Respiratory System PDF

Respiratory System It is composed of the two lungs and a series of airways that are responsible for transporting air into the lungs. In addition, these airways also heat, moisten and clean the air so that it can enter the lungs. In the lungs, gaseous exchange will take place, capturing oxygen from...

Respiratory System It is composed of the two lungs and a series of airways that are responsible for transporting air into the lungs. In addition, these airways also heat, moisten and clean the air so that it can enter the lungs. In the lungs, gaseous exchange will take place, capturing oxygen from the air and eliminating carbon dioxide. The respiratory tract is formed by: nasal cavity, mouth, pharynx, larynx, trachea, bronchi and bronchioles. Respiratory epithelium Most of the respiratory tract is composed of pseudostratified columnar epithelium with cilia. It also has goblet cells that secrete mucus to trap particles or microorganisms suspended in the air. The cilia of this epithelium will move the mucus towards the pharynx, so that it is eliminated by expectoration or swallowing. Nose • External part On the outside, the nose is covered by skin with abundant sebaceous glands. Nasal bones and cartilages maintain its shape. • Inner part: nasal cavity The nasal cavity is divided into two halves by the nasal septum. From this partition come three spirally shaped bony shells called turbinates. The nostrils communicate with the outside and have a thin skin with abundant sebaceous and sweat glands and short, stiff hairs that prevent the passage of large particles of dust in the air. The rest of the nasal cavity is covered by respiratory epithelium, except in the upper part. The conjunctiva below the epithelium is highly vascularized and contains abundant seromucous glands, as well as lymphoid tissue. When the inspired air enters the nasal cavity, it collides with the turbinates and turbulences are created that cause all the air to come into contact with the walls of the nasal cavity. Thanks to the vascularization the air will heat up, and all particles and microorganisms that may be suspended in the air adhere to the mucus in the wall secreted by the goblet cells and seromucous glands. Then the cilia will move the mucus to expel it. Moisture from the mucus will also hydrate the air and condition it to continue its path to the lungs. Pharynx It is a tubular organ that begins at the end of the nasal cavity and extends to the opening of the larynx and esophagus. It is an organ common to the respiratory and digestive apparatus. It is divided into three regions: - Nasopharynx: the first part at the end of the nasal cavity. It is lined by respiratory epithelium and has a vascularized conjunctiva with abundant seromucosal glands and lymphoid tissue. - Oropharynx: located after the nasopharynx, communicates with the mouth and presents flat stratified epithelium. In the connective tissue there are important accumulations of lymphoid tissue known as tonsils. - Laryngopharynx: the last fragment, communicates with the larynx and esophagus. The areas facing the esophagus have flat stratified epithelium, while the parts near the larynx have respiratory epithelium. In its walls we also find smooth and skeletal muscles that intervene in swallowing. Larynx It is a short and rigid tube located between the pharynx and the trachea. It is responsible for phonation and prevents the entry of solids or liquids into the respiratory system during swallowing. In the upper part there is a membrane of elastic cartilage, the epiglottis, which closes the entrance to the larynx during swallowing to avoid the passage of food or liquids to the respiratory system. Inside the larynx we have a respiratory epithelium and connective tissue with seromucous glands and lymphoid elements. In the mucosa there are folds called vocal cords that contain an elastic connective tissue attached to muscles that control phonation. Trachea It is a tube of about 12 cm length located after the larynx. Its wall is reinforced by rings of hyaline cartilage that prevent the trachea from collapsing. These rings are not closed on the back. In that area, the wall of the trachea contains smooth muscle that will control the diameter of the trachea. The interior of the trachea is lined by respiratory epithelium and a connective tissue rich in elastic fibers, seromucous glands and lymphoid elements. Bronchial tree The trachea bifurcates into two primary bronchi that will penetrate the lungs. The extrapulmonary part of the main bronchi has a structure identical to that of the trachea, but with a smaller diameter and a thinner wall. Inside the lung, primary bronchi are divided into secondary (lobar) and tertiary (segmental) bronchi. In these bronchi there are no rings of cartilage. The bronchi branch into bronchioles. They continue with the respiratory epithelium and the conjunctiva with elastic fibers, glands and lymphoid elements. The smooth muscle appears as two layers surrounding the entire wall of the bronchus. Tertiary bronchi branch into bronchioles, which are less than 1mm in diameter. In the bronchioles there is no cartilage and the epithelium is simple cuboidal. Clara cells will appear in the epithelium; these cells have a protein secretion that also helps to eliminate toxins from the inhaled air. In addition, this secretion is tensoactive, maintaining surface tension to keep the bronchioles open. Each bronchiole is subdivided to give rise to several terminal bronchioles, which constitute the final stretch of the respiratory tract. The terminal bronchioles branch to give rise to the respiratory bronchioles, which end in the so-called alveolar sacs. These alveolar sacs do not have their own walls but are formed by a sequence of pulmonary alveoli. Alveoli They are small sacks with thin walls that allow the exchange of oxygen and carbon dioxide between the air and the blood. The alveoli are separated from each other by the interalveolar septa (of different thickness and formed by connective tissue). The walls of the alveoli are coated by two types of cells. Type 1 pneumocytes are alveolar cells that line most of the alveolar surface. They are flattened cells that are closely linked to each other and act as an epithelium. Type 2 pneumocytes are alveolar cells that secrete pulmonary surfactant proteins to reduce surface tension and prevent the alveoli from collapsing. In addition, within the alveoli there are alveolar macrophages. They live in the lumen of the alveoli and phagocytize dust particles or inhaled microorganisms to maintain the sterile environment inside the lungs. Lungs The right lung is subdivided into three lobes and the left into only two, due to the space occupied by the heart. In their medial zone, they all present a notch, the hilum, through which pulmonary arteries and veins, as well as lymphatic vessels, enter and leave. The lobes are separated from each other by connective walls. The lobes are divided into bronchopulmonary segments In the thoracic cavity, there is a serous membrane covering the lungs, the pleura, composed of two membranes: the visceral pleura, adhered to the lung and formed by elastic connective tissue covered by a flat simple epithelium; and the parietal pleura, more external, covering the walls of the thoracic cavity, also formed by flat simple epithelium and dense connective tissue. Between both layers there is a cavity filled with serous fluid that allows the lungs to move without friction during ventilation. Airways and Gas Exchange - YouTube