The lungs and lung disease

Structure of human lungs
1. Trachea
  1. Supported by rings of cartilage to prevent collapse when breathing in
  2. Walls made up of muscle and ciliated epithelium
  3. Goblet cells produce mucus that traps dirt/pathogens
2. Bronchi
  1. 2 subdivisions of trachea
  2. Lined with cilia
  3. Supported by rings of cartilage, amount reduces are bronchi get smaller
3. Bronchioles
  1. Subdivisions of the bronchi
  2. Lined with muscle
    1. Allows them to constrict and control airflow
4. Alveoli
  1. Air sacs at the end of bronchioles
  2. Contain collagen and elastin
    1. Fibrous proteins, collagen - high tensile strength, elastin is elastic!
    2. Mixed to prevent elastin overstretch
  3. Squamous epithelium
    1. Thin cells - short diffusion pathway
  4. Large sa:v ratio
  5. Partially permeable
  6. Rich supply of capillaries
    1. Narrow so red blood cells are flattened against them
      1. Shorter diffusion distance
      2. Slows rbc's allowing more time for diffusion
    2. Endothelium is one cell thick
Equations
1. Pulmonary ventilation = tidal volume (dm^3) x ventilation rate (min^-1)
2. Fick's Law
  1. Diffusion is proportional to
    1. Surface area x conc. gradient / length of diffusion pathway
Pulmonary Tuberculosis
1. Caused by 2 species of rod-shaped bacteria
  1. Mycobacterium tuberculosis
  2. Mycobacterium bovis
2. Symptoms
  1. Persistent cough
  2. Tiredness
  3. Loss of appetite
  4. Weightloss
  5. Development can lead to coughing up blood and fever
3. Transmission
  1. Airborne droplets
  2. Close contact over long period of time
  3. Infected cows milk
  4. People with reduced immunity more susceptible, eg:
    1. HIV/AIDS
    2. Very young and old
    3. Immunosuppressant drugs
4. Course of infection
  1. 1. The bacteria grow and divide in the upper regions of the lungs
  2. 2. The body's immune system responds with white blood cells accumulating in the area
  3. 3. This causes inflammation, enlargement of lymph nodes - PRIMARY INFECTION
  4. 4. Some bacteria remain in tubercules surrounded by white blood cells with the bacteria and infected phagocytes in the middle
  5. 5. POST-PRIMARY INFECTION can occur years later when the immune system is weakened
  6. 6. The bacteria reproduce quickly, destroying the lungs and causing cavities
    1. Hence, sufferers cough up damaged tissue and bacteria, and scar tissue develops
  7. 7. The bacteria may spread to other regions if they reach blood supply
Pulmonary fibrosis
1. Scar tissue on epithlium
  1. Irreversibly thickens the alveoli walls
2. Longer diffusion pathway
  1. Less efficient gas exchange
  2. Smaller lung volume
3. Reduces elasticity
  1. Lack of elastic recoil
  2. Makes breathing more difficult
  3. Difficult to maintain conc. gradient
4. Effects
  1. Shortness of breath
  2. Chronic, dry cough
  3. Pain and discomfort in chest
  4. Weakness and fatigue
5. Causes
  1. Microscopic injury (asbestosis)
  2. Unknown (idopathic)
    1. Damage to alveoli resulting in overproduction of fibroblasts
Asthma
1. Causes
  1. Genetic predisposition
  2. Allergens
  3. Anxiety, cold air, exercise can worsen or trigger asthma
2. 1. Allergens cause white blood cells on the linings in the bronchi and bronchioles to produce histamine
3. 2. Histamine causes the following effects in the airways
  1. Inflammation
  2. Increased mucus secretion
  3. Fluid leaving capillaries and entering airways
  4. Contraction of smooth muscle surronding bronchioles constricting airways
4. Effects
  1. Greater resistance to the flow of air
  2. Difficult to ventilate lungs and maintain conc. gradient
  3. Difficulty breathing
    1. Wheezing
  4. Tigh-chest feeling
  5. Coughing
Emphysema
1. Usually a result of long term smoking
2. Particles from smoke cause immune response, over a long time of smoking the enzymes released by white blood cells breaks down elastin
3. Lack of elastic recoil
4. Alveoli burst
  1. Reduced surface area
5. Alpha-1 Antitrypsin Deficiency
  1. Mutation to the gene coding for the enzyme alpha-1 antitrypsin,gets stuck in the liver
  2. Enzyme protects the lungs from neutophil elastane which breaks down elastin
  3. Often looks like emphysema
  4. Injection of alpha-1 antitrypsin and gene therapy is promising

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The lungs and lung disease

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