RESPIRATORY SYSTEM
Main function?
• To ensure that O2 is brought into the body
and ready for cellular use all the time
(cellular respiration in mitochondria)
sugar + O2  energy + water + CO2
• To ensure that CO2 can leave each cell
and is removed from the body (we can’t
store it)
In order for gas exchange to occur, several
requirements are essential:
1) a tube to connect internal/external environments
2) muscles to bring the air in contact with the
exchange surface
3) a moist surface where gas exchange occurs
through diffusion
Human Respiratory System
• air enters the body through nostrils then nasal passages
(also through mouth during exercise)
• passes through the pharynx (throat) to the opening of the
trachea (windpipe – made of c-shaped cartilage rings to
keep it open)
• Passes over the epiglottis, through the larynx (voice box)
• travels down the trachea (made of cartilage rings to keep
it open)
• Then air goes down the trachea (10-12 cm
long), then into two tubes (the lower respiratory
tract)
• from the trachea, air passes into the right and
left bronchus, which enter the right and left lung.
• Each lung is divided into lobes. The right lung
has three lobes and the left lung has two.
• Inside the lungs, each bronchus divides into a
network of bronchioles.
• Each bronchiole ends in a grape-like cluster of
tiny sacs called alveoli (singular – alveolus).
• alveoli walls are very thin, single-celled, and
surrounded by capillaries
Point of interaction between the respiratory and
circulatory systems – this is where gas exchange
happens
• After inhalation, the concentration of O2 in the
alveoli is higher than in blood in the capillaries
next to the lungs
• Therefore O2 diffuses out of alveoli into
capillaries.
• CO2 is higher in the capillaries than in the
alveoli, so it diffuses into the alveoli to be
exhaled
The mechanics of breathing
The brain controls it all – breathing movements,
breathing rate, air volume, gas levels in blood,
etc.
What causes air to move in and out of lungs?
Changes in air pressure – controlled by the
diaphragm and rib (intercostal) muscles
Inhalation
• Rib muscles contract and diaphragm moves
down
• This expands the rib cage upward and outward,
floor of chest cavity moves down
• volume of lungs increases (they expand)
therefore air comes in (pressure inside lungs is
lower than pressure outside lungs, air moves
along the concentration gradient)
Exhalation
• Begins when diaphragm and rib muscles
relax – reduces volume of chest cavity
• ribs move in and diaphragm moves up
• volume of lungs decreases (higher
pressure) , and air is forced out (lower
pressure outside)