1. Respiratory system
Respiration is the process by which the body takes oxygen in and removes carbon dioxide
Every cell in our body needs a constant supply of oxygen (O2) and food to maintain life and to keep the body operating effectively.
Respiration is a process that occurs in practically all living cells. It uses oxygen as a vital ingredient to free energy from food and can be characterised by the following equation:
This process is made possible through the respiratory system that facilitates the exchange of gases between the air we breathe and our blood. The respiratory system acts to bring about this essential exchange of gases (CO2 and O2) through breathing; the movement of air in and out of the lungs.

2. Respiratory system

3. The parts of the respiratory system and their functions
1) Oxygen enters the body through the mouth or nose. Through the nasal cavities the air is warmed, moistened and filtered for any foreign material
2) The pharynx serves as a common passage for air to the trachea. It leads from the nasal cavity to the larynx (voice box), located at the beginning of the trachea
3) Trachea is a hollow tube, strengthened by rings of cartilage. After entering the chest cavity or thorax, the trachea divides into a right and left bronchus (bronchial tube), which lead to the right and left lung.
4) The inner lining of the air passages, produces mucus that catches and holds dirt and germs. It is also covered in microscopic hairs (cilia) that remove dirt, irritants and mucus through steady, rhythmic movements

4. Respiratory system Lung Function
5) Lungs consist of two bag-like organs, situated on either side of the heart and enclosed in the thoracic cavity by the ribs at the side and sternum at the front, vetebral column at back and diaphragm below.
The light, soft lung tissue is compressed and folded like a sponge and is composed of tiny air pockets
6) The right and left bronchi that deliver air to the lungs divide into a number of branches or bronchioles within each lung. These bronchioles branch many times, eventually terminating in clusters of tiny air sacs called alveoli (singular-alveolus). The walls of the alveoli are extremely thin, with a network of capillaries (tiny vessels carrying blood) surrounding each like a string bag. This is where oxygen from the air we breathe is exchanged for carbon dioxide from our bloodstream.

5. Respiratory system Lung Function Inspiration = breathing in
Expiration = breathing out
During inspiration
Diaphragm contracts and flattens, external intercostal muscles (between ribs) lift ribs outwards and upwards. This movement increases volume in chest cavity and pulls the walls of lungs outwards, which in turn decreases the air pressure within lungs. In response to this, air from outside the body rushes into lungs through air passages.
During expiration
Diaphragm relaxes and moves upwards, intercostal muscles allow ribs to return to their resting position. Volume of chest cavity has decreased, which increases the air pressure inside lungs. Air is consequently forced out to make pressure inside and outside the lungs about equal.

7. Respiratory system Exchange of gases
During Inspiration, alveoli are supplied with air high in oxygen and low in carbon dioxide. However, blood in capillaries arriving at the alveoli is low in oxygen and high in carbon dioxide. Different concentrations of oxygen and carbon dioxide result between the blood and air result in a pressure difference.
Gases such as oxygen and carbon dioxide move from areas of high concentration or pressure to areas of low concentration or pressure. Oxygen, therefore, moves from the air in the alveoli across the alveolar–capillary wall into the blood, where it attaches itself to haemoglobin in the red blood cells. At the same time, carbon dioxide is unloaded from the blood into the alveoli across the alveolar–capillary wall to be breathed out. This two-way diffusion is known as the exchange of gases (or gaseous exchange).

8. Exchange of gases, using the same principle, occurs between blood in the capillaries of the arterial system and the cells of the body; for example, the muscle cells. Here, oxygen is unloaded to the cells while carbon dioxide resulting from cell metabolism is given up to the blood. Blood that is high in carbon dioxide content (deoxygenated blood) is carried back to the lungs where it unloads carbon dioxide.

9. Effect of physical activity on respiration
Respiratory system
Effect of physical activity on respiration
1) Rate and depth of breathing increase moderately, even before exercise begins, as body’s nervous activity is increased in anticipation of exercise
2) Once exercise starts, the rate and depth of breathing increase rapidly. This is thought to be related to stimulation of the sensory receptors in the body’s joints as a result of movement. Further increases during exercise result mainly from increased concentration of carbon dioxide in the blood, which triggers greater respiratory activity.
3) Increase in rate (frequency) and depth (tidal volume) of breathing provide greater ventilation and occur, generally in proportion to increases in exercise effort.