The study of how organisms function is called

Publisher Summary

This chapter presents the physiology of guinea pigs. It provides a comprehensive review of three of the more intensively reported areas of guinea pig physiology—hematological, cardiovascular, and reproductive. Studies of normal parameters and facets of function in the guinea pig are largely piecemeal. There are relatively few reports which have as their principal goal the elucidation of physiological norms for guinea pig. Most available normative data are ancillary to disease-oriented studies. The chapter discusses the potentially useful information from a comparative view, especially relative to guinea pig as a model for human disease. Guinea pig has been used extensively in hematological studies; consequently, there is considerable data on cellular elements, physiological properties, and biochemical characteristics of circulating blood and bone marrow. The guinea pig is particularly well suited for the studies in reproductive physiology because of easy handling, distinct signs of estrus, and behavior related fairly distinct to physical changes in the reproductive tract. Of all the small laboratory mammals, the guinea pig reproductive system most resembles man in that it has a long cycle, ovulates spontaneously, and has an actively secreting corpus luteum. Under laboratory conditions, domestic guinea pigs are polyestrous, nonseasonal breeders, although slight seasonal variations in reproductive performance have been reported. Guinea pig atria are frequently used for physiological and pharmacological studies of action potential, contraction strength, and their interrelationships.

What Is Human Physiology?

Physiology is the dynamic study of life. Physiology describes the “vital” functions of living organisms and their organs, cells, and molecules. For centuries, the discipline of physiology has been closely intertwined with medicine. Although physiology is not primarily concerned with structure—as is the case for anatomy, histology, and structural biology—structure and function are inextricably linked because the living structures perform the functions.

For some, physiology is the function of the whole person (e.g., exercise physiology). For many practicing clinicians, physiology may be the function of an individual organ system, such as the cardiovascular, respiratory, or gastrointestinal system. For still others, physiology may focus on the cellular principles that are common to the function of all organs and tissues. This last field has traditionally been called general physiology, a term that is now supplanted by cellular and molecular physiology. Although one can divide physiology according to varying degrees of reductionism, it is also possible to define a branch of physiology—for example, comparative physiology—that focuses on differences and similarities among different species. Indeed, comparative physiology may deal with all degrees of reductionism, from molecule to whole organism. In a similar way, human physiology deals with how the human body functions, which depends on how the individual organ systems function, which depends on how the component cells function, which in turn depends on the interactions among subcellular organelles and countless molecules. Thus, human physiology takes a global view of the human body; but in doing so, it requires an integrated understanding of events at the level of molecules, cells, and organs.

Physiology is the mother of several biological sciences, having given birth to the disciplines of biochemistry, biophysics, and neuroscience, as well as their corresponding scientific societies and journals. Thus, it should come as no surprise that the boundaries of physiology are not sharply delineated. Conversely, physiology has its unique attributes. For example, physiology has evolved over the centuries from a more qualitative to a more quantitative science. Indeed, many of the leading physiologists were—and still are—trained as chemists, physicists, mathematicians, or engineers.

Abstract

Physiology of the mammalian uterus is maintained by a variety of cytokines and growth factors. Many of these factors are expressed in response to ovarian steroid hormones in uterine epithelial and stromal cells, and act in a paracrine fashion to maintain homeostasis of this tissue during the reproductive cycle. These factors are also responsible for preparing the uterine environment for successful establishment of pregnancy. Disruption of the uterine stromal–epithelial crosstalk involving cytokines and growth factors often results in altered uterine physiology, leading to pathological conditions or unsuccessful pregnancy outcomes. An in depth understanding of the role of these myriad cytokines and growth factors has helped to advance the understanding of mechanisms underlying uterine physiology and reproductive medicine.

LEVELS OF ORGANIZATION

Medical physiology applies basic principles from chemistry, physics, and biology to the study of human life. Atoms are safely in the realm of chemistry. Physiologic study begins with molecules and continues through the interaction of the organism with its environment (Fig. 1-1).

Physiology is the study of normal body function. Physiology extends to the molecular level, the study of the regulation of the synthesis of biomolecules, and to the subcellular level, details of the provision of nutrients to support mitochondrial metabolism. Physiology includes cellular function, the study of the role of membrane transport, and describes organ function, including the mechanics of pressure generation by the heart. Integrative physiology is the study of the function of the organism, including the coordinated response to digestion and absorption of the nutrients in a meal.

The components of physiology are best approached as organ systems. This approach allows all aspects of one system, e.g., the circulatory system, to be discussed, emphasizing their commonalities and coordinated function.

