Interactions between processes going on internally and the environmentTopic 17: INTRODUCTION TO ANIMAL PHYSIOLOGY (lecture 26)OBJECTIVES:1. Know the basic constraints on passive diffusion into (and inside of) organisms asmodeled by the passive diffusion equation.2. Understand the basic physical interactions between an organism and itsenvironment.Physiology- is the study of the physico-chemical basis of function; that is, physical andchemical principles, in conjunction with anatomical information, are used to examinefunctional 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 (epithelialtissue [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 particularfunction(table 40.1 is overview of the various organ systems; in this last unit we will explorethe digestive, circulatory, respiratory, immune, excretory, endocrine & nervous andmuscular systems)Interactions between processes going on internally and the environmentFig. 40.10- animals are heterotrophs; they obtain carbon from other organisms. Theprocess by which carbon compounds are catabolized is known as bioenergetics 1. food intake (from the outside)2. food processing and absorption3. cellular catabolism yielding ATP and waste heat4. waste heat is generally dissipated to the outside5. waste carbon compounds are eliminated6. the above processes must involve influx of oxygen and efflux of CO2; water is alsoexchanged between the inside and the outside of the organismbottom line: food, oxygen and generally water must be transported in and wastes,sometimes water and CO2 must be transported out.1The design, body plan and size of animal influence how materials can be transported inand out of organisms.PASSIVE Diffusion- recall in our discussion of membrane transport we said thatdiffusion in the passive movement of materials from areas of high concentration toareas of low concentration; the principles of diffusion can also be applied to diffusioninto 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)/dWhere 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 diffusioncoefficient; defines the intrinsic diffusivity of a substance in a material), the equationbecomesJ = (D x A x C)/d; what is important here is that J is directly proportional to D andindirectly 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 tothe interior due to the fact that the d value is much larger. There are important practicalimplications-Fig. 40.7- small organisms (unicellular) or thin organisms (Hydra) can rely exclusivelyon the passive diffusion of substances in and out.However, larger organisms cannot; they rely on convection (convection- the bulkmovement of the medium (air or fluid) and all the materials dissolved or suspended init).Fig. 40.8- the constraints of passive diffusion in relation to structural complexity, sizeand 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 materialsthroughout GI tract; absorbed nutrients are transferred to blood where there aremoved by convection throughout2. Oxygen and carbon dioxide movement in and out of respiratory system primarily byconvection in large active organisms and gases are transported by convection inblood3. Certain waste materials are transported out of the blood and into the urine wherethey leave the body by bulk
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