The respiratory system is responsible for providing oxygen for the blood to take to the body's tissues and removing carbon dioxide, one of the waste products of cellular metabolism. The respiratory system is closely interrelated with the heart and circulatory system. These two systems can be grouped together in medicine to form the cardiopulmonary system.
The respiratory system consists of the following:
* Two lungs, the vital organs of the respiratory system.
*Upper and lower airways
*Terminal air sacs called alveoli
*Thoracic cage
*Muscles of breathing
There are two separate processes of breathing. The first is ventilation, which is the bulk movement of the air down to the terminal end of the lungs where the actual gas exchange takes place with the bloodstream. The second is respiratory, which is the process of gas exchange where oxygen is added to the blood and carbon dioxide is removed. Since the gas exchange in the lungs occur between the blood and the air in the external atmosphere, it is called external respiration. The oxygenated blood is transported internally via the cardiovascular system to the cells and tissues where gas exchage is now termed internal respiration.
THE UPPER AIRWAYS OF THE RESPIRATORY TRACT
The upper airway function include:*Heating or cooling inspired gases to body temperature ( 37 degrees Celsius )
* Filtering ( inhaled ) particles from the inspired gases
* Humidifying inspired gases to a relative humidity of 100 %
* Providing for the sense of smell, or olfaction
* Providing sounds, or phonation
*Ventilating, or conducting the gas down to the lower airways
The upper airways, starts at the nose, which are responsible for initially conditioning the inhaled air. The nose is a rigid structure made of cartilage and bone. There are 3 main regions contained within the space behind the nose, called the nasal cavity. The two nasal cavities are separated by a wall called the septal cartilage. The first region is the vestibular region, which is located inside the nostrils and contains the coarse nasal hairs that act as the first line of defense for the respiratory system. The hairs, called vibrissae, are covered with sebum,a greasy substance secreted by the sebaceous glands of the nose. It helps to trap large particles and keeps the nose hairs soft and pliable. The vestibular helps filter out large particles so they do not enter the lungs. The next is olfactory region, it is on the roof of the nasal cavity. And it keeps inspired gases into the region and does not allow it to go reach deeper into the lungs. The last is respiratory region, it warms and moistens air so airways do not dry out. The respiratory region possesses three scroll- like bones known as turbinates, or conchae. These split up the gas into 3 channels.
The second part is the pharynx, a hollow, muscular structure lined with epithelial tissues. It is also called throat, begins behind the nasal cavities and is divided into three sections: nasopharynx, oropharynx and laryngopharynx.
The nasopharynx is the uppermost section and begins right behind the nasal cavities. Air brethe through the nose passes through here. This section contains lymphatic tissue. The oropharynx is located right behind the oral or buccal cavity. Anything swallowed passes through this section. This section contains palatine tonsils. The laryngopharynx is the lowermost section. Its common name is voice-box. The larynx is a semi-rigid structure composed of cartilage. The " Adam's apple" is the largest cartilage. Air that is breathed and anything that is swallowed passes through this section. Glottis mechanism, directs the flow of " traffic "( air to the lungs and food and liquid to the stomach ). The glottis is the opening that leads into the larynx and eventually the lungs. The leaf-shaped, fibrocartilage, flap like structure that closes over the opening of the larynx when you swallow and opens up when you breathe is called epiglottis.
THE LOWER RESPIRATORY TRACT
Upon leaving the vocal cords in the larynx, the inspired air enters the trachea. The trachea extends from the cricoid cartilage of the larynx to the sixth cervical vertebrae. The cartilage found in the trachea is in the C-shaped structures. The trachea is the largest bronchus. Once the trachea reaches the center of the chest, it begins its first branching, or bifurcates, in two bronchi, the right and left main stem and can be called as generation 1. The site of bifurcation is called carina. Now the bronchi must branch into the five lobar bronchi ( generation 2 ) that correspond to the five lobes of the lungs. Each lung lobe is further divided into specific segments, ad the next branching of bronchi are called the segmental bronchi ( generation 3 ). The branching becomes more numerous with tiny sub-segmental bronchi ( generation 4 to 9 ) branching deep within each lung segment. The diameter of sub segmental bronchi ranges from 1 to 6 mm. Cartilaginous rings are now irregular pieces of cartilage and will soon fade away completely. Now we reach the very tiny airways called bronchioles ( generation 10 to 15 ) that average only 1 mm in diameter. They have no cartilage layer, and the epithelial lining becomes ciliated cuboidal. The cilia, goblet cells and submucosal gland, are almost all gone by generation 15. Now we reach the terminal bronchioles ( generation 16 ), which have an average diameter of .5 mm, no goblet cells, no cartilage, no cilia, and no submucosal glands. This marks the end of the conducting areas.
The next airways beyond the terminal bronchiole is called respiratory bronchiole ( generation 17 to 19 ) because a small portion of gas exchange takes place here. Alveolar ducts ( generation 20 to 22 ) originate from the respiratory bronchioles wherein the walls of the alveolar ducts are completely made up of simple squamous cells arranged in a tubular configuration. The alveolar ducts give way to the grape bunch-like structures of several connected alveoli, better known as the alveolar sacs ( generation 23 ).