Physiology-Based Pharmacokinetic Modeling

Physiology-based pharmacokinetic modeling (PBPK) relies on blood flow rates and binding characteristics of drugs to various tissues and circulating proteins to describe the distribution of drugs between the central compartment and specific organs and tissues [14]. While intuitive, data that define the binding characteristics of drugs are often limited to plasma or serum binding data – for example, data on drug binding to endothelium compared to muscle tissue is often unknown [19]. Similarly, blood flow rates and the relationships between body size and health status on these blood flow rates must be known [20]. As expected, much of this information is very difficult to obtain empirically in humans compared to animals. As a result, PBPK approaches have been used extensively in preclinical development and are useful to explain differences in drug distribution between species [21]. The distributions of a few drugs, such as ciprofloxacin, digoxin, lidocaine and paclitaxel, have been explained in humans using PBPK models [22–24]. In this setting, PBPK models have been constructed to include key organs such as the heart, lung, liver, kidneys, muscle and adipose tissue. The remaining organs/tissues are lumped into two compartments, namely rapidly equilibrating tissue and slow equilibrating tissue. This approach leads to the construct of a six to seven “compartment”-type model with differential equations to explain the concentration–time profiles within these compartments [14]. A key criticism of this approach includes the collection of fewer data points than the number of parameters that are estimated, which reduces the reliability of the overall model. Hence, PBPK models represent an important step toward characterization of tissue-level PK, which may improve our understanding of individualized pharmacologic response [21]. However, this tool still requires refinement and is not an approach that is routinely utilized in population PK analysis for drug development [21].

Physiology and ecology are defined and a bridge is cast between the two disciplines. Physiology requires consideration of the various parts of plant organisms and their functions which are grouped into biochemical functions of dissimilation, assimilation, synthesis of macromolecules and specific natural products, and developmental functions of growth, differentiation, and orientation in space. Functions are organized into complex signaling and regulation networks. Ecology requires consideration of all conditions of the existence of organisms. The important external control parameters are grouped into abiotic and biotic environmental factors. Factors are interacting in functional networks of physiological ecology. The physiology–ecology relations are illustrated for the case of photosynthesis. Structures and functions involved in photosynthesis span about 15–16 and about 32 orders of magnitude in space and in time, respectively. The major environmental control parameters determining the physiological ecology of photosynthesis are hydraulic limitations and high irradiance which acting together may cause overenergization of the photosynthetic apparatus, formation of reactive oxygen species, and oxidative stress. Different photosynthetic physiotypes, C3 and C4 photosynthesis and Crassulacean acid metabolism are equipped in different ways to deal with such stress. Miniaturized equipment for measuring photosynthesis allows advancing physiological ecology of photosynthesis from autecology to synecology.

Parturition

The physiology of parturition is a complex process in all mammals. Successful birth ultimately depends on a precise synchronization with the appropriate maternal and fetal physiology and behaviour. Parturition is fundamental to mammalian reproduction. There are many common mechanisms but the physiology of parturition in mammals is highly diverse and almost species specific. In all species examined to date prostaglandins and oxytocin/mesotocin are critically important as regulators of uterine contractions among other roles. A broad range of other hormones are also involved, but the details of these endocrine interactions vary widely between species.

Immunity

Physiology: FSH in its general regulation of proteins plays a role in the formation of immunoglobulins, compliment, and other protein products of the immune system. It also regulates specific elements of immunity such as monocytes.28

Pathophysiology: A chronic oversolicitation of FSH can participate in hyper- and autoimmune states in two ways. The first is oversolicitation of proteins. The second is TSH relaunching. TSH plays a role in the solicitation of the exocrine pancreas, increasing the uptake of exogenous proteins. It stimulates lymphocytes and stimulates the thyroid—all conditions favorable for dysregulation of immunity.

Abstract

Exercise physiology is the science of human performance under physical stress and the relationships between physical activity and the structure and function of the human body. From an evolutionary point of view, exercise physiology helps us to better understand human adaptational capabilities, and it provides valuable insights into today’s problems regarding the so-called “lifestyle diseases.” To this end, it demonstrates the complex interactions between metabolism, thermoregulation, and the cardiovascular, respiratory, and muscular systems. Adaptation processes in human endurance and strength through exercise training—or the lack thereof—can be quantified via different means of ergometry, allowing for comparison of athletic performance using standardized parameters such as maximum oxygen consumption. Applied exercise physiology also helps us to better understand the limits of human performance, especially when that performance takes place under challenging environmental conditions.