E109 Midterm 1

Intracellular fluid

Fluid inside cells

Extracellular Fluid

Fluid not inside cells (includes plasma and interstitial fluid)

Plasma

Liquid fraction of blood (blood - cells)

Interstitial fluid

extracellular fluid not inside cardiovascular system

Most common cation/anion in extracellular fluid

Na+ (Sodium), Chloride (Cl-)

Most common cation in intracellular fluid

K+ (potassium)

Homeostasis

stability of internal environment, maintained by exchange between internal and external environments.

Mass Balance

Total = Existing + Intake + Production - Excretion - Broken down

Electroneutrality

Positive charges = Negative Charges

A cell has an internal solute concentration of [Na+] = 14mM, water enter the cell and the cell volume doubles. What is the final internal [Na+] after the water enters the cell?

7mM ( CV= CV)

How to find unknown volume of a solution to which you have added a known amount of something

concentration = mass added/ volume (C = m/v)

Concentration = how much solute in liquid

Volume = how much liquid

Molecules that easily cross membrane

Nonpolar, small molecules (O2, CO2, steriods)

Molecules that cross membrane but not as readily

Small polar molecules (H2O, urea)

Molecules that do not cross membrane

Ions (Charged) and Large polar molecules (Glucose)

What affects membrane permeability?

Polar/Non polar

Large/Small

Changed/ Uncharged

Diffusion

• Driven by random movement (no energy needed)

• High concentration →low concentration

Which direction will a single molecule move?

Can equally move left or right (random movement)

Which direction will many molecules move?

High concentration →low concentration (net movement)

When there are the same amount of molecules in each side:

Both sides exchange the same amount of molecules (no net diffusion).

When one side has more molecules than the other side:

The side with more molecules will have its molecules moving to the other side. But the side with less molecules will not have as many molecules to move to the other side. So more molecules will be entering the side with less molecules (high → low concentration).

Fick’s Law (UNDERSTAND CONCEPTUALLY)

• J = - DA (C avg /X avg)

• J = Rate of diffusion across a membrane (mol/s)

• D = diffusion coefficient (m²/s^-1)

• A = surface area (m²)

• C/X = concentration gradient (mol/m³)

• C avg = C1 - C2

• Greater the area = greater the diffusion rate

• Greater the concentration gradient = greater the diffusion rate

• If C1=C2, C avg= 0, so J =0

Simple Diffusion

Can pass right through membrane lipids without protein

Channel facilitated diffusion

Molecules go straight through channel

Carrier facilitated diffusion

Molecule enters through opening side (leaving side closed), once molecule inside protein, leaving side opens and opening side closes. Conformation change occurs.

Cell keeps facilitated diffusion going without using ATP when transporting glucose by:

Converting glucose/ using it up so there’s still a lower concentration of glucose inside the cell

Properties of protein mediated transport across membranes

• specificity - protein is specific about what it is transporting

• affinity - strength of binding (binding too strong = slow down transport, no binging = no transport)

• saturation - percent of all binding sites occupied

• competition - if two different solutes can bind to same protein

Simple Diffusion

J and (C/X) are linear

Carrier facilitated diffusion (Saturation)

Reaches max rate of transport (saturation is 100%) when all protein carriers are full

Carrier facilitated diffusion (Specificity)

Reaches max rate of transport earlier because all protein carriers are full

Passive Transport

Molecules move themselves down gradient

• Simple diffusion

• Facilitated diffusion

Active Transport

Movement in opposite direction, requires energy

• Primary active transport (uses ATP at the same time)

• Secondary active transport (uses energy stored by action of primary transport)

Water transport across membranes

• no carriers for water

• no active transport for water

• channels for water (aquaporins)

• water will move down ITS concentration gradient via diffusion

Molarity

number of moles/liter

Osmolarity

number of