Biology - Gas exchange in humans (2.46 - 50)

Parts of the lung

• trachea

• ribs

• intercostal muscles

• pleural membrane

• bronchus

• bronchioles

• alveoli

• diaphragm

Inhalation process

• Diaphragm contracts (flattens down)

• Intercostal muscles contract (goes out)

• Volume of thorax increases

• Pressure in thorax decreases

• Air flows in from high to low pressure

Exhalation process

• Diaphragm relaxes (moves up into dome shape)

• Intercostal muscles relax (move in)

• Volume of thorax decreases

• Pressure in thorax increases

• Air flows out from high to low pressure

How are alveoli adapted for gas exchange (5)

• High surface area - many alveoli sacs, maximises rate of diffusion

• Alveoli have thin, single layer of cells - minimises distance for diffusion

• Ventilation maintains a steep concentration gradient for diffusion (high level of oxygen, low level of CO2)

• Many capillaries/ good blood supply - maintain concentration gradient

• Moist lining - allows dissolved gas to diffuse

Harmful chemicals in cigarettes

• Nicotine - narrows blood vessels and increases heart rate → increased blood pressure

• Carbon monoxide - binds to haemoglobin with a greater affinity than oxygen

• Tar - carcinogen (increase likelihood of cancer)

Diseases caused by smoking

• Chronic bronchitis - increased mucus production blocks bronchioles → higher chance of infection and chronic coughing

• Emphysema - result of frequent infection, walls of alveoli break down, reducing SA for gas exchange in lungs → breathlessness → non reversible

• Lung cancer - result of carcinogens in cigarettes (e.g. tar) → tumor, can spread to other parts of the body

• Coronary heart disease

Coronary heart disease (5)

• Nicotine damages artery wall → easier for cholesterol to stick

• Fatty substances such as cholesterol build up in the wall of an artery

• Layer becomes thicker, blocking some of the artery → increased blood pressure

• Artery wall is damaged and becomes rough

• Damages area causes a blood clot to form → can block the artery → cells and tissues don’t have enough oxygen and glucose for respiration

how to measure breathing (practical)

• Spirometer

• Displacement of water

• Peak flow metre

• Vital capacity with a balloon

• Spirogram

Vital capacity and tidal volume

• Vital capacity: maximum lung capacity

• Tidal volume: normal breathing volume