CHAPTER 1 RESPIRATION

THE HUMAN BREATHING MECHANISM• Gas exchange in lungs is called breathing. This

exchange involves the taking in and letting out of air.

Adaptation of alveoli for efficient gas exchange

• Large surface area• The lungs have millions of alveoli to provide a large

surface area for gas exchange

• Very thin walls• The wall of each alveolus is one cell thick to provide a

very short distance for the diffusion of gases

• Moist inner surface• To let oxygen dissolve in the moisture before diffusing

across the alveolar wall

• Surrounded by numerous blood capillaries• Help to transport gases to and from alveoli quickly

Mechanism of human breathing• The breathing mechanism consists of 2 phases:• Taking in of air ------ Inhalation• Letting out of air ---- Exhalation

Comparison between inhalation and exhalation

Inhalation Exhalation

Diaphragm flattens Diaphragm arches upwards

Intercostal muscles contract

Intercostal muscles relax

Ribcage moves upwards and outwards

Ribcage moves downwards and inwards

Volume of thoracic cavity increases

Volume of thoracic cavity decreases

Air pressure decreases Air pressure increases

Air flows into lungs Air is forced out of the lungs

Composition of air in respiration

Content Inhaled air Exhaled air

Oxygen 21 % 16 %

Carbon dioxide 0.04 % 6 %

Nitrogen 78 % 78 %

Water vapour Variable Saturated

Temperature Variable 37º C

The transport of oxygen in human body

The diffusion of oxygen from the alveoli into the blood capillaries

• Air that reaches alveoli is called alveolar air. It is rich in oxygen and poor in carbon dioxide

• The blood that reaches the capillaries surrounding the alveoli is poor in oxygen and rich in carbon dioxide

• Gas exchange takes place in the lungs by diffusion• Oxygen diffuses from alveoli into red blood cells in the

capillaries• At the same time, the red blood cells in the capillaries

release carbon dioxide which diffuses into alveolihttp://www.youtube.com/watch?v=1J8KFmoylEs

The transport of oxygen by blood

• Red blood cells contain oxygen carrying pigment called haemoglobin

• Oxygen combines with haemoglobin to form oxyhaemoglobin

Oxygen + haemoglobin oxyhaemoglobin

The diffusion of oxygen from the blood capillaries into the body cells

• Oxygen has a higher concentration in the capillaries than in body cells

• Carbon dioxide has a higher concentration in the body cells than in capillaries

• Oxyhaemoglobin releases oxygen which diffuses into the body cells

• Carbon dioxide diffuses into the blood at the same time

Importance of healthy respiratory systemSubstances harmful to the respiratory system

Air pollutant Harmful substances

Cigarette smoke Nicotine, tar

Gases from factories Sulphur dioxide, nitrogen dioxide

Exhaust fumes Carbon monoxide

Haze Smoke, dust

Effects of harmful substances on the respiratory system

• Nicotine• Causes addiction to cigarette smoking• Causes rapid heartbeat, increases blood pressure and

rapid breathing• Diseases: emphysema, heart disease and stroke

• Tar • Contains carcinogens (substances that cause cancer)• Irritates respiratory tract, causing ‘smoker’s cough’

• Sulphur dioxide• Cause irritation of respiratory system• Cause both temporary and permanent damage to lungs

• Carbon monoxide• Combines haemoglobin in the blood faster than oxygen• Poisonous gas• Causes suffocation• Low concentration of carbon monoxide can cause dizziness, headaches and fatigue• High concentration of carbon monoxide is fatal

• Particulate matter (fine particles in the air)• Causes coughing, nasal congestion, watery nose, constant sneezing

Diseases of respiratory system

• Asthma • Narrowing of bronchi and bronchioles due to contraction of muscles• Difficult to breathe, wheezing and feeling tightness in chest

• Bronchitis • Inflammation of lining of bronchioles due to infection by bacteria or viruses, or chemicals found in tobacco smoke• Patients may turn blue especially at the lips and fingers due to poor oxygenation of blood

• Lung cancer

• Emphysema• Structure of alveoli is broken down by coughing• Cannot take in enough oxygen and becomes very shortness of breath.

• Heart disease• Nicotine raises the blood pressure and increases the level of ‘bad’ cholesterol in blood• Suffer from stroke or heart attack