exchange surfaces

• respiratory surfaces:

  • unicellular or micro-organisms: body surface (plasma membrane) (small size -> large S.A.: Vol
  • thin/flat animals eg tapeworm: body surface large S.A: Vol
  • sluggish animal eg jellyfish: body surface, low metabolic rate -> low req. for oxygen uptake, no need for specialised respiratory surfaces
  • plants - spongy mesophyll cells
  • fish: gill lamellae
  • tinsects: tracheoles
  • mammals and birds: lung alveoli
• Structure of the airways (trachea, bronchi and bronchioles):

  the cells lining the airways are ciliated epithelia which have goblet cells interspersed between them. There is cartilage, elastin and smooth muscle surrounding the epithelia. Macrophages are also present which ingest any bacteria which have entered airways during breathing.

  • goblet cells (lining airways) secrete mucus. the mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the lungs
• Structure of airwars (p2)

  • cilia (on surface of cells lining airways) beat the musus. This moves the mucus (plus trapped microorganisms and dust) particles away from the alveoli towards the mouth; where its swallowed. This helps prevent lung infections.
  • elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help process of breathing out. on breathing in, lungs inflate and the elastic fibres are stretched. then the fibres constrict to help push air out when exhaling
• structure of airways (p3):

  • smooth muscle in the walls of the trachea, Bronchi and bronchioles allows their diameter to be controlled. During exercise the smooth muscle relaxes, making tubes wider. there's less resistance to airflow and air can move in and out of lungs more easily
  • rings of cartilage support walls of trachea and bronchi provide support. strong but flexible - stops trachea and bronchi constricting when you breathe in and pressure increases
• properties of alveoli as a gas exchange surface:

  1. large S.A: numerous alveolar sacs contain many alveoli, alveoli can expand easily during inhalation, allowing more air in, extensive capillary network associated with alveoli
  2. permeable: non-polar O2 and CO2 diffuse easily across phospholipid bilay, H gases dissolve in inner hydrophpbic region of bilayer
  3. steep conc grad maintained: O2 - blood removes this gad in RBC -> maintaining high conc. in blood for exchange, inhalation increases conc. of this gas in alveoli -> maintaining high conc. in alveoli for exchange, Alveoli -> blood
• properties of alveoli as a gas exchange surface:

  3. steep conc grad maintained (p2): CO2 - blood delivers gas in capillaries -> maintaining a high conc. in blood for exchange, exhalation decreases conc. of this gas in alveoli -> maintaining a low conc. in alveoli for exchange, blood -> alveoli

  4. short diffusion distance: squamous epithelial cells of alveolar wall are flat and thin, diffusion distance is minimised, O2 crosses 5 membranes, alveolar wall only 1 cell thick, endothelial cells of capillaries are flat + thin, capillary wall = 1 cell thick
• properties of alveoli as a gas exchange surface:

  5. moist: water lines airsacs -> gases can dissolve and diffuse across membrane, water contains surfactant (detergent), reduces surface tension of moist surface of alveoli so alveoli dont collapse