Chapter 5c

Membrane Dynamics

Figure 5-25

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

AquaporinMoves freely through cells by special channels of aquaporin

Figure 5-26

Osmosis and Osmotic Pressure

• Osmolarity describes the number of particles in solution

Volumesequal

Osmotic pressure isthe pressure that must beapplied to B to oppose osmosis.

Volumeincreased

Volumedecreased

Two compartments areseparated by a membrane that is permeable to water but not glucose.

Water moves byosmosis into the moreconcentrated solution.

Glucosemolecules

Selectivelypermeablemembrane

A B

1

3

2

Table 5-5

Osmolarity: Comparing SolutionsHyper / Hypo / Iso are relative terms

Osmolarity is total particles in solutionNormal Human body around 280 – 300 mOsM

Table 5-6

Tonicity

• Solute concentration = tonicity• Tonicity describes the volume change of a

cell placed in a solution

Figure 5-27a

Tonicity

• Tonicity depends on the relative concentrations of nonpenetrating solutes

Figure 5-27b

Tonicity

• Tonicity depends on nonpenetrating solutes only

Figure 5-28

Tonicity

• Tonicity depends on nonpenetrating solutes only

(a)

(b)

(c)

(d)

Cell

Solution

H2O

Plasmolysis and Crenation

• RBC’s

Table 5-7

Osmolarity and Tonicity

Table 5-8

Intravenous Solutions

Electricity Review

1. Law of conservation of electrical charges2. Opposite charges attract; like charges repel

each other3. Separating positive charges from negative

charges requires energy4. Conductor versus insulator

Figure 5-29b

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 5-29c

Separation of Electrical Charges

• Resting membrane potential is the electrical gradient between ECF and ICF

Figure 5-30

Measuring Membrane Potential Difference

The voltmeter

Cell

The chart recorder

Saline bath

A recording electrode

Input

The ground ( ) or referenceelectrode

Output

Figure 5-31a

Potassium Equilibrium PotentialArtificial cell

(a)

Figure 5-31b

Potassium Equilibrium Potential

(b)

K+ leak channel

Figure 5-31c

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

Concentrationgradient

Electricalgradient

(c)

Figure 5-32

Sodium Equilibrium Potential• Single ion can be calculated using the Nernst Equation

• Eion = 61/z log ([ion] out / [ion] in)

150 mM0 mV

15 mM+60 mV

Figure 5-33

Resting Membrane Potential

Extracellular fluid0 mV

Intracellular fluid-70 mV

Figure 5-34

Changes in Membrane Potential

• Terminology associated with changes in membrane potential

PLAY Interactive Physiology® Animation: Nervous I: The Membrane Potential

1Low glucose levels in blood.

No insulinsecretion

Metabolismslows.

ATPdecreases.

ATPMetabolismGlucose

Cell at restingmembrane potential.No insulin is released.

KATP

channels open.

Insulin in secretory vesicles

K+ leaks out

of cellVoltage-gated Ca2+ channel closed

GLUT transporter

(a) Beta cell at rest

2 3 4 5

Figure 5-35a

Insulin Secretion and Membrane Transport Processes

1Low glucose levels in blood.

Glucose

(a) Beta cell at restFigure 5-35a, step 1

Insulin Secretion and Membrane Transport Processes

1Low glucose levels in blood.

Metabolismslows.

MetabolismGlucose

GLUT transporter

(a) Beta cell at rest

2

Figure 5-35a, steps 1–2

Insulin Secretion and Membrane Transport Processes

1Low glucose levels in blood.

Metabolismslows.

ATPdecreases.

ATPMetabolismGlucose

GLUT transporter

(a) Beta cell at rest

2 3

Figure 5-35a, steps 1–3

Insulin Secretion and Membrane Transport Processes

1Low glucose levels in blood.

Metabolismslows.

ATPdecreases.

ATPMetabolismGlucose

KATP

channels open.

K+ leaks out

of cell

GLUT transporter

(a) Beta cell at rest

2 3 4

Figure 5-35a, steps 1–4

Insulin Secretion and Membrane Transport Processes

1Low glucose levels in blood.

No insulinsecretion

Metabolismslows.

ATPdecreases.

ATPMetabolismGlucose

Cell at restingmembrane potential.No insulin is released.

KATP

channels open.

Insulin in secretory vesicles

K+ leaks out

of cellVoltage-gated Ca2+ channel closed

GLUT transporter

(a) Beta cell at rest

2 3 4 5

Figure 5-35a, steps 1–5

Insulin Secretion and Membrane Transport Processes

1

Glycolysisand citric acid cycle

ATP

Ca2+ signal triggersexocytosis and insulin is secreted.

Ca2+

Ca2+

High glucose levels in blood.

Metabolismincreases.

ATPincreases.

Glucose

Cell depolarizes andcalcium channelsopen.

KATP channels close.

Ca2+ entry acts as anintracellularsignal.

GLUT transporter

(b) Beta cell secretes insulin

2 3 4 5

6

7

Figure 5-35b

Insulin Secretion and Membrane Transport Processes

1High glucose levels in blood.

(b) Beta cell secretes insulinFigure 5-35b, step 1

Insulin Secretion and Membrane Transport Processes

Glucose

1

Glycolysisand citric acid cycle

High glucose levels in blood.

GLUT transporter

(b) Beta cell secretes insulin

2

Figure 5-35b, steps 1–2

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

1

Glycolysisand citric acid cycle

ATP

High glucose levels in blood.

GLUT transporter

(b) Beta cell secretes insulin

2 3

Figure 5-35b, steps 1–3

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

ATPincreases.

1

Glycolysisand citric acid cycle

ATP

High glucose levels in blood.

KATP channels close.

GLUT transporter

(b) Beta cell secretes insulin

2 3 4

Figure 5-35b, steps 1–4

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

ATPincreases.

1

Glycolysisand citric acid cycle

ATP

Ca2+

High glucose levels in blood.

Cell depolarizes andcalcium channelsopen.

KATP channels close.

GLUT transporter

(b) Beta cell secretes insulin

2 3 4 5

Figure 5-35b, steps 1–5

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

ATPincreases.

1

Glycolysisand citric acid cycle

ATP

Ca2+

Ca2+

High glucose levels in blood.

Cell depolarizes andcalcium channelsopen.

KATP channels close.

Ca2+ entry acts as anintracellularsignal.

GLUT transporter

(b) Beta cell secretes insulin

2 3 4 5

6

Figure 5-35b, steps 1–6

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

ATPincreases.

1

Glycolysisand citric acid cycle

ATP

Ca2+ signal triggersexocytosis and insulin is secreted.

Ca2+

Ca2+

High glucose levels in blood.

Cell depolarizes andcalcium channelsopen.

KATP channels close.

Ca2+ entry acts as anintracellularsignal.

GLUT transporter

(b) Beta cell secretes insulin

2 3 4 5

6

7

Figure 5-35b, steps 1–7

Insulin Secretion and Membrane Transport Processes

Glucose

Metabolismincreases.

ATPincreases.

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