This document provides a comprehensive overview of the physiological principles underlying homeostasis and the function of the endocrine system. It covers the structural organization of the body from cells to organ systems, emphasizing the roles of different fluid compartments including the intrace...
Module
1:
Homeostasis
and
the
Endocrine
System
Homeostasis
and
Fluid
Compartments:
Body
Components:
-
Differentiation
allows
the
specific
cells
to
gain
specialized
functions
-
Tissue
:
formed
by
groups
of
cells
with
related
functions
-
Types:
muscle,
nervous,
connective,
and
epithelium
-
Form
the
organs
that
work
together
to
perform
a
specific
function
-
Organ
:
functional
unit
-
Organ
system
:
multiple
organs
acting
together
to
perform
a
specific
function
-
10
organ
systems
in
the
body
-
Skin
:
the
largest
organ
of
the
body,
acts
as
a
protective
barrier
from
the
outside
world,
hydrophobic
(allows
the
body
to
retain
water)
-
Entry
:
respiratory
system
(allows
for
the
entrance
of
oxygen
and
expulsion
of
CO2)
and
the
GI
system
(allows
food
and
nutrients
to
enter
and
solid
waste
to
be
removed
from
the
body)
-
Transport
:
mainly
the
cardiovascular
system
that
takes
nutrients
(from
GI)
and
delivers
them
to
all
the
cells.
Takes
in
gases
coming
in
from
the
lung
and
delivers
it
to
the
tissues
and
organs
in
the
body
-
Exit
:
renal
(liquid
waste
and
excess
ions
and
excess
water)
and
GI
(removes
solid
waste)
Fluid
Compartments:
1.
Intracellular
Fluid
Compartment
(ICF):
all
fluids
inside
the
cells,
consisting
of
cytosol
and
fluid
in
the
cell
nucleus.
It
is
bounded
by
the
plasma
membrane.
a.
The
largest
of
the
two
fluid
compartments
b.
⅔
of
the
total
fluid
in
the
body
c.
Inside
cells
have
very
high
levels
of
K+
and
small
concentrations
of
Na+
d.
Negatively
charged
protein
cells
are
also
present
2.
Extra
Fluid
Compartment
(ECF):
what
is
immediately
outside
of
all
of
the
cells
a.
⅓
of
the
total
fluid
in
the
body
b.
High
concentrations
of
Na+
and
small
concentrations
of
K+
→
Can
be
further
divided
into…
1.
Intravascular
Compartment
(IV):
within
the
blood
vessels
a.
Also
contains
proteins
2.
Interstitial
Fluid
Space:
the
little
space
between
the
vascular
and
the
cells
themselves
(filled
with
connective
tissues)
a.
There
is
an
equilibrium
of
equal
distribution
due
to
the
leaky
epithelial
cells
that
line
the
blood
vessels,
allowing
materials
to
move
from
one
compartment
to
another.
Disequilibrium
between
the
ECF
and
the
ICF:
-
The
sodium-potassium
pump,
driven
by
the
ATPase
enzyme,
maintains
ion
concentration
gradients
by
pumping
sodium
and
potassium
into
cells. -
This
activity
ensures
a
steady
state
where
inputs
and
outputs
are
balanced
but
maintains
a
disequilibrium
of
sodium
and
potassium
across
cell
membranes.
-
Small
leaks
between
the
compartments
allow
K+
to
leak
out
into
the
ECF
Body
Water
Compartments:
-
Total
Body
Water
:
-
Constitutes
about
60%
of
an
individual's
body
weight
-
For
a
70
kg
male,
this
amounts
to
~42
liters
of
water
-
ICF
:
for
a
70
kg
male,
this
equals
~28
liters
-
ECF
:
for
a
70
kg
male,
this
equals
~14
liters
-
Intravascular
fluid
constitutes
¼
of
the
ECF
or
1/12th
of
total
body
water
-
For
a
70
kg
male,
this
amounts
to
~3.5
liters
of
plasma
Self-Regulating
Mechanisms:
-
Equilibrium
:
equal
amount
of
substance
and
is
present
between
the
IV
and
the
IS
-
No
net
transfer
of
substance/energy
-
No
barrier
to
movement
-
No
energy
expenditure
to
maintain
(bc
of
leaky
epithelial
cells)
-
Steady
State
:
the
constant
amount
of
substance
in
our
compartments
and
is
present
between
the
ECF
and
the
ICF
-
Input
will
=
the
output
-
Concentration
can
be
dissimilar
and
requires
energy
to
maintain
(use
ATP)
What
is
Homeostasis?
