
Vocal folds
Falso vocal cords
Vestibular folds
Glottis
Opening between vocal folds
Vibrate to produce sound as air rushes up from lungs
Vocal folds
–Superior to vocal folds
–No part in sound production
–Help to close glottis during swallowing
Vestibular folds
Voice production
- Speech-intermittent release of expired air while opening and closing glottis
- Pitch determined by length and tension of vocal cords •Loudness depends upon force of air
- Chambers of pharynx, oral, nasal, and sinus cavities amplify and enhance sound quality
- Sound is “shaped” into language by muscles of pharynx, tongue, soft palate, and lips
Valsalva’s maneuver
–Glottis closes to prevent exhalation
–Abdominal muscles contract
–Intra-abdominal pressure rises
–Helps to empty rectum or stabilizes trunk during heavy lifting
–Used as an orthopedic test for herniated discs (Part of Dejerine’s Triad)
May act as sphincter to prevent air passage
Vocal folds (Ex: Valsalva’s maneuver)
Trachea
Windpipe–from larynx into mediastinum
Trachealis muscle
–Connects posterior parts of cartilage rings
–Contracts during coughing to expel mucus
Carina
–Last tracheal cartilage
–Point where trachea branches into two main bronchi
Bronchial tree
Air passages branch about 23 times
The trachea branches into …
Right and left main (primary) bronchi
–Each main bronchus enters hilum of one lung
Each main bronchus branches into …
Lobar (secondary) bronchi (three on right, two on left)
–Each lobar bronchus supplies one lobe
Each lobar bronchus branches into …
Segmental (tertiary) bronchi
–Segmental bronchi divide repeatedly
Segmental bronchi become …
–Bronchioles-less than 1 mm in diameter
–Terminal bronchioles-smallest-less than 0.5 mm diameter
Terminal bronchioles branch into …
Respiratory bronchioles –> alveolar ducts –> alveolar sacs
Clusters of aveoli
Alveolar sacs
Make up most of lung volume
300 million alveoli
Alveolar walls
Single layer of squamous epithelium (type I alveolar cells)
Secrete surfactant and antimicrobial proteins
Scattered cuboidal type II alveolar cells
Surfactant
Reduces surface tension preventing collapse of alveoli
Right lung
–3 lobes
–Superior, middle, inferior lobes separated by oblique and horizontal fissures
Left lung
–Cardiac notch-concavity for heart
–2 lobes
–Separated into superior and inferior lobes by oblique fissure
Deliver systemic venous blood to lungs for oxygenation
Pulmonary arteries
Carry oxygenated blood from respiratory zones to heart
Pulmonary veins
Bronchial arteries
–Arise from aorta and enter lungs at hilum
–Part of systemic circulation
–Supply oxygenated blood to all lung tissue except alveoli
–Bronchial veins anastomose with pulmonary veins
Pleurae
Thin, double-layered serosa; divides thoracic cavity into two pleural compartments and mediastinum
On thoracic wall, superior face of diaphragm, around heart, between lungs
Parietal pleurae
On external lung surface
Visceral pleura
Pleural fluid
Fills slitlike pleural cavity
–Provides lubrication and surface tension –> assists in expansion and recoil
Two phases of pulmonary ventilation
- Inspiration-gases flow into lungs
2. Expiration-gases exit lungs
Atmospheric pressure
–Pressure exerted by air surrounding body
–760 mm Hg at sea level = 1 atmosphere
Negative respiratory pressure =
Less than P atm
Positive respiratory pressure =
Greater than P atm
Zero respiratory pressure =
P atm
–Pressure in alveoli
–Fluctuates with breathing
Intrapulmonary (intra-alveolar) pressure (P pul)
–Pressure in pleural cavity
–Fluctuates with breathing
–Always a negative pressure (<p></p>
Intrapleural pressure (P ip)
Transpulmonary pressure =
(P pul – P ip)
–Keeps airways open
–Greater transpulmonary pressure –> larger lungs
Lungs collapse if …
P ip = P pul or P atm
Atelectasis (lung collapse) due to …
–Plugged bronchioles –> collapse of alveoli
–Pneumothorax - air in pleural cavity
Boyle’s law
P1V1 = P2V2
Responsible for 75% of air entering lungs during normal quiet breathing
Diaphragm
Responsible for 25% of air entering lungs during normal quiet breathing
