NURS113 Lecture Notes - Lecture 25: Semipermeable Membrane, Body Fluid, Electrolyte
14 Jun 2018
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UNIT 11: FLUID, ELECTROLYTES AND ACID-BASE IMBALANCES
Fluid and Electrolyte Disorders
What do body fluids do?
- Contains water and electrolytes
- Surrounds cells to lubricate and act as solvent for metabolic chemical reactions
- Transports oxygen, nutrients, chemical messengers, and waste products to their destinations
Composition of the intracellular compartment (ICF)
- Fluid inside cell
- ⅔ body fluid in adults
- High potassium concentration
- Contains impermeable proteins
Composition of the extracellular compartment (ECF)
- Fluid outside cells, including body cavities (CSF, fluid
in joint spaces)
- ⅓ body fluid in adults with a higher sodium
concentration
- Consists of
- Interstitial compartment (between cells)
- Intravascular compartment (in blood vessels)
Fluid barriers
- Plasma and interstitial fluid separated by walls of blood
vessels
- Proteins that cannot cross the cell membrane and so it stays inside the cell
- High potassium inside and high sodium outside when cell is at rest
- ECF and ICF separated by cellular plasma membranes
- Major differences between ECF and ICF
- Presence of proteins in ICF that cannot permeate the cell membrane
- Unequal distribution of sodium and potassium
Osmosis
- Diffusion of water across a
semipermeable membrane from
lower solute concentration (so
higher water) to area of higher
solute concentration (low water)
- LOW SOLUTe to HIGH
solute → going to
maintain the solute
concentration and
balance the water concentration as well
- So promotes the retention of water
- Consider the density of solute in solution
- Net diffusion of water is known as osmosis
**eventually, you are going to get into a steady state of homeostasis in terms of the different solutes and
solvents**
Effects of osmosis on cell size and volume
- Tonicity - the effect the solution has on cell volume and size
- 3 types of IV solutions (intravenous)
- Isotonic
- Hypotonic
- Hypertonic
Isotonic solutions
- Water concentration in the solution is same as the water concentration in the
cell
- When you give someone IV and it is the same concentration within the
interstitial and intracellular space (because all compartments have the same
concentration of solutes, there is no movement anywhere. Water does not go into the
cell to make it bigger, or leave to make it shrink)
- No movement of water into or out of cells
- Cells neither shrink or swell
- Eg: 0.9% NS (normal saline)
- When you give them this, you are ensuring their cells do not get
bigger or smaller → is an isotonic solution
Hypotonic solutions
- Solute concentration in solution less than solute concentration in the cell
(ahh, so because the solute concentration is less in the vascular compared
to in the cell, fluids will go from the less concentrated (solution) to the more concentrated (cell),
which means water goes into cells → hypotonic)
- Fluid to vasculature system, the fluid you give has a solute concentration that is less than
what is in the cell; because there is a difference in solute concentration between the
intracellular and the intravascular; water is going to move from the vascular space into
the cell
- Go from a higher concentration area to a lower concentration area
- This causes the cell to swell → water going in to maintain osmotic balance or the steady
state. Enough hypotonic solution more water going in and eventually will burst
- Water moves from solution into cell
- Cell swell and may eventually burst
- Eg: 0.45% NS
- Half of the normal saline which means LESS solute
Hypertonic solutions
- Solute concentration in solution is greater than the solute concentration in the cell
- In vascular space, and they have a HIGHER concentration of solutes than what is in the
cell. Low concentration of water. So the cell shrinks, because the cell solutes want to go
from the high concentration of water to a lower concentration, which means water goes
out the cell and causing the cell to shrink (water leaving it)
- Water moves from cell into solution
- Conditions when the cell is too big, so you MUST shrink the size of the cell. You give a
hypertonic solution in order to do so
- Cells shrink and crenate
- Eg: 3% NS
- Higher concentration of solute than what is in the cell (which would be like 0.9% because
that is what isotonic is)
**always
think: how do
you want the
cell to be in
the end? Do
you want the
cell to shrink?
Use
hypertonic**
Fluid
distribution
- Maintenance of fluid distribution
between the vascular and interstitial
Document Summary
Surrounds cells to lubricate and act as solvent for metabolic chemical reactions. Transports oxygen, nutrients, chemical messengers, and waste products to their destinations. Fluid outside cells, including body cavities (csf, fluid in joint spaces) (cid:1151) body fluid in adults with a higher sodium concentration. Plasma and interstitial fluid separated by walls of blood vessels. Proteins that cannot cross the cell membrane and so it stays inside the cell. High potassium inside and high sodium outside when cell is at rest. Ecf and icf separated by cellular plasma membranes. Presence of proteins in icf that cannot permeate the cell membrane. Diffusion of water across a semipermeable membrane from lower solute concentration (so higher water) to area of higher solute concentration (low water) Low solute to high solute going to maintain the solute concentration and balance the water concentration as well. Consider the density of solute in solution. Net diffusion of water is known as osmosis.
