Lecture 1

Body Fluid Compartments and Transport Across Cell Membranes

What does total water in body =

total body water (~60% of BW)

What are the Two major fluid compartments?

Intracellular fluid

Extracellular fluid

How much of the ~60% of BW of total body water is Intracellular fluid?

~40% BW

How much of the ~60% of BW of total body water is Extracellular fluid?

~20% BW

What makes up Extracellular fluid?

Interstitial fluid

Plasma

What is the breakdown of total body water in Extracellular fluid?

Interstitial fluid = ~16% BW

Plasma = ~4% BW

What is the estimate of total body water in blood volume?

6-8% or 60-80 mL/kg BW

W/ average of 70 mL/ Kg BW

Where is Intracellular fluid (ICF) located?

Inside cells

Where is Extracellular fluid (ECF) located?

Outside cells

What does Interstitial fluid do to cells?

bathes cells

How much total body of water does a 20kg dog have?

We know ~60% of BW is total body water:

20kg x 0.6 = 12 kg = 12 L

What is the extracellular fluid (ECF) volume of a 105 kg pig?

We know ECF ~20% of BW is total body water:

105kg x 0.2 = 21 L or 21,000 mL

What does a MOLE describe?

Amount of substance

What does EQUIVALENT describe?

Amount of electrical charge

What does OSMOLE describe?

Number of dissolved particles

What do we measure concentrations in?

mol/ L or mmol/L, mEq/L, Osm/L, or mOsm/L

Osmolarity is measured in and what does it measure?

osmoles/L

Measures the number of dissolved particles

Clinically, what does osmolarity determine?

Water movement between compartments

What does pH express?

H ion concentration

Define electroneutrality?

Refers to the principle that the total positive charge in a solution must equal the total negative charge in each body fluid compartment.

What are major ions in ECF?

Major cation = Na+

Major anions = Cl- and HCO3

What are major ions in ICF?

Major cation = K+

Major anions = proteins & organic phosphates

Osmolarity same in ECF and ICF =

electroneutrality maintained

What is the average osmolarity?

290-300 mOsm/L

What does ionized Ca =

Free Ca (unbound)

Able to interact

What does bound Ca =

Not free to interact or not available Ca

Bounds to minerals or proteins

The compositions of Extracellular and Intracellular fluid must be what in Osmolarity?

Must equal the same to be balanced

Are cell membranes freely soluble to all solutes?

NO

They are selectively permeable

What does selectively permeable mean?

Only certain things get to move in certain directions

What maintains the selective permeability in cell membranes?

Transport mechanisms

**does not create just maintains

What two types of pumps directly use ATP?

Na+/ K+ ATPase pump

Ca2+/ ATPase pump

What pump is on every cell in the body?

Na+/K+ ATPase pump

Pumps Na+ put of cell and K+ into cell

What is the job of Ca2+/ ATPase pump?

To pump Ca out of cells

What is allowed due to K+ differences?

Allows nerve and muscle cells to have resting membrane potentials

What is allowed due to Na+ differences?

Upstroke of action potentials in nerve and muscle cells and absorption of nutrients

What is allowed due to Ca2+ differences?

Excitation-contraction coupling in muscle cells

Transporters for what utilize Na+ gradients but do not directly use energy (secondary transporters)

Glucose, amino acids (AA), Ca2+, and H+

What are cell membranes composed of?

Lipids and proteins

What are the two ways transport can occur cross cell membranes?

Down an electrochemical gradient

Against an electrochemical gradient

Which transports occur down an electrochemical gradient?

Simple or facilitated diffusion

Do simple or facilitated diffusion need input of energy?

NO

But facilitated uses a carrier & simple is NOT carrier-mediated

Which transports occur against an electrochemical gradient?

Primary Transport

Secondary Transport

Energy and carrier status of Primary transport?

Direct input of energy

Uses a carrier

Energy and carrier status of Secondary transport?

Indirect input of energy

Uses a carrier

What occurs when two solutions are separated by a membrane permeable to the solute?

The solute will equilibrate across the membrane

What variables determine diffusion rate (Fick’s law)?

Concentration gradient

Partition coefficient

Diffusion coefficient

Thickness of membrane

Surface area

Describe the concentration gradient?

Depends on driving force

Larger the concentration difference the greater the driving force

Describe Partition coefficient

Based on lipid solubility of solute

If high lipid solubility = increase partition coefficient & moves easily

Describe Diffusion coefficient

Based on size of solute and viscosity of solution

Small solutes in non-viscous solution diffuse readily (increases diffusion coefficient)

Describe thickness of membrane

Increased thickness = moves slower

Describe Surface area

Greater surface area = high diffusion rate

A substance that is lipid soluble, small, traveling through a non-viscous solution and a thin membrane will diffuse?

Quickly