fluid compartments and transport process - lecture 03

biol2p97

total body water

• approximately 60% of body weight

• total body water can be separated into different compartments

extracellular fluid (ECF)

• plasma (blood volume)

• interstitial (area between cells)

ICF total body water

2/3

ECF total body water

1/3

interstitial plasma (ECF)

1/4

fluid (ECF)

3/4

uneven distribution of solutes - chemical disequilibrium

• hallmark of a living organism

• continuous input of energy keeps the body in this state

• when solutes leak from one compartment to another, energy is required to return them

uneven distribution of solutes - ionic imbalance

changes lead to electrical signals (especially for nerves) to carry information to and from the brain

transport processes

• movement of material between body compartments

• a variety of mechanisms are used

  • some require energy (ATP)

  • some require concentration/pressure gradients

types of transport can be separated based on

• energy requirements

• physical requirements

types of transport

• diffusion

• protein mediated transport

• vesicular transport

diffusion

the movement of molecules from high concentration to low concentration

• called the concentration gradient or chemical gradient

passive process

no energy required

rate of diffusion depends on

• size of the concentration gradient

• distance the molecules need to travel

• temperature

• molecular size

• permeability of the membrane

diffusion - temperature

high temp = molecules move faster

diffusion - molecular size

small molecules move faster than larger ones

Fick’s law of diffusion across membranes - rate of diffusion varies with:

• surface area of the membrane

• concentration gradient

• membrane permeability

Fick’s law of diffusion across membranes - membrane permeability varies with:

• lipid solubility

• molecular size

changing the composition of the membrane can change its permeability

true

cell membrane permeability

• selectively permeable

• lipophilic molecules, carbon dioxide, oxygen move across easily

• polar molecules, ions, proteins have trouble diffusing on their own

diffusion across a membrane

only hydrophobic molecules (and to a small degree water) can diffuse across the phospholipid bilayer

protein-mediated transport

helps hydrophilic and charged molecules cross membranes

transporter proteins

aids in general movement of molecules across cell membrane

transporter proteins - two general types

• channel proteins

• carrier proteins

channel proteins

• creates a water-filled pore that links the ECF with the ICF

• cylindrical transmembrane protein subunits

types of channel proteins

mostly in a closed state

• chemically gated

• voltage gated

• mechanically gated

gated channels

open and close in response to signals

open channels

• or also called pores are usually open

• sometimes referred to as leaky channels

carrier proteins

• changes conformation with specific substrates

  • small organic molecules (glucose, amino acids)

  • ions

carrier proteins - uniport carriers

transport only one kind of substrate

carrier proteins - symport carriers

moves two or more substrates in the same direction across the membrane

carrier proteins - antiport carriers

move substrates in opposite directions

carrier proteins - cotransporters

moves more than one type of molecule at a time

facilitated diffusion can use carrier proteins

• some polar molecules in and out of the cell

• they do this with the help of carrier proteins