External intercostals
Process of inspiration
–Active process –> inspiratory muscles (diaphragm and external intercostals) contract
–Thoracic volume increases –> intrapulmonary pressure drops (to -1 mm Hg)
–Lungs stretched and intrapulmonary volume increases
–Air flows into lungs, down its pressure gradient, until P pul = P atm
Forced inspiration
Vigorous exercise, COPD –> accessory muscles (scalenes, sternocleidomastoid, pectoralis minor) –> further increase in thoracic cage size
Process of expiration
–Normally passive process –> Inspiratory muscles relax
–Thoracic cavity volume decreases
–Elastic lungs recoil and intrapulmonary volume decreases –> pressure increases (P pul rises to +1 mm Hg) –Air flows out of lungs down its pressure gradient until P pul = 0
Forced expiration
Active process; uses abdominal (oblique and transverse) and internal intercostal muscles
Three factors that hinder air passage and pulmonary ventilation; require energy to overcome
- Airway resistance
- Alveolar surface tension
- Lung compliance
Breathing movements become more strenuous
As airway resistance rises
–Can prevent life-sustaining ventilation
–Can occur during acute asthma attacks; stops ventilation
Severe constriction or obstruction of bronchioles
Dilates bronchioles, reduces air resistance
Epinephrine
The attraction of liquid molecules to one another at a liquid-gas interface
Surface tension
–Detergent-like lipid and protein complex produced by type II alveolar cells
–Reduces surface tension of alveolar fluid and discourages alveolar collapse
Surfactant
Infant respiratory distress syndrome
Insufficient quantity of surfactant in premature infants, alveoli collapse after each breath
Lung compliance
The ease with which lungs can be expanded (distensibility)
High lung compliance =
Easier to expand lungs
Three factors that diminish lung compliance
- Nonelastic scar tissue replacing lung tissue (fibrosis) 2.Reduced production of surfactant
- Decreased flexibility of thoracic cage
Three homeostatic imbalances that reduce lung compliance
- Deformities of thorax
- Ossification of costal cartilage
- Paralysis of intercostal muscles
Four respiratory volumes used to assess respiratory status
–Tidal volume (TV)
–Inspiratory reserve volume (IRV)
–Expiratory reserve volume (ERV)
–Residual volume (RV)
Amount of air inhaled or exhaled with each breath under resting conditions
Tidal volume
Amount of air that can be forcefully inhaled after a normal tidal volume inspiration
Inspiratory reserve volume
Amount of air that can be forcefully exhaled after a normal tidal volume expiration
Expiratory reserve volume
Amount of air remaining in the lungs after a forced expiration
Residual volume
Maximum amount of air that can be expired after a maximum inspiratory effort
Vital capacity
Vital capacity (VC) =
TV + IRV + ERV
Anatomical dead space
–No contribution to gas exchange
–Air remaining in passageways; ~150 ml
Alveolar dead space
Non-functional alveoli due to collapse or obstruction
Total dead space
Sum of anatomical and alveolar dead space
Percentage of tidal volume that reaches respiratory zone
70% (30% remains in conducting zone)
Flow of gases into and out of alveoli during a particular time
Alveolar ventilation rate (AVR)
Increases AVR
Slow, deep breathing
Decreases AVR
Rapid, shallow breathing
Rate of loading and unloading of O2 regulated to ensure adequate oxygen delivery to cells
- Decreased P O2 = decreased O2% –> increased unloading O2
- Increased P O2 = increased CO2% –> increased unloading O2
- Increased H+ = increased acidity = lower pH –> increased unloading O2
- Increased temp –> increased unloading O2
Instrument for measuring respiratory volumes and capacities
Spirometer
Spirometry can distinguish between …
–Obstructive pulmonary disease
–Restrictive disorders
Increased airway resistance (e.g., bronchitis)
Obstructive pulmonary disease
Reduced TLC due to disease (i.e. TB) or fibrosis
Restrictive disorders
Dalton’s law of partial pressures
