Respiratory System Flashcards
The organs and tissues involved in gas exchange
Nose
Mouth
Pharynx
Larynx
Trachea
Bronchi
Lungs
Diaphragm
Ribs
Pleura
Alveoli
Capillaries
2 respiratory zones
Conducting & Respiratory Zones
Conducting Zone
nose > pharynx > larynx > trachea > bronchi > bronchioles
- facilitates passage of air into and out of respiratory system
- traps debris and pathogens from incoming air via mucous membrane
- warms and humidifies air
Respiratory Zone
terminal bronchioles > alveolar ducts > alveolar sacs > alveolus
- facilitates the exchange of gas between the circulatory and respiratory systems
- alveolar sacs are enwrapped by capillaries to form the respiratory membrane (~ 0.5mm thick)
- simple diffusion of gases occurs between blood and air
Pulmonary arteries branch to
supply blood to the pulmonary
capillaries, where gas exchange
occurs within the lung alveoli.
Gas exchange through
passive diffusion
Oxygenated blood returns via
pulmonary veins to the left atrium
Cells of the Alveoli (3)
Type I pneumocytes / Type 1 alveolar cells:
Most abundant (97%), involved in gas exchange.
Type II pneumocytes / Type 2 alveolar cells:
Produce and secrete surfactant, a phospholipid (both hydrophilic and hydrophobic) that lines the inner alveolar surface to reduce surface tension.
Alveoli macrophages:
Phagocytic cells that remove foreign debris and pathogens
Fick’s Law of Diffusion
Shorter distance – Greater rate of diffusion
Greater surface area – Great rate of diffusion
The pleurae of the lungs
Each lung is encased in a thin, two-layered, fluid-filled membrane called the pleura. Inner visceral pleura, outer parietal pleura, and between pleural cavity filled with pleural fluid.
Functions of the pleura
* Lubrication: reduces friction during breathing
* Surface tension: helps position of the lungs against the thoracic wall
* Division:isolates the respiratory system from other major organs
Boyle’s law
the absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies,
if the temperature and amount of gas is unchanged (confined).
an inverse relationship between
pressure and volume
P1V1 = P2V2
when volume increases pressure decreases and vice versa
Pulmonary Ventilation
Pulmonary ventilation refers to the moving of air in and out of the lungs.
A mechanical process that depends on volume changes in the thoracic cavity.
∆ Volume → ∆ Pressure → flow of gases
Such changes in volume are driven by the contraction/relaxation cycling of intercostal muscles and the diaphragm.
steps involved in breathing in
- Inspiratory muscles contract
- Thoracic cavity volume increases
- Intrapulmonary volume increases
- Intrapulmonary pressure decreases
(-1 mm Hg) - Air flows in until pressure equalises
Key factors influencing negative intra-pleural pressure
Surface tension
* Pleural fluid provides surface tension between pleural layers
Lung Pressures
Elastic force by the lungs (inwards)
* Elastic tissue in lung recoils and pulls lung inwards
* Visceral pleura pulled inwards
Elastic force by the thoracic cage (outwards)
* Thoracic wall tends to naturally pull away from lung
* Parietal pleura pulled outwards
Pressure gradients: quiet breathing
Note this is quiet breathing (eupnea).
Tidal volume is the amount of air that
moves in or out of the lungs with each
respiratory cycle. 400-500 ml.
Transpulmonary pressure
* pressure difference across the whole lung, between alveolar space and pleural space
* ptp = palv – pip
* the net distending pressure applied to the lung by contraction (and relaxation) of the inspiratory muscles
* is force that keeps the lungs open
Modes of Breathing
Quiet vs Forced breathing
Quiet breathing
Quiet breathing (normal breathing / eupnea)
* Occurs at rest, without cognitive thought
* Inspiration: diaphragm, external intercostal muscles
* Expiration: relaxation of diaphragm and intercostal muscles
* Diaphragmic vs costal breathing
Forced breathing (hypernea)
Requires extra muscle contractions in BOTH inspiration and expiration
∆ Volume → ∆ Pressure → flow of gases
Hypereupnea: Fast-forced breathing
Inspiration
Accessory muscles assist external
intercostal muscles to elevate the ribs and enlarge the thorax
1) Scalene muscles
(elevate 1st and 2nd ribs)
2) Serratus anterior and posterior
3) Pectoralis minor and major
4) Sternocleidomastoid
Exhalation
Internal intercostal muscles and transversus thoracis depress the ribs
At very rigorous breathing Exhalation
Abdominal muscles compress abdominal contents & reduce the
volume of the thoracic cavity
1) External & internal obliques
2) Transversus abdominis
3) Rectus abdominis
Physical factors influencing ventilation
- Airway resistance
- Lung compliance and elastic recoil
- Alveolar surface tension
Airway resistance
- Friction from air moving against walls or airways
- Depends mostly on the diameter of the airway
Large lumen, high flow velocity, increased branching contribute to turbulence & therefore resistance
Overall, the greatest resistance occurs in the medium-sized bronchi.
Resistance in large bronchi is low because of their large diameters, whereas resistance in small bronchi is low because of their large total cross-sectional area.
The most important causes of increased airway resistance include bronchospasm, secretions, and mucosal oedema, as well as volume-related and flow-related airway collapse.
Pathophysiology – asthma involves increased airway resistance
Bronchoconstriction vs Bronchodilation
Bronchoconstriction
- PSNS acetylcholine via muscarinic
receptors
[Anticholinergics (atropine)] - Leukotrienes, histamine
and bradykinin
[Antihistamines (fexofenadine)]
[Leukotrine antagonists (montelukast)]
Bronchodilation
- SNS - no direct innervation
but beta2-receptors
[Beta-agonists (salbutamol)]
Lung compliance and elastic recoil
Compliance
* Change in volume per unit change in pressure
* Ability for lungs to be stretched
* a measure of elastic resistance
Elastic recoil (Lung elasticity)
* Ability for lungs to rebound
* A key driving force during expiration
Pressure - Volume characteristics
As the transpulmonary pressure
increases, lung volume increases
pressure – volume curve
represents both elastic and airway resistance properties of the lungs
Lung Compliance - Pathophysiology
Diseases:
Fibrosis = stiffer, less compliant
Emphysema = increased compliance
Compliance determines 65% of work of breathing. If a lung has low compliance, it requires more work for breathing
Compliance vs Elastance
Lung compliance is important because
it is inversely proportional to elastance
High compliance = less elastic recoil; low compliance = more elastic recoil.
Factors affecting compliances: surface tension, elastic fibres, surfactant
Alveolar surface tension
Water molecules are charged and attracted to each other ???
Law of LaPlace
Magnitude of inward-directed pressure (P) in a bubble (alveolus) = 2 x Surface tension (T) / Radius (r) of bubble (alveolus)
