Topic 17: INTRODUCTION TO ANIMAL PHYSIOLOGY (lecture 26)
OBJECTIVES:
1. Know the basic constraints on passive diffusion into (and inside of) organisms as
modeled by the passive diffusion equation.
2. Understand the basic physical interactions between an organism and its
environment.
Physiology- is the study of the physico-chemical basis of function; that is, physical and
chemical principles, in conjunction with anatomical information, are used to examine
functional processes at the cell, tissue, organ and systemic (multiple organ systems)
levels. It is one of the oldest of all disciplines of biology.
Hierarchy of biological structure:
1. cells- individual independent units usually specialized for a particular function (ca.,
nerve cells, muscle fibers [cells], red blood cells etc.).
2. tissue- an aggregation of similar cells playing a common functional role (epithelial
tissue [protection, transport]; connective tissue [support, protection])
3. organs- a collection tissues which together perform a very specialized function (ca.,
stomach, liver, heart etc.)
4. organ systems- assembly of organs which together are involved in a particular
function
(table 40.1 is overview of the various organ systems; in this last unit we will explore
the digestive, circulatory, respiratory, immune, excretory, endocrine & nervous and
muscular systems)
Interactions between processes going on internally and the environment
Fig. 40.10- animals are heterotrophs; they obtain carbon from other organisms. The
process by which carbon compounds are catabolized is known as bioenergetics
1.
2.
3.
4.
5.
6.
food intake (from the outside)
food processing and absorption
cellular catabolism yielding ATP and waste heat
waste heat is generally dissipated to the outside
waste carbon compounds are eliminated
the above processes must involve influx of oxygen and efflux of CO2; water is also
exchanged between the inside and the outside of the organism
bottom line: food, oxygen and generally water must be transported in and wastes,
sometimes water and CO2 must be transported out.
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The design, body plan and size of animal influence how materials can be transported in
and out of organisms.
PASSIVE Diffusion- recall in our discussion of membrane transport we said that
diffusion in the passive movement of materials from areas of high concentration to
areas of low concentration; the principles of diffusion can also be applied to diffusion
into and diffusion inside of an organism.
We can make the diffusion equation more accurate by adding another to term to it,
namely the distance through which the material is diffusing (d):
J = (P x A x C)/d
Where J= rate of diffusion, A = area over which the material is diffusing, C=
concentration gradient, d= diffusion distance. If we change P to D (the diffusion
coefficient; defines the intrinsic diffusivity of a substance in a material), the equation
becomes
J = (D x A x C)/d; what is important here is that J is directly proportional to D and
indirectly proportional to d. D values for many substances in organisms are low.
Furthermore, the larger the animal the slower the rate of diffusion from the outside to
the interior due to the fact that the d value is much larger. There are important practical
implicationsFig. 40.7- small organisms (unicellular) or thin organisms (Hydra) can rely exclusively
on the passive diffusion of substances in and out.
However, larger organisms cannot; they rely on convection (convection- the bulk
movement of the medium (air or fluid) and all the materials dissolved or suspended in
it).
Fig. 40.8- the constraints of passive diffusion in relation to structural complexity, size
and activity have led to the evolution of a variety of bulk transport systems in animals.
1. ingestion of food involves bulk movement of suspended or dissolved materials
throughout GI tract; absorbed nutrients are transferred to blood where there are
moved by convection throughout
2. Oxygen and carbon dioxide movement in and out of respiratory system primarily by
convection in large active organisms and gases are transported by convection in
blood
3. Certain waste materials are transported out of the blood and into the urine where
they leave the body by bulk transport
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