BIOL273 Chapter Notes - Chapter 1: Dependent And Independent Variables, Endocrine System, Biorhythm

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3 Feb 2013
Chapter 1
Homeostasis depends on mass balance (pg. 13)
2 options to maintain mass balance:
1. excretion
a. through urine, feces, lungs, or skin
e.g. CO2 lungs, drugs/artificial food additives-liver and kidneys
foreign substance in the body = xenobiotic
2. convert the substance to a different substance through metabolism
a. convert original nutrient to a diff. molecule through metabolic pathway aka
Excretion Clears Substances from the Body
Clearance: volume of blood cleared of substance x per unit of time
Hepatocytes: liver cells, metabolize diff types of molecules, esp. xenobiotics > resulting metabolites
may be secreted to intestine for excretion in the feces/into the blood for excretion by kidneys
Homeostasis does not mean equilibrium
Stability of the extracellular fluid compartment (ECF)
- Easy to monitor by taking a blood sample
- plasma: fluid compartment of blood
- dynamic steady state: materials constantly moving back and forth between the two
compartments (ECF and ICF) , no net movement of materials b/t the compartments
- steady state does not mean equilibrium(same composition in two compartments but diff.
concentrations of substances)
e.g. Na+ and Cl- more oncentrated in ECF, K+ more in ICF = ECF and ICF exist in a state of
Control Systems and Homeostasis
- regulated variables: key functions that has to be kept within acceptable range by
physiological control if the variable strays from setpoint
Two patterns of control mechanisms:
1) local control
o restricted to the tissue or cell involved /region where change took place (local)
o sense change and responds, usually by releasing a chemical
o e.g. cells lining small blood vessels sense low concentration of oxygen> secrets chemical
signal>signal molecule diffuses to nearby muscles in blood vessel wall> message to
relax which dilates blood vessel increasing blood flow into tissue (more oxygen to area)
2) long-distance reflex control
o widespread changes require long distance communication and coordination
o e.g. blood pressure which is body-wide
o reflex control: any long-d pathway that uses nervous system, endocrine system, or
response loop: has an input signal, integrating center, output signal -> expanded
to 7 steps: stimulus(change that occurs when regulated variable out of range) ->
sensor (monitors the variable, activated by stimulus then sends input signal to
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