1. IB objective 6.4 Pgs. 889-897 Campbell
Gas Exchange
IB objective 6.4
Pgs Campbell

2. Gaseous exchange in animals
Gaseous exchange is the exchange of gases between an organism and its surroundings
Intake of oxygen and release of carbon dioxide
This exchange takes place by diffusion
Three factors determine the rate:
1. the size of the surface area
2. difference in concentration
3. length of the diffusion path
Therefore, thin surfaces

3. For many reasons … Mammals have lungs Ventilation system:
Specialized organs for gas exchange
Large, thin surface
Protected by the thorax (chest)
Must be ventilated
Ventilation system:
Pumping mechanism that moves air into and out of the lungs
Maintains concentration gradient for diffusion
Blood circulation system
Respiratory pigment (hemoglobin)

4. The working lungs Lungs are housed in the thorax Airtight
Lined by the pleural membrane
Secretes pleural fluid which protects the lungs from friction
Formed by the rib cage and its muscles (intercostal muscles) and the diaphragm (floor)
Separates the abdomen from the thorax

5. The working lungs
The lungs connect with the pharynx at the rear of the mouth by the trachea
Air reaches the trachea from the mouth and nose, passes through the larynx
Glottis
Epiglottis
The trachea has incomplete rings of cartilage which prevent collapse under pressure from food

6. The working lungs
The trachea then divides into two bronchi (one to each lung)
Smooth muscle and cartilage rings
The finest bronchioles end in air sacs (alveoli)

7. The structure of the thorax

8. Alveoli

9. Alveoli

10. How we breath (ventilation)
Air is drawn into the alveoli when air pressure in the lungs is lower than atmospheric pressure
Air is forced out when pressure is higher than atmospheric pressure
Since the thorax is air tight, pressure changes in the lungs occurs when the volume of the thorax changes

11. Ventilation The volume of the thorax is increased when:
The ribs are moved up and out
The diaphragm is lowered
Contraction of diaphragm
The volume of the thorax is decreased when:
Muscles relax
Diaphragm is more dome-shaped
Ribs move down and in

12. Inspiration vs. expiration
Inspiration (inhalation)
Structure/outcome
Expiration (exhalation)
Muscles contract, flattening of diaphragm
Diaphragm
Muscles relax, pressure form abdomen pushes up
Contract, rib cage up and out
External intercostal muscle
Relax
Internal intercostal muscle
Contract, moves rib cage down and in
Increases
Volume of thorax cavity
Decreases
Falls below atmospheric pressure
Air pressure of thorax
Rises above atmospheric pressure In
Air flow
Out

13. Ventilation

14. Alveolar structure Arranged in clusters Served by tiny bronchiole
Elastic connective tissue in their walls
Capillary system wraps around the clusters
Each capillary is connected to a branch of the pulmonary artery and is drained by a branch of the pulmonary vein
Pulmonary circulation
Supplied with deoxygenated blood from the right side of the heart
Returns oxygenated blood to the left side of the heart to be pumped to the rest of the body

15. Alveoli

16. Why are lungs are so efficient
Feature
Effects and consequences
Surface area of alveoli
Huge; 700 million alveoli in our lungs (70 m2)
Wall of alveoli
Very thin, flattened epithelium; diffusion pathway is very short
Capillary supply to alveoli
Network of capillaries; maintains concentration gradient of O2 and CO2
Surface film of moisture
O2 dissolves in water lining the alveoli; O2 diffuses into the blood