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 Anatomy Draw 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.