The respiratory system of humans comprises of a complex set of tissues and organs, which gets oxygen from the surrounding and carry it to the lungs. The basic role of the respiratory system is to provide the blood with oxygen so that the blood can convey oxygen to every body part. The respiratory system achieves this through inhalation and exhalation. When one breathes, oxygen is inhaled while carbon dioxide is exhaled. This gaseous exchange is the means of the respiratory system to get oxygen to the blood. The tissues and organs, which constitute the respiratory system of humans, are the pharynx and nose, the lungs, as well as the trachea (The Franklin Institute, 2013).
The nasal cavity is the preferable entry for air from outside into the respiratory system. The hairs lining the inner wall are part of the cleansing system of air. The nose comprises of the nasal cavity as well as the outer nose. The nose’s bridge is bone, and the majority of the outer nose is cartilage. The nares open to the outside while the choane goes to the pharynx. The nasolacrimal duct and the paranasal sinuses lead to the nasal cavity. The nasal cavity is separated by the nasal septum. The front vestibule comprises of hairs that get hold of debris. Lining the nasal cavity is the pseudo-stratified ciliated columnar epithelium, which traps debris and carries it to the pharynx. The nasal cavity’s superior part comprises the olfactory epithelium (Seeley, Stephens, & Tate, 2004).
The oral cavity is the digestive tract part that is bordered by the lips anteriorly, by the fauces posteriorly by the cheeks laterally, by the palate superiorly, and by a muscular floor inferiorly. The oral cavity is categorized into two areas namely the vestibule, the gap between the lips or cheeks and the alveolar procedures that contain the teeth. The other area is the oral cavity proper that lies medial to the alveolar processes. The mouth is covered with damp stratified scaly epithelium that offers protection against abrasion. Air also gets in via the mouth, particularly in persons who have a habit of mouth-breathing or those who have nasal passages that may be temporarily impeded for instance, by a cold (Seeley, Stephens, & Tate, 2004).
The pharynx is the ordinary opening of the respiratory and digestive systems. It gets air from the nose and food, drink, and air from the mouth. On the inferiorly side, the pharynx is linked to the respiratory system at the larynx and at the esophagus, to the digestive system. The pharynx is classified into three areas namely the oropharynx, the laryngopharynx, as well as the nasopharynx. Thenasopharynx is the bigger component of the pharynx and stretches from the choanae to the soft palate that is a partial partition of muscle and connective tissue that separates the oropharynx from the nasopharynx. The uvula is the soft palate’s posterior extension. The soft palate precludes swallowed materials from getting into the nasopharynx as well as the nasal cavity.
Lining the nasopharynx is a mucous membrane that contains pseudostratified ciliated columnar epithelium with goblet cells. Debris-laden mucus that comes from the nose is carried via the nasopharynx and ingested. Two auditory tubes that originate from the center ears lead to the nasopharynx. Air goes through these auditory tubes to balance atmospheric air pressure and the middle ears. The nasopharynx posterior surface comprises the pharyngeal tonsil, or adenoid that assists in fighting against infection. A pharyngeal tonsil that is enlarged can hinder the normal breathing as well as the air passage via the auditory tubes. Theoropharynx stretches from the uvula to the epiglottis. The mouth opens into the oropharynx via the fauces. Therefore, food, air, as well as drink all goes through the oropharynx. Stratified squamous epithelium that is moist lines the oropharynx and defends it against excoriation. Two tonsils set known as the lingual tonsils, and the palatine tonsils are situated close to the fauces. Thelaryngopharynx expands from the epiglottis tip to the esophagus and goes through posterior to the larynx. The laryngopharynx is covered with stratified squamous epithelium that is moist (Seeley, Stephens, & Tate, 2004).
The epiglottis is a tissue flap that protects the trachea entrance, closing once anything is ingested that is supposed to go into the esophagus as well as the stomach (Saskatchewan Lung Association, 2013). It’s inhered in the cartilage of the thyroid and protrudes as a free flap in the direction of the tongue. The epiglottis is distinguished from the other cartilages because it comprises of elastic instead of hyaline cartilage. In the process of swallowing, the epiglottis covers the larynx opening and precludes materials from getting into it (Seeley, Stephens, & Tate, 2004).
