What is Respiratory System?
o Respiratory system is the group of tissue and organs that helps in the process breathing, exchange of gases and helps in the transportation oxygen to the cells and exhaling carbon-dioxide from the body.
o Here the organs of respiratory system are discussed where the most important organs are the air passage, lungs and muscles.
o There are other organs along with them that is nose and nasal cavity, larynx, bronchi, bronchioles, pharynx etc.
Respiratory System Diagram
Respiratory System Organs and Respiratory System Function
1. Nose and Nasal Cavity
o It is a Part of the respiratory system that has external opening and are first organ of the system that makes the airway for the system.
o Nose is made of cartilage, bone, skin and muscles that protects nasal cavity. The nasal cavity functions to filter, moisture and keep the air warm.
o Nasal cavity lining is covered with hair and mucus that helps in trapping dust, pollen other contaminants and prevents entering the system.
o Similarly, the exhaled air is passes from the nasal cavity then to the environment.
o Oral cavity is the other opening for the respiratory tract.
o Nose is responsible for the normal breathing but the oral cavity / mouth fulfills the need of the air when compromised by the nasal cavity.
o The airway path from mouth is shorter and the air does not moisturize or warm the entering air.
o The mouth has not any hair or mucus lining present in the mouth to trap the contaminates. But the inhaled air from mouth is more compared to nose because of the bigger diameter of the tract and shorter pathway.
3. Pharynx / Throat
o Pharynx is found superior to the esophagus and posterior to the nasal cavity.
o There are three parts of pharynx namely, nasopharynx, oropharynx and laryngopharynx.
• Nasopharynx: It is found in the superior to the pharynx and posterior to nasal cavity. Air first passes through the nasopharynx then to the oropharynx.
• Oropharynx: It is found in the backside of the oral cavity. Air that enters from the oral cavity enters the respiratory tract through oropharynx part of the pharynx.
• Laryngopharynx: The passage where both the air and food passes through it. It is located between the esophagus and larynx covered by smooth mucus membrane. The air is passed to the laryngopharynx then directed to the opening of larynx.
o The opening of larynx is the epiglottis, flap like covering for the trachea and esophagus.
o Epiglottis ensure that no food particles enter the trachea by covering the covering it and prevents choking.
o Voice box / larynx that acts as connection between trachea and laryngopharynx located in the anterior position of neck and superior to the trachea. larynx is made up of cartilage.
o Epiglottis makes up for one of the cartilages.
o Thyroid cartilage found inferior to the epiglottis helps to hold the anterior part of the larynx and also helps in protecting vocal folds.
o Cricoid cartilage helps hold the larynx open and support the end is located inferior to thyroid cartilage.
o The vocal folds in the larynx responsible to produce sounds. It is made up of the mucus membrane that vibrates for the production of sound.
o The pitch change is due to speed and tension of vibration.
5. Trachea / Windpipe
o Pseudostratified ciliated columnar epithelium 5m long C shaped tube covered by cartilaginous rings.
o The rings allow the trachea to remain open for the air all the time.
o The open end is located at the posterior of esophagus and helps expand the esophagus when accommodate the mass of food when passed through esophagus.
o Trachea is responsible to pass the air to the lungs.
Cellular Structure of Respiratory System
o The lining of the trachea is covered with epithelium and also produces mucus that traps the contaminants that escaped the nasal cavity and prevents it to enter from the lungs.
o Cilia that is present in epithelium helps in the moving the mucus superiorly to the pharynx that is then where it is swallowed and digested later.
6. Bronchi and Bronchioles
o Trachea is followed by the left and right branches known as primary bronchi leading to the lungs.
o Then primary bronchi divided to form small secondary bronchi which leads the air to the lobes of lungs (2 lobes in the left lung and 3 lobes to the right lung).
o Secondary bronchi are divided into smaller tertiary bronchi within each lobe.
o Bronchioles are made by the splitting the tertiary bronchi throughout the lungs.
o These bronchioles spilt to form terminal bronchioles.
o Bronchioles are responsible to conduct air through the alveoli of the lungs.
o The bronchi and the bronchioles form the shape of tree and the main function of the bronchi and bronchioles are to carry air to the lungs from the trachea.
o Primary bronchi consist of ring-shaped cartilage rings that helps to hold the airway to hold firmly.
o As the bronchi splits to form secondary bronchi the cartilage of rings spread and walls of the bronchi contains more of smooth muscles and elastin to it that helps bronchi to be more flexible and contractile.
o When the air requirement increases then the bronchi and bronchioles are dilated by smooth muscles.
o Large sac spongy pair of organs found in the thorax located lateral to the heart and superior the diaphragm.
o Each lung is covered by the pleural membrane provides lung with space to expand along with the negative pressure space.
o Negative pressure is when the lung is passively filled by air even when relaxed.
o Both lungs are slightly different with each other in size and shape due to the heart present in the left side. Therefore, right lung is slightly bigger than the right lung has 3 lobes present.
o Lungs consists of millions of tiny sacs known as alveoli and inner side of the lung is made up of spongy tissue with capillaries.
o Alveoli are present in the terminal bronchioles and have cup shaped structure surrounded by the capillaries.
o The alveoli are covered with the simple squamous epithelium that helps exchanging the gases in the capillaries present in the alveoli.
8. Muscles of Respiration
o There are set muscles that covers the lungs and help lung to inhale and exhale air.
o Diaphragm, muscle present below the thorax. When the diaphragm contracts it moves up into the abdominal cavity inhaling air into lungs by expanding the thoracic cavity and when the diaphragm is relaxed the air is exhaled out of the lungs.
o Diaphragm with the intercostal muscles helps the lungs during expansion and relaxation.
o Intercostal muscles are found between the ribs and are of two types – internal intercostal muscles (help in exhalation) and external intercostal (helps in expansion during inhale of air).
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Respiratory System Citations
- Anatomy and physiology of respiratory system relevant to anaesthesia. Indian J Anaesth. 2015 Sep; 59(9): 533–541.
- Respiratory System Disease. Pediatr Clin North Am . 2016 Aug;63(4):637-59.