External Respiration - External respiration occurs in the lungs, and involves the exchange of oxygen into, and carbon dioxide out of the bloodstream.
Internal Respiration - Internal respiration occurs in all body cells, and involves the exchange of oxygen into, and carbon dioxide out of the bloodstream. The cells use the oxygen and glucose sugar to obtain energy, and produce carbon dioxide and water as waste products.
Glucose Sugar + Oxygen → Carbon Dioxide + Water + Energy
C6H12O6 + O2 → CO2 + H2O + Energy
Functions of Respiratory Organs
Air, containing 20% oxygen, enters the body through nostrils
Air is cleaned and warmed as it passes through the nasal cavity
Mucus and nose hairs serve to filter dust from the air
Mucus also moistens the inhaled air
Cavity at back of nose and mouth
Both food and air pass through the pharynx
When we swallow food, a flap called the epiglottis closes over the top of the larynx and below it, the trachea (windpipe) to prevent food entering the lungs
As air passes through the vocal cords, different pitches of sound are produced
Lies in front of the oesophagus (food tube)
Protected at the front by C-shaped cartilage
Fine hair-like hairs called cilia on the walls of the trachea 'brush' dust upwards and out of the respiratory tract
Bronchi (Singular - Bronchus)
The trachea branches into 2 tubes called the bronchi - one going to each lung
Mucus and cilia cover the walls of the bronchi
The right and left bronchi branch into many smaller tubes called the bronchioles
Walls of bronchioles are lined with mucus and cilia
Alveoli (Singular - Alveolus)
These are balloon -like air sacs at the ends of the bronchioles
The walls of the alveoli are very thin, and are surrounded by fine blood capillaries
Exchange or diffusion of oxygen into the blood from the inhaled air, and of carbon dioxide out of the blood to the exhaled air takes place
Large, dome-shaped muscle that lies at the base of the chest cavity
The diaphragm contracts during inhalation, and relaxes during exhalation
Did You Know That...? Asthma is a chronic inflammatory disease of the respiratory tract that affects a quarter of a billion people worldwide. About half of child sufferers show much reduced symptoms in adulthood.
Mechanics of Breathing
The diaphragm and muscles between the ribs, and muscles attaching to the collarbone all contract
This pulls the rib cage upwards at the top, outwards, and downwards at the bottom
The chest cavity and the lungs inside expand in volume, creating lower air pressure inside the lungs compared with the outside air
Air is then drawn into the lungs
The 3 lots of muscles relax
The volume of the chest cavity and the lungs reduces
The air pressure inside the lungs is then higher than the outside air, so air is forced out of the lungs
Control of Breathing
The respiratory control centre is in the hindbrain or Medulla Oblongata
If too much carbon dioxide is detected in the bloodstream, it stimulates the respiratory tract to breathe.
After exercise, people have a fast breathing rate to rid the body of excess carbon dioxide. At the same time, they are taking in oxygen.
Did You Know That...? People yawn to get rid of carbon dioxide on waking or when fatigued. However, the reason for "contagious" yawning is unknown.