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Chapter 5

BIOD27H3 Chapter Notes - Chapter 5: Facilitated Diffusion, Passive Transport, Dynamic Equilibrium


Department
Biological Sciences
Course Code
BIOD27H3
Professor
A.Elia
Chapter
5

Page:
of 32
Human Physiology (Fifth Edition)
Silverthorn, D. U.
Chapter 5 Membrane Dynamics
Mass Balance and Homeostasis
To maintain homeostasis, the body
uses mass balance
The law of mass balance: if the
amount of a substance in the body
has to stay constant, any gain must
be offset by an equal loss;
oTotal amount of x in the body =
intake + production excretion
metabolism
To maintain mass balance, the
body can use excretion (elimination
of material from the body through
urine, feces, lungs, skin) or
metabolize the substance into a
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different substance (which will
create a new mass balance
disturbance through addition of
metabolite)
Excretion Clears Substances
from the Body
oClearance: rate at which a
molecule leaves the body by
excretion, metabolism, or both;
usually expressed as a volume of
blood plasma cleared of x per unit
of time;
oKidney and liver major organs
involved in clearing materials
from the body
oSaliva, sweat, breast milk, and
hair contain solutes cleared
from the body
oMass flow = concentration x
volume flow; used to determine
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the rate of uptake, output, or
production of x, as well as its
movement from one compartment
to another
Homeostasis Does Not Mean
Equilibrium
oHomeostasis often refers to the
stability of the extracellular fluid
compartment (consisting of the
plasma and interstitial fluid)
oDynamic disequilibrium
(chemical disequilibrium): state
of the two fluid compartments in
which the different
concentrations of solutes in the
ECF and ICF create a
concentration gradient; continual
input of energy is needed to keep
the body in this state
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