Total pressure exerted by mixture of gases = sum of pressures exerted by each gas
–Pressure exerted by each gas in mixture
–Directly proportional to its percentage in mixture
Partial pressure
Henry’s law
Gas mixtures in contact with liquid
–Each gas dissolves in proportion to its partial pressure
Amount of each gas that will dissolve in liquid depends on …
- Solubility–CO2 20 times more soluble in water than O2; little N2 dissolves in water
- Temperature–as temperature rises, solubility decreases
Blood flow reaching alveoli
Perfusion
Amount of gas reaching alveoli
Ventilation
Matched (coupled) for efficient gas exchange
Perfusion and ventilation
Hb affinity for O2 increases as …
O2 binds
Hb affinity for O2 decreases as …
O2 is released
Percentage of bound oxygen that is unloaded during one systemic circulation
Only 20-25%
If oxygen levels in tissues drop …
–More oxygen dissociates from hemoglobin and is used by cells
–Respiratory rate or cardiac output need not increase
Hypoxia
Inadequate O2 delivery to tissues –> cyanosis (blue tissues)
Too few RBCs; abnormal or too little Hb
Anemic hypoxia
Impaired/blocked circulation
Ischemic hypoxia
Cells unable to use O2, as in metabolic poisons
Histotoxic hypoxia
Abnormal ventilation; pulmonary disease
Hypoxemic hypoxia
Especially from fire; 200X greater affinity for Hb than oxygen
Carbon monoxide poisoning
A vasodilator that plays a role in blood pressure regulation
Nitric oxide (NO)
A vasoconstrictor and a nitric oxide scavenger (destroys NO)
Hemoglobin
As oxygen binds to hemoglobin …
–Nitric oxide binds to a cysteine amino acid on hemoglobin
–Bound nitric oxide is protected from degradation by hemoglobin’s iron
Released as oxygen is unloaded, causing vasodilation
Nitric oxide
Picks up carbon dioxide and also binds nitric oxide and carries these gases to the lungs for unloading
Deoxygenated hemoglobin
CO2 transported in blood in three forms
–7 to 10% dissolved in plasma
–20% bound to globin of hemoglobin (carbaminohemoglobin)
–70% transported as bicarbonate ions (HCO3–) in plasma
Resists change in blood pH
Carbonic acid–bicarbonate buffer system
Changes in respiratory rate and depth affecting blood pH
–Slow, shallow breathing –> increased CO2 in blood –> drop in pH
–Rapid, deep breathing –> decreased CO2 in blood –> rise in pH
Ventral respiratory group (VRG)
–Rhythm-generating and integrative center
–Sets eupnea (12–18 breaths/minute)
–Its inspiratory neurons excite inspiratory muscles via phrenic nerve (diaphragm) and intercostal nerves (external intercostals)
–Expiratory neurons inhibit inspiratory neurons
Normal respiratory rate and rhythm
Eupnea (12-18 breaths/minute)
Dorsal respiratory group (DRG)
–Near root of cranial nerve IX
–Integrates input from peripheral stretch and chemoreceptors; sends information to VRG
Pontine respiratory centers
- Influence and modify activity of VRG
- Smooth out transition between inspiration and expiration and vice versa
- Transmit impulses to VRG - modify and fine-tune breathing rhythms during vocalization, sleep, exercise
Breathing depth is determined by …
How actively the respiratory center stimulates respiratory muscles
Breathing rate is determined by …
How long the inspiratory center is active
Increased blood CO2 levels resulting in increased rate and depth of breathing
Hypercapnia
Increased depth and rate of breathing that exceeds body’s need to remove CO2
Hyperventilation
Decreased blood CO2 levels –> cerebral vasoconstriction and cerebral ischemia –> dizziness, fainting
Hypocapnia
Breathing cessation from abnormally low Pco2
Apnea
Acidosis may reflect:
- Carbon dioxide retention
- Accumulation of lactic acid
- Excess fatty acids in patients with diabetes mellitus
Respiratory system controls will attempt to raise the pH by …
Increasing respiratory rate and depth
Influence of high brain centers
1.Hypothalamic controls act through limbic system to modify rate and depth of respiration
–Example-breath holding that occurs in anger or gasping with pain
2.Rise in body temperature increases respiratory rate
