RS of a human performs a vital function of gas exchange – delivery of oxygen and removal of carbon dioxide, as well as helps to regulate the acid-base balance (pH) in the body.

There are three main types of breathing:

• External (exchange of oxygen and carbon dioxide between the alveolar air and blood ca-
  pillaries in lungs).
  
• Internal (the exchange of gases between the cells of the body and blood).
  
• Cellular (utilization of oxygen and production of carbon dioxide in cells).

Respiratory system comprises of:

• Airways;
  
• Lungs;
  
• Musculoskeletal system associated with breathing.
  
  
  

The airways are:

• Airways;
• Lungs;
• Musculoskeletal system associated with breathing.

The airways are:

• Nasal cavity (Nose and nasal cavity are conducting channels for air).
• Throat (In the throat area there is a connection of oral and nasal cavities). Throat functions: movement of food from the mouth into the esophagus and conducting air from the nasal cavity (or oral cavity) into larynx. In the throat respiratory and digestive paths cross.
• Larynx (The larynx connects the throat to the trachea (windpipe) and contains vocal apparatus).
• Trachea (Trachea - cartilaginous tube with a length of about 10-15 cm. In order for food not to get into the trachea, at its entrance, there is the so-called palatal veil. Its purpose – to block the entry into the trachea every time food is swallowed. The trachea extends from the pharynx to the 5th thoracic vertebra, where it divides into right and left bronchi).
• Bronchi (Right bronchus usually shorter and wider than the left. Each bronchus enters to the lung and is further divided into secondary bronchi, 1 into each fraction (a total of 5 fractions), further go tertiary bronchi and smaller terminal bronchioles, that branch to respiratory bronchioles, further to the alveolar ducts, which carry on their walls small bubbles – the alveoli. At this very level the gas exchange occurs).

The lungs consist of:

• Bronchi, bronchioles and alveolar sacs.
• Arteries, capillaries and veins of the pulmonary circulation.

The lungs have the form of spongy, porous conical formations lying in both halves of the thorax. The smallest structural element of lung – a lobule, consists of terminal bronchiole leading to the pulmonary bronchiole and alveolar sac. The walls of the pulmonary bronchiole and alveolar sac form recesses – the alveoli. Such a structure increases the respiratory surface of lungs, which is 50-100 times the body surface. With age, the surface area of the alveoli tends to decrease.

The elements of the musculoskeletal system associated with breathing, are:

• Ribs (Thanks to its articulation with the vertebrae ribs move upward and outward, increasing the distance from the spine to the sternum, and the lateral dimensions of the thoracic cavity).
• Intercostal muscles.
• Diaphragm (The diaphragm - a muscle-tendon partition that separates the chest cavity from the abdominal. This is the main muscle involved in normal inspiration).
• The auxiliary respiratory muscles.

The auxiliary respiratory muscles - those muscles, which contract and change the volume of the chest. Muscles heading from the head, neck, hands, and some upper thoracic and lower cervical vertebrae, as well as external intercostal muscles connecting the rib to rib, lift the ribs and increase the volume of the chest.

• Mechanism of breathing movements (picture on the left)
• The change in shape of the thorax during inspiration and expiration(picture on the right)

Under the influence of nerve impulses muscles involved in breathing contract (diaphragm, intercostal muscles, and others.). The diaphragm lowers (flattens), thereby increasing the vertical volume of the thoracic cavity. Other auxiliary respiratory muscles increase the thorax breadth. As a result, the lungs stretch, the pressure therein drops and becomes lower than the atmospheric pressure. Due to the pressure difference between the atmospheric and pulmonary air, the outside air rushes into the lungs. As you exhale the same muscles relax (diaphragm thus rises), the ribs are lowered, the volume of the thorax decreases, the lungs are compressed, the pressure in them increases (above atmospheric pressure) and the air rushes out.

Muscles involved in breathing, divided into:

• inspiratory muscles (breathing proper and auxiliary ones)
• expiratory muscles.

Breathing proper muscles change the volume of the thorax.

Auxiliary breathing muscles perform two functions, the main - the movement of the peripheral links of the body (head, shoulder blades, pelvis). However, when the peripheral links are fixed, these muscles can move the ribs.

Diaphragm. When it contracts, diaphragm cupula flattens, the volume of the thorax increases in the vertical direction. When the abdominal muscles are stressed, intra- abdominal pressure increases and it becomes more difficult for diaphragm to work (as well as for the iliac - costal muscles and square muscle).

• Exterior and interior intercostal muscles (their work made more difficult, if the muscle belt of the upper extremities is stressed).
• The muscles lifting the ribs.
• Rear upper serratus (lifts the ribs).
• Rear lower serratus (lowers and spreads the ribs). Its work is made difficult when abdominals are stressed.
• The quadratus lumborum – works on diaphragm breathing.
• Ilio-costal muscle.

Auxiliary muscles of inspiration:

• Scalene muscles (work as a breathing muscles when cervical part of the spinal column and the head are fixed. Lift ribs 1-2);
• lower bundles of serratus anterior muscle (with fixed scapula pull the lower ribs upwards);
• minor and major pectorals;
• subclavian muscle (works when upper extremities belt is fixed);
• spine extensors;
• sternoclavicular-mastoid muscle;
• muscles lifting scapula;
• rhomboid muscles;
• upper bundles of trapezius muscle.

Expiration muscles:

• rectus abdominis,
• external and internal oblique abdominal muscles,
• transversus abdominis.

When performing expiration, the thoracic cavity falls down under its own weight and due to elastic force of the ribs cartilages. However, forced expiration during physical exercises needs additional pressure, which is delivered by expiratory muscles.

Depending on what area of the chest mainly moves and what muscles contract, there are three types of breathing indetified:

• Upper thoracic,
• Lower thoracic,
• Abdominal (diaphragm breathing) and mixed.

In men, abdominal breathing type prevails, when the volume of thoracic cavity increases mainly due to diaphragm contraction. In women, instead, thoracic breathing prevails, because transverse dimension of the chest increases most.

It is important to determine prevailing type of breathing by analyzing the degree of muscle utilization.