Lecture 17 - Respiration I
1. Cellular Respiration
a. Anaerobic
b. Aerobic
2. External Respiration
a. The movement of gases
(oxygen and carbon dioxide)
between the external
environment and the cells of
the organism
❖External respiration
➢Major function of external respiration is gas exchange
■ Uptake of molecular O2 from environment
■ Discharge of CO2 into environment
➢Another major function is acid base balance
❖Animals require continuous supply of O2
❖Environmental reservoirs of oxygen
➢Atmosphere is major reservoir (21% of O2)
➢Bodies of water also have dissolved O2
■ O2 not very soluble in water
❖Respiratory surfaces
➢Cutaneous respiration: small or thin animals can use their body
surface for gas exchange
■ Ex. caenorhabditis elegans
● No respiratory or circulatory system
● O2 diffuses slowly through water (about 3 million
times slower than through air)
● All cells must be close to the respiratory surface
(<1mm)
➢In large animals, the body surface does not have enough area to
support all of the cells
■ Specialized respiratory surfaces have evolved
■ In many animals a closed circulatory system with one or
more hearts serves as a medium between cells and a
specialized respiratory system.
, ■ However not all animals with specialized respiratory surfaces
transport O2 and CO2 via a closed circulatory system
❖Aquatic animals
➢Advantage of aqueous respiratory medium
■ Respiratory surfaces stay moist
■ Water not lost by evaporation
➢Disadvantage of aqueous respiratory medium
■ O2 concentration relatively low
■ Therefore, exchange must be very efficient
❖Aquatic animals - gills
➢Gills originate as evaginations (out
foldings) of the body surface
■ In general, gills are organs that
absorb dissolved oxygen from an
aqueous respiratory medium and
excrete CO2
■ Can be located all over the body
(ex. Sea star)
■ Can be restricted to a local body
region (ex. fish)
➢Gas exchange at gills is maximized by:
■ Large surface area
■ Countercurrent exchange
■ Ventilation: increase water flow over gills
❖Counter current exchange
❖Aquatic Animals - Ventilation
➢Ventilation - any method of increasing contact between the respiratory
medium and the respiratory surface
, ■ Usually requires expenditure of energy
➢Examples of ventilation
■ Ciliated surface
■ Paddle like appendages to push water over gills
■ Swimming: increased water flow over gills “ram ventilation”
❖Respiratory systems of echinoderms
➢Sea stars have external papulae that function as gills for gas exchange
➢Papulae are scattered over the body surface
➢Each papula projects outward through
a hole in the dermal skeleton
➢Cilia on the inner and outer surfaces
beat in opposite directions, allowing
counter - current exchange of gases
➢Fluid in coelom (body cavity) transports
dissolved gases
➢Tube feet of sea stars are also
important sites of gas exchange
❖respiratory system of Teleost fish
➢Gills are anatomically localized
➢Large surface area for gas exchange
➢Ventilate by bulk flow of water over gills
➢Closed circulatory system
➢Counter current exchange
1. Cellular Respiration
a. Anaerobic
b. Aerobic
2. External Respiration
a. The movement of gases
(oxygen and carbon dioxide)
between the external
environment and the cells of
the organism
❖External respiration
➢Major function of external respiration is gas exchange
■ Uptake of molecular O2 from environment
■ Discharge of CO2 into environment
➢Another major function is acid base balance
❖Animals require continuous supply of O2
❖Environmental reservoirs of oxygen
➢Atmosphere is major reservoir (21% of O2)
➢Bodies of water also have dissolved O2
■ O2 not very soluble in water
❖Respiratory surfaces
➢Cutaneous respiration: small or thin animals can use their body
surface for gas exchange
■ Ex. caenorhabditis elegans
● No respiratory or circulatory system
● O2 diffuses slowly through water (about 3 million
times slower than through air)
● All cells must be close to the respiratory surface
(<1mm)
➢In large animals, the body surface does not have enough area to
support all of the cells
■ Specialized respiratory surfaces have evolved
■ In many animals a closed circulatory system with one or
more hearts serves as a medium between cells and a
specialized respiratory system.
, ■ However not all animals with specialized respiratory surfaces
transport O2 and CO2 via a closed circulatory system
❖Aquatic animals
➢Advantage of aqueous respiratory medium
■ Respiratory surfaces stay moist
■ Water not lost by evaporation
➢Disadvantage of aqueous respiratory medium
■ O2 concentration relatively low
■ Therefore, exchange must be very efficient
❖Aquatic animals - gills
➢Gills originate as evaginations (out
foldings) of the body surface
■ In general, gills are organs that
absorb dissolved oxygen from an
aqueous respiratory medium and
excrete CO2
■ Can be located all over the body
(ex. Sea star)
■ Can be restricted to a local body
region (ex. fish)
➢Gas exchange at gills is maximized by:
■ Large surface area
■ Countercurrent exchange
■ Ventilation: increase water flow over gills
❖Counter current exchange
❖Aquatic Animals - Ventilation
➢Ventilation - any method of increasing contact between the respiratory
medium and the respiratory surface
, ■ Usually requires expenditure of energy
➢Examples of ventilation
■ Ciliated surface
■ Paddle like appendages to push water over gills
■ Swimming: increased water flow over gills “ram ventilation”
❖Respiratory systems of echinoderms
➢Sea stars have external papulae that function as gills for gas exchange
➢Papulae are scattered over the body surface
➢Each papula projects outward through
a hole in the dermal skeleton
➢Cilia on the inner and outer surfaces
beat in opposite directions, allowing
counter - current exchange of gases
➢Fluid in coelom (body cavity) transports
dissolved gases
➢Tube feet of sea stars are also
important sites of gas exchange
❖respiratory system of Teleost fish
➢Gills are anatomically localized
➢Large surface area for gas exchange
➢Ventilate by bulk flow of water over gills
➢Closed circulatory system
➢Counter current exchange