3.Cortical controls-direct signals from cerebral motor cortex that bypass medullary controls
–Example-voluntary breath holding
Hering-Breuer Reflex (inflation reflex)
Stretch receptors in pleurae and airways stimulated by lung inflation
•Inhibitory signals to medullary respiratory centers to end inhalation and allow expiration
•Acts as protective response more than normal regulatory mechanism
Increased ventilation (10 to 20 fold) in response to metabolic needs
Hyperpnea
Remain surprisingly constant during exercise
Pco2, Po2, and pH
Three neural factors cause increase in ventilation as exercise begins
- Psychological stimuli—anticipation of exercise
- Simultaneous cortical motor activation of skeletal muscles and respiratory centers
- Excitatory impulses to respiratory centers from proprioceptors in moving muscles, tendons, joints
Symptoms of acute mountain sickness (AMS) - quick travel to altitudes above 2400 meters
–Atmospheric pressure and Po2 levels lower
–Headaches, shortness of breath, nausea, and dizziness
–In severe cases, lethal cerebral and pulmonary edema
–Ex: AMS is common in travelers to ski resorts
Respiratory and hematopoietic adjustments to long-term move to high altitude
Acclimatization
Steps of acclimatization
1.Chemoreceptors become more responsive to Pco2 when Po2 declines
2.Ventilation increases and stabilizes in a few days to 2–3 L/min higher than at sea level
3.Decline in blood O2 stimulates kidneys to accelerate production of EPO
•RBC numbers increase slowly to provide long-term compensation
The time it takes to get the benefit of high altitude training for increased performance
3-4 weeks
Evidence also suggests that living at _____ and training at _____ seems to produce the best results for increased performance
High altitudes (~8000 ft) Low altitudes (~4000ft)
Chronic obstructive pulmonary disease (COPD)
–Exemplified by chronic bronchitis and emphysema
–Irreversible decrease in ability to force air out of lungs
–Treated with bronchodilators, corticosteroids, oxygen, sometimes surgery
Other common features of COPD
- History of smoking in 80% of patients
- Dyspnea - labored breathing (“air hunger”)
- Coughing and frequent pulmonary infections
- Most develop respiratory failure (hypoventilation) accompanied by respiratory acidosis, hypoxemia
Chronic bronchitis
Inhaled irritants –> chronic excessive mucus & Inflamed and fibrosed lower respiratory passageways –> Obstructed airways –> Impaired lung ventilation and gas exchange –> Frequent pulmonary infections
Emphysema
Permanent enlargement of alveoli; destruction of alveolar walls; decreased lung elasticity –> Accessory muscles necessary for breathing –> exhaustion from energy usage
Asthma - reversible COPD
–Characterized by coughing, dyspnea, wheezing, and chest tightness
–Active inflammation of airways precedes bronchospasms
–Airway inflammation is immune response
–Airways thickened with inflammatory exudate magnify effect of bronchospasms
–~1 in 12 people in N. America suffer from asthma
Tuberculosis (TB)
–Infectious disease caused by bacterium Mycobacterium tuberculosis
–Symptoms-fever, night sweats, weight loss, racking cough, coughing up blood
–Treatment- 12-month course of antibiotics
–Leading cause of cancer deaths in North America
–90% of all cases result from smoking
–Metastasizes rapidly and widely; most victims die within 1 year of diagnosis
Lung Cancer
Three most common types of lung cancer
- Adenocarcinoma
- Squamous cell carcinoma
- Small cell carcinoma
Cystic fibrosis
–Most common lethal genetic disease in North America
–Abnormal, viscous mucus clogs passageways –> increased bacterial infections
•Affects lungs, pancreatic ducts, reproductive ducts
Treatment for cystic fibrosis
Mucus-dissolving drugs; manipulation to loosen mucus; antibiotics
Development of respiratory system
- By 28th week, premature baby can breathe on its own
- Two weeks after birth before lungs are fully inflated
- Respiratory rate is highest in newborns (40-80 respirations per minute and slows until adulthood 12-18 per minute)