Principles of Human Physiology
Concepts in physiology
Physiologist use various concepts to describe the function of the human body. These concepts are:
Homeostasis and control systems |
Shows how physiological systems are always operating at a preset level of activity |
| Structure-Function relationships | Physiologists study the mechanism of the human body and need to know both the structure and the function of body parts: organ systems, tissues, cells, and molecules. In particular, physiologists study molecular interactions, mechanical properties of cells, tissues and organs and compartmentalization of larger systems into smaller specialized systems. |
| Communication | Physiological systems are composed of component systems/parts that communicate with each other using direct cell to cell contact (junctions, synapses) or diffusible signals (hormones, growth factors, neurotransmitters). |
| Movement across membranes | Signals and nutrients need to be moved in and out of the body, throughout the body, and in and out of cells. The latter requires the transport, diffusion and pumping of molecules across cell membranes. |
| Biological energy | To maintain homeostasis and the continuous metabolic and mechanical functioning of the body, cells spend energy, which they extract from caloric nutrients. Extracted energy and the molecular building blocks derived from nutrients are used for the synthesis of all molecular and cellular structures of the body. |
| Mass balance | Homeostasis means a steady state of a system. The main properties such as temperature, size, fluid content, energy expenditure do not change much and stay within a certain range. However, the body continuously removes old components and replaces them with new ones to minimize molecular and cellular damage. Thus a continuous supply and excretion of molecules is a hallmark of living organisms and homeostatic systems. Mass balance says that the what goes into a systems equals what is retained and excreted by the system. If not, the system growths or shrinks. |
| Mass flow | The movement of material within the body occurs at a certain rate and amount, i.e., there is a flow rate that is adjusted to the capacity of the cells to metabolize. |
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