6.4 Gas Exchange System

2.5 Arteries & Veins Artery Vein

• Thick walls of smooth muscle with elastic fiber

• Small lumen• Valves prevent

backflow of blood

• Thin walls of smooth muscle with thin elastic fiber

• Large lumen• Valves maintain

one-way flow of blood

• Carry blood away from heart under very high pressure and high speed

• Return blood to heart with less pressure under low pressure and low speed

Scientists have found a new culprit in spreading the disease that's been driving the world's frogs to the brink of extinction: crayfish. In the last few decades, the disease caused by the chytrid fungus has been a disaster for frogs and other amphibians. More than 300 species are nearly extinct because of it. Many probably have gone extinct, but it can be difficult to know for sure when a tiny, rare species disappears from the face of the Earth. (Related photos: "Ten Most Wanted 'Extinct' Amphibians.")

Land-based organisms have evolved internal ventilation system which allow for gas exchange of blood

adequate lung ventilation gas exchange cell respiration and the energy

needs of cells, tissues, organs and organisms

6.4.2 Why do we need a ventilation system?

1. Large organisms: Oxygen cannot diffuse directly into ALL cells from the air/wastes cannot be directly ejected from the body

2. Land-borne: Gases need moist surfaces for diffusion

3. Ventilation maintains large concentration gradient between alveoli and blood

6.4.4 Ventilation system• Trachae, Lungs, Bronchi, Bronchioles, Alveoli

6.4.2 Ventilation system• alveoli = the millions of thin-walled,

dead-ends of the bronchioles forming clusters of air sacs acting as the respiratory surface

• large surface area: surface area of the alveolar epithelium - 100 m2

• thin: single cell layer of epithelium across which diffusion occurs

• moist: gasses need to dissolve before passing membranes

• rich blood supply: extensive net of capillaries for transport of gasses to and from alveoli

6.4.2 Ventilation system• High concentration gradient (CG) • Breathing in: increases CG of oxygen between blood and

alveoli, oxygen diffuses into blood• Breathing out: increase CG of carbon dioxide between blood

and alveoli, carbon dioxide diffuses into alveoli

6.4.5 How does ventilation occur? • Controlled by inverse relationship between

pressure and volume (i.e. increase in volume decrease in pressure)

• ‘Partial vacuum’

6.4.5 How does ventilation occur?

Asthma

• Causes airways to narrow and swell

• Result: wheezing, difficulty breathing

• Triggers: House dust mite, pollen, cigarette smoke, anxiety, stress etc.