Gaseous Exchange in Bony Fish + Countercurrent Flow

simple gills ex

• papulae of echinoderms

complex gills

• highly convoluted gills of fish

external gills

• not enclosed within the body

• epithelium is damaged

• organism must constantly be moving to ensure a continuous flow of fresh water

• resistance to movement

internal gills of mollusks - explain how they work

• mantle cavity contains gills and opens to outside

• muscular contractions pulls water inside over the inhalant siphon

• o2 diffuses into blood

• water is pushed out by exhalent siphon

Internal gills of crustaceans in branchial chambers - explain how it works

• branchial chamber opens beneath a limb

• the constant movement of a limb pulls water into the branchial chamber

• water passes over gills and o2 diffuses

• water then exists chamber

where are gills of bony fish located

• between buccal and opercular cavity

how do the buccal and opercular cavity act as pumps

• oral valve in mouth is opened, jaw is depressed, pulls water into buccal cavity

• opercular cavity expands once oral valve closes

• operculum is opened drawing water into gills to outside

bony vs cartilagenous fish

• bony fish have an operculum while cartilaginous fish dont

• cartilaginous fish have their gills exposed

functions of operculum

• protects gills

• controls movement of water in and out of the opercula

ram ventilation

• fish have immobile opercula

• swim with mouth partially open forcing water over their gills

  • eg tuna

remoras

• use ram ventilation when shark is swimming

• when shark stops swimming uses its opercula

inspiration of water

• buccal cavity is open, pressure decreases so water moves inside

• pressure of water pushes on posterior operculum preventing water from entering

• muscle in the operculum contract - enlarging opercular cavity, decreasing pressure hence water moves into opercular cavity

• gas exchange takes places as water is pushed through the opercular cavity

expiration of water

• mouth and entrance to esophagus close, buccal cavity is raised moving water into the opercular cavity

• gill filaments overlap at their tips slowing water down, allowing for more gaseous exchange

• pressure forces posterior end of operculum to open and water exits

structure of gills in bony fish - how many pairs of gills are present

4-5 covered by an operculum

gill arch

between mouth cavity and opercular flaps

contains two rows of gill filaments - primary lamellae

and each primary lamellae has a secondary lamella which is a thin membranous sheet

(capillaries are present in the lamellae)

water flows past lamellae in one direction only

adaptations of gills

• countercurrent flow to maintain a constant gradient

• gill arches are lined with gill filaments which increase SA

• dense network of blood capillaries

• between blood capillaries and water it is only 2 cells thick

  • lamellae and capillaries are lined with squamous epithelia which is thin and flat

countercurrent flow vs concurrent flow

• countercurrent flow allows o2 saturation to reach 85% while concurrent flow only 50% - inefficient

• at first concurrent flow has a higher gradient but then eventually reaches equilibrium

where is concurrent flow present + define it

• when blood in the gill plates flows in the same direction as the water

  • cartilaginous fish

Countercurrent flow + define

• when blood in the gill plates moves parallel to the flow of water

• Maximizes oxygenation as blood is constantly meeting water of a higher o2 content so maintain a diffusion gradient

• by Fick’s law it increases change P (concgradient)

• while a smaller gradient then concurrent flow it is more efficient

• hence, fish gills are the most efficient respiratory organ