-
The
maintenance
of
extracellular
fluid
(ECF)
constituents
as
relatively
constant
-
Cells
require
very
specific
factors
and
tightly
regulated
environments
(amount
of
oxygen,
amount
of
CO2,
amount
of
hydrogen
ions,
temperature,
amount
of
glucose)
-
ECF
acts
as
a
“buffer
zone.”
-
Organs
act
on
the
ECF
to
try
and
keep
their
contents
under
a
very
narrow
range
that
is
compatible
with
the
cells'
lives.
-
The
central
theme
of
physiology
Homeostatic
Control
and
Reflex
Loops:
Three
Components
of
Reflex
Loops:
1.
Sensor
:
detects
specific
signals
or
stimuli
2.
Integration
Center:
This
center
contains
the
set
points
compatible
with
the
cells
and
evaluates
the
incoming
signals
to
see
if
they
match
the
body's
needs. 3.
Effectors
:
generate
responses
to
bring
the
body
back
to
the
normal
condition
General
Concepts:
1.
The
human
body
is
an
interdependent
set
of
self-regulating
systems
whose
primary
function
is
maintaining
an
internal
environment
compatible
with
living
cells
and
tissues.
2.
The
stability
of
internal
variables
is
achieved
by
balancing
inputs
and
outputs
to
the
body
and
among
organ
systems.
Regulation
of
Homeostasis:
Homeostatic
Controls:
→
Local
Homeostatic
Controls:
1.
Paracrine
Control
:
a.
Occurs
at
a
local
level
among
neighboring
cells
b.
Mechanism:
i.
Cell
#1
secretes
a
chemical
signal
ii.
This
chemical
acts
on
a
neighboring
cell,
Cell
#2
iii.
Cell
#2
has
a
receptor
protein
that
binds
the
chemical,
leading
to
its
activation
iv.
Once
activated,
Cell
#2
produces
a
response
c.
Common
in
the
GI
tract
2.
Autocrine
Contro
l:
a.
A
cell
regulates
its
activity
b.
Mechanism:
i.
Cell
#
secretes
a
chemical
ii.
This
chemical
feeds
back
to
the
same
cell,
regulating
its
activity
3.
Gap
Junctions
:
a.
Neighboring
cells
are
physically
connected
through
structures
called
gap
junctions
or
nexus
b.
Mechanism:
i.
Gap
functions
form
a
bridge
between
two
cells
ii.
The
bridge
allows
ions
to
flow
directly
from
one
cell
to
another
c.
In
the
heart,
gap
junctions
enable
cardiac
muscle
cells
to
contract
and
relax
in
a
coordinated
manner,
ensuring
the
heart
functions
as
a
unified
organ
→
Reflex
Loops:
essential
for
coordinated
function
across
different
parts
of
the
body
1.
Endocrine
System
:
a.
Uses
hormones
to
communicate
over
long
distances
b.
Mechanism:
i.
An
endocrine
cell
secretes
a
hormone
into
the
bloodstream
ii.
The
hormone
travels
through
the
blood
and
reaches
target
cells
with
specific
receptors
iii.
These
receptors
can
be
on
the
cell
surface
or
inside
the
cell
iv.
The
target
cells
respond
to
the
hormone
by
altering
their
activity
c.
Insulin
regulates
blood
sugar
levels
by
acting
on
cells
in
various
tissues
2.
Nervous
System
:
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