structure of gills

• Fish gills


  • Water enters through mouth and passes out through gills
  • Each gill is made of lots of thin plates called gill filaments or primary lamellae
  • Gill filaments give a big surface area for exchange of gases (and so increase the rate of diffusion)
  • Gill filaments are covered in lots of tiny structures called gill plates or secondary lamellae
  • Gill plates increase the surface area even more
  • Each gill is supported by a gill arch
  • Gill plates have lots of blood capillaries and have a thin surface layer of cells to speed up diffusion between the water and the blood
• counter-current system

  • In the gills of a fish, blood flows through the gill plates in one direction and water flows over in the opposite direction.
  • The counter-current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen
  • Means that a steep concentration gradient is maintained between the water and the blood - so as much oxygen as possible diffuses from the water into the blood.
• counter-current system

  A) blood leaves gill plate with high oxygen concentration

  B) blood enters gill plate with low oxygen concentration

  C) water flows towards gill plate with high oxygen conc

  D) water flowing away from gill plate with low oxygen conc

  E) blood flow

  F) water flow

  
• structure of gills

  A) artery (deoxygenated blood to gill)

  B) gill arch

  C) vessels (oxygenated blood from the gill)

  D) gill plate/secondary lamella

  E) gill filaments/ primary lamella