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Membrane Dynamics. 5. Mass Balance in the Body. To maintian a constant amount of substance in the body any amount gain must be equal to that lost. Figure 5-2. Mass Balance and Homeostasis. Clearance

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Membrane Dynamics


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mass balance in the body
Mass Balance in the Body

To maintian a constant amount of substance in the body any amount gain must be equal to that lost.

Figure 5-2

mass balance and homeostasis
Mass Balance and Homeostasis
  • Clearance
    • Rate at which a molecule disappears from the body - excretion occurs in the form of urine, feces, lungs, or integument and metabolism which uses substances as substrates and creates metabolites(liver & kidneys).
    • Mass flow = concentration  volume flow (amount X/min) (amountX/vol) (vol/min)
      • Also takes into account the movement through compartments and whether it crosses the membrane
  • Homeostasis  equilibrium – the chemical compositions in the ECF and ICF are not at equilibrium but each is maintained at a constant state
    • Osmotic equilibrium- water is the only substance that reaches it
    • Chemical disequilibrium- greater concentration in one compartmemt
    • Electrical disequilibrium- inside of cells is slightly more negative
homeostasis
Homeostasis

Distribution of solutes in the body fluid compartments

  • The compartments in the body are in a state of chemical dynamic disequilibrium- no net movement of materials

Figure 5-3a

homeostasis1
Homeostasis

Selective permeability of the plasma membrane helps to maintian disequilibrium at constant [solute]

Figure 5-3b

diffusion
Diffusion

Map of membrane transport

The size of a

molecule and

its lipid solubility

determine how it

will cross the

memebrane.

Membranes are selectively permeable

Figure 5-4

diffusion seven proprieties
Diffusion: Seven Proprieties
  • Passive process- does not require energy input but used the kinetic energy in the molecules
  • High concentration to low concentration- direction of molecule movement along a concentration gradient
  • Net movement until concentration is equal- diffusion will continue across non-living mediums until dynamic equilibrium is reached
  • Rapid over short distances- diffusion is proportional to the square of the distance between two points. In living systems transport mechanisms compensate for delays
  • Directly related to temperature- directly proportional to temperature changes
  • Inversely related to molecular size- the smaller the radius, the lower the friction, the faster the movement across a medium
  • In open system or across a partition- diffusion is limited by the permeability of the barrier.
slide8
A hypertonic solution
    • Has a higher concentration of solute
  • A hypotonic solution
    • Has a lower concentration of solute
  • An isotonic solution
    • Has an equal concentration of solute
slide9

Molecules of dye

Membrane

Equilibrium

(a) Passive transport of one type of molecule

Equilibrium

(b) Passive transport of two types of molecules

Molecules still move across the membrane once equilibrium is reached, but the movement is simultaneously equal in both directions.

Figure 5.11

simple diffusion
Simple Diffusion

Fick’s law of diffusion – takes into account the various components that influence simple diffusion

Figure 5-6

membrane proteins function
Membrane Proteins Function
  • Structural proteins – forms cytoskeleton, cell junctions, and link cells to EC matrix
  • Enzymes – carry out reactions just outside or inside the cell and transfer signals
  • Membrane receptor proteins – play a role in signaling by activating a response when a ligand binds, also involved in vesicle transport.
  • Transporters – move molecules across membranes
    • Channel proteins – directly link ECF and ICF by having a fluid filled compartment, open at both ends
    • Carrier proteins – not open at both ends, bind ligand but don’t have a fluid continum
membrane transport proteins
Membrane Transport Proteins

Water channels and ion channels are examples of open channels. Carriers are proteins that change shape as they transport molecules across the membrane. They may carry one or more molecules at a time.

Figure 5-9a

types of carrier mediated transport
Types of Carrier-Mediated Transport

Substrate specific for ions or molecules too large for channel proteins

Figure 5-12a

types of carrier mediated transport1
Types of Carrier-Mediated Transport

Carrier proteins never create a continuous passageway. Movement through carriers is slower than through protein channels because of the conformation change.

Figure 5-12c

gating of channel proteins
Gating of Channel Proteins

Gated channels are either chemically, mechanically, or voltage-gated.

We will learn more about gated channel during nervous and muscular system

Figure 5-11

types of carrier mediated transport2
Types of Carrier-Mediated Transport
  • Gates control the direction of flow from either end via conformational changes
facilitated diffusion
Facilitated Diffusion

Diffusion of glucose into cell

  • How is the concentration gradient maintained for glucose?

