The system through which breathing is done is called respiratory system. The organs involved in respiration are collectively called the respiratory system. Different parts of human respiratory system are-
1. Anterior Nostrils: The two side-by-side openings in front of the nose are called anterior nostrils. It is the first part of the trachea. It is divided into two openings by the nasal septum. The front nostrils are always open. Air enters through this passage.
Function: Air enters through the nostrils and carbon dioxide is expelled.
2. Vestibule: The inner part of the nose after the nostrils is called the vestibule. Its walls have hairs. Hairs act as filters and clean the air.
3. Nasal Cavity: The part after vestibule is called nasal cavity. Its inner wall consists of ciliated epithelium, mucous membranes, olfactory cells, blood vessels, nerve endings, oil glands and numerous hairs. Olfactory cells help in receiving olfactory stimuli.
Function: It moistens dry air and cools hot air. Ciliated cells and mucous membranes trap dust and germs. Olfactory cells help in receiving olfactory stimuli.
4. Posterior Nostrils: The opening through which the nostrils open into the nares is called Choana.
Function: Air enters the nostrils through this orifice.
5. Nasopharynx: The part from posterior nostril to larynx is called nasopharynx. It is an identical part of esophagus and trachea.
6. Larynx: The larynx is a small cartilaginous organ located below the pharynx. It produces voice so it is called Voice organ. It is not silent as it contains cricoid, thyroid, arytenoid, cuneiform, corniculate and epigøtis cartilages. It opens through an opening called Glottis. At the top of the larynx is a small flap called the Epiglottis. Thyroid cartilage is the largest of the laryngeal cartilages and is known as Adam’s apple. Inside the larynx are mucous membranes and 6 elastic vocal cords. When under tension the vocal cords are vibrated by air and produce sound.
Function: Epigypsy prevents food from entering the larynx. Vocal cords produce vowels or sounds.
7. Trachea: The part from the vocal cord to the fifth thoracic vertebra is called the trachea. It is a hollow tube. Its length is 12 cm and diameter is 2 cm. It is also known as Wind pipe. It is composed of 16-20 hyaline cartilage rings in a C (semi ring) shape. The cartilage is called the tracheal ring. Because the rings are connected by fibrous tissue, the trachea does not collapse. The inner wall of the trachea is covered by ciliated mucous membrane and the outer wall by connective tissue.
Function: Moves air through the trachea. The cilia of the mucous membrane prevent the entry of foreign matter.
8. Bronchial or Respiratory tree: The end of the trachea divides and forms two branches. Right and left branches. Both branches are called bronchus. The point where the trachea divides is called the carina. The right bronchus is surrounded by 9-12 and the left bronchus by 6-8 cartilaginous rings. The right branch divides into 3 parts and enters the right lung and the left branch divides into 2 parts and enters the left lung. Each branch divides repeatedly to form numerous bronchioles. Each bronchiole contains numerous tiny air chambers. These are called alveoli. Alveolus is the structural and functional unit in the lungs. The entire trachea looks like an inverted tree and is called the respiratory tree.
Function: Air enters the lungs from the trachea through the bronchus and air containing CO2 leaves the lungs through the trachea.
9. Lung: The light pink colored large and soft organ like sponge in human chest is called lung. Human body has two lungs. Right and left lung. The two lungs together weigh 2.9 pounds. The right lung is large and weighs 625 grams. It is divided into three lobes by horizontal fissure and oblique fissure. Superior lobe, middle lobe and inferior lobe. Left lung small weight 565 grams. It is divided into two lobes by the oblique fissure. Superior Lobe and Inferior Lobe. There are 10 lobules in the right lung and 8 in the left lung. Each lobule is composed of alveoli. The space through which the bronchi, blood vessels and lymphatic channels enter the lungs is called Alveoli. The bronchi, blood vessels and alveolar ducts are surrounded by connective tissue and form the root of the lungs.