Chapter 1RESPIRATIONHuman need oxygen in the air to live. Oxygen is required during breathing. We will be healthy and active if we get clean air to breathe. What is the function of oxygen in our body?

1.1 Human Breathing MechanismBreathing is a physical process in which air is inhaled or taken in and exhaled or given out by a living body.The system that helps human to breathe is the human respiratory system.

The Human Respiratory System3. Parts of the humanrespiratory system are:Nasal cavityTracheaBronchusBronchiolesAlveolusLungsDiaphragm

The Structure of the LungsAlveolus (air sacs)

4. Each alveolus is surrounded by a network of thin-walled blood vessels called capillaries.bronchiolecapillariesair sacAlveolus

Mechanism of human breathingThe breathing mechanism consists of two phases. The taking in of air is called inhalation. The letting out of air is called exhalation.During breathing, the lungs expand and return to their normal size to pump air into and out of them.The movements of the ribs and the diaphragm bring about breathing.

During inhalation, the rib cage moves upwards and outwards. The diaphragm contracts, move downwards and flattens. The thoracic becomes bigger and causing the air pressure to decrease. The higher air pressure outside forces the air into the lungs.Inhalation

During exhalation, the rib cage moves downwards and inwards. The diaphragm expands and curve upwards. The thoracic becomes smaller and causing the air pressure to increase. The higher air pressure in the lungs forces the air out.Exhalation

Detailed structure of alveolusAir movementAlveolar wall (one-cell thick)Exit of bloodEntry of bloodThin layer of moistureRed blood cellCapillary

Adaptation of the alveoli for efficient gas exchange1. Large surface area to provide a large surface area for gas exchange2. Very thin walls as one-cell thick to provide a very short distance for the diffusion of gases.3. Moist inner surface so that oxygen can dissolve easily.4. Surrounded by many blood capillaries that help to transport gases to and from the alveoli quickly.

1.2 Transport of Oxygen in the Human BodyDuring inhalation, air is taken into the lungs through the nasal cavity, through the trachea, bronchi, bronchioles and finally alveoli.The air that reaches the alveoli is rich in oxygen and poor in carbon dioxide. The movement of oxygen from the alveolus into blood capillaries involves diffusion.Diffusion is the movement of molecules from a region of higher concentration of the molecules to a region of lower concentration of the molecules.

Oxygen diffuses from the alveoli into the red blood cells in the capillaries.At the same time, the red blood cells in the capillaries release carbon dioxide which diffuses into the alveoli. Red blood cells contain the oxygen-carrying pigment called haemoglobin.Oxygen combines with haemoglobin to form oxyhaemoglobin.The blood containing oxyhaemoglobin is transported from the lungs to other parts of our body.

Gas exchange also takes place between the capillaries and the body cells.Oxygen has a higher concentration in the capillaries than in the body cells.Carbon dioxide has a higher concentration in the body cells than in the capillaries.Oxyhaemoglobin releases oxygen which diffuses in the body cells.Carbon dioxide diffuses into the blood at the same time.

1.3 The Importance of A Healthy Respiratory System

The substances which are harmful to the respiratory systemThe air that we breathe in may contain substances which are harmful to our respiratory system.For example,

Air pollutantHarmful substances Cigarette smokeNicotine, tar, carcinogens, irritants, carbon monoxideGases from factoriesSulphur dioxide, nitrogen dioxideExhaust fumesCarbon monoxideHaze Smoke, dust

Effects of harmful substances on the respiratory systemNicotine a. Nicotine is the drug that causes addiction to cigarette smoking. b. Nicotine causes rapid heartbeat, increased blood pressure and rapid breathing. c. The diseases related to nicotine include emphysema, heart disease and stroke.

2. Tar a. Tar contain carcinogens (substance that cause cancer). b. Tar blackens the lungs and irritates the respiratory tract, causing smokers cough.

3. Sulphur dioxide a. The burning of coal and oil at factories and power station emits SO2. b. Exposure to SO2 can cause irritation of the respiratory system, coughs, breathing difficulties, bronchitis and lung cancer.

4. Carbon monoxide a. It commonly found in the smoke vehicles. b. Low concentration of CO can cause dizziness, headaches and fatigue whereas high concentration can be fatal.

5. Haze a. Continuous exposure can cause coughing, nasal congestion, watery nose, constant sneezing and chest pain. b. It can cause illness like asthma, bronchitis and pneumonia.