Chapter 1 Introduction to Physiological Principles
I.
Overview
Definition: Animal physiology is the study of how
living animals work (function).
―function
―integrative science
―(a few) laws and concepts
1.
Animal physiologists study the
structure and function of the various parts of an animal, and how these parts
work together to allow animals to perform their normal behaviors and to respond
to their environments.
2.
Almost a million different
species of animals have been described by scientists, and it is estimated that 7
million may live on Earth.
3.
Physiology is a central
discipline in biology linking the basic molecular and cellular mechanisms to
characteristics of whole organisms.
4.
Phenotype is the physiological
properties of an animal, while genotype is the specific genetic makeup of an
animal. Phenotypes of animals are determined in large part by genotypes. Thus,
both the genotype of an animal and its environment interact through development
to produce the phenotype of the adult organism.
II.
Unifying Themes in Animal
Physiology
Despite of the great diversity of organisms on Earth, there
are 4 unifying themes that apply to all physiological processes.
1.
Integration
(1)
Levels of biological
organization show the organization of the living world by biologists: atoms
à
molecules (macromolecules)
à
cells
à
tissues
à organs
à
systems
à
organisms
à populations
à
communities
à
ecosystems
à biosphere.
(2)
Animal physiologists study
phenomena at multiple levels of biological organization.
(3)
Reductionism is a
philosophical approach that assumes complex processes can be understood in terms
of their components.
(4)
Animal physiologists ask a
wide range of questions, including basic and applied biology.
(5)
Animal physiologists play an
important role in understanding human health and disease.
(6)
The August Krogh principle:
For every biological problem, there is an organism on which it can be most
conveniently studied. The design of experiments is based on the unusual
characteristics of an animal. The August Krogh principle is to choose the
optimally suited animal for carrying out those experiments needed to answer
particular questions.
(7)
Model organism is a species
that is widely used in biological research, because it has properties that make
it particularly suitable for research purposes.
2.
Laws of physics and chemistry
(1)
Animals are constructed from
natural materials and obey physical and chemical laws. Physics and chemistry are
the basis of animal physiology.
(2)
The laws of diffusion help to
understand the evolution of animal structure (form) and function. Developed by
Adolf Fick in 1855, Fick's first law of diffusion states that substances diffuse
from areas of high concentration to areas of low concentration. Fick's second
law considers that the amount of a substance that diffuses across a surface,
such as a cell membrane, is proportional to the area of that surface, and is
inversely proportional to the distance across which the substance must diffuse.
(3)
Developed by Robert Brown in
1827, Brownian motion considering the random movement of particles in a
solution: the time needed for a particle to diffuse across a given distance is
proportional to the square of the distance (t
α x2).
(4)
Developed by Galileo Galilei
in 1638, the bones of larger animals are proportionately thicker than the bones
of smaller animals. Isometry (isometric scaling) states morphology or physiology
change is in direct proportional to body mass. Allometry (allometric scaling)
states the differential growth rates of the parts of a
living organism's body.
(5)
Developed by Max Rubner in
1873, the basal metabolic rate (BMR) of dogs of various sizes (body mass:
M) has a constant scaling coefficient (a)
of 0.67 (2/3), i.e., BMR = a x M, where a is 0.67.
(6)
Developed by Max Kleiber in
1932, the value of the scaling coefficient (a) was close to 0.75 (3/4) when he
assembled a much larger data set relating body size and basal metabolic rate in
a variety of species of birds and mammals. This implies that surface
area-to-volume ratios cannot explain metabolic scaling relationships.
(7)
Endotherms are animals that
maintain their bodies at a metabolically favorable temperature and generate heat
internally. Ectotherms are animals with body temperature determined primarily by
external factors.
3.
Structure (form), function,
and evolution
(1)
Structure and function are
highly connected. It is impossible to understand physiology (function) without an
understanding of anatomy (structure), and vice versa.
(2)
The relationship between
structure and function is strongly correlated that it is possible to make
inferences about function simply by looking at structure. Function is based on
structure.
(3)
Structure and function are the
products of evolution. Proximate cause is the immediate or direct cause of an
organismal structure, function, or behavior. Ultimate cause is the evolutionary
advantage of a particular organismal structure, function, or behavior.
(4)
Animals have many traits in
common. One of the best ways to understand how an animal works is to establish
in which ways the animal is similar to other organisms.
(5)
Adaptation is a change in the
genetic structure of a population or group as a result of natural selection
over evolutionary time.
(6)
Phenotypes among organisms may
be either homologous or analogous.
Homology is similarity due to inheritance of genes from
a shared ancestor, such as camels and llamas.
Analogy is similarity of
function that have different origins, for example, the wings of a fly, a moth,
and a bird. Divergent evolution is the accumulation of differences
between groups, leading to the formation of new species.
(7)
Homoplasy can evolve in a
variety of ways:
1)
Convergent evolution is the
independent evolution of similar traits in distantly related or unrelated taxa.
2)
Parallel evolution is the
evolution of a shared underlying trait in similar ways in two distinct but
related lineages.
4.
Regulation and homeostasis
(1)
Most organisms are faced with
environmental variation. Animals utilize a variety of mechanisms to compensate
for these environmental changes across different time scales and at different
levels of biological organization.
(2)
Animals can be physiological
conformers or regulators. Conformer is an animal that allows internal conditions
to change when faced with variation in external conditions, such as an
ectotherm. Regulator is an animal that maintains relatively constant internal
conditions regardless of the conditions in the external environment, such as an
endotherm.
(3)
Promoted by Walter Cannon in
1929, homeostasis is a state of internal constancy that is maintained as a
result of active regulatory processes in the face of environmental
perturbations. For example, your body temperature remains relatively constant
only because numerous physiological processes actively change, adjusting the
rates of heat production and heat loss.
(4)
Allostasis is the process and
regulatory mechanisms of achieving homeostasis through change.
(6) Feedback loops control
physiological pathways. For example, a negative feedback maintains homeostasis,
while a positive feedback causes explosive responses.
(7)
Acclimatization is the process
of change in response to natural environmental variation.
―reversible
e.g., mountain climbing
Acclimation is the persisting change in a specific function due to prolonged exposure to experimental conditions.
―experimental induction
―reversible
e.g., place an
experimental animal in mountain
(8)
Phenotypic plasticity
represents that animals can reversibly or irreversibly alter their phenotype in
response to environmental conditions. Polyphenism is a particular phenotype that
exists in two or many forms of irreversible phenotypic plasticity, generally
involving alternative developmental pathways.