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Respiratory Tissues
Organisation of the Body
| Question | Answer |
|---|---|
| Functions of respiratory system | Gas exchange - O2 and CO2 Synthesis - collagen and elastin Metabolism - ATP production Secretion - mucus, surfactant Defence - mechanical and immunological barriers |
| Conducting portion | Delivery and removal of air Conduit through which air can travel to and from lungs Conditions air - filter, moistens and warms via rich blood supply in nasal mucosa Nasal cavity to terminal bronchioles |
| Respiratory portion | Gas exchange Exchange of gases between air and blood Thin walled pouches Respiratory bronchioles, alveolar ducts and alveoli |
| Design of conducting portion | Patency of airways maintained by bone, cartilage Elastic and collage fibres and smooth muscle give flexibility and extensibility A lining of epithelial cells with glands gives protection, defence and secretory functions |
| Design of respiratory portion | Thin walled pouches where gaseous exchange can take place Rich capillary network and thin cellular membranes |
| Mucous membrane | Line all body cavities continuous with external surface Respiratory epithelium + lamina propria Covers, protects and provides secretory and absorptive functions Submucosa and adventitia found beneath |
| Cell types in respiratory epithelium | Ciliated pseudostratified columnar epithelium Ciliated columnar cells Mucous goblet cells Basal cells Small granule cells Brush cells |
| Ciliated columnar cells | 30% of cells 300 cilia on each cell beating 1000-1500 time a min Cilia beat upwards and outwards - mucociliary escalator Beneath cilia - small mitochondria for beating and Golgi, ribosomes and RER |
| Cilia | Axoneme core - 9x2 + 2 Motor protein dynein - produces force for bending via coordinated Ca flux through gap junctions Microtubule gliding by ATP by hydrolysis |
| Goblet cells | Produce mucus 30% of cells Viscosity of mucus depends on relative contributions from goblet cells and seromucous glands Mucus traps particulate matter and pollutants |
| Mucociliary escalator | Meta chronicity is fundamental to effective mucociliary transport Unidirectional power stroke Maintained by Ca flux via gap junctions Forms an electrical syncytium |
| Bronchiectasis | Irreversible dilation of bronchial tree caused by destruction of elastic and muscle tissue Caused by reoccurring inflammation Leads to increased infections |
| Primary ciliary dyskinesia | Autosomal recessive Immobile cilia Absence of dynein arms due to mutations in DNAI1 and DNAH1 for dynein heavy chain |
| Cystic fibrosis | Affects chloride ion channel in lungs, pancreas, liver and intestine Names due to appearance of cysts and fibrosis Most common life limiting autosomal recessive disease in Europeans |
| Mutation occurring in CF | CFTR Disrupts ion transport Defective transport of Cl and water so cells take up extra NA Mucus becomes thick and traps bacteria Obstruction of airways followed by infection Cough chronic purulent secretions and dyspnea are common symptoms |
| New treatment for CF | UK Cystic Fibrosis gene therapy Oxford, Edinburgh and London alongside Boehringer and biomedica New viral vector based therapy uses replication deficient lentiviral vector in inhaled formation to introduce CFTR gene |
| Basal cells | Small rounded cells that lie on the basal lamina 30% of cells Do not extend to lumen Undergo mitosis and differentiate into other cell types Stem cells |
| Small granule cells | Diffuse neuroendocrine system 3-4% of cells Small granules and dense cores Contain neuroendocrine hormones like serotonin Contract smooth muscle and control respiration |
| Brush cells | 3% of cells Narrow columnar cells with short blunt apical microvilli Have afferent nerve endings - are considered to be sensory receptors |
| Effect of smoking | Most lung cancers start from epithelial cells Smoking transforms respiratory epithelium into stratified squamous epithelium Initial step in differentiation into a tumour |
| Types of lung cancer | Non small cell - 80% Squamous cells - 31% Adenocarcinoma - 29.4% Large cell - 10% Small cell - 20% |
| Lamina propria | Connective tissue with mucous and serous glands Contains MALT - lymphocytes, plasma cells, macrophages, neutrophils and eosinophils Rich blood supply Elastic fibres - elastic lamina separates it from submucosa |
| Mucous and serous glands | Aid viscosity of mucous Mucous - mucus to supplement goblet cells Serous - watery low viscosity secretions to dilute mucus Secrete lysozyme, lactoferrin and protease inhibitors |
| Tissues below the mucosa | Submucosa - larger glands and elastic lamina between this and mucosa Cartilage - patency Muscle - flexibility and extensibility Collagenous and elastic connective tissue fibres - support |
| Nasal cavity | Large surface for warming air Stratified squamous, respiratory and olfactory epithelium Venous plexus - rich vascular network High capillary permeability Vibrissae - filter dust out High goblet to ciliated cell ratio |
| Olfactory epithelium | Olfactory receptor neurons - smell perception, bipolar neurons whose apical end forms olfactory vesicle Sustentacular cells - support Basal cells - small stem cells |
| Bowmans glands | Olfactory glands Produce odorant binding protein Large affinity for odorant molecular and carries odorants to receptors on cilia Also produce IgA, lactoferrin, lysoferrin and lysozyme |
