RESPIRATORY

• Respiratory system 


  the organ system responsible for gas exchange, consisting of the lungs, airways, and respiratory muscles
• alveoli


  tiny air sacs in the lungs where gas exchange occurs, allowing oxygen to enter the bloodstream and carbon dioxide to be removed
• bronchi


  the main airways leading from the trachea into the lungs, which further divide into smaller bronchioles
• bronchioles


  small air passages within the lungs that branch off from the bronchi and lead to the alveoli
• trachea


  the tube that connects the larynx to the bronchi, allowing air to pass to and from the lungs
• diaphragm 


  a dome-shaped muscle beneath the lungs that contracts and relaxes to facilitate breathing by expanding and compressing the chest cavity
• larynx 


  the structure containing the vocal cords, located at the top of the trachea, which plays a crucial role in speech production and protecting the airway during swallowing
• respiratory rate


  the number of breaths taken per minute, typically measured at rest and during physical activity
• hypoxia 


  a condition characterised by inadequate oxygen supply to the body tissues, often leading to symptoms such as shortness of breath and cyanosis
• pharynx


  the throat, a muscular tube situated behind the nasal cavity and mouth, serving as a passage for both air and food
• pulmonary circulation


  the circulation of blood between the heart and lungs, where oxygen is picked up and carbon dioxide is released
• inspiration


  the process of inhaling oxygen from the air into the lungs and exhaling carbon dioxide out of the lungs
• tidal volume


  the volume of air inspired or expired during normal breathing, without any additional effort
• vital capacity


  the maximum volume of air that can be forcibly exhaled after maximum inhalation, representing total lung capacity
• gas exchange


  the process by which oxygen is transported from the air into the bloodstream and carbon dioxide is removed from the bloodstream into the air
• surfactant 


  a substance produced by the alveoli that reduces surface tension, preventing the collapse of the alveoli during exhalation
• respiratory centre


  the area of the brain responsible for regulating breathing, located in the medial oblongata and pons
• cilia


  tiny hair-like structures lining the respiratory tract that help to trap and remove foreign particles and mucus from the airways
• Topography

  • Lungs are surrounded by pleural membranes - double layer membrane allowing for expansion during ventilation
  • Thoracic cavity is enclosed by ribs
  • Ribs connect via external and internal intercostal muscles
• diaphragm


  sheet of muscle that forms the floor of the thoracic cavity - separates the thoracic cavity from the abdominal cavity
• nose

  • allows airflow into the throat then into the lungs
  • air is warmed, filtered and humidified in the nasal passage
• nasal turbinates

  • network of bones, vessels and tissues on the outer walls of the nasal passage
  • responsible for warming, filtering, humidifying air
  • swell and shrink to regulate nasal airflow
  • infections lead to inflammation and congestion
• nasal sinuses

  • air pockets in bones surrounding the nose
  • drain into the nasal passage to deliver clear mucus
  • inflammation can cause sinusitis
• mouth

  • allows airflow into throat then to the lungs
  • also site of food intake
  • pharynx forms the separation between the trachea and the oesophagus
  • air can travel down to the lungs due to the presence of the epiglottis
• epiglottis

  • flap of cartilage covered with membrane
  • remains open during inspiration to allow air into the pharynx and into the trachea
  • epiglottis closes when swallowing, shutting off the larynx and forcing food into the oesophagus
• ciliated epithelial tissue

  • trachea and bronchi are lined with ciliated epithelial tissue
  • cilia contains proteins that contract to produce wave-like motions
  • responsible for wafting mucus, bacteria and debris back up the trachea to the throat
  • then swallowed and destroyed by acid in the stomach
• Alveoli

  • Small air filled sacs
  • Wall consists of single layer of thin epithelium
  • Site of gas exchange
  • Contains elastic tissue to allow for expansion during ventilation
  • Highly vascularised
• inspiration

  1. external intercostal muscles contract
  2. moves ribs up and out
  3. pleural membrane is pulled outwards
  4. thoracic cavity volume has increased therefore pleural cavity pressure decreases
  5. inner pleural membrane moves outwards pulling on lung surface and causing alveoli to expand
  6. decrease in alveoli pressure to below atmospheric pressure
  7. air is drawn into lungs
• expiration

  1. external intercostal muscles relax
  2. moves ribs downwards and inwards
  3. outer pleural membrane moves inwards
  4. diaphragm relaxes and domes
  5. thoracic cavity volume has decreases therefore pleural cavity pressure increases
  6. inner pleural membrane moves inwards
  7. elastic tissues also recoil causing alveoli to contract
  8. increase in alveoli pressure to above atmospheric pressure
  9. air is pushed out of lungs
• forced expiration

  • contraction of intercostal muscles causes ribs to be pulled in and down more forcefully expelling air more rapidly from lungs
• Efficient exchange factors

  • Large surface area for exchange
  • Short diffusion distance
  • High concentration gradient
• alveoli in efficient exchange factors

  • walls of alveoli are one cell thick. thickness decreases the diffusion pathway making gas exchange quicker
  • many alveoli in the lungs for a large surface area
  • ventilation maintains a high concentration of oxygen and a low concentration of carbon dioxide in the air in the alveoli
  • alveoli are highly vascularised which aids in the maintenance of a concentration gradient
• gas exchange in the body

  • deoxygenated blood is brought to the alveoli by the pulmonary artery and enters a single cell thick capillary made of epithelium
  • due to concentration gradient, carbon dioxide is lost from erythrocyte into the alveoli and oxygen moves into erythrocyte from alveoli
  • oxygenated blood is then brought back to the heart via the pulmonary vein where it is pumped back around the body
  • carbon dioxide is expelled from the alveoli during expiration
• surfactant


  a mixture of phospholipids and proteins that acts to reduce surface tension of water on epithelium and prevents alveoli sticking together during inspiration
• homeostatic control of ventilation

  • breathing rate is regulated by medulla oblongata
  • carbon dioxide decreases blood pH
  • chemoreceptors in arteries of neck and medulla detect this change
  • as pH decreases, respiratory centre sends nerve impulses to respiratory muscles to increase the breathing rate
  • results in decreased carbon dioxide concentration in blood, increasing blood pH
  • respiratory centre then signals breathing rate to be slowed again as homeostasis has been restored