294
G. SHELTON
to be met by the ventilatory system in its widest scnse. Nor is this chapter
concerned with details of the gas exchange process since this, too, is
discussed elsewhere (see chapter by Randall, “Gas Exchange in Fish,”
this volume), The broader problem to be discussed here is essentially
that of the regulation of ventilation and perfrision so that the gas exchanger is able to function and, as far as possible, meet the nceds of
the cells. Previous articles in which these aspects of fish rc>spiration have
been reviewed are those of Black ( 1951), Fry ( 1957), Hughes and
Shelton ( 1962), and Hughes ( 1964).
If a multistage system such as that involved in the transfer of
respiratory gases between environment and cell enzymes is to operate
satisfactorily, then control becomes a matter of some complexity. Prosser
(1955) has pointed out that an organism can survive in an altered environment in different ways. At one extreme it may change its internal
state with the environment (physiological adjustment), or alternatively
it may regulate the internal state at a constant level over wide environmental fluctuations (physiological regulation). The control systems responsible for physiological regulation seldom result in complete homeostasis so that adjustment and regulation invariably occur together,
particularly at the extremes of the regulated range. This is true of the
fish respiratory system, and although environmental changes result in
adaptive regulation of an immediate or longer term type (see Hughes,
1964) these are frequently accompanied by adjustments in metabolism.
11. THE RESPIRATORY PUMP
In the gill breathing vertebrates there is a surprising diversity of
mechanisms whose function is one of maintaining a flow of water over
the respiratory surface. Water is usually taken in through the mouth
and, in those fish possessing it, the spiracle, is passed ovrr the gills, and
leaves through separate branchial or common opercular openings on
either side of the body. This unidirectional flow pattern is thought to
be the most effective way of bringing the environment into intimate
contact with the gill epithelium since anatomical dead space is not
necessarily a characteristic of such a system, although it may in fact
exist ( Saunders, 1961; Hughes, 1965; chapter by Randall, “Gas Exehange
in Fish,” this volume ) . It has also been clainwd that unidirectional flow
reduces the work of ventilation as compared to a tidal flow system
(Hughes and Shelton, 1962). This generalization may be open to ques-
G. SHELTON
to be met by the ventilatory system in its widest scnse. Nor is this chapter
concerned with details of the gas exchange process since this, too, is
discussed elsewhere (see chapter by Randall, “Gas Exchange in Fish,”
this volume), The broader problem to be discussed here is essentially
that of the regulation of ventilation and perfrision so that the gas exchanger is able to function and, as far as possible, meet the nceds of
the cells. Previous articles in which these aspects of fish rc>spiration have
been reviewed are those of Black ( 1951), Fry ( 1957), Hughes and
Shelton ( 1962), and Hughes ( 1964).
If a multistage system such as that involved in the transfer of
respiratory gases between environment and cell enzymes is to operate
satisfactorily, then control becomes a matter of some complexity. Prosser
(1955) has pointed out that an organism can survive in an altered environment in different ways. At one extreme it may change its internal
state with the environment (physiological adjustment), or alternatively
it may regulate the internal state at a constant level over wide environmental fluctuations (physiological regulation). The control systems responsible for physiological regulation seldom result in complete homeostasis so that adjustment and regulation invariably occur together,
particularly at the extremes of the regulated range. This is true of the
fish respiratory system, and although environmental changes result in
adaptive regulation of an immediate or longer term type (see Hughes,
1964) these are frequently accompanied by adjustments in metabolism.
11. THE RESPIRATORY PUMP
In the gill breathing vertebrates there is a surprising diversity of
mechanisms whose function is one of maintaining a flow of water over
the respiratory surface. Water is usually taken in through the mouth
and, in those fish possessing it, the spiracle, is passed ovrr the gills, and
leaves through separate branchial or common opercular openings on
either side of the body. This unidirectional flow pattern is thought to
be the most effective way of bringing the environment into intimate
contact with the gill epithelium since anatomical dead space is not
necessarily a characteristic of such a system, although it may in fact
exist ( Saunders, 1961; Hughes, 1965; chapter by Randall, “Gas Exehange
in Fish,” this volume ) . It has also been clainwd that unidirectional flow
reduces the work of ventilation as compared to a tidal flow system
(Hughes and Shelton, 1962). This generalization may be open to ques-