Respiratory System Lecture Notes PDF

DR.BUTHAINAH ALEZZI OSOUL-EL-DEEN-UNIVERSITY-COLLEGE Department of pharmacy Lecture Four Respiratory System The complex of organs and tissue which are necessary to exchange blood carbon dioxide...

DR.BUTHAINAH ALEZZI OSOUL-EL-DEEN-UNIVERSITY-COLLEGE Department of pharmacy Lecture Four Respiratory System The complex of organs and tissue which are necessary to exchange blood carbon dioxide (CO2) with air oxygen (O2). Function: Act of breathing, which includes inhaling and exhaling air in the body; the absorption of oxygen from the air in order to produce energy; the discharge of carbon dioxide, which is the by product of the process. The respiratory system consists of two divisions with distinct structural elements that reflect their unique functions. These include: The conducting airways, which serve to conduct, clean, warm, and moisten the air. This portion is composed of the nose, pharynx, larynx, trachea, bronchi, and bronchioles. The respiratory airways, which facilitate gas exchange. These are located entirely within the lung and are represented by respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. 1  DR.BUTHAINAH ALEZZI Some of these structures lie outside the lungs (extrapulmonary) and need cartilaginous supports in their walls, which provide rigidity and flexibility. Some of the structures are inside the lungs (intrapulmonary), where the need for structural support is less. The respiratory bronchioles constitute an area of transition between the conducting and respiratory portions. Functions of the conducting portion are to provide a route for the air to reach the lungs and also for conditioning the air. Air-conditioning during its passage through the conducting portion includes : filtration (by hairs) cleansing (by mucus and ciliary action) moistening (by mucus) warming or cooling (by heat exchange via blood vessels) These air-conditioning functions are performed by a specialized epithelium, the "respiratory epithelium", which lines much of the surface of the conducting portion. 2  DR.BUTHAINAH ALEZZI NOSE and NASAL CAVITY The external nostrils (nares) and vestibule have coarse hairs to filter large particles. The nose is divided by the nasal septum into two chambers. The surface of these chambers is lined with respiratory epithelium The nasal cavities are lined by a ciliated.pseudostratified columnar epithelium containing the cell bodies of bipolar nerve (olfactory) cells. of these olfactory cells contain proteins that act as odorant receptors. And on apart from the superior chamber, which is lined by a specialized olfactory (smell) receptor (Regio olfactoria). Regio olfactoria The olfactory region (about 10 cm2) is lined by a highly specialized sensory 3  DR.BUTHAINAH ALEZZI "epithelium", which is in fact composed of neurons and glia. This is unique as neurons are usually not in direct contact with the external environment. The mucosa of the nasal cavities has: olfactory nerves olfactory glands that secrete onto the epithelial surface a proteinaceous substance, that keeps the surface moist and provides a trap for aromatic substances. There are eight (8) different cell types within the respiratory system epithelium 1. Ciliated Cells: These are the most abundant airway epithelial cells. They are found from the trachea to respiratory bronchioles and contain approximately 200-300 cilia per cell. 2. Goblet (Mucous) Cells: This cell type, which is present in the trachea and bronchi, has a wide, extended apical region, these cells contribute to the mucous secretion lining the airways 3. Basal (Short) Cells These cells, which are found in the trachea and bronchi, do not reach the airway lumen and have nuclei that are close to the basal lamina, thereby giving the epithelium a pseudostratified appearance. 4. Clara Cells (Bronchiolar Epithelial Cell) :These non-ciliated columnar epithelial cells are found in bronchioles. These cells play a major role in the metabolism of exogenous agents (e.g., atmospheric pollutants), and act as progenitor cells for bronchiolar epithelium following lung injury. 5. Brush Cells: This non-ciliated columnar cell, found in trachea and bronchi, is distinguished by a dense population of long, straight, blunt microvilli on the luminal surface and epitheliodendritic (afferent) synapses near the cell base. The function of these cells is unknown, although a chemoreceptor and sensory function is suspected. 4  DR.BUTHAINAH ALEZZI 6. Dense core granule cells (small granule cell, neuroendocrine cell) These cells are found throughout the airways, either as isolated cells or clusters called neuroepithelial bodies (often found near airway junctions). Resembling endocrine cells, they are roughly triangular in shape, have basally located secretion granules, and touch the basal lamina. These cells are reported to secrete a variety of amine and peptide products. Their role in regulating lung function is incompletely understood. With the light microscope these cells are difficult to distinguish from basal cells. 7. Serous Cells These non-ciliated secretory cells are found predominantly in the trachea and bronchi. They have round nuclei, abundant rough endoplasmic reticulum, and dense apical secretory granules. They secrete glycoproteins and lysozymes and probably contribute to the low viscosity periciliary fluid covering the bronchial epithelium. Along with the mucous cells, they populate the epithelium of the extensive submucosal gland network of the trachea and proximal airways. 