PNB 2264 Lecture Notes - Lecture 2: Fluid Compartments, Extracellular Fluid, Body Cavity
5 Sep 2019
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PNB 2264 Lecture 2– Homeostasis, Feedback Loops
➢Homeostasis
○Homeostasis: the body’s tendency to maintain relatively stable internal
conditions
■ 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
Document Summary
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. Levels of oxygen and carbon dioxide in the blood. Compartmentalization : the separation of different areas of the body (e. g. body cavities are separated by membranes, allowing each cavity to body cavities, organs, fluid, etc. ) 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.
