Chapter 5c
Membrane
Dynamics
The Body Is Mostly Water
• Distribution of
water volume in
the three body
fluid
compartments
• 1 liter water
weighs 1 kg or
2.2 lbs
• 70 kg X 60% =
42 liters for avg
154 lb male
Figure 5-25
Aquaporin
Moves freely through
cells by special
channels of aquaporin
Osmosis and Osmotic Pressure
A
B
Volume
increased
• Osmolarity
describes the
number of
particles in
solution
Selectively
permeable
membrane
Volume
decreased
Glucose
molecules
1
2
Two compartments are
separated by a membrane that
is permeable to water but not
glucose.
Water moves by
osmosis into the more
concentrated solution.
Volumes
equal
3
Osmotic pressure is
the pressure that must be
applied to B to oppose osmosis.
Figure 5-26
Osmolarity: Comparing Solutions
Hyper / Hypo / Iso are relative terms
Osmolarity is total particles in solution
Normal Human body around 280 – 300 mOsM
Table 5-5
Tonicity
• Solute concentration = tonicity
• Tonicity describes the volume change of a
cell placed in a solution
Table 5-6
Tonicity
• Tonicity depends on the relative
concentrations of nonpenetrating solutes
Figure 5-27a
Tonicity
• Tonicity depends on nonpenetrating solutes
only
Figure 5-27b
Tonicity
Cell
H2O
Solution
(a)
(c)
(b)
(d)
• Tonicity depends on nonpenetrating solutes
only
Figure 5-28
Plasmolysis and Crenation
• RBC’s
Osmolarity and Tonicity
Table 5-7
Intravenous Solutions
Table 5-8
Electricity Review
1. Law of conservation of electrical charges
2. Opposite charges attract; like charges repel
each other
3. Separating positive charges from negative
charges requires energy
4. Conductor versus insulator
Separation of Electrical Charges
• Resting membrane potential is the electrical
gradient between ECF and ICF
(b) Cell and solution in chemical and electrical disequilbrium.
Intracellular fluid
Extracellular fluid
Figure 5-29b
Separation of Electrical Charges
• Resting membrane potential is the electrical
gradient between ECF and ICF
Figure 5-29c
Measuring Membrane Potential Difference
The voltmeter
A recording electrode
Input
Output
The ground (
electrode
) or reference
Cell
Saline bath
The chart recorder
Figure 5-30
Potassium Equilibrium Potential
Artificial cell
(a)
Figure 5-31a
Potassium Equilibrium Potential
K+ leak channel
(b)
Figure 5-31b
Potassium Equilibrium Potential
• Resting membrane potential is due mostly
to potassium
• K+ can exit due to [ ] gradient, but electrical gradient will
pull back; when equal resting membrane potential
Concentration
gradient
Electrical
gradient
(c)
Figure 5-31c
Sodium Equilibrium Potential
• Single ion can be calculated using the Nernst Equation
• Eion = 61/z log ([ion] out / [ion] in)
15 mM
+60 mV
150 mM
0 mV
Figure 5-32
Resting Membrane Potential
Intracellular fluid
-70 mV
Extracellular fluid
0 mV
Figure 5-33
Changes in Membrane Potential
• Terminology associated with changes in
membrane potential
PLAY
Interactive Physiology® Animation: Nervous I:
The Membrane Potential
Figure 5-34
Insulin Secretion and Membrane Transport
Processes
3
1
2
4
5
Low glucose
levels in blood.
KATP
Metabolism ATP
Cell at resting
slows.
decreases. channels open. membrane potential.
No insulin is released.
K+ leaks
out
of cell
Glucose
Metabolism
Voltage-gated
Ca2+ channel
closed
ATP
GLUT
transporter
No insulin
secretion
Insulin in
secretory vesicles
(a) Beta cell at rest
Figure 5-35a
Insulin Secretion and Membrane Transport
Processes
1
Low glucose
levels in blood.
Glucose
(a) Beta cell at rest
Figure 5-35a, step 1
Insulin Secretion and Membrane Transport
Processes
1
2
Low glucose
levels in blood.
Metabolism
slows.
Glucose
Metabolism
GLUT
transporter
(a) Beta cell at rest
Figure 5-35a, steps 1–2
Insulin Secretion and Membrane Transport
Processes
3
1
2
Low glucose
levels in blood.
