Download PDF Color of Atlas Physiology 5th edition, completely revised and expanded by Agamemnon Despopoulos

Sinopsis

The existence of unicellular organisms is the epitome of life in its simplest form. Even simple protists must meet two basic but essentially conflicting demands in order to survive. A unicellular organism must, on the one hand, isolate itself from the seeming disorder of its inanimate surroundings, yet, as an “open system” (! p. 40), it is dependent on its environment for the exchange of heat, oxygen, nutrients, waste materials, and information.

“Isolation” is mainly ensured by the cell membrane, the hydrophobic properties of which prevent the potentially fatal mixing of hydrophilic components in watery solutions inside and outside the cell. Protein molecules within the cell membrane ensure the permeability of the membrane barrier. They may exist in the form of pores (channels) or as more complex transport proteins known as carriers (! p. 26 ff.). Both types are selective for certain substances, and their activity is usually regulated. The cell membrane is relativelywell

permeable to hydrophobic molecules such as gases. This is useful for the exchange of O2 and CO2 and for the uptake of lipophilic signal substances, yet exposes the cell to poisonous gases such as carbon monoxide (CO) and lipophilic noxae such as organic solvents. The cell membrane also contains other proteins—namely, receptors and enzymes. Receptors receive signals from the external environment and convey the information to the interior of the cell (signal transduction), and enzymes enable the cell to metabolize extracellular substrates.

Let us imagine the primordial sea as the external environment of the unicellular organism (!A). This milieu remains more or less constant, although the organism absorbs nutrients from it and excretes waste into it. In spite of its simple structure, the unicellular organism is capable of eliciting motor responses to signals from the environment. This is achieved by moving its pseudopodia or flagella, for example, in response to changes in

the food concentration.

Content

1. Fundamentals and Cell Physiology
2. Nerve and Muscle, PhysicalWork
3. Autonomic Nervous System (ANS)
4. Blood
5. Respiration
6. Acid–Base Homeostasis
7. Kidneys, Salt, and Water Balance 
8. Cardiovascular System 
9. Thermal Balance and Thermoregulation 
10. Nutrition and Digestion 
11. Hormones and Reproduction 
12. Central Nervous System and Senses

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