8. Intermediate: These non-ciliated columnar cells are immature and replace cells cast off from the epithelium. They may differentiate into mucous secreting Goblet cells or ciliated cells. These cells may be difficult to distinguish from brush cells. Most food that we eat is "tasted" by chemoreception of the olfactory organ. The taste buds of the tongue can only distinguish between sweet, bitter, acid and salt. People suffering from colds are unable to distinguish the aromas of food and typically do not have an appetite. Larynx The larynx is an irregular tube connecting the pharynx to the trachea. The larynx has two functions: phonation (creation of sounds for speech). control of the air pathway so that only air (and not food or foreign objects) reaches the 5  DR.BUTHAINAH ALEZZI lower respiratory passages. During swallowing the larynx moves upwards and directs the food to the oesophagus. If anything other than air enters the larynx there is a cough reflex (to prevent fluids or food entering the trachea). In cases of drowning, the cough reflex may cause uncontrolled laryngeal spasm, preventing oxygen reaching the lungs and death by asphyxiation. Autopsies of bodies after drowning commonly reveal lungs that are virtually free of water. The mucosa of the larynx has two pairs of folds. The false vocal cords (upper folds) are separated from the true vocal cords (lower folds) by the laryngeal ventricle. The true vocal cords, by modifying the slit-like opening (rimaglottidis) enable us to produce sounds. The true vocal cords consist of: stratified squamous epithelium vocal ligament (connective tissue, which is mainly elastic bundles) vocal muscle (skeletal muscle, which regulates the tension of the folds). The false vocal cords consist of: respiratory epithelium lamina propriawith many exocrine glands Irregular plates of hyaline cartilage provide support and protection for the larynx. Lymphatic nodules are common in the lamina propria of the larynx, especially in the area of the false vocal. Trachea The trachea is a short tube (about 10 cm long) extending from the larynx to the bifurcation at the beginning of the two primary bronchi. The trachea is lined with typical respiratory epithelium. In the lamina propria there are about 20 C-shaped rings of hyaline cartilage (the open ends are posterior). The open ends of each ring are connected by a bundle of smooth muscle. A dense fibroelastic ligament continuous 6  DR.BUTHAINAH ALEZZI with the perichondrium of each ring connects adjacent rings. This ligament prevents overdistention of the lumen. The trachea – the tube connecting the throat to the bronchi. The bronchi – the trachea divides into two bronchi (tubes). One leads to the left lung, the other to the right lung. Inside the lungs each of the bronchi divides into smaller bronchi. The broncheoli - the bronchi branches off into smaller tubes called broncheoli which end in the pulmonary alveolus. Pulmonary alveoli – tiny sacs (air sacs) delineated by a single-layer membrane with blood capillaries at the other end. Lungs The lungs are covered by a thin tissue layer called the pleura. The same kind of thin tissue lines the inside of the chest cavity. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath. The structure of the lungs includes the bronchial tree – air tubes branching off from the bronchi into smaller and smaller air tubes, each one ending in a pulmonary alveolus. 7  DR.BUTHAINAH ALEZZI Histology of the Alveolar Region Five major cell types are present in the alveolar region of the lung 1. Alveolar Type I Cell (Squamous alveolar epithelial cell) These elongated thin cells line the alveoli and cover a large surface area (approximately 95% of the alveolar surface) due to extreme flattening and marked cytoplasmic attenuation. These cells form an extended, continuous surface of minimal thickness that is permeable to gases and is the major location of gas exchange. 2.Alveolar Type II Cell (Great alveolar cell, granular pneumocyte): These cells form tight junctions with Type 1 cells, and are often positioned in alveolar corners and at alveolar septal junctions. These secretory cells protrude into the alveolar lumen. 3. Capillary Endothelial cell :The pulmonary capillary bed is the largest vascular bed in the body--covering a surface area of 70 m2. It receives the entire cardiac output. Endothelial cells are specialized for both gas 4. Alveolar macrophages These large cells wander freely in the alveoli. Located in the aqueous hypophase of the surfactant layer, they move over the alveolar surface ingesting microorganisms and inhaled particulate matter. 5. Interstitial cells a progenitor cell is noted during lung development that is capable of differentiation into fibroblasts or smooth muscle cells. Interstitial cells of the alveolar region are primarily fibroblasts with ramified cytoplasmic extensions. There are normally a few alveolar macrophages trundling around the alveoli scavenging for debris that is not removed by the mucociliary apparatus. When more debris collects with pathologic processes, then blood monocytes migrate into the alveoli and become macrophages. The mucociliary apparatus consists of all the ciliated epithelium, along with the submucosal glands and goblet cells, that secrete serous and mucinous secretions. The 8  DR.BUTHAINAH ALEZZI function of the mucociliary apparatus is to trap and expel debris that has been inhaled. In general, particles above 10 microns in size do not get past the nasopharynx; particles averaging 5 to 10 microns are trapped by the mucociliary apparatus. Particles 1 to 5 microns in size must be phagocytosed by macrophages in the alveoli. Particles less than 1 micron remain suspended and are exhaled. The lungs are covered by a thin tissue layer called the pleura. The same kind of thin tissue lines the inside of the chest cavity. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath. The structure of the lungs includes the bronchial tree – air tubes branching off from the bronchi into smaller and smaller air tubes, each one ending in a pulmonary alveolus. 9