Respiratory System and Mechanics of Breathing I Flashcards
Only simple organisms can rely solely on _______exchange of O2 and CO2 with the environment.
diffusive
• Problem of ________distance is overcome in larger
organisms by ________the diffusion processes with
______processes.
diffusion
coupling
convectional
The tracheo-bronchial tree has volume, but no
gaseous exchange takes place.
nose, pharynx, larynx, trachea, bronchi, and bronchioles make up what?
conducting
portion of
the resp. system
Tidal Volume
VT ~
500 mL
Total alveolar gas volume
~
3000 mL
Anatomical
deadspace VD
~
150 mL
PA = PB when?
With open airways
& no air flow:
• The chest wall
tends to recoil _______:
outwards
The lungs are
highly ________:
elastic
The lungs are
highly elastic: which results in
– Reduces Pip (below atmospheric pressure (PB or Patm) – Pulls the chest wall inward
Pressures that
determine lung volume:
PA & Pip
Given the forces acting on the chest wall (FCW) and the lungs (FL), why don't the lungs collapse?
The pleural membranes
What do we call the the volume of air in
the lungs when PA = PB?
functional residual capacity
The pleural membranes:
• cover the outer surface of the lungs (visceral) and thoracic cavities (parietal) • are coupled together by a thin layer of liquid (~20 µm) This layer of liquid: • acts as a lubricant • allows the lungs to move relative to the chest wall
Intra-pleural pressure (Pip) is the pressure in
the sealed
space between the pleural membranes.
Mechanics of Breathing
- Movement of air into and out of the lungs
- Process of “bulk flow”
- Achieved by generating pressure differences
Thoracic movements are transmitted to the lungs by
pressure changes in the intra-pleural space.
The work of breathing is done by
the respiratory muscles.
To change lung volume & generate air flow (V) it is necessary to create a
pressure gradient
Compliance is the reciprocol
of elastance
• FRC is determined by the
Compliance of the Lung and Chest Wall.
• Compliance is the inverse of
Elastance & is a measure
of how easy the lungs inflate.
• Reduced outward mobility of chest wall decreases
compliance
e.g. Severe obesity, constrictive bandages
• Similarly, reduced lung volumes decreasing ?
C
e.g. pulmonary oedema, fibrosis, intra-bdominal pressure (late pregnancy).increased
Using a spirometer (to adjust lung volume) and a pressure transducer (to measure airway pressure) can construct a curve
showing
relationship when respiratory
muscles are fully relaxed (black line).
At high lung vols recoil of both
Lungs & Chest wall is
+ve.
When flow is zero:
Ptotal = Pelastic = V/C
Ventilation:
the movement of gas
into & out of the lungs
Ventilation Mechanism:
bulk flow (diffusion is too slow) Air moves down its pressure gradient
Respiratory muscles utilised to ?
(intercostals & others) are
utilized to change thoracic volume & therefore
create the pressure gradients
Thoracic movements are transmitted to the lungs by
pressure changes in the intra-pleural space.
Inspiratory muscles:
• Diaphragm (dome descends) • External intercostals (raise & enlarge ribcage) • Accessory muscles (during exercise)
Expiratory muscles:
• Passive during quiet breathing. • At other times: the muscles of the abdominal wall & the internal intercostals.
open pneumothorax (“collapsed lung”) secondary to trauma.
On inspiration, the negative intrathoracic
pressure generated causes air to flow into
the lungs through the airways and into the
intrapleural space through the chest wall
defect.
• Air in the pleural space will press on the
lung, which can then partially or fully
collapse, causing dyspnoea.
• If air builds up in the pleural space, it can
push against the heart or the aorta – a
tension pneumothorax à Medical
emergency!
Minute Ventilation:
Volume of air
shifted in & out of the lungs per minutes
Vt x fr
Alveolar Ventilation eqn
VA = fR x (VT - VD)
This expt showed that surface
tension contributed a large part to
the _______ ______ ______of the lungs
static recoil force
Saline-filled lungs: vs. Air-filled lungs
Saline-filled lungs:
• Lungs inflated with saline have a much larger compliance
Air-filled lungs:
• show the effects of elastic elements and surface tension
• require larger pressures during inflation (hysteresis)
Alveoli cell types
• Type I cells: gaseous exchange • Type II cells : secrete surfactant • Many elastic fibres • Many capillaries Large volume of blood in pulmonary circulation (entire RV output!)
For surfactant & water, ____areas have the surface tension reduced much more than ____areas.
small
large
Transmural pressure (P) is directly proportional to
surface
tension (T) and inversely proportional to radius (r).
_______law & the properties of pulmonary surfactant are
important for understanding the mechanics of the lung.
Laplace’s
The opening and closing of the _____airways account for
many of the properties of whole lung mechanics that were
once attributed to opening and closing of ______ alveoli.
small
spherical
dyspnoea.
difficult or laboured breathing
