#13347 - Tissues Of The Respiratory System - Organisation of the Body

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 collapse- maintains 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 muscle- allows 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 core-made 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 mucus- positively 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 transport- obstruction of pulmonary airways followed by bacterial airways- chronic cough, dyspnea (laboured breathing)

c) Basal ‘short cells’

-stem cells of respiratory epithelium – small rounded cells that lie on the basal lamina – make up 30% of the respiratory epithelium

-don’t extend to the luminal surface of epithelium

-undergo mitosis and differentiate into other cell types

d) small granule cells- Kluchitsky/ K cells

-3% of total cell population- Neuroendocrine cells – innervated by the ANS

-small granules and dense cores- contain neuroendocrine hormones e.g serotonin – the serotonin released important in stimulating secretory and persitalsic movements, vagal efferents nausea

e) Brush cells

-constitute 3% of the total cell population- narrow columnar cells with short blunt apical microvilli

-also have afferent nerve ending- considered as sensory receptors

-Submucosa and adventitia are found beneath the mucosa.

Cancer: -the respiratory epithelium is susceptible to damage from pollutants- most lung cancers start from respiratory epithelium. Smoking transforms respiratory epithelium into stratified squamous epithelium. Initial step in differentiation into a tumour

Lamina propria

-the respiratory epithelium is supported by the lamina propria

-connective tissue with mucous glands (supplementa that produced by goblet cells) and serous glands (watery proteinaceous low viscosity secretions that dilute the mucus- serous secretions also contain immunoglobulins, lysozyme, enzymes

-it also has an important role in defence: Mucosal Associated Lymphoid Tissue: Lymphocytes, plasma cells, macrophages, neutrophils and eosinphils

-it also has a rich blood supply

-elastic fibres separate it from the underlying submucosa

Submucosa: larger glands

Cartilage:

Muscle: Flexibility and extensibility

Collagenous and elastic tissue fibres: support

Regional specialisation of the conducting zone

Nasal cavity

-the nose is subdivided into two nasal cavities by a cartilaginous nasal septum

-vestibule region close to the external environment and subject to damage- stratified squamous epithelium – multiple layers provide a barrier protecting the tissue from damage

-nasal cavity and paranasal sinuses are lined with respiratory mucosa Pseudostratified columnar ciliated epithelium- have extensive surface

-Function: warm the inspired air, increase the humidity, provide a sense of smell

Structure : venous plexus rich vascular network: warming inspired air-the permeabilities of capillaries are high- important in defence

-the ratio of goblet to ciliated cell ratio is higher in nasal cavity than lower airways

vibrissae filter out large dust particles

-Functions are enhanced by turbinate system of bones- project into the nasal cavity

Olfactory epithelium: found on superior conchae, three types of cells

-olfactor receptor neurons- bipolar neurons whose apical end forms olfactory vesicle- cilia have odour receptors

-sustentacular cells/ supporting cells

-Basal cells: small stem cells at the base that replace other cells

Lamina propria of olfactory mucosa:

-Bowman’s glands: olfactory glands which produce odourant binding protein- these are large affinity oderant proteins that carry oderant to the receptors on cilia.

-these glands also produce, IgA, lysozyme, isoferrin, isozyme

TRACHEA

-Trachea has three layers mucosa, submucosa, adventitia with cartilage

-Respiratory mucosa

-the submucosa has numerous seromucous glands- produce a more fluid mucous

-the walls of the trachea are reinforced by 10-12 cartilage rings- C shaped hyaline cartilage rings with open end on posterior surface, smooth muscle trachealis bridge open ends of cartilage- contraction of this muscle is involved in the cough reflex- decrease diameter of the lumen

-collagenous and elastic fibres link individual cartilages and allow both the lengthening and shortening

BRONCHI

-Mucosa is similar to that of the trachea: respiratory epithelium is less tall, less goblet cells

-the lamina propria has abundance rings elastin in upper layers and is separated from the submucosa by a layer of smooth muscle

-submucosa fewer seromucinous glands

-cartilage is in falttened interconnected plates rather than distinct- cartilages are more irregular than found in trachea- isolated plates or islands of cartilage

BRONCHIOLES

-Each bronchus divides into bronchioles

-epithelium has ciliated columnar cells and a few goblet cells : there is no cartilage or submucosal glands

-wall is composed of smooth muscle

-as the airways decrease in size, there a decrease in size, decrease in glands and goblet cells-lined with ciliated cuboidal cells and clara cells

-clara cells have a protective role- these are columnar cells with domed shaped apices and short blunt microvilli- produces secretory protein (lysosomes) and surfactant like material that coats the surface of the epithelium. Clara cells engulf airborne toxins, break them down via cytochrome P-450 in the SER.

-Club cells are mitotically active- divide and differentiate to form both ciliated and non ciliated cells

TERMINAL BRONCHIOLES

-Increase in smooth muscle and...