Gas Exchange and Breathing

1
Gas Exchange and Breathing

• Characteristics of a Gas Exchange Surface
• Structure and Functioning of the Gas Exchange
  System

2
The Need for Gas Exchange and Ventilation

• In humans O2 is used in cell respiration (in
  cytoplasm and mitochondria) and CO2 is released
• Gas exchange happens in the alveoli of human
  lungs O2 diffuses from the air into the alveoli
  to blood capillaries, CO2 diffuses in opposite
  direction
• A ventilation system maintains a high conc. Of O2
  in the alveoli
• Ventilation in humans is produced by changes in
  pressure in the chest cavity. Changes in pressure
  are carried out by the action of two sets of
  muscles in the breathing apparatus diaphragm
  and the intercostal muscles

3
How are alveoli adapted to gas exchange?
4
Adaptations of the alveoli to gas exchange

• Alveoli are small (100 um in diameter) but the
  lungs contain hundreds of millions of alveoli
  (huge overall surface area for gas exchange)
• Walls of the alveoli and capillaries consist of a
  single layer
• The capillaries surrounding the alveoli contain
  high CO2 and low O2 concentration
• Cells in the alveolus secrete a fluid which helps
  keep the walls moist facilitating gas diffusion
• The walls of the alveoli produce a natural
  detergent that prevents the walls from sticking
  together. Certain alveolar cells synthesize a
  mixture of lipoproteins called surfactant
  (secreted into alveolar air spaces continuously,
  reduces surface tension thus decreasing tendency
  of alveoli to collapse

5
Ventilation of the Lungs

• Air is inhaled into the lungs through trachea,
  bronchi and bronchioles
• Air is exhaled via the same route
• What are the structures involved in gas
  exchange???

6
Gas Exchange Structures
Structure Description Function
Nostrils/Nasal cavity Internally supported by bone and cartilage. w/numerous internal hairs Entrance to the nasal cavity warms-up air remove particles from air
Larynx Glottis/epiglottis Top of trachea.. Composed of muscles, cartilage and elastic tissue Houses vocal cords Prevents foreign objects from entering trachea
Pharynx Cavity line-up by mucous epithelium Passageway of food. Aids in producing sounds
Trachea Cartilage (25 c-shaped). Flexible, cylindrical. 2.5 cm dia. 12.5 cm length. In front of esophagus. Line-up with ciliated mucus Passageway of air. Continues to remove particle of air
7
Structures of the Gas Exchange System (cont)
Bronchi (bronchus) Branched cartilaginous tube. Lined-up by mucous epithelium Conducts air form trachea to bronchioles
Bronchiolus Branched cartilaginous tube. Lined-up by mucous epithelium Conducts air from bronchioles to alveoli
Diaphragm Muscle tissue. Dome-shaped Inhalation and Exhalation
Lungs Contain alveoli, blood vessels, lymphatic vessels and nerves of the lower resp. tract Gas exchange (diffusion of gases)
8
Ventilation of the Lungs

• INHALING
• The external intercostal muscles contract,
  raising the ribs and elevating sternum
• The diaphragm contracts becoming flatter and
  moving downwards
• The muscle movements increase the volume of the
  thorax. Lungs expand, partial lung pressure
  decreases
• The pressure inside the thorax therefore drops
  below atmospheric pressure
• Air flows into the lungs from outside the body
  until the pressure inside the lungs rises to
  atmospheric pressure

• EXHALING
• The internal intercostal muscles relax following
  inhalation. Abdominal organs spring back to
  original shape, moving the ribcage down and in
• The diaphragm pushes up into a dome shape
• The muscle movement decrease the volume of the
  thorax. Lungs contract, partial lung pressure
  increases
• Therefore pressure inside the thorax rises above
  atmospheric pressure
• Air flows out from lungs to outside of the body.
  Lung pressure falls below atmospheric pressure

9
Self-planned laboratory

• How does exercise affect the functioning of the
  heart and lungs
• Exercise increases cardiac output
• Cardiac output stroke volume X heartrate
• Stroke volume volume of blood ejected by the
  ventricles in one beat