Topic 6.4 Gas Exchange

6.4.1 distinguish between:

• Ventilation – breathing (air in and out of lungs)

• Gas Exchange – diffusion of gases. Occurs in 2 places:

• Cellular Respiration – What is it and where does it take place?

Diffusion

• Protists, sponges, cnidarians, and flatworms all obtain oxygen and get rid of carbon dioxide via diffusion with the aqueous environment in which they live.

• In all animals, the respiratory surface must be moist and thin. In many it is highly branched to provide greater surface area.

6.4.2 Need for ventilation system

• We are large so our surface area/volume ratio is not favorable for the diffusion of gases.

• Our exterior surface (skin) is not suited for the exchange of gases. Respiratory surfaces should be moist.

• A ventilation system ensures that the transfer of gases is encouraged due to concentration gradients.

6.4.4 AnatomyDraw and label

• Nasal cavity – separated from mouth by palate. Warms, filters, moistens air

• Pharynx – common passageway for respiration and digestion

• Larynx – top of trachea, contains vocal cords. Opening to larynx is glottis, protected by epiglottis

• Trachea – C shaped rings of cartilage support. Forks into 2 bronchi.

• Bronchi branch to form bronchioles

• Tips of bronchioles end in clusters of air sacs called alveoli where gas exchange occurs.

• Each lung has about 300 million alveoli

• Each alveoli cluster is surrounded by a capillary bed.

3.4.3 Alveolar structure

• The small spherical shape of alveoli provide a large surface area for gas exchange

• Single cell thickness makes it easy for gases to diffuse through alveoli wall

• Moisture allows for efficient diffusion

• Capillary bed ensures gases do not have to diffuse far to reach circulatory system

Question

• Pneumonia (excess mucus) and smoking (tar) create an extra lining inside of each of the alveoli. Describe how and why this could become life-threatening.

Ventilation

• Mammals – negative pressure breathing.

• Recall that there is an inverse relationship between pressure and volume.

• Diaphragm and intercostal muscles change the size of thoracic cavity which changes air pressure in lung. Air always flows from high pressure to low.

Inspiration

• Diaphragm contracts (moves down) and intercostal muscles raise rib cage.

• Volume of thoracic cavity increases which lowers air pressure in lungs (partial vacuum)

• Air flows from high pressure (atmosphere) to low pressure (lung) via your mouth/nasal passages trachea bronchi……

Expiration

• Diaphragm and intercostal muscles relax. Diaphragm rises and rib cage collapses.

• Pressure in thoracic cavity increases. Air flows from high pressure (lung) to low pressure (atmosphere) and exits the way it entered.