Chp 1 Function on the Ecological Stage

Animal Physiology: Study of how animals function Importance: For basic understanding of physiology since human are part of the animal kingdom Important practical applications for health and disease, management Mechanism and Origin: Physiology’s two central questions What is the mechanism by which a function is accomplished? How did the mechanism originate?

The importance of physiology The study of mechanism: How do modern day animals carry out their functions? study or organ, cell functions and metabolism The study of origin: Why do modern-day animals possess the mechanisms they do?  they inherited it from ancestors + it was beneficial adaptation through selection Mechanism and adaptative significance are distinct concepts that do not imply each other: Adaptation can be achieved through different mechanisms

This book’s approach to physiology Physiological mechanisms can be explain from a combination of evolutionary origin, environmental adaptations Environmental physiology: Mechanistic physiology: study of mechanism Evolutionary physiology: study of evolutionary origins Comparative physiology: compare the physiology of various groups Environmental physiology: study of the physiological responses to changes in environment All of these approaches are interrelated

Animals Molecules forming an animal are constantly changing The structure of an animal (organ system) persists through time The cells are exposed to the internal environment The internal environment might be permitted to change with the external environment  conformity The internal environment might be kept constant despite varying external environments  regulation

Homeostasis: internal constancy critical to maintain proper function Claude Bernard: recognized the constancy of the internal environment “Constancy of the internal environment is the condition for free life” Walter Cannon (1871-1945) – introduced the term “homeostasis = coordinated physiological processes which maintain most of the constant states in the organism”.

Homeostasis is critical to mammals, but it is not important for survival in some other groups Regulation and conformity have their own advantages/disadvantages: Regulation: Costs energy but permits cells to function in a constant internal environment despite changing external conditions Conformity: Cells are subjected to changes when external environment changes. However, if they survive it, the energy cost is minimal.

Time in the lives of animals 1- physiological responses to change in external environment 2- internally programmed changes of physiology 3- evolutionary responses: at the level of populations (1) Responses to changes: Acute responses: responses within minutes Chronic responses: long term changes to the physiology Acclimation: physiological responses to small changes in the environment Acclimatization: responses to a larger change in the environment (ex: winter and summer)

2- internally programmed changes of physiology Phenotypic plasticity: phenotypic changes that an individual (single genotype) can undergo with changing environment Internally programmed changes: genetically programmed: can be due to development or to biological clocks - development: Hb expression - biological clocks: - daily rhythm - seasonal rhythm ..

The importance of body size Size determines many functions (scaling): - gestational time - rate of energy use - age of sexual maturity

Environments All the chemical, physical, and biotic components of an organism’s surroundings. Earth’s major physical and chemical environments: Temperature: -70oC in Antarctica to 50oC in some deserts  most tissues are killed at temp>45oC Oxygen: 21% O2 in air, less in soil, high altitude, low solubility in water Water: universal solvent. Is the place of origin of life. Blood of marine invertebrates has a similar composition to sea-water (SW). Osmosis effect if water salinity changes Presence of microenvironments and microclimates Animals modify their environments

Evolutionary processes Evolutionary physiology: study of the origin and maintenance of physiological traits Some processes are adaptive (due to natural selection), others are not (= founder effect -due to genetic drift) Pleiotropy: when a trait is common in a population because it is closely correlated with another trait favored by selection

The study of adaptations Comparative method: today animals are the products of yesterday life. We inherited the adaptations Studies of laboratory populations over many generations Single-generation studies of individual variation Creation of variation for study Study of the genetic structure of natural populations Phylogenetic reconstruction Evolutionary potential depends on the available genetic variation