8.2: Main Functions for Homeostasis
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- 84037
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The muscle system performs three functions that help maintain homeostasis: movement, support, and heat production.
Movement
The movement produced by muscles allows a person to carry out the last step in negative feedback systems: making an adjustment to a change in conditions. Movement is used to get away from impending danger (e.g., fire, falling objects), escape from unfavorable conditions (e.g., intense sunlight), and eliminate wastes and unwanted materials (e.g., carbon dioxide, splinters).
Movement is also important in taking positive actions. It allows a person to move toward, obtain, and use items and conditions that promote the welfare of the body and quality of life. These needs include basic physical needs (e.g., food, water, shelter) and other needs (e.g., social interactions, recreational activities). Movement allows people to rearrange their environment and construct and repair useful and decorative artifacts to suit human requirements and desires.
Support
The muscle system provides support when muscle contractions prevent the movement of a part of the body. Support maintains proper positional conditions of parts of the body so that they function well. For example, muscle contractions can maintain an upright posture. This activity includes holding the bones in place and preventing the protrusion of the organs in the lower trunk. With proper posture, circulation is improved because blood vessels are open rather than pinched shut, and respiration is assisted because the lungs have room to inflate easily. Holding the head up positions the eyes for viewing the surrounding environment.
Heat Production
Heat production is essential for maintaining a proper and fairly stable body temperature because most people live in environments that are cooler than normal body temperature. Therefore, the body is always losing heat to the environment, just as any warm object or substance, such as warm food, loses heat and becomes cool. However, if the body is allowed to become cool, this will make the rate of its chemical reactions too slow to sustain life functions (e.g., heartbeat, respiration, brain activities) and perform effective negative feedback responses. Therefore, to prevent cooling of the body, the amount of heat loss must be balanced by an equal amount of heat production.
Heat is produced by many chemical reactions in the body, but the muscle system is the main heat producer. One reason for this is that the muscle system is one of the largest systems, usually accounting for one-third or more of body mass. Second, the muscle system is one of the most active systems in the body. When a person is awake but resting, this activity involves steady muscle contractions (muscle tone) that help maintain posture. This system is especially active and produces much more heat when a person is forcefully contracting muscles during vigorous exercise. Still, the muscle system performs many chemical reactions even when the muscles are relaxed; this is why a sleeping person remains warm.