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Lecture 2

PNB 2264 Lecture Notes - Lecture 2: Fluid Compartments, Extracellular Fluid, Body Cavity

Physiology and Neurobiology
Course Code
PNB 2264
John Redden

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PNB 2264 Lecture 2– Homeostasis, Feedback Loops
Homeostasis: the body’s tendency to maintain relatively stable internal
Allows for a balance in which internal conditions are not completely
constant, but vary within a normal range
Example: measuring specific nutrient levels in the blood (glucose,
proteins, vitamins and minerals, etc.) and comparing values with a
reference range to determine if an individual is deficient or
exceeding the acceptable limit (i.e. within the homeostatic range
or not)
Examples of homeostatic processes include:
Body temperature
Concentration of ions, sugar, protein, etc.
Levels of oxygen and carbon dioxide in the blood
Blood pressure
pH of blood
Homeostasis example → Compartmentalization
Compartmentalization: the separation of different areas of the body (e.g.
body cavities, organs, fluid, etc.)
Body cavities are separated by membranes, allowing each cavity to
maintain a unique microenvironment
Compartmentalization allows for organs, etc. to differ in the contents they
hold, rate of flow, pH, and other characteristics
Ex: pH in the stomach, ion concentration in the blood, and
temperature in the testes are unique to those areas, differ through
the rest of the body
Fluids are compartmentalized inside (intracellular fluid) and outside
(extracellular fluid) of cells
Intracellular fluid (ICF): made up of cytosol
Extracellular fluid (ECF): made up of plasma (blood), interstitial
fluid (fluid surrounding cells), and other fluids
Feedback Loops
Closed feedback loop: the stimulus creates a response which in turn acts on
the stimulus
Stimulus and response are related to each other
Open feedback loop: the stimulus creates a response that has no impact on the
stimulus, but rather is pre-emptive, preparing the body for an anticipated event
Stimulus and response are unrelated to each other
Also known as feed forward mechanism
Ex: salivating in the presence of food; increased heart rate before a race
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