Respiratory model in human body

What is respiratory system?

It is a biological system consisting of specific organs and structures involved in bringing air (oxygen) into lungs and removing carbon dioxide from body which is a waste product produced by human body. This all occurs during the process of breathing.

Apart from breathing respiratory system has other functions as well:

1. Filtering/cleaning of air entering nose
2. Humidification and warming of air
3. Speech
4. Protective cough reflex in case of foreign body entering airways

Organs of respiratory system:

• Nose
• Pharynx
• Larynx
• Trachea
• 2 bronchi
• Bronchioles
• Alveoli
• 2 lungs

Respiratory system is divided into upper and lower respiratory track.

Upper respiratory track: It includes nose, pharynx and larynx. The role of upper respiratory track is to draw air inside and then push it down the lower respiratory track during the process of inhalation (breathing in) and expel carbon dioxide coming from lower respiratory track out to the environment during exhalation (breathing out).

Lower respiratory track: It includes trachea, bronchi, bronchioles, alveoli and lungs. Trachea, bronchi and bronchioles transport air to alveoli where gas exchange takes place. During the process of gas exchange in alveoli, oxygen from the air in alveoli enters blood vessels called capillaries surrounding alveoli and carbon dioxide, which is the waste product in blood goes into alveoli from capillaries.

Trachea divides into right and left bronchi. Each bronchus enters lung and divides into smaller airways called bronchioles inside lung. Bronchioles then end up into alveoli.

Pharynx

Pharynx is part behind mouth and nasal cavity and above the esophagus (food pipe) and the larynx (voice box).

Pharynx is divided into 3 parts:

1. Nasopharynx , part behind nose
2. Oropharynx , part behind oral cavity/mouth, it continues into esophagus (food pipe).
3. Laryngopharynx / Hypopharynx , part behind larynx

Larynx

Larynx also called voice box extends from root of tongue and lies in front of laryngopharynx /hypopharynx. It continues into trachea.

Trachea

Trachea or wind pipe is continuation of larynx and extends downwards until it divides. The trachea is 100 mm long and ranges from 15 mm to 20 mm in diameter. The trachea divides at the level of the fourth vertebral body into right and left main bronchi. The right main bronchus is ∼25 mm long (7–10 mm in diameter). The right main bronchus is wider, shorter and more vertical than the left main bronchus and, hence, foreign bodies tend to lodge more frequently into the right main bronchus. The left main bronchus is longer, measuring ∼40 mm in length (7–10 mm in diameter).

Bronchus, bronchioles and alveoli

• Main bronchus on each side branch out and become narrow as they approach the lung forming secondary and tertiary bronchi.
• Tertiary bronchi divide further to form smaller airways called bronchioles.
• Bronchioles divides into terminal bronchioles, then respiratory bronchioles which in turn evolve into alveoli which is the site of gas exchange.
• Alveoli form bunches called alveolar sacs.
• Alveoli are surrounded by small blood vessels called capillaries.
• Oxygen from alveoli during inhalation enter capillaries and carbon dioxide from blood is released into alveoli from where it goes out of the body during exhalation passing through all the above-mentioned structures.