Gas exchange in humans

What happens in inhalation

• Diaphragm contracts and flattens

• External intercostal muscles contract

• Pull the ribs up and out

• Thorax volume increases

• Air pressure decreases

• Air drawn in

What happens in exhalation

• Diaphragm relaxes and moves up into dome shape

• External intercostal muscles relax

• Pull the ribs down and in

• Thorax volume decreases

• Air pressure increases

• Air pushed out

What happens in forced exhalation

• Internal intercostal muscles contract

• Pull the ribs down

• Thorax volume decreases more and faster

• Greater volume of gases exchanged

How are alveoli adapted

• Rounded alveolar sacs = large sa:v ratio

• Layer of moisture on the surface to dissolve gases

• One cell thick walls

• Good blood supply

Pleural cavity

Space between pleural membranes filled with fluid to reduce friction

Effect of nicotine

• Narrows blood vessels

• Inreases blood pressure

• Increases heart rate

• Blood clots in arteries

• Heart attacks/strokes

Effect of CO

• Binds to haemoglobin

• Strain on breathing system

• CHD/strokes

Effect of tar

• Carcinogen

• Enlarges goblet cells

• More mucus produced

• Destroys cilia

• Infection

• Phagocytes release elastase

• Alveoli become less elastic

• Alveoli burst