respiratory system

• Lungs


  The organ responsible for gas exchange in humans
• Parts of the lungs

  • Bronchiole
  • Bronchus
  • Trachea
  • Lungs
  • Diaphragm
  • Muscles
  • Alveoli
  • Trachea
• Trachea

  • Passageway through which air moves into and out of the lungs, held open by C-shaped rings of cartilage
• Bronchi


  • The two bronchi branch off from the trachea, held open by rings of cartilage
• Bronchioles


  • Smaller branches off the bronchi, carries air down to the alveoli
• The cartilage is required in the trachea and bronchi to maintain the airway (keep it open) when the pressure changes during inspiration and expiration (proper terms for breathing)
• Trachea


  • Lined with ciliated epithelium and goblet cells
• Ciliated epithelium


  Cilia (hairs) on the epithelium beat to move mucus up and out of the lungs
• Goblet cells


  Produce mucus to trap any dirt or pathogens
• The mucus is then swallowed and destroyed in the hydrochloric acid in the stomach
• Alveoli


  • Highly folded, large surface area for increased diffusion of gases
  • Wall is one cell thick, made of squamous epithelium
  • Cells are squashed, providing short diffusion distance for faster gas exchange
• Gas exchange in alveoli

  1. Oxygen diffuses from alveolar air space, across squamous epithelium of alveolus, across smooth endothelium of capillary and into red blood cells

  2. Carbon dioxide diffuses from blood, across smooth endothelium wall of capillary, across squamous epithelium of alveolus into alveolar air space
• Not all of the air in the alveolus is fully replaced when ventilating the lungs, however there is still a diffusion gradient between the blood and the alveolar air
• Inspiration


  1. Diaphragm contracts and flattens

  2. External intercostal muscles contract

  3. Rib cage moves up and out

  4. Lung volume increases

  5. Pressure in lungs less than pressure outside

  6. Air drawn into lungs
• Expiration


  1. Diaphragm relaxes and back into dome shape

  2. External intercostal muscles relax

  3. Rib cage moves down and in

  4. Lung volume decreases

  5. Pressure in lungs greater than pressure outside

  6. Air forced out of lungs
• In forced expiration you can exhale with more force if you contract the internal intercostal muscles, as this brings the rib cage down more quickly
• Chronic Obstructive Pulmonary Disease (COPD)

  A group of lung conditions that make it difficult to expire air as the airways have become narrowed
• COPD

  • Chronic means it's a long term condition that cannot be cured
  • Emphysema is one type of COPD, bronchitis is another
  • Alveoli in the lungs are broken down, reducing the surface area, so there is less diffusion of oxygen into the blood
  • Damaged alveoli also undergo less recoil so the oxygen poor/carbon dioxide rich air is not completely expired during ventilation
  • Fibrosis is also common, causing thickening of the epithelial tissue in the lungs, so the alveoli become thicker, increasing the diffusion distance
• Common symptoms of COPD

  • Decreased levels of oxygen in the blood
  • Increased breathing rate
  • Increasingly short of breath/breathlessness/wheezing
  • Dizziness and tiredness
  • Cough and chest infections
• Risk factors for COPD

  • Exposure to air pollution
  • Working with chemicals, dust and fumes
  • Genetic condition known as Alpha-1 deficiency
  • Smoking or breathing second hand smoke
  • Respiratory problems in childhood
• Measuring percentage saturation of oxygen in blood

  Using a finger pulse oximeter
• Normal values for blood oxygen saturation should be above 92%
• Measuring respiratory rate


  1. Watching the chest rise and fall and counting how many times this happens per minute

  2. At rest, inspiration lasts around 2 seconds

  3. At rest, expiration lasts around 3 seconds

  4. So a person at rest should have a respiratory rate of 12 breaths per minute

  5. Normal is considered between 12 and 20 breaths per minute

  6. Below 12 breaths per minute is considered low

  7. Above 25 breaths per minute is considered high
• Normal body temperature range

  From 36.5°C to 37.2°C for a healthy adult
• Body temperature can vary depending on gender, recent activity, food and fluid consumption, time of day and in females of a certain age range the stage of the menstrual cycle
• Measuring body temperature


  1. Using a thermometer, normally inserted into the mouth under the tongue, under the armpit, inside the ear hole, or on/near the forehead

  2. Most thermometers are digital, but traditional ones can still be used
• Tissue fluid


  A substance that baths all the cells of your body, formed when blood enters the capillary
• Formation of tissue fluid

  1. Reduction in diameter size of the capillary compared with the arterioles creates a high hydrostatic pressure

  2. This pressure forces most of the fluid in the blood plasma out through the leaky capillary endothelium walls

  3. Fluid contains water with dissolved oxygen and nutrients such as glucose and amino acids

  4. Oxygen can then diffuse into the cells and be used in respiration

  5. Loss of fluid from the blood plasma causes a decrease in the hydrostatic pressure in the blood

  6. Large plasma proteins remain in the plasma and create a low water potential inside the blood capillary towards the venous end

  7. This draws some of the water back into the blood capillary, bringing with it some of the dissolved carbon dioxide (a waste product from respiration)

  8. Not all of the tissue fluid can be brought back into the blood plasma, so some drains into lymphatic capillaries
• Lymphatic system


  • Made up of a series of lymph nodes and lymphatic vessels
  • Removes excess tissue fluid and drains this fluid back into the blood circulation near the right atrium
  • Also plays a major role in the immune response
• Lymphatic system


  1. Lymphatic capillaries drain fluid away from the tissues into lymph

  2. Lymph then drains into large lymphatic vessels, which can have valves to prevent backflow

  3. Lymph drains into lymph nodes, which filter the lymph as it passes through

  4. Lymph nodes contain lymphocytes and macrophages which respond to bacteria, damaged cells and malignant cells in the lymph