Helps to keep it from building up or leaving the cell.

Figure 5-15

primary active transport
Primary Active Transport

ECF

1

ATP

ADP

5

2

3 Na+ from

ICF bind

ICF

P

ATPase is

phosphorylated

with Pi from ATP.

2 K+ released

into ICF

Protein changes

conformation.

Protein changes

conformation.

P

3 K+ released

into ICF

4

3

2 K+ from

ECF bind

P

P

Mechanism of the Na+-K+-ATPase

ATP is used as an energy source

Figure 5-17

primary active transport1
Primary Active Transport

ECF

1

ATP

ADP

2

3 Na+ from

ICF bind

ICF

P

ATPase is

phosphorylated

with Pi from ATP.

ATP is hydrolyzed into ADP to release the energy

ATP is a molecule used for energy during cellular reactions.

The energy obtained from nutrient molecules is stored in ATP during cellular respiration

Figure 5-17, steps 1–2

primary active transport2
Primary Active Transport

ECF

1

ATP

ADP

2

3 Na+ from

ICF bind

ICF

P

ATPase is

phosphorylated

with Pi from ATP.

Protein changes

conformation.

3 Na+ released

into ICF

3

P

Three sodium ions bind, pump gets energyzed, conformation change occurs,sodium is released.

Figure 5-17, steps 1–3

primary active transport3
Primary Active Transport

ECF

1

ATP

ADP

2

3 Na+ from

ICF bind

ICF

P

ATPase is

phosphorylated

with Pi from ATP.

Protein changes

conformation.

3 K+ released

into ICF

4

3

2 K+ from

ECF bind

P

P

The conformation allows two potassium ions to bind and the dephosphorylation changes the conformation again allowing the ions into the cell

Figure 5-17, steps 1–4

primary active transport4
Primary Active Transport

ECF

1

ATP

ADP

5

2

3 Na+ from

ICF bind

ICF

P

ATPase is

phosphorylated

with Pi from ATP.

2 K+ released

into ICF

Protein changes

conformation.

Protein changes

conformation.

P

3 K+ released

into ICF

4

3

2 K+ from

ECF bind

P

P

Figure 5-17, steps 1–5

secondary active transport
Secondary Active Transport

1

Na+ binds to

carrier.

3

Glucose binding

changes carrier

conformation.

Intracellular fluid

Lumen of

intestine

or kidney

Na+

Na+

SGLT

protein

Glu

Glu

[Na+] high

[Glucose] low

[Na+] low

[Glucose] high

Na+ released into cytosol.

Glucose follows.

4

2

Na+ binding

creates a

site for glucose.

Na+

Na+

Glu

Glu

Mechanism of the SGLT Transporter- uses potential energy of the concentration gradient created by primary active transport which used ATP directly.

Figure 5-18

secondary active transport1
Secondary Active Transport

1

Na+ binds to

carrier.

Intracellular fluid

Lumen of

intestine

or kidney

Na+

SGLT

protein

Glu

[Na+] high

[Glucose] low

[Na+] low

[Glucose] high

Active transport allowd for a greater Na concentration in the ECF and lower in the ICF. Na will move along the gradient

Figure 5-18, step 1

secondary active transport2
Secondary Active Transport

1

Na+ binds to

carrier.

Intracellular fluid

Lumen of

intestine

or kidney

Na+

SGLT

protein

Glu

[Na+] high

[Glucose] low

[Na+] low

[Glucose] high

2

Na+ binding

creates a

site for glucose.

Na+

Glu

Glucose will be able to bind after Na binds and the carrier will take it against its concentration gradient

Figure 5-18, steps 1–2

secondary active transport3
Secondary Active Transport

1

Na+ binds to

carrier.

3

Glucose binding

changes carrier

conformation.

Intracellular fluid

Lumen of

intestine

or kidney

Na+

Na+

SGLT

protein

Glu

Glu

[Na+] high

[Glucose] low

[Na+] low

[Glucose] high

2

Na+ binding

creates a

site for glucose.

Na+

Glu

  • Uses the energy of one molecule moving down its concentration gradient in symport or antiport

Figure 5-18, steps 1–3

secondary active transport4
Secondary Active Transport

1

Na+ binds to

carrier.

3

Glucose binding

changes carrier

conformation.

