Form 3 Science

Chapter 1 –

Respiration

The Human Breathing mechanism…• Respiration is the living process in which energy is released from the

food we eat.• The oxygen needed for respiration is taken in from the atmosphere and

carbon dioxide is released.• The exchange of gases which occurs in the lungs is known as breathing. The Structure of the Human Respiratory System• Air enters the nose through nostrils. The walls of the nostrils are lined

with hairs to trap dust particles in the air. • Nasal cavity is the interior area of the nose. It is lined with a sticky

mucus that traps bacteria and other foreign particles in inhaled air. • Air enters the lungs through the trachea. The trachea is kept open by C-

shaped rings of cartilage.• Bronchi are the two main air passages into the lungs. Each bronchus

branches into smaller tubes called bronchioles.• Bronchioles end in tiny air sacs called alveoli (singular: alveolus). The

alveoli are surrounded by blood capillaries.• Intercostal muscles move the ribs up and down during breathing.• Diaphragm controls the volume of the thoracic cavity.

The Human Breathing mechanism…

Flow of Air from the Atmosphere to the Lungs…• The passage of air in the human respiratory system can be summarized as

follows:Nostrils nasal cavity trachea bronchus bronchiole alveolus

The Breathing Mechanism• Inhalation is the taking in of air into the lungs. • The air which enters the lungs is called inhaled air.• Exhalation is the release of air from the lungs into the atmosphere.• The air expelled is called exhaled air.

The Breathing Mechanism…

Inhalation ExhalationThe external intercostal muscles contract.

The external intercostal muscles relax.

The rib cage moves upwards and outwards.

The rib cage moves downwards and inwards.

The diaphragm contracts and flattens.

The diaphragm relaxes and curves upwards.

The volume of the thoracic cavity increases.

The volume of the thoracic cavity decreases.

The air pressure in the thoracic cavity decreases.

The air pressure in the thoracic cavity increases.

Air enters the lungs (inhalation) Air is forced out of the lungs (exhalation).

Transport of Oxygen in the Human Body…The Diffusion of Oxygen from the Alveoli into the Blood Capillaries• During inhalation, air is taken in and reaches the alveoli.• (a) The concentration of oxygen in the alveoli is higher than the

concentration of oxygen in the blood capillaries. • (b) The concentration of carbon dioxide in the blood capillaries is higher

than the concentration of carbon dioxide in the alveoli.

• As a results, gaseous exchange takes place between the blood capillaries and the alveoli through the process of diffusion.

• Oxygen diffuses from the alveoli to the blood capillaries. Carbon dioxidediffuses from the blood capillaries to the alveoli.

• After gaseous exchange has taken place, blood rich in oxygen (oxygenated blood) leaves the lungs and is then transported to the heart and then to the rest of the body.

Parts Oxygen Content Carbon Dioxide Content

Alveoli High Low

Capillaries Low High

Gaseous exchange between an alveolus and the blood capillaries surrounding the alveolus

Adaptations of the alveoli for efficient gaseous exchange…• Millions of alveoli in the lungs provide a very large surface area for gaseous

exchange.• Have thin walls. The wall of each alveolus is one-cell thick to allow easy

diffusion of gases. • Each alveolus is surrounded by a network of blood capillaries which transport

gases to and from the alveolus rapidly. • The surface of each alveolus is moist so that gases can dissolve in the

moisture before diffusing across the alveolus. Transport of oxygen by red blood cells in human blood

(a) Red blood cells contain the oxygen-carrying pigment called haemoglobin.(b) Oxygen combines easily with haremoglobin to form oxyhaemoglobin

Oxygen + haemoglobin oxyhaemoglobinThe diffusion of oxygen from the blood capillaries into the body cells

(a) Gaseous exchange takes place between the blood capillaries and the body cells(b) As a result, oxyhaemoglobin releases oxygen and oxygen diffuses from the blood capillaries to the body cells.(c) Carbon dioxide diffuses from the body cells to the blood capillaries.

The Importance of a Healthy Respiratory System…• Air contains pollutants such as cigarette smoke, toxic gases from factories

and vehicles, and microorganisms.• Pollutants are harmful substances that can cause diseases or even death. Effects of Harmful Substance in Polluted Air• Sulphur dioxide irritates the throat and damages lung tissues.• Oxides of nitrogen can lead to haze which causes throat irritation and

breathing difficulties.• Coal, dust and asbestos result in a blocked respiratory tract which leads to

breathing difficulties. Asbestos dust is a carcinogen that can cause lung cancer.

• Carbon monoxide competes with oxygen to combine with haemoglobin. This reduces the amount of oxygen in the blood.

• Cigarette smoke(a) Tar contains carcinogens that can cause lung cancer. It can deposit on the lungs and blacken it.(b) Nicotine in the tobacco causes an addiction to smoking.

• Bacteria or viruses can cause influenza, whooping cough or pneumonia.

Diseases Related to the Respiratory System…• Asthma: Narrowing of the bronchi and bronchioles, and this causes difficulty

in breathing.• Lung Cancer: Heavy smokers have higher risk of getting lung cancer.• Emphysema: Alveoli are broken down. This reduces the surface are for

gaseous exchange and causes difficulty in breathing. • Bronchitis: Persistent cough caused by infection by bacteria or viruses and

cigarette smoke. Improving the Quality of Air• Good practices to improve air quality involve the participation of all parties.

These include:(a) Campaign to avoid smoking or quit smoking(b) Ban smoking in public areas(c) Avoid open burning (d) Encourage the use of public transport(e) Implementation of law and regulation to control air pollution