Lecture 1: Body Fluid Compartments and Transport Across Cell Membranes

Total body water describes…

total amount of water in the body

Lean animals have a [higher/lower] percentage of body water compared to obese animals

higher

Total body water is __% of body weight (BW)

~60%

Total body water present in the intracellular fluid is __% of BW

~40%

Total body water present in extracellular fluid is __% of BW

20%

ECF is divided into _______ and _______

interstitial fluid and plasma

Interstitial fluid and plasma are components of the ______.

ECF

Total body water present in the interstitial fluid is __% of BW

~16%

Total body water present in the plasma is __% of BW

~4%

average blood volume

70 ml/kg BW or 7%

mole: amount of substance

equivalent: amount of electrical charge

osmole: number of dissolved particles

concentration units

mol/L or mmol/L

mEq/L

Osm/L or mOsm/L

osmoles/L

concentration units for osmolarity

what does osmolarity describe clinically?

osmoles/L

determines water movement between compartments

electroneutrality

in each body compartment, total positive charges must equal the total negative charges

major ions in the ECF

Na+

Cl-

HCO3-

Na+ mEq/L concentrations in the ECF and ICF

ECF: 140

ICF: 14

K+ mEq/L concentrations in the ECF and ICF

ECF: 4

ICF: 120

Ca2+ mEq/L concentrations in the ECF and ICF

ECF: 2.5

ICF: 1×10^-4

Cl- mEq/L concentrations in the ECF and ICF

ECF: 105

ICF: 10

HCO3- mEq/L concentrations in the ECF and ICF

ECF: 24

ICF: 10

pH in the ECF and ICF

ECF: 7.4

ICF: 7.1

osmolarity mOsm/L concentration in the ECF and ICF

ECF: 290

ICF: 290

What is ionized Ca2+?

free Ca2+, unbound, typically low within the cell to prevent unwanted contractions

major ions in the ICF

K+

proteins

organic phosphates

Na+/K+ ATPase

• directly uses ATP

• Na+ out of cell

• K+ into cell

Ca2+/ATPase pump

• directly uses ATP

• Ca2+ out of cell

What ion concentration difference allows nerve and muscle cells to have resting membrane potentials?

K+ (higher inside cell)

What ion concentration difference allows for the upstroke of action potentials in nerve and muscle cells, as well as the absorption of nutrients?

Na+ difference (higher outside cell)

What ion concentration difference allows for excitation-contraction coupling in muscle cells?

Ca2+ difference (typically lower in cell, but when high causes contraction)

Cell membranes are composed of ______ and ____.

lipids and proteins

What types of lipids are present in the cell membrane? What do they allow to happen?

phospholipids, cholestarol, glycolipids

allow free permeability to lipid substances

• Ex. CO2, O2, fatty acids, steroid hormones

What are the functions of the proteins present in the cell membrane?

transporters, receptors, enzymes, channels

• can be integral, transmembrane, or peripheral

Describe the phospholipid component of the cell membrane

Forms lipid bilayer - amphipathic

• hydrophilic head (glycerol)

• hydrophobic tail (fatty acids)

integral proteins

span the cell membrane once

transmembrane proteins

span the cell membrane more than once

can be:

• hormone or neurotransmitter receptors

• pores

• ion channels

peripheral proteins

only on one side of the cell membrane

Describe the structure indicated by letters A, B, and C.

peripheral protein

integral protein

gated ion channel (transmembrane protein)

What types of transport can occur down an electrochemical gradient? Does this require energy?

simple or facilitated

No energy input needed

What types of transport can occur against an electrochemical gradient? Does this require energy?

primary transport

• uses a carrier and direct energy input

secondary transport

• uses a carrier and indirect energy input

Which type of transport does not require energy, and is not carrier mediated?

simple diffusion

Which type of transport does not need energy, but is carrier mediated?

facilitated diffusion

Which type of transport is carrier mediated, but does not require energy?

facilitated diffusion

Which type of transport is carrier mediated, and uses indirect energy?

secondary active transport

What are the 5 variables that determine diffusion rate (Fick’s Law)?

