Chapter 40 (2)

Faced with environmental fluctuations, animals manage their internal environment by either __ or __.

An animal is said to be a __ for a particular environemtal varibale if it uses internal control mechanisms to regulate internal change in the face of external fluctuation.

An animal is said to be a __ for a particular environmental variable if it allows its internal condition to conform to external changes in the variable.

_ and __ represent extremes on a continuum. An aimal may regulate some internal conditions while allowing others to conform to the environment.

The steady body temperature of a river otter and the stable concentration of solutes in a freshwater bass are examples of __, which means "steady state", or internal balance. In achieving __, animals maintain a relatively constant internal environment even when the external environment changes significantly.
o Like many animals, humans exhibit __ for a range of physical and chemical properties, like body temp or pH.

How does an animal achieve homeostasis?

Fluctuations in the variable above or below the __ serve as the __. A receptor, or __, detects the stimulus and triggers a __, a physiological activity that helps return the variable to the __.

Homeostasis in animals relies largely on __, a response that reduces, or "damps" teh stimulus.
e.g sweating

Homeostasis is a __, the interplay between external factors that tend to change the internal environment and internal control mechanisms that oppose such changes. __ reduces but doesn't eliminate changes in the internal environment. Additional fluctuation occurs if a variable has a __- an upper and lower limit- rather than a single __. Regardless of whether there is a __ or a normal range, __ is enhanced by mechanisms that reduce fluctuations, such as insulation in the case of temp and physiological buffers in the case of pH.

Although __ also occur in animals, these circuits do not usually contribute to __. Unlike __, __ triggers mechanisms that amplify rather than diminish the stimulus.

The __ and normal ranges for __ can change under various circumstances. In fact, so-called __ in teh internal nvironment are essential to normal body functions. Some __ are associated with a particular stage in life, such as the radical shift in hormone balance that occurs during puberty. Other __ are __, such as the variation in hormone levels responsible for women's menstrual cycles. Over the short term, __ mechanisms maintain the __ in effect during a particular interval. Over the longer term, __ allows regulated change in teh set point and therefore in teh body's internal environment.

One way in which the normal range of homeostasis may change is through __, teh process by which an animal adjusts to changes in its external environment. __, a atemporary change during an animal's lifetime, should not be confused with __, a process of change in a population brought abou tby natural selection over many generations.