Respiratory Tract PDF

Respiratory Tract Anna Rees  Describe the gross and microscopic structure of the respiratory tract Intended Explain the link between the structure and Learning function of the respiratory tract, including which parts are conducting passages and whi...

Respiratory Tract Anna Rees  Describe the gross and microscopic structure of the respiratory tract Intended Explain the link between the structure and Learning function of the respiratory tract, including which parts are conducting passages and which Outcomes are gas exchange surfaces. Loading…  Gross Structure Respiratory Tract  Nose The lateral wall of the nasal cavity consists of bony ridges called conchae or turbinates which provide a large surface area covered in highly vascularized mucous membrane to warm and humidify inspired air. Loading… Under each turbinate, there is a groove or meatus. The paranasal air sinuses (frontal, sphenoid, ethmoid and maxillary) drain into these meatuses via small ostia, or openings. Pharynx Pharynx The pharynx extends from the base of the skull to the inferior border of the cricoid cartilage, where it is continuous anteriorly with the trachea and posteriorly with the oesophagus. It is described as being divided into three parts: the nasopharynx, oropharynx and laryngopharynx, which open anteriorly into the nose, mouth and larynx, respectively The pharynx is part of both the respiratory and gastrointestinal systems. The nasopharynx is situated above the soft palate and opens anteriorly into the nasal cavities at the choanae (posterior nares). During swallowing, the nasopharynx is cut off from the oropharynx by the soft palate. Larynx  Larynx The larynx is continuous with the trachea at its inferior end. At its superior end, it is attached to the U-shaped hyoid bone and lies below the epiglottis of the tongue. The larynx consists of a cartilaginous skeleton linked by a number of membranes. This cartilaginous skeleton comprises the epiglottis, thyroid, arytenoid and cricoid cartilages. The larynx has three main functions: 1. As an open valve, to allow air to pass when breathing. 2. Protection of the trachea and bronchi during swallowing. The vocal folds close, the epiglottis is pushed back covering the opening to the larynx, and the larynx is pulled upwards and forwards beneath the tongue. 3. Speech production (phonation). Trachea Trachea The trachea is a cartilaginous and membranous tube of about 10 cm in length. It extends from the larynx to its bifurcation at the carina (at the level of the fourth or fifth thoracic vertebra) The trachea is approximately 2.5 cm in diameter and is supported by C-shaped rings of hyaline cartilage Loading… The rings are completed posteriorly by the trachealis muscle Respiratory Tree Inside the thorax, the trachea divides into the left and right primary bronchi at the carina. The right main bronchus is shorter and more vertical than the left (for this reason, inhaled foreign bodies are more likely to pass into the right lung). The primary bronchi within each lung divide into secondary or lobar bronchi. The lobar bronchi divide again into tertiary or segmental bronchi. The airways continue to divide, always splitting into two daughter airways of progressively smaller calibre until eventually forming bronchioles.  Zones within Respiratory Tree 1. The conducting zone (airways proximal to the respiratory bronchioles), involved in air movement by bulk flow to the end respiratory units. 2. The respiratory zone (airways distal to the terminal bronchiole), involved in gaseous exchange. As the conducting zone does not take part in gaseous exchange, it can be seen as an area of ‘wasted’ ventilation and is described as anatomical dead space. Acinus The acinus is the part of the airway involved in gaseous exchange (i.e., the passage of oxygen from the lungs to the blood and carbon dioxide from the blood to the lungs). The acinus consists of: Respiratory bronchioles, leading to the alveolar ducts. Alveolar ducts, opening into two or three alveolar sacs, which in turn open into several alveoli. Note: alveoli can also open directly into alveolar ducts and a few open directly into the respiratory bronchiole. Multiple acini are grouped together and surrounded by parenchymal tissue, forming a lung lobule. Lobules are separated by interlobular septa. The blood-air interface  The blood–air interface is a term that describes the site at which gaseous exchange takes place within the lung. The alveoli are microscopic blind-ending air pouches forming the distal termination of the respiratory tract; there are 150–400 million in each normal lung. The alveoli open into alveolar sacs and then into alveolar ducts. The walls of the alveoli are extremely thin and are lined by a single layer Blood-air of pneumocytes (types I and II) lying on a basement membrane. The alveolar surface is covered with alveolar interface lining fluid. The walls of the alveoli also contain capillaries. It should be noted that: Average surface area of the alveolar–capillary membrane = 50–100 m2. Average thickness of alveolar–capillary membrane = 0.4 mm. Microscopic Structure Don’t get lost in all the words…. Microscopic…what do you need to know? Ciliated pseudostratified columnar epithelium Pseudostratified columnar epithelia are tissues formed by a single layer of cells that give the appearance of being made from multiple layers, especially when seen in cross section. The nuclei of these epithelial cells are at different levels leading to the illusion of being stratified. However, this tissue is made of a single layer of cells and each cell is in contact with the basement membrane. The coordinated action of cilia on longer columnar cells facing the lumen moves the mucus along with the particulate matter away from the lung. Goblet Cell a specialized type of epithelial cell that secrete mucins, which are significant components of mucus most often found in the respiratory and gastrointestinal tracts, where they make up part of the surface epithelium. The secretion of mucus in these tracts lubricates and protects the lining of the organs The increased activity or number of goblet cells has been associated with some diseases.  Nose and Nasopharynx- microscopic Bronchioles The epithelium here is ciliated and cuboidal Bronchioles contain no cartilage, meaning these airways must be kept open by radial traction, and there are no glands in the submucosa. The smooth-muscle layer is prominent. Adjusting the tone of the smooth-muscle layer alters airway diameter, enabling resistance to air flow to be effectively controlled. Bronchi and Bronchiole Cross section Respiratory Bronchiolies The respiratory bronchioles are lined by ciliated cuboidal epithelium, which is surrounded by smooth muscle. Goblet cells are absent but there are a few alveoli in the walls; thus, the respiratory Loading… bronchiole is a site for gaseous exchange.  Alveoli – Microscopic Structure Alveoli An alveolus is a blind-ending terminal sac of respiratory tract Simple squamous epithelium Most gaseous exchange occurs in the alveoli. Because alveoli are so numerous, they provide the majority of lung volume and surface area. The majority of alveoli open into the alveolar sacs. Communication between adjacent alveoli is possible through perforations in the alveolar wall, called pores of Kohn. The alveoli are lined with type I and type II pneumocytes, which sit on a basement membrane. Type I pneumocytes are structural, whereas type II pneumocytes produce surfactant. Alveolar Macrophages The most numerous of all cells in the lung are the alveolar macrophages (dust cells), which drift through the alveolar lumens and the connective tissue between them clearing up debris through phagocytosis. These macrophages “eat” the dust particles that escape from mucus in the higher parts of the respiratory tract, as well as other debris that is not trapped and cleared out by your mucus. If your lungs are infected or bleeding, the macrophages also function to phagocytize bacteria and loose blood cells. At the end of each day, as many as 100 million of these alveolar macrophages will expire as they ride up the mucociliary escalator to be swallowed at the esophagus and digested— this is how debris from the lungs is removed. Collateral Ventilation Collateral Ventilation