Intracellular fluid

Lumen of

intestine

or kidney

Na+

Na+

SGLT

protein

Glu

Glu

[Na+] high

[Glucose] low

[Na+] low

[Glucose] high

Na+ released into cytosol.

Glucose follows.

4

2

Na+ binding

creates a

site for glucose.

Na+

Na+

Glu

Glu

The cotransported molecules may be ions or uncharged molecules.

Figure 5-18, steps 1–4

carrier mediated transport
Carrier-Mediated Transport
  • Specificity – moves only one molecule or different closely related molecules
  • Competition – due to a difference of affinity for molecules that are closely related, there are competitive inhibitors that block the binding and not moved across the cell
  • Saturation – like enzymes as [substrate] so does rate
    • Transport maximum – a point when all carrier binding sites are full- limits rate
vesicular transport
Vesicular Transport
  • Phagocytosis
    • Cell engulfs bacterium or other particle into phagosome- a large vesicle; requires ATP for cytoskeleton movement
  • Endocytosis
    • Membrane surface indents and forms vesicles- different process than phagocytosis
    • Active process which can be nonselective (pinocytosis) or highly selective
    • Potocytosis uses caveolae (“little caves”)- lipid anchored proteins that bind ligands to concentrate then, transport across epithelium, or cell signaling.
    • Receptor-mediated uses clathrin-coated pits- very specific
receptor mediated endocytosis and exocytosis
Receptor-Mediated Endocytosis and Exocytosis

1

Extracellular fluid

Ligand binds to membrane receptor.

9

Exocytosis

Receptor-ligand migrates to

clathrin-coated pit.

2

8

Transport vesicle

and cell membrane

fuse (membrane

recycling).

Clathrin-

coated pit

3

Endocytosis

Receptor

Clathrin

Transport vesicle

with receptors moves

to the cell membrane.

7

4

Vesicle loses

clathrin coat.

4

Receptors

and ligands

separate.

5

To lysosome or

Golgi complex

Intracellular fluid

6

Ligands go to lysosomes

or Golgi for processing.

Endosome

A very specific form of endocytosis. Receptors bring in molecules such as cholesterol

Figure 5-24

transepithelial transport
Transepithelial Transport

Polarized cells of transporting epithelia

-combine active and passive transport

-use different transporter types at the apical and basolateral sides

Figure 5-25

transepithelial transport of glucose
Transepithelial Transport of Glucose

1

Na+ glucose symporter

brings glucose into cell

against its gradient using

energy stored in the Na+

concentration gradient.

Glu

[Glucose] low

Na+ [Na+] high

Lumen of kidney

or intestine

1

2

GLUT transporter

transfers glucose to ECF

by facilitated diffusion.

Apical

membrane

Glu

Na+ [Na+] low

[Glucose] high

3

Na+ -K+- ATPase pumps Na+

out of the cell, keeping ICF

Na+ concentration low.

Epithelial

cell

Basolateral

membrane

Glu

Na+

K+

2

3

ATP

Extracellular

fluid

Glu

[Glucose] low

[Na+] high Na+

K+

Figure 5-26, steps 1–3

the body is mostly water
The Body Is Mostly Water

Distribution of water volume in the three body fluid compartments

Figure 5-28

osmosis and osmotic pressure
Osmosis and Osmotic Pressure

Osmolarity describes the number of particles in solution

Figure 5-29

osmolarity comparing solutions
Osmolarity: Comparing Solutions
  • Solution A = 1 OsM Glucose
  • Solution B = 2 OsM Glucose
  • B is hyperosmotic to A
  • A is hyposmotic to B
  • What would be the osmolarity of a solution which is isosmotic to A? to B?
tonicity
Tonicity

Tonicity describes the volume change of a cell placed in a solution

tonicity1
Tonicity

Tonicity depends on the relative concentrations of nonpenetrating solutes

Figure 5-30a

tonicity2
Tonicity

Tonicity depends on nonpenetrating solutes only

Figure 5-30b

water balance in animal cells
Water Balance in Animal Cells
  • The survival of a cell depends on its ability to balance water uptake and loss
  • Osmoregulation is the control of water balance in animals

Animal

cell

Normal

Lysing

Shriveled

Plasma

membrane

Plant

cell

Shriveled

Flaccid (wilts)

Turgid

(b) Hypotonic solution

(a) Isotonic solution

(c) Hypertonic solution

Figure 5.13