The Respiratory System
The Respiratory System
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• Composed of structures that
allow:
– Passage of air from
outside the body to the
lungs
– Gas exchange to occur
• Three main functions:
– Supply O2 to the blood
– Remove CO2 from the
blood
– Regulate blood pH (acidbase balance)
• Divided into two zones:
– Conductive zone
Respiratory System Structure
Nasal cavity
Mouth
Epiglottis
Pharynx
Larynx
Trachea
Right and left
primary bronchi
Smooth muscle
Secondary bronchi
Terminal bronchiole
Tertiary bronchioles
Respiratory bronchiole
Alveolar sacs
Pulmonary venule
Pulmonary arteriole
The Conductive Zone
• The conductive zone is
composed of structures
that transport air to the
lungs:
– Mouth and nose
– Larynx
– Trachea
– Primary and
secondary bronchi
– Tertiary and terminal
bronchioles
• Filters air taken in with
each breath
The Respiratory Zone
• The respiratory zone is
composed of structures
involved with the
exchange of gases:
– Respiratory
bronchioles
– Alveolar ducts
– Alveolar sacs
Mechanisms of Breathing
• Inspiration:
– Contraction of diaphragm
– Thoracic cavity expands
• Air pressure in thoracic
cavity is lower than air
pressure outside the body
– Air rushes in to lungs to
restore balance
• Lung pressure =
atmospheric pressure
• Expiration:
– Alveolar sacs recoil as
diaphragm relaxes
– Air is expelled
– Thoracic cavity reduces
– Lung pressure>atmospheric
pressure
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Ventilation
• Ventilation (VE) is the volume
of air moved by the lungs in 1 min
• Influenced by two factors:
– Tidal volume (VT)
• Volume of air in each breath
– Respiratory frequency (f)
• Number of breaths taken per minute
Respiratory Control Centres
• Respiratory control centres found within brain stem:
– Medulla oblongata
• Inspiratory centre
– 15-20 breaths per minute at rest
• Expiratory centre
– Two main functions:
» Ensure the inspiratory muscles never completely
relax
» Stimulate forceful expiration when required (during
exercise)
– Pons
• Pneumotaxic and apneustic centres
– Ensure smooth transition of inhalation to exhalation
– Fine-tune the breathing pattern
Gas Exchange
• Diffusion mediates gas exchange
– Diffusion is the movement of a gas,
liquid, or solid from a region of high
concentration to low concentration
• Can only occur if a difference in
concentration exists
– Concentration gradient
• Diffusion pathway
– Area through which gases move from
the lungs into the blood; from the
blood into the tissue, and back
– Rates of diffusion depend on:
• Size of concentration gradient
• Thickness of barrier between two
areas
• Surface area between two areas
Oxygen/Carbon Dioxide Transport
• Oxygen (O2) transport within the blood achieved in two
ways:
– O2 dissolved within the plasma
• Represents 2% of O2 found in the blood
– Binds to hemoglobin
• Carbon dioxide (CO2) transport achieved in three
ways:
– Trace amounts of CO2 dissolved within the plasma
– Binds to hemoglobin
– Bicarbonate system
External and Internal Respiration
• External respiration is the result of two main factors:
– Increase in pulmonary ventilation (VE)
• Maintains necessary gradients in the partial pressures of
both O2 and CO2
– Increase in blood flow to the lungs
• Caused by and increase in cardiac output
• Internal respiration involves exchange of gases at tissue level –
extraction of O2 at tissues is increased
• Occurs as result of four main factors:
– Increase in partial pressure of oxygen (PO2) gradient
– Increase in partial pressure of carbon dioxide (PCO2)
– Decrease in pH
– Increase in temperature
Flow of External and Internal
Respiration
a-vO2 Difference
The effect of training on the
respiratory system
• Few adaptations
• Increase in VE
• Increased in strength and endurance of
respiratory muscles