Metabolism ATP
slows.
decreases.
Glucose
Metabolism
ATP
GLUT
transporter
(a) Beta cell at rest
Figure 5-35a, steps 1–3
Insulin Secretion and Membrane Transport
Processes
3
1
2
4
Low glucose
levels in blood.
KATP
Metabolism ATP
slows.
decreases. channels open.
K+ leaks
out
of cell
Glucose
Metabolism
ATP
GLUT
transporter
(a) Beta cell at rest
Figure 5-35a, steps 1–4
Insulin Secretion and Membrane Transport
Processes
3
1
2
4
5
Low glucose
levels in blood.
KATP
Metabolism ATP
Cell at resting
slows.
decreases. channels open. membrane potential.
No insulin is released.
K+ leaks
out
of cell
Glucose
Metabolism
Voltage-gated
Ca2+ channel
closed
ATP
GLUT
transporter
No insulin
secretion
Insulin in
secretory vesicles
(a) Beta cell at rest
Figure 5-35a, steps 1–5
Insulin Secretion and Membrane Transport
Processes
3
5
1
2
4
High glucose
levels in blood.
KATP channels
Metabolism ATP
increases. increases. close.
Cell depolarizes and
calcium channels
open.
6
Ca2+ entry
acts as an
intracellular
signal.
Ca2+
Glucose
Glycolysis
and citric
acid cycle
ATP
Ca2+
7
GLUT
transporter
Ca2+ signal
triggers
exocytosis
and insulin
is secreted.
(b) Beta cell secretes insulin
Figure 5-35b
Insulin Secretion and Membrane Transport
Processes
1
High glucose
levels in blood.
Glucose
(b) Beta cell secretes insulin
Figure 5-35b, step 1
Insulin Secretion and Membrane Transport
Processes
1
2
High glucose
levels in blood.
Metabolism
increases.
Glucose
Glycolysis
and citric
acid cycle
GLUT
transporter
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–2
Insulin Secretion and Membrane Transport
Processes
1
2
High glucose
levels in blood.
Metabolism ATP
increases. increases.
Glucose
Glycolysis
and citric
acid cycle
3
ATP
GLUT
transporter
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–3
Insulin Secretion and Membrane Transport
Processes
1
2
High glucose
levels in blood.
KATP channels
Metabolism ATP
increases. increases. close.
Glucose
Glycolysis
and citric
acid cycle
3
4
ATP
GLUT
transporter
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–4
Insulin Secretion and Membrane Transport
Processes
3
5
1
2
4
High glucose
levels in blood.
KATP channels Cell depolarizes and
Metabolism ATP
increases. increases. close.
calcium channels
open.
Ca2+
Glucose
Glycolysis
and citric
acid cycle
ATP
GLUT
transporter
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–5
Insulin Secretion and Membrane Transport
Processes
3
5
1
2
4
High glucose
levels in blood.
KATP channels Cell depolarizes and
Metabolism ATP
increases. increases. close.
calcium channels
open.
6
Ca2+ entry
acts as an
intracellular
signal.
Ca2+
Glucose
Glycolysis
and citric
acid cycle
ATP
Ca2+
GLUT
transporter
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–6
Insulin Secretion and Membrane Transport
Processes
3
5
1
2
4
High glucose
levels in blood.
KATP channels Cell depolarizes and
Metabolism ATP
increases. increases. close.
calcium channels
open.
6
Ca2+ entry
acts as an
intracellular
signal.
Ca2+
Glucose
Glycolysis
and citric
acid cycle
ATP
Ca2+
7
GLUT
transporter
Ca2+ signal
triggers
exocytosis
and insulin
is secreted.
(b) Beta cell secretes insulin
Figure 5-35b, steps 1–7
Summary
• Mass balance and homeostasis
•
•
•
•
•
•
•
Law of mass balance
Excretion
Metabolism
Clearance
Chemical disequilibrium
Electrical disequilibrium
Osmotic equilibrium
Summary
• Diffusion
• Protein-mediated transport
•
•
•
•
Roles of membrane proteins
Channel proteins
Carrier proteins
Active transport
Summary
• Vesicular transport
• Phagocytosis
• Endocytosis
• Exocytosis
• Transepithelial transport
Summary
• Osmosis and tonicity
• Osmolarity
• Nonpenetrating solutes
• Tonicity
• The resting membrane potential
• Insulin secretion