concentration gradient

partition coefficient

diffusion coefficient

thickness of membrane

surface area

The larger the concentration difference, the [greater/lesser] the driving force. This driving force determines the ______.

greater

concentration gradient

The higher the lipid solubility, the [higher/lower] the ease of movement, and the [higher/lower] the partition coefficient.

higher

higher

The partition coefficient is determined by the _________ of a solute.

lipid solubility

The diffusion coefficient is based on the ______ of a solute and the _______ of a solution.

size

viscosity

The [larger/smaller] the solute and the [increased/decreased] viscosity of a solution allow for an increased diffusion coefficient (allows for faster diffusion).

smaller

decreased

4 factors that determine membrane permeability

partition coefficient

diffusion coefficient

thickness of a membrane

surface area

What 2 factors make up the electrochemical gradient?

electrical forces and concentration forces

What are the two additional consequences that a charge of a diffusing ion has?

• a diffusion potential can be created when a charged solute diffuses down its concentration gradient

  • a potential difference across a membrane will alter the rate of diffusion of a charged solute

Diffusion of a positively-charged ion will [slow down/quicken] if diffusing into an area of positive charge.

slow down

diffusion potential

potential difference created across a membrane because of an ion concentration difference

Facilitated diffusion proceeds [slower/faster] at a low solute concentration due to a limited number of carriers.

faster

GLUT4 transporter in skeletal and adipose tissue (insulin-responsive transporter) is an example of what type of transport?

facilitated diffusion

• transports glucose into cells

• D-galactose also competes for binding

saturation

• feature of carrier-mediated transport

• carrier proteins have a limited number of binding sites for solute

  • rate of transport is higher at lower solute concentrations

stereospecificity

• feature of carrier-mediated transport

• binding sites for solute on carrier proteins are specific

  • transporters for D-glu won’t transport L-glu

competition

• feature of carrier-mediated transport

• binding sites are specific, but carriers may recognize and bind chemically-related solutes

  • D-galactose can bind carriers for D-gly

What type of transport is carrier-mediated, and uses direct energy?

primary active transport

primary active transport (what it is, examples)

• one or more solutes moved against a concentration gradient directly using ATP

• Na+/K+ ATPase pump

• Ca2+ ATPase pump

• H+/K+ ATPase pump

Na+/K+ ATPase pump

• primary active transport

• present in membranes of ALL cells

• uses 20-40% of cellular ATP in many tissues

• 3 Na+ pumped out of cell, 2 K+ pumped in

  • creates a charge separation and potential difference

• inhibited by cardiac glycosides (digoxin, ouabain, oleandrin)

Ca2+ ATPase pump

• primary active transport

• Plasma-membrane Ca2+ ATPase (PMCA)

  • 1 Ca2+ out of the cell

• Sarcoplasmic and endoplasmic reticulum Ca2+ ATPase (SERCA)

  • 2 Ca2+ from ICF into SR

H+/K+ ATPase pump

• primary active transport

• parietal cells of gastric mucosa

• pumps H+ into lumen of stomach

  • inhibited by proton pump inhibitors (omeprazole, Prilosec, Prevacid)

secondary active transport

• indirectly uses energy by utilizing Na+ gradient to transport solutes against their concentration gradient

  • maintained by Na+/K+ ATPase pump

• co-transport (symport)

• counter-transport (antiport)

co-transport (symport)

• secondary active transport

• all solutes transported in the same direction

• Na+/glucose co-transporter (SGLT 1) (intestine and renal tubule)

• Na+/amino acid co-transporter (intestine and renal tubule)

• Na+/K+/2Cl- co-transporter (renal tubule)

counter-transport (antiport)

• solutes move in opposite directions

  • Na+ moves into cell, other solute moves out

  • Ca2+/Na+ exchange

  • Na+/H+ exchange

Body water is distributed between the _______ and ______.

ICF and ECF

Cell membranes are ________ permeable.

selectively

Lipid-soluble molecules diffuse _______.

directly

carrier proteins exhibit ________, ________, and _______.

saturation

stereospecificity, and competition

Primary active transport uses ATP _________.

directly

Secondary active transport uses ____________ established by primary active transport.

ion gradients