chapter 7

• how is diffusion alone enough to supply needs of single celled organisms

  1. metabolic activity low so O2 and CO2 demand also low

  2. SA:V ratio is large
• why does SA:V decrease

  it decreases as organism gets bigger, distances substances have to travel from out to in increases, so gases can't be exchanged fast enough or in large amounts for survival
• increased surface area

  provides area needed for exchange, overcomes SA:V limitation, e.g plant root hair cells and human villi
• thin layers


  distance substances have to travel is short, making process fast and efficient, e.g alveoli in lungs and villi in intestine
• good blood supply


  good blood supply maintains steep concentration gradient for diffusion, e.g the alveoli and gills
• ventilation to maintain diffusion gradient

  for gases ventilation system helps maintain concentration gradients and makes process more efficient, e.g alveoli and gills of fish ventilation means a flow of water carrying dissolved gases
• where does gaseous exchange take place

  the alveoli at the lungs

  
• nasal cavity features

  - large SA with good blood supply

  - hairy lining which secrete mucus to trap dust + bacteria

  - moist surface so gases dissolve helping them to pass across the gas exchange surface
• trachea


  main airway, supported by incomplete rings of cartilage, which carries warm moist air down from the nasal cavity into the chest.
• what are the trachea and its branches lined with

  ciliated epithelium with goblet cells between and below the epithelial cells
• goblet cells


  secrete mucus onto lining of trachea to trap dust and microorganisms that have escaped the nose lining, goes to throat and swallowed
• bronchus

  similar in structure to trachea with same supporting rings of cartilage but they are smaller
• bronchioles

  have a diameter of 1mm or less and have no cartilage rings, the walls contain smooth muscle and it helps change amount of air coming into lungs, lined with thin layer of epithelium to make some exchange possible
• alveoli


  tiny air sacs where main gaseous exchange occurs, consists of layer of thin and flattened epithelial cells with some collagen and elastin fibres

  
• alveoli features

  1. elastic tissue allows to go through elastic recoil

  2. diameter of 200-300 micrometres
• main alveoli adaptations

  1. large surface area, combined is 50-75m2

  2. thin layers, single epithelial cell thick, diffusion short

  3. good blood supply, supplied by 280 mill capillaries, bring CO2 and take O2 away maintaining gradient

  4. good ventilation, breathing moves air in and out maintaining gradient for CO2 and O2
• inner surface of alveoli

  thin layer of solutions of water, salts and lung surfactant, oxygen dissolves in water before diffusing into blood
• lung surfactant


  chemical mixture containing phospholipids and both hydrophilic and hydrophobic proteins, which coats the surfaces of the alveoli and prevents them collapsing after every breath.
• how is air moved in and out

  result of pressure changes in the thorax brought by the breathing movements = ventilation
• diaphragm


  broad, dome shaped sheet of muscle which forms the floor of the thorax
• where are the external and internal intercostals

  between the ribs
• what lines the thorax

  pleural membranes which surround the lungs
• what is the space between the pleural membrane

  pleural cavity that is filled with thin layer of lubricating fluid so membranes slide easily over each other as you breathe
• inspiration

  - active process

  - diaphragm contracts, flattens and lowers

  - external intercostals contract moving ribs up and out

  - volume of thorax increases so pressure decreases
• expiration

  - passive process

  - diaphragm relaxes, domes up and rises

  - external intercostals relax moving ribs down and in

  - elastic fibres in alveoli in lungs return to normal length

  - volume of thorax decreases so pressure increases
• forceful exhalation

  internal intercostal muscles contract moving rib cage down and in faster and harder, and abdominal muscles contract to increase pressure in lungs rapidly
• peak flow meter


  a simple device that measures the rate at which air can be expelled from the lungs
• vitalographs


  patient breathes out as quickly as possible through a mouth piece, graph produced showing amount of air breathed out and how fast
• spirometer


  an instrument used to measure respiratory volumes
• tidal volume


  volume of air which moves in and out of the lungs with each resting breath
• vital capacity


  volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath
• inspiratory reserve volume


  the maximal volume of air that can be breathed in over and above a normal inhalation
• expiratory reserve volume

  the extra amount of air that can be forced out of the lungs over and above the normal exhalation
• residual volume


  volume of air that is left in the lung after a forced exhalation, cannot be measured directly
• total lung capacity

  vital capacity + residual volume
• breathing rate


  number of breaths taken per minute
• ventilation rate


  total volume of air inhaled in one minute
• ventilation rate formula


  tidal volume x breathing rate
• insects exoskeleton

  external skeleton made of chitin where little or no gaseous exchange can take place
• how has the gaseous exchange system of insects evolved

  do not have blood pigments that carry oxygen, oxygen is delivered directly to cells and carbon dioxide is removed directly as well