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BIO204 Physio Lecture note 2.docx

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Ingo Ensminger

BIO204 Nov.23/2011 Chapter 41: Animal form and function (pg.969-976) 41.4 Homeostasis  Homeostasis is the maintenance of relatively constant chemical and physical conditions in an animal's cells, tissues, and organs.  Constantcy of physiological states can be achieved by 2 processes: conformation or regulation.  Conformational homeostasis is homeostasis that occurs by conformation to the external environment. For example, the body temperature of Antarctic rock cod closely matches that of the surrounding seawater.  Regulatory homeostasis requires a physiological mechanism that adjusts the internal state to keep it near a specific value or within limits that can be tolerated, regardless of the external conditions.  Epitheliums interface between internal and external environments; plays a key role in achieving homeostasis. Epithelium responsible for creating an internal environment that is diff from external environment and for maintaining physical and chemical conditions inside an animal that are constant.  Epithelium plays a vital role in creating an internal environment that is dramatically different from the external environment and in maintaining physical and chemical conditions inside an animal that are relatively constant.  Its most basic function is to control the exchange of materials across surfaces.  When homeostasis occurs, conditions inside the body allow molecules, cells, tissues, organs and systems to fcn at an optimal level. Role of regulation and feedback  To achieve homeostasis, animals have regulatory systems that constantly monitor internal conditions such as temperature, blood pressure, blood pH, and blood glucose.  Each of these variables has a set point – a normal or target value.  Regulatory systems typically consist of three general components: a sensor, an integrator and an effector  A sensor is a structure that senses some aspect of the external or internal environment.  An integrator is a component of the nervous system that evaluates the incoming sensory information and "decides" if a response is necessary to achieve homeostasis.  An effector is any structure that helps to restore the desired internal condition.  Homeostatic systems are based on negative feedback in which effectors reduce or oppose the change in internal conditions. 41.5 How do animals regulate body temperature?  Heat flows downhill form regions of high temp to regions of low temp. Individual warmer than surroundings then lose heat. Cooler than environment then gain heat.  All animals exchange heat with their environment in four ways: conduction, convection, radiation, and evaporation.  Conduction is the direct transfer of heat between two physical bodies that are in contact with each other.  Rate at which conduction occurs depends on SA of transfer, steepness of temperature difference between 2 bodies and how well each body conducts heat.  Convection is a special case of conduction in which heat is exchanged between a solid and a liquid or gas rather than between two solids.  Radiation is the transfer of heat between two bodies that are not in direct physical contact.  Evaporation is the phase exchange that occurs when liquid water becomes a gas. Only leads to heat loss.  Heat exchanges critical in animal physio because ind can get too hot or cold and ie, overheating = enzymes and protein denature and cease fcing and may lead to excessive water loss and dehydration. Body temp and homeostasis  Many animals can control their body temperature through the process of thermoregulation (Figure 41.17). info about body temp constantly monitored by temperature receptors located throughout body.  In mammals, this process is regulated through negative feedback.  In response cool sensors and heat sensors alter the pattern of electrical signals that they send to adjacent neurons.  Neural signals from temperature receptors in the skin (the sensors) are interpreted by the hypothalamus (the integrator), which then causes a variety of responses, ranging from metabolic to behavioral (the effectors).  Electrical signals that originate with temperature receptors in skin, SC, and anterior hypothalamus are transmitted to an integrator located in the brain.  If mammal becomes cold, cells in the posterior hypothalamus regions of brain sends signal effectors that return body tempera
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