The larynx comprises of an external covering of nine cartilages, which are linked to each other by ligaments and muscles. Of the nine cartilages, six occur in pairs while three are not paired. The biggest cartilage is the unpaired thyroid cartilage also known as the Adam’s apple. The unpaired cricoid is the most inferior larynx cartilage that forms the larynx base on which the rest of the cartilages rest. The epiglottis is the third unpaired cartilage. The paired arytenoids cartilages unite with the posterior, superior cricoids cartilage border while the paired corniculate cartilages are inhered in the superior arytenoid cartilages tips. The paired cuneiform cartilages are found in a mucous membrane, in front of the corniculate cartilages. Two ligaments pairs go from the arytenoid cartilages anterior surface to the thyroid cartilage posterior surface. The superior ligaments are lined by a mucous membrane known as the vestibular folds. If the vestibular folds go hand in hand, they preclude food as well as liquids from getting into the larynx while swallowing and preclude air from getting out of the lungs, like when a person is holding his or her breath. The inferior ligaments are lined with a mucous membrane referred to as the vocal folds. The vocal folds together with the opening between them are referred to as the glottis. The vestibular folds, as well as the vocal folds, are covered with stratified squamous epithelium. The rest of the larynx is covered with pseudostratified ciliated columnar epithelium. A mucosal epithelium inflammation of the vocal folds is referred to as laryngitis (Seeley, Stephens, & Tate, 2004)
The trachea is a membranous tube, which comprises of dense even connective tissue as well as smooth muscle strengthened by 15–20C-shaped cartilage pieces. The cartilages back the frontal as well as lateral tracheal sides. They defend the trachea and uphold an open tube for air. The posterior trachea l wall lacks cartilage and constitutes an elastic ligamentous membrane as well as smooth muscle bundles known as the trachealis muscle. The smooth muscle contraction may reduce the tracheal diameter. While coughing, this activity makes air to flow faster via the trachea that aids in expelling mucus, as well as foreign materials. The esophagus is located immediately behind the cartilage-free tracheal posterior wall (Seeley, Stephens, & Tate, 2004).
The mucous membrane covering the trachea comprises of pseudo-stratified ciliated columnar epithelium having many goblet cells. The cilia impel mucus as well as foreign molecules engrafted in it in the direction of the larynx, where the mucus gets into the pharynx and is ingested. Steady tracheal irritation, like it takes place in smokers, may make the epithelium of the trachea to turn into moist stratified squamous epithelium, which has no cilia, as well as goblet cells. As a result, the usual tracheal epithelium function is lost.
The main bronchi split into secondary bronchi in every lung. There exist two inferior bronchi in the left lung, and three in the right lung. The inferior bronchi, successively, produce tertiary bronchi. The bronchi proceed to branch, lastly producing bronchioles that have a diameter that is below 1 mm. The bronchioles further split a number of times to turn into even smaller terminal bronchioles. These split to produce respiratory bronchioles with a restricted capability for gaseous exchange due to a few connected alveoli. The respiratory bronchioles produce alveolar ducts that are similar to long branching halls with several open entrances. The alveolar ducts terminate as two or three alveolar pouches that are chambers linked to more than two alveoli (Seeley, Stephens, & Tate, 2004).
The tissue neighboring the alveoli comprises elastic fibers, which permit the alveoli to enlarge during aspiration and shrink back during exhalation. The lungs are very stretchy, and if inflated, they are able to expel the air and go back to their initial, uninflated condition. The respiratory bronchioles walls comprise of collagenous as well as elastic connective tissue with smooth muscle bundles (Seeley, Stephens, & Tate, 2004).
Reference List
Saskatchewan Lung Association. (2013). Inside the Human Body - The Respiratory System. Retrieved May 1, 2013, from https://www.lung.ca/children/grades7_12/respiratory/respiratory_system.html
Seeley, R., Stephens, T. D., & Tate, P. (2004). Anatomy and Physiology (6th ed.). New York: The McGraw Hill Companies.
The Franklin Institute. (2013). Body Systems: Respiratory System. Retrieved May 1, 2013, from http://www.fi.edu/learn/heart/systems/respiration.html
