Respiratory system

Your respiratory system includes the following:

• Nose and Nasal Cavity
• Sinuses
• Mouth/ Oral Cavity
• Pharynx(Throat)
• Epiglottis
• Larynx(Voicebox)
• Trachea(Windpipe)
• Bronchi
• Bronchial
• Alveoli
• Lungs
• Diaphragm

Figure 1: Respiratory system

1. Nose and Nasal Cavity: 
• The nose is an important part of the respiratory System trough which atmospheric air enters into the body and goes out of the body. It is made up of bones & cartilages and has a central partition wall(Nasal Septum) & 2 sidewalls.
• Nasal Cavity- is triangular in shape with the apex pointing superior. This is made up of Roof which in turn made up of bones forming the base of the skull. It also consists of a base/floor which is made up of palatine bones. The main task of the Nasal cavity and nose is the filtration of air during breath-in and this is done by the small hair-like structure called cilia present in the nose. Filtration of air is also facilitated by mucus secreted by nasal walls. This traps Dust, Pollens, and other pollutants present in atmospheric air. 
• The Sinuses are hollow spaces in the bones of your head. Small openings connect them to the nasal cavity. The sinuses help to regulate the temperature and humidity of the air you breath-in, as well as to lighten the skull and to give tone to your voice.
• The Oral Cavity also serves as a secondary opening for the respiratory system. It has disadvantages as the air goes via oral cavity does not have any filtration, temperature regulation, and humidification but it also has an advantage that is Oral cavity has a wider opening so it can facilitate greater intake of air during exercise.
2. Pharynx(Throat): 
• The pharynx is a muscular tube-like passage that lies just behind the nasal cavity & the oral cavity and it connects posterior nasal and oral cavity to Larynx and esophagus. It is divided into Nasopharynx is the part that lies behind the nasal cavity, Oropharynx is the part that lies behind the oral cavity and Laryngopharynx is the part which lies behind the Larynx. The air which we inhale through the nose or oral cavity goes to Pharynx and from there it has 2 ways - Trachea and the esophagus but the esophagus is contracted structure in normal condition, so air passes to Trachea.
• The Adenoids are overgrown lymph tissues at the top of the throat. When your adenoids interfere with your breathing, they are sometimes removed. The lymph system, consisting of nodes (knots of cells) and connecting vessels, carries fluid throughout the body. This system helps your body resist infection by filtering out foreign matter, including germs, and producing cells (lymphocytes) to fight them.
• The Tonsils are lymph nodes in the wall of your pharynx. Tonsils are not an important part of the germ-fighting system of the body. If they become infected, they are sometimes removed.
3. Larynx(Voicebox): 
• The Larynx is airway passage next to the throat and also known as Voicebox or Adam’s Apple and contains Vocal cords. It made up of many cartilages and has the support of ligaments & muscles. The main function of Larynx is that it connects Pharynx to Trachea. It produces the sound.
• Epiglottis- is the flap of tissue/cartilage and it guards the entrance of the Trachea. It closes Laryngeal inlet when anything is swallowed to prevent it from going to Trachea and to pass it to the esophagus. Epiglottis cartilage is connected to Thyroid cartilage in the front. 
• The Vocal cords- are attached thyroid cartilage at the front and Arytenoid Cartilage behind. The muscles and movement of Arytenoid cartilage lead to the movement of vocal cords. The exhaled air vibrates when it passes through the narrowed passage of vocal cords and this produces the sound or also called pronation.
4. Trachea(Windpipe) and its parts: 
• The trachea (windpipe) extends from the larynx toward the lungs. It is 5 inches in a length and 3/4 inches in diameter and it is lined by mucus membrane. 
• The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The rings of cartilage provide structural support and prevent the trachea from collapsing. 
• Bronchial Tree: The trachea is divided into 2 branches at T4(Thoracic vertebra 4) level called as Primary or Principal Left and Right Bronchi. Right Bronchi is short & broad and Left is long & narrow. Primary Bronchi are further divided into secondary bronchioles and then secondary bronchioles are divided into Tertiary bronchioles and these Tertiary bronchioles again divide & redivide about 20 times to form conducting bronchioles. Conducting bronchioles are then form 4-5 series divisions of Respiratory bronchioles. These Respiratory bronchioles are ended at Alveoli. 
• Alveoli are sac-like structures in which actual gas exchange happens. An alveolus is approximately 200 μm in diameter with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area available for gas exchange. Alveoli are surrounded by pulmonary capillaries. Alveoli give O2 and takes CO2 from blood cells in Pulmonary capillaries.
5. Lungs:
• We have 2 lungs in the Thoracic cavity. They are in a conical shape with apex projecting above clavicular bones and base towards a diaphragm. 
• The Right lung is divided into 3 lobes/sections and the left lung is divided into 2 lobes.
• Lungs are covered by a thin layer called Plura. The 2 layers of Plura have a cavity in between them. This cavity has a fluid that minimizes friction during lung expansion.
• This cavity has a negative pressure which is (-7.5 mm) of water during inhalation and (-5 mm) of water during exhalation.
• Gaseous exchange happens at Lungs. The De-oxygenated blood is carried to the Lungs from the right ventricle by Pulmonary Arteries. This Pulmonary artery divides innumerable times to form Capillaries that are surrounded around the Alveoli. The walls of ALveoli and Capillaries are single-layered and hence there occurs gaseous exchange of O2 and CO2 leading to the oxygenation of blood. 
• The blood is collected by Capillaries and ultimately carried to the heart by pulmonary veins into Left Atrium. From Left Atrium it goes to Left Ventricle from where it is pumped into Aorta and supplied to the body.

References:

• Gnosis Medical Yoga Teacher textbook.