How do we breathe in and out?
Breathing is a process that moves air in and out of the lungs.
It is the only process that delivers oxygen to where it is needed in the body and removes carbon dioxide. Each breathing cycle involves two stages; * Inhalation (inspiration) when lungs expand and air is pulled into them * Exhalation (expiration) when the lungs reduce in volume and air leaves the lungs.
Inhalation and exhalation are produced by movements of two sets of muscles; the diaphragm and the muscles between the ribs which are known as the intercostal muscles.
Internal intercostal muscles are used for inhalation and the external intercostal is used during exhalation. Breathing out is easier since both gravity pulling the ribs down and the elasticity of the lungs aid to collapse the lungs and squeeze air out. Humans generally breathe with the diaphragm and external intercostal muscles only, it is only when exercising that we use other muscles. During exercise, it is very significant that your breathing rate is matched to your activity because during exercise you will need extra oxygen; therefore, the body makes the lungs take in more ait to supply.

Breathing in; Inhalation * When you inhale, your diaphragm tightens and moves downwards. This therefore increases the space in your chest cavity, into which your lungs expand.
Breathing out; Exhalation * When you exhale, your diaphragm relaxes and moves upward into the chest cavity.
The intercostal muscles between the ribs also relax to reduce the space in the chest cavity.

The structure of the Respiratory System
As shown in the below diagram, the human respiratory system contains the; nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli which together forms the lungs.
Preliminary cleaning takes place in the nose where air is; cleaned, warmed and moistened.

Air enters the body through the nose or the moth, air entering the nose travels into the nasal cavity which has numerous arteries, veins and capillaries. The air passes through the nasal cavity into the pharynx. From the pharynx, the air moves through the larynx and into the trachea which leads straight into the lungs. The trachea, bronchi and bronchioles and lined with cilia and kept moist by mucus secretions. The mixture of cilia and mucus filers out the solid particles from the air and warms and moistens the air avoiding damage to the tissues that form the lungs.

The respiratory system is divided into two different parts; * The upper respiratory tract which includes the nose, mouth and the beginning of the trachea (the section that takes air in and out) * The lower respiratory tract includes; trachea, bronchi, bronchiole and the lungs.

Definition: * Vital Capacity is defined as the amount of air that can be expelled from the lungs after breathing in as deeply as possible. A person’s vital capacity can be measured by a spirometer. A normal adult has a vital capacity between 5 and 5 litres. A human’s vital capacity depends on age sex, height, weight and ethnicity. * Ventilation rate is also known as the respiratory rate, pulmonary rare. It is the number of breaths taken within a set of time, typically 60 seconds. Human respiration rate is measured when a person is at rest and involves counting the number of breaths.
Birth to 6 weeks: 30–60 breaths per minute
6 months: 25–40 breaths per minute
3 years: 20–30 breaths per minute
6 years: 18–25 breaths per minute
10 years: 15–20 breaths per minute
Adults: 12–20 breaths per minute * Tidal volume is defined as the volume of air inspired or expired in a single breath during regular breathing, is also known as the tidal air. Tidal volume is measured in milometers. * The maximum ventilation capacity is the maximum volume of air that can be taken during one breath. The effect of training a vital capacity and maximum breathing capacity
Exercise will increase vital capacity because lungs need more oxygen to supply the muscles with nutrients. Therefore, the more you exercise the more nutrients you will need to support the system.
During exercise, the muscle cells respire more than they do at rest. This indicates that oxygen and glucose will be delivered to them more quickly and waste carbon dioxide must be removed more rapidly. Effects on your breathing rate from exercise include; a faster plus, quicker breathes and longer breathes, but it depends on what type of exercise you are doing, for example; aerobic and anaerobic. When you begin to train, you will notice muscle contraction, raised body temperature and pulse, and a deeper breathing known as the tidal volume. When this occurs, the vital capacity of your breathe will deepen.