Human Biology - EDEXCEL IGCSE - Gaseous Exchange

Gaseous Exchange

Lungs:

During inhalation, the external intercostal muscles contracts and the internal relaxes which pushes the ribs up and out. Apart from this, the diaphragm contracts, pulling the diaphragm down and flat. All this creates a high volume in the chest (thorax) and therefore low pressure. This causes air to be pulled into the lungs as there is higher pressure outside. During exhalation, the opposite happens meaning the ribs are pulled down and in and the diaphragm goes back to a dome shape. This creates high pressure which pulls the air out of the lungs.

Lung capacity - the volume of air the lung takes in different phases of the respiratory cycle. This can be measured with a spirometer.

1. Vital capacity - maximum lung capacity
2. Tidal volume - normal volume of air in the lungs during quiet breathing.

When the brain detects a too large or too little concentration of oxygen or carbon dioxide in the blood it changes the breathing rate to change the amount of air it takes in. e.g. if there is too much carbon dioxide, the breathing rate rises to breathe out the carbon dioxide.

Diseases from smoking:

1. Emphysema - chemicals from cigarettes damage the elastic tissue in the lungs, reducing the surface area of the alveoli and, therefore, the speed and amount of oxygen it absorbs.
2. Lung cancer - carcinogenic chemicals in cigarette tar causes cancer.
3. Bronchitis - cigarette smoke paralyses cilia in the trachea meaning phlegm and microbes enter the lungs, this can cause infections.
4. Heart disease - nicotine in the cigarettes leads to the hardening and narrowing of blood vessels. This can lead to heart attacks.
5. Lethargy - cigarette smoke contains carbon monoxide which means less oxygen are carried around the body
6. Nervousness - cigarettes contain nicotine which is addictive so withdrawal symptoms occur when one is not smoking.

Investigating the effects of exercise on breathing:

1. Breath into a double bubbler with limewater or bicarbonate indicator for twenty seconds.
2. Do vigorous exercise for three minutes.
3. Repeat step one with a new double bubbler. 

After exercise, the limewater is usually more cloudy and the indicator should be more yellow. This is because your breathing is more concentrated in carbon dioxide and also because the breathing rate is high after exercise.

Effects of exercise:

1. Muscles need more energy so breathing rate increases to supply more oxygen for respiration and to oxidise carbon dioxide.
2. Heart rate increases to pump more oxygen around the body and faster.
3. Arterioles widen to stop blood pressure from increasing.
4. Blood diverted from inactive organs (e.g. stomach/liver) towards muscles through vasodilation and constriction

Benefits of regular exercise:

1. Improves body posture, muscle tone and weight loss.
2. Strengthen bones and muscles.
3. Improves endurance, flexibility and overall fitness.
4. Less risk of coronary diseases by lowering blood pressure.
5. Lowers the heart rate and relaxes blood vessels.