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TISSUES OF THE RESPIRATORY SYSTEM Overview
-lungs are site of respiratory gas exchange and consist of an assembly on thin walled sacs that must be partially inflated
-The rigidity of the chest wall resists the inherent tendency for the lungs to collapsemaintains a slightly negative pressure between the outer surface of the lung and the inner wall of the thorax
-thin film of fluid coats the pleural membranes and allows movement of lungs within the thoracic cavity Function: Gas exchange (c02, 02) Synthesis (collagen, elastin) Metabolsim (ATP production), Secretion (mucous, surfactant) Defence (non specific and specific) Respiratory tract a) physiologically the respiratory tract can be divided into the: Conducting zone: -nasal passages, pharynx, larynx, trachea, bronchi to the terminal bronchioles Function: Regions of the lung whose main function is to deliver inspired air from the mouth and nose to the gas exchanging zone of the lungs. It filters, warms and humidifies the inspired air- rich blood supply in the nasal mucosa structure: the patency (state of being open) of conducting airways is maintained by bone, cartilage (rigid structural support, elastic and collagen fibres, smooth muscleallows for extensibility and flexibility)
-most of the conducting zone is lined by a mucous membrane 'mucosa': mucous membranes line viscera of all body cavities that are in continuity of all external surfaces. The mucous membrane consists of respiratory epithelium and lamina propria. The mucosa covers, protects and provides secretory and absorptive functions.
-respiratory epithelium pseudostratified columnar epithelium is made up of five different cell types a) ciliated columnar cells
- make up for 30% of the cell population, roughly there is 300 cilia on the apical surface of each cell. Normal cilary beat synchronous wave like motion, frequency is 1000-1500 beats per minute-function: cilia move the mucus towards the throat where it is swallowed
-cilary compromise of precisely arranged microtubules- there is an axenome coremade up of 9x2 + 2 microtubule arrangement. Attahced to each doublet microtubule is motor protein dyenin and using the energy of ATP hydrolysis walks along to the adjacent pair and cause microtubules to slide against each other. In a synchronised manner this creates the force to bend the cilia- beat 7-22 times a second.
-the mucociliary escalator keeps mucus on the move: metachronicity which is the coordinated beating of cili is fundamental to effective mucociliary transport. The unidirectional power stroke is maintained by calcium influx via the gap junctions forming an electrical syncytium to enable metachronicity
-if the mucociliary action can go wrong: primary cilary dyskinesia/kartengers syndrome-autosomal recessive trait- mutations in DNA 1 gene in chromosome 9- abscence of dyenin arms there is chronic recurrent respiratory infections
-beneath the cilia are many mitochondria for ciliary beating - act as a mucocillary escalator- it beats upwards and outwards to shift mucus
-within these cells there are Golgi, RER, few ribosomes b) mucous goblet cells:
-makes up 30% of the total cell population.
-Light microscopy: cytoplasm of the cells packed with RER, prominent GOLGI, few mitochondria- protein component mucigen is synthesied by the RER and passed to the Golgi where it combines with carbohydrates - neutral and acidic proteoglycans and is packaged into membrane containing secretory granules
-accumlation of secretory granules forms a distended apical cytoplasm- granules are released by excocytosis
-Goblet cells secrete at a steady basal rate- stimulated by local irritation Function of mucus: prevents the lining of the respiratory tract from drying, humidifies the inspired air, sticky surface trap for fine dust particles and pollutants
-viscosity of the mucous depends on the various contributions from the goblet cells and the seromucous glands
-Cystic fibrosis- autosomal recessive disorder- mutation in the chloride channel 'cystic fibrosis transmembrane conductance regulator' - the protein doesn't fold properly and never reaches the cell- the CFTR is normally found in epithelial cells and the protein moves chloride out of an epithelial cell to the covering mucuspositively charged sodium follows anions to maintain electrical balance- increase in total electrolyte concentration in mucus- movement of water out of cell by osmosis
-accumlation of thick sticky mucus- more difficular for mucociliary transportobstruction of pulmonary airways followed by bacterial airways- chronic cough, dyspnea (laboured breathing) c) Basal 'short cells'
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