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Section 2 (Patho) (Mechanics of breathing (Patton (2005) Human Body in…

- - - - Inspiration
        
        the diaphragm and intercostal muscles are inspiratory muscles
        
        the diaphragm is the dome shaped muscle spearating the abdominal cavity from the thoracic cavity
        
        the diaphragm flattens when it contracts during inspiration pulling it downwards towards the abdominal cavity
      - Expiration
        
        Quiet expiration is normally a passive process
        
        beginning when the inspiratory muscles relax
        
        elastic nature of lung tissue allows the organs to recoil and decrease in size as air leaves the alveoli and flows outwards
    - - Changes in the size of the thoracic cavity cause changes in the air pressure in the lungs
        
        Air has a tendency to move from areas of high pressure to low pressure
        
        Respiratory muscles cause this change of shape
  - - - during difficult breathing the muscles of the nexk, shoulders and abdomen will come into play
        
        initercostal muscles occupy the spaces between the 12 pairs of ribs
    - - dome shaped muscular structure separating the thoracic and abdominal cavities
        
        attached via tendon and muscle fibres to the ribs and sternum.
        
        when contracted pulls downward and enlarges the thoracic cavity
        
        decreases pressure in the thoracic cavity
- - - - external respiration occurs via the diffusion of gases into and out of the blood between the capillaries and alveoli.
        
        oxygen in the blood is in low concentration so oxygen from the air will tend to diffuse into the blood where it can attach to haemoglobin molecules
        
        Carbon Dioxide content is high in the blood. Mostly in the form of bicarbonatye ions.
  - - - blood arriving in the lungs is deoxygenated with a high concentration of CO2
        
        CO2 diffuses down its concentration gradient into the alveoli until equilibrium with alveolar air is reached
        
        by the same process oxygen diffuses from the alveoli into the blood
- - - - gases will tend to diffuse until equilibrium has been reache i.e. the point at which relative concentrations of gases are equal
      - Alveoli are structured to maximise surface area and minimise thickness of wall.
        
        Diffusion will occur at greater rate across this thin membrane
- - - - Airways decrease in size as they subdivide down the lungs. They tend to be surrounded by supporting cartilage until they are less than 1mm in diamter.
        
        These bronchioles are capable of collapsing
        
        to prevent collapse they contain elastic fibers
    - - this is called the mucous elevator
  - - - here macrophages are responsible for removal and destruction of pathogens and irritants
    - - adjacent alveoli are not completely independent structures
        
        they share thin membranous walls which contain pores to allow for pressure to equalise across alveoli.
- - - - anatomical components of the airway cleanse warm and humidify inspired air
      - the airways are lined with ciliated epithelial cells which are in turn coated with a mucous blanket
        
        the mucous is sticky and designed to capture airborn pathogens and irritants.
        
        the ciliated cells have hair like protuberances which are able to move or beat. In this way mucous and trapped irritants and pathogens are moved upwards towards the pharynx
        
        In the pharynx the mucous can be swallowed and then gut action can breakdown and destroy harmful pathogens
- - - - Smaller air passages, alveoli, connective tissue, blood vessels, lymph vessels and nerves embedded in an elastic connective tissue matrix.
      - Alveoli
        
        From the trachea or windpipe, the airways continually subdivide down until they reach the terminal bronchioles. This is end of the conducting portion of the airway
        
        Distgal to the terminal bronchioles are respiratorybronchioles and alveolie
        
        there are about 150million alveoli in each lung
        
        it is within these structures that gaseous exchange takes place.
        
        the alveoli are not supported by smooth muscles like the higher airways as they are so thin and delicate (a single layer of simple squamous epithelial cells)
        
        Instead they are supported by a loose network of elastic connective tissue in which macrophages, fibroblasts, nerves, blood and lymnph vessels are embedded.
        
        They are surrounded by a dense network of capillaries
        
        Gaseous exhange occurs across the respiratory membrane (external respiration) - this is the the site where the alveolar wall is fused to the capillary wall.
- - - - This decrease in CO2 causes bicarbonate and hydrogen ions in erthyrocytes to combine and form carbonic acid which is converted by carbonic anhydrase to carbon dioxide and water.Most of this CO2 diffuses into the alveoli to be exhaled further driving the reaction in the direction of producing more CO2.
        
        As bicarbonate levels in the cell decrease bicarbonate ions are actively drawn into the erythrocytes in a process which results in the release of chloride ions into the blood. this is called the reverse chloride shift
- - - - located in the carotid and aortic bodies sensitive to increases in PaCO2 and decreases in PaO2
        
        When stimulated these send nerve impulses to the respiratory centres in the brain to alter respiratory rate
    - - located throughout the lungs
        
        designed to stop harmful overinflation
- - - - Concerned here with external respiration - the exchange of oxygen and caerbon dioxide between the atmosphere and body tissues
- - - - This refers to the ability of the lungs to stretch and distend.
    - - the tendency of a structure to return to its initial size after being distended lungs are highly elastic and contain elastic tissues made of elastin which resist distension
    - - fluid in the alveoli called surfactant
- - - - Proteinases - cause destruction of the extracellular elastic matrix