3.3.2 Gas exchange

• Unicellular organisms adaptions for gas exchange:

  • Folds in membrane- increases SA:V ratio
  • One cell thick- creates a shorter diffusion distance
• Tracheal system- tubular network throughout the entire body of an insect, made of tracheal tubes and tracheoles
• In the tracheal system, air enters via the spiricals, and insects use their muscles to create pressure changes to bring air inside of the body
• Tracheal tubes- supported by chitin, branch into tracheoles
• Chitin- tough polysaccharide which holds the tracheal tube and tracheoles open
• Tracheoles- branches from the tracheal tubes, ends of tracheoles are embedded in tissue and filled with fluid
• Insects have to balance gas exchange (through the spiracles) and water loss, because when the spiracles are open to take in oxygen and remove carbon dioxide, water is lost.
• Oxygen being supplied to resting muscle in an insect: water is further from the muscle as oxygen isn’t being used or taken in as much during the resting period

  
• Oxygen being supplied to active muscle in an insect: there is a lower level of liquid in the tracheoles as it is drawn down into the muscle, so there is a shorter diffusion distance

  
• Operculum- protects the gills by preventing any solids from entering and damaging the gills
• Gill lamella- thin, flat, transparent tissue that lines the gills and allows for gas exchange, makes up the gill filaments
• Gill filaments- thin, full of capillary structures, large SA:V ratio
• Are the gills an internal or external structure?

  external
• Breathing in (fish):

  • Fish opens mouth
  • Operculum closes
  • Floor of the fish mouth drops, volume inside the mouth increases
  • Pressure inside the mouth decreases
  • Water (with oxygen) gets sucked in, across the gill filaments, gaseous exchange occurs
• Breathing out (fish):

  • Fish closes mouth
  • Operculum is open
  • Floor of fish mouth lifts up, volume inside the mouth decreases
  • Pressure inside mouth increases
  • Water (with carbon dioxide) is forced out over gill filaments, gaseous exchange occurs
• Counter current exchange system- the blood flows in one direction, the water flows in the opposite direction, which maintains a concentration gradient, oxygen diffuses from water to blood, system works along the whole length of the lamella.
• Water and blood move in opposite directions, meaning a concentration gradient can be established so diffusion can continue to occur

  A) 100

  B) 90

  C) 80

  D) 70

  E) 60

  F) 50

  G) 40

  H) 30

  I) 20

  J) 10

  K) 0

  L) 0

  
• The percentage of oxygen in the blood will always be lower than the percentage of oxygen in the water so that oxygen is able to diffuse from the higher concentration in the water to the lower concentration in the blood. As both substances move further along the length of the lamella, the percentage of gas decreases, since the gas is continuously moving off in opposite directions, taken by the blood

  
• Trachea- a tube which allows gases to enter and exit the lungs
• Layers of the trachea:

  • C rings of cartilage- prevents collapse of breathing passages
  • Middle layer of smooth muscle- controls diameter of trachea and bronchi by contracting and relaxing
  • Elastic fibres- stretches and recoils to return trachea to original shape
  • Goblet cells- produces mucus to trap dust or germs
  • Ciliated epithelial cells (cilia)- wafts mucus which has trapped dust or germs
• Alveoli, bronchioles, bronchi, trachea, nasal passage
• Adaptions of alveoli:

  • Thin cells- decreases diffusion distance
  • Moist surface- dissolves gases so they can be diffused easily
  • Close to capillaries- maintains concentration gradient and decreases diffusion distance
• Establishing a concentration gradient across the alveoli:

  In the blood, there is a high carbon dioxide concentration and a low oxygen concentration. In the alveoli, there is a low carbon dioxide concentration and a high concentration of oxygen. This establishes a concentration gradient. This gradient is maintained by the movement of blood through the capillaries.
• Maintaining the gradient and exchanging gases in the alveoli:

  In the alveoli, carbon dioxide diffuses in and is exhaled, maintaining the low concentration inside the alveoli. Oxygen diffuses out of the alveoli after being inhaled, and into the blood. After the gases are exchanged, there is a low carbon dioxide concentration and a high oxygen concentration in the blood which can be sent around the body to oxygenate cells and tissues.
• Intercostal muscles- internal and external, which work antagonistically to move the ribcage
• Inhalation (active process):

  • Diaphragm contracts, moving down and flattening
  • Internal intercostal muscles relax
  • External intercostal muscles contract, causing ribcage to move up and out
  • Volume of the chest cavity increases, lung volume increases
  • Air pressure decreases creating a pressure gradient, so more air has to be drawn into the lungs
• Exhalation (passive process):

  • Diaphragm relaxes, moving up and expanding
  • Internal intercostal muscles contract
  • External intercostal muscles relax, causing ribcage to move down and in
  • Volume of the chest cavity decreases, lung volume decreases
  • Air pressure increases creating a pressure gradient, so air is pushed out of the lungs
• Pulmonary ventilation rate- total volume of air moved into the lungs in one minute, dependent of tidal volume and breathing rate
• Tidal volume- volume of air moving in or out of the lungs with each breath at a resting rate
• Breathing rate- number of breaths taken per minute
• Pulmonary ventilation rate= tidal volume x breathing rate
• Vital capacity- the maximum volume of air that can be breathed in or out in one breath
• Forced expiratory volume- maximum amount of air you can forcefully blow out of your lungs in one second
• Tuberculosis:

  • Symptoms- difficulty breathing, chest pain
  • Causes- bacteria
  • Long term damage- permanent lung damage
  • Treatments- long course of antibiotics
• Lung cancer:

  • Symptoms- difficulty breathing, chest pains
  • Causes- smoking, exposure to chemicals
  • Long term damage- lung damage, infections, prolonged breathing difficulty
  • Treatments- chemotherapy, radiotherapy
• Emphysema:

  • Symptoms- difficulty breathing, chest pains
  • Causes- smoking (damages air sacs in lungs)
  • Long term damage- weakened alveoli (less oxygen into bloodstream), shorter life expectancy
  • Treatments- stop smoking, antibiotics, anti-inflammatory drugs, oxygen treatment
• Asthma:

  • Symptoms- difficulty breathing, chest pains
  • Causes- inflammation of breathing tubes when triggered
  • Long term damage- airway and lung damage
  • Treatments- inhalers
• Cystic fibrosis:

  • Symptoms- difficulty breathing, chest pains
  • Causes- inherited (faulty gene)
  • Long term damage- frequent chest infection, difficulty gaining weight, shortened life expectancy
  • Treatments- antibiotics, mucus thinning medicine (widens airways, clears lungs)
• Difference between healthy lungs and emphysema-affected lungs:

  • Emphysema-affected lungs have a smaller surface area than healthy lungs, so rate of diffusion is decreased
  • Emphysema-affected lungs have thicker walls than healthy lungs, so diffusion distance is longer
  • Diffusion is less efficient and takes longer, causing breathing to be more difficult