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• Asthma is a condition that affects the airways carrying air into and out of the lungs.
• Smoking causes lung disease, heart disease and increased risks of several different types of cancer due to its effects on the gas exchange system.
• Exercise increases the demands of the gas exchange system as there is a greater need for oxygen in respiration, and a larger production of carbon dioxide that needs to be removed.

Asthma is a very common condition that affects the bronchioles - the small tubes that carry air in and out of your lungs. It is a chronic condition with two main components:

1. Constriction; the tightening of the muscles surrounding the airways
2. Inflammation; the swelling and irritation of the airways.

This may lead to symptoms such as coughing, wheezing, chest tightness, or shortness of breath.

When a person with asthma is exposed to a trigger, the airways leading to the lungs become more inflamed or swollen than usual, making it harder to breathe. The airways also get smaller due to a tightening of the muscles surrounding the airways. Finally, the airways can become congested due to a build-up of mucus, which is secretedby goblet cells that line your trachea.

Symptoms such as coughing, wheezing, chest tightness, or shortness of breath can be treated using asthma relievers. Relievers are drugs that relax and open up the airways, making it easier to breathe. Relievers are often administered using a device called an inhaler. This lets you breathe the medicine in through your mouth and directly into your lungs.

Smoking is the act of inhaling and exhaling the fumes of burning plant material, most commonly tobacco in a cigarette.

Tobacco smoke contains many harmful substances and carcinogens such as:

• Nicotine
• Tar
• Carbon monoxide

Tobacco smoke

Goblet cells in the lining of the trachea, bronchi and bronchioles produce sticky mucus. This traps dirt and pathogens. Cells with tiny hair-like projections called cilia then move the mucus out of the lungs.

Many chemicals in tobacco smoke and tar destroy cilia, which causes mucus to start to build up in the small airways making it harder for the smoker to breathe. This also increases the chance of getting bronchitis.

Nicotine

Nicotine causes the blood vessels to become narrower, which increases blood pressure. Narrower blood vessels can lead to heart conditions such as coronary heart disease as these blood vessels are more susceptible to become blocked with cholesterol.

The consequence of this blockage is that less red blood cells carrying oxygen will be able to travel to the heart. Therefore, less aerobic respiration can take place in important cells such as the cardiac muscle cells and can lead to a heart attack.

Tar

Tar forms a sticky layer inside the lungs and causes the breakdown of the walls of the alveoli causing them to merge together. This reduces the surface area to volume ratio, which means less gas exchange takes place and can lead to emphysema. Tar also increases the chances of getting lung cancer.

Carbon monoxide

Carbon monoxide binds irreversibly to haemoglobin found in red blood cells, reducing its ability to carry oxygen. This means that the circulatory system has to work harder, increasing the risks of heart disease and strokes.

Did you know?

Cigarette butts are the most littered item on Earth.

Exercise causes the frequency and depth of breathing to increase. This can be measured by looking at the following:

• Breathing rate (the number of breaths you take per minute)

• Tidal volume (the volume of air breathed in and out in one breath)

Increasing the intensity of exercise will mean that the cells in your body are respiring more aerobically so will require more oxygen to be delivered to them, hence the increase in your breathing.

When a person exercises more, the body grows more new capillaries; a process called capillarisation. Capillarisation takes place at the alveoli in the lungs and in the skeletal muscles. This has the effect of increasing the amount of oxygen that can be transferred to the working muscles as well as increasing the amount of carbon dioxide that can be removed.

Regular exercise also has some additional effects, including an increase in the:

• Strength of the diaphragm and intercostal muscles
• Vital lung capacity; the volume of air that can be forcibly exhaled after inhaling fully.

Find out how to measure vital lung capacity.