1 endocrine system 2 nervous system these systems

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1. endocrine system 2. nervous system these systems allow tissues, organs, and organ systems to act in concert with one another Endocrine System the signalling molecules of the endocrine system are hormones hormones can exert their effects at a great distance from where they are produce d for a cell to be affected it must have one or more receptors for that specific hormone compared to the nervous system, hormones are rather slow acting... dispersal can take several seconds , but the signal tends to be long- lasting since hormones may persist in the bloodstream for a period of time (minutes, hours) Nervous System information is transmitted along specific pathways to exact locations... the actual signal is typically a nerve impulse... a change in membrane voltage propagated along the length of an axon communication between the cells at apposing cell membranes occurs at a specialized region called a synapse the cell-to-cell transfer of the electrical signals is called synaptic transmission and communication at a synapse may be electrical , involving ion flow between the cells or chemical , involving the diffusion of neurotransmitter molecules the speed of information flow is extremely fast, typically milliseconds , and the duration of the effect may also be extremely short fig. 40.6a (above) and 40.6b (below) Signalling by the endocrine system (above) and
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Animal Form and Function 15 REGULATING THE INTERNAL ENVIRONMENT: FEEDBACK LOOPS AND HOMEOSTASIS animals manage their internal environment by either being regulators or conformers regulators use internal control mechanisms to alter their internal environment when faced with a change in the external environment e.g. the river otter in fig. 40.7 conformers have an internal environment that is allowed to match their external environment e.g. the largemouth bass in fig. 40.7 HOMEOSTASIS Claude Bernard (Fr. 19 th century physiologist) noted that many animals maintain a relatively constant internal environment he postulated that this relatively constant milieu interieur was a prerequisite for our continued good health “homeostasis” was actually coined by Walter Cannon, a 20 th century American physiologist homeostasis is the maintenance of an organism’s “steady state” when faced with situations that would change any one of many vital parameters but here “steady state” does NOT mean “unchanging”... homeostasis maintains the body in a dynamic equilibrium homeostatic control systems maintain an animal’s internal conditions within the normal range... e.g. blood pH and volume, arterial pressure, blood [glucose], body temperature, etc. e.g. blood ~pH 7.4 ± 0.1 unit e.g. normal human body temp. is ~37 ° C and ranges in healthy people from ~36 – 38 ° C homeostatic control systems have several components... (see fig. 40.8 for a nonliving example) a sensor , often a receptor, that monitors the condition of a variable an integrator
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