Exchange & transport systems

• What are xerophytes? 


  Plants specially adapted for life in warm, dry or windy habitats where water loss is a problem.
• What is ventilation?


  Consists of inspiration & expiration. Controlled by movements of diaphragm, internal & external intercostal muscles & ribcage.
• Structure of gas exchange system in humans:

  Air enters trachea (windpipe)-splits into 2 bronchi-1 bronchus leads to each lung. Each bronchus branches off into smaller tubes called bronchioles. End in alveoli (small air sacs). Gases exchanged here. Ribcage, intercostal muscles & diaphragm work to move air in & out.
• Inspiration:


  External intercostal & diaphragm muscles contract. Causes ribcage to move upwards & outwards & diaphragm to flatten, increasing volume of thoracic cavity. Lung pressure decreases to below atmospheric pressure. Air flows down pressure gradient (down trachea into lungs). Active process (requires energy).
• Expiration:


  External intercostal & diaphragm muscles relax. Ribcage moves downwards & inwards & diaphragm curves upwards again. Volume of thoracic cavity decreases, causing air pressure to increase to above atmospheric pressure. Air forced down pressure gradient & out lungs. Normal expiration- passive process.
• Forced expiration:


  External intercostal muscles relax & internal intercostal muscles contract, pulling ribcage further down & in.
• Alveoli structure:


  Alveoli surrounded by network of capillaries. Wall of each alveolus made from single layer of thin, flat cells (alveolar epithelium). Walls of capillaries made from capillary endothelium. Walls of alveoli contain elastin protein- helps alveoli recoil after inhaling & exhaling air. O2 diffuses out alveoli across alveolar epithelium & capillary endothelium into haemoglobin in blood. CO2 diffuses into alveoli from blood.
• Adaptations of alveoli:


  Thin exchange surface-alveolar epithelium 1 cell thick (short diffusion pathway which speeds rate of diffusion). Large surface area as there's millions of alveoli. Steep concentration gradient of O2 & CO2 between alveoli & capillaries- increases rate. Constantly maintained by flow of blood & ventilation.
• What are the measures of lung function?

  Tidal volume, ventilation rate, forced expiratory volume1 (FEV1) & forced vital capacity (FVC).
• What is tidal volume?


  Volume of air in each breath.
• What is ventilation rate?


  Number of breaths per minute.
• What is forced expiratory volume1 (FEV1)?


  Max volume of air that can be breathed out in 1 second.
• What is forced vital capacity (FVC)?


  Max volume of air possible to breathe forcefully out lungs after deep breath in.
• How do lung diseases affect us?

  Reduce rate of gas exchange in alveoli. Less O2 can diffuse into blood, cells receive less O2 & aerobic respiration reduced. Less energy released.
• What is Tuberculosis ?

  Bacterial infection- immune system responds by forming walls around infected tissue, these become hard lumps (tubercles) & lung tissue within them dies. S.A reduced due to damage. Tidal volume decreases (less air inhaled with each breath). Ventilation rate increases to take in more O2.
• Symptoms of tuberculosis?


  Ventilation rate increases, persistent cough, coughing up blood & mucus, chest pains, shortness of breath & fatigue.
• What is Fibrosis?


  Scar tissue in lungs due to dust or asbestos. Scar tissue thicker & less elastic than normal lung tissue. Lungs can't expand fully-greater diffusion distance. Tidal volume & FVC reduced. Diffusion slower across thicker scarred membrane.
• Symptoms of fibrosis?


  Higher ventilation rate, shortness of breath, dry cough, chest pain, fatigue & weakness.
• What is asthma?


  Airways inflamed & irritated due to allergic reaction to pollen, dust, animal hair etc. Smooth muscle lining of bronchioles contracts, lots of mucus produced. Reduced air flow into alveoli. FEV1 reduced.
• Symptoms of asthma?


  Wheezing, tight chest & shortness of breath.
• What is Emphysema?


  Foreign particles trapped in alveoli (from cig smoke or air pollution). Inflammation causes phagocytes to respond & they break down elastin in walls of alveoli. Alveoli can't recoil so air remains in them & their walls are destroyed so S.A reduced.
• Symptoms of emphysema?


  Shortness of breath, wheezing, increases ventilation rate.
• What is a risk factor?


  Factor that correlates with an increased chance of suffering from a particular disease.