| Trachea | Three layers - mucosa, sub mucosa and adventitia with cartilage Lined with respiratory epithelium Numerous seromucous glands in submucosa produce more fluid mucous |
| Cartilage rings | C shaped rings of hyaline cartilage - open ends posterior Trachealis bridges gap - contraction involved in cough reflex to decrease diameter of lumen Collagenous and connective tissue links cartilage to allow lengthening and shortening of trachea |
| Mucosa of the bronchi | Muscle layer consists of criss-crossing bundles Lamina propria has abundance of mucus and serous glands Cartilage more irregular than trachea - isolated plates or islands of hyaline cartilage |
| Bronchioles | Lack cartilage Smooth muscle in walls As airway decreases in size - decrease in glands and goblet cells, epithelial cells become cuboidal Lined with ciliated cuboidal cells and club cells |
| Club cells | Columnar cells with dome apices and short microvilli Produce surfactant like material to reduce mucus thickness Important in defence to degrade toxins inhaled via cytochrome P450 Divide to regenerate the bronchiolar epithelium |
| Terminal bronchioles | Increase in smooth muscle and elastic tissue Muscle contracts at end of expiration and relaxes during inspiration |
| Asthma | Bronchioles constrict, become inflamed and excessive mucous is produces Caused by environmental and genetic factors Triggered by an allergen crossing bronchiole epithelium Dysregulated immune response |
| Process underlying asthma | Allergen crosses epithelium Antibodies produces with interact with mast cells - degranulate Causes release of vasoactive amines Cause contraction of smooth muscle, vasodilation, increased vascular permeability and platelet aggregation |
| Is asthma genetic | High heritability Identification of ADAM33 - a susceptibility gene using GWAS Expressed in muscle and involved in airway wall remodelling |
| Respiratory bronchioles | Transition between conducting and respiratory portions Mucosa similar to terminal bronchioles except walls interrupted by saclike alveoli which increase in number Smooth muscle and elastic connective tissue 80% of cells are club cells |
| Alveolar ducts | Lined with simple squamous epithelial cells Sphincter like smooth muscle cells appear and knobs between adjacent alveoli |
| Alveoli | Rich matrix of elastic and reticular fibres provides support of duct and alveoli Loss of elasticity and breakdown of elastic fibres gives rise to emphysema Alveoli become confluent creating blebs |
| Emphysema | Smoking increases macrophages Recruit neutrophils releasing elastase that destroys elastin Elastase is neutralised by a-antitrypsin - reduced release or deficiency in gene Airways collapse and leads to obstruction and secondary infection |
| Interalveolar septum | 2 thin squamous epithelial layers Between these lie capillaries, elastic and reticular fibres and connective tissue - interstitium Richest capillary network Pores of Kohn allow communication between alveoli |
| Cell types in alveoli | Type 1 cells make up 90% - form gas exchange surface Type 2 cells make up 10% - secrete surfactant to lower surface tension Alveolar macrophages- dust cells |
| Type 1 cells | Squameous epithelial Organelles grouped round nucleus leaving cell minimal thickness readily permeable to gases Form occluding junctions with eachother preventing seepage of extracellular fluid into lumen |
| Air blood barrier | Simple squamous epithelial cells of bronchiole for part of air blood barrier Endothelial cells of capillary wall forms other part 3 main components - cytoplasm of alveolar cells and endothelial cells, fused basal laminae of close alveolar and endothelia |
| Movement of O2 and CO2 | Passive diffusion in response to pressure difference of gases within blood and alveolar lamina When air pressure is high inside lungs air flows out When air pressure is low inside lungs air flows in |
| Type 2 cells | Rounded Found in groups Type 2 cells have occluding junctions and desmosomal junctions with type 1 cells Divide by mitosis to replace their own population and also type 1 population |
| Role of type 2 cells | Secrete surfactant Lamellar bodies synthesize phospholipids, GAGs and proteins that comprise surfactant Released at apical surface of cell where it forms a broad lattice like network known as tubular myelin |
| Respiratory distress syndrome | Affects infants born before surfactant production begins Deficiency results in increased surface tension collapse of alveoli Surfactant replacement therapy is used Also caused by mutations in SP-B3 or lipid transporter |
| Alveolar macrophages | Phagocytose particulate matter in lumen of alveoli maintain sterile environment Produce proteolytic and lysosomal enzymes Kill bacteria through peroxide producing mechanisms Assist in uptake of surfactant |
| Common causes of inflammation | Cold Influenza Croup Diphtheria Whooping cough Pneumonia Pleurisy TB Sinusitis |
| Defence mechanisms | Filtration Sneeze/cough reflex Mucociliary escalator Lysozyme, lactoferrin and transferrin Opsonin Phagocytic cells Surfactant proteins NO |
| Specific immunity | Mucosal immune system Aggregated of immune tissue - adenoids, BALT and NALT containing B and T lymphocytes |
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