How does water move in the body? The cell membrane is semi-permeable Water can move freely Water is...
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Transcript of How does water move in the body? The cell membrane is semi-permeable Water can move freely Water is...
How does water move in the body?
• The cell membrane is semi-permeable
• Water can move freely
• Water is in equilibrium between cells and extracellular fluids (osmotic equilibrium)
• Ions and solutes are disequilibrium
• Osmosis water moves along its concentration gradient across a semi-permeable membrane
Distribution of solutes in the body fluid compartments
plasma
Intracellular fluid
Interstitial fluid
Distribution of solutes in the body fluid compartments
Ions and solutes are in disequilibrium
Ions and solutes are in disequilibrium
• Water can cross the cell membrane
Na+
K+
Na+
K+
proteins
Osmosis
• water moves along its concentration gradient across a semi-permeable membrane
• Water moves to dilute a solute
Osmosis
Osmotic pressure is pressure exerted to counter the movement of water to dilute something
Osmolarity
• Describes the number of particles in solution• Know this and the direction of water movement
can be predicted
• # of particles in 1 liter of solution
• Is expressed as osmoles/L, or OsM
• If very dilute: milliosmoles/L, or mOsM
• Human body, approx 300 mOsM
Osmolarity: number of particles in 1L
• 1 M glucose = 1 OsM glucose
• 1M NaCl = 2 OsM NaCl, because NaCl disassociates to 2 ions in solution.
Na+ Cl-
Compare the osmolarity of 2 solutions:
• Solution A
• 1 OsM glucose
• A is hyposmotic to B
• (A has fewer particles than B)
• Solution B
• 2 OsM glucose
• B is hyperosmotic to A
• (B has more particles than A)
• Solution C
• 1 OsM NaCl
• C is hypotonic to B
• (C has fewer particles/L than B)
Compare the osmolarity of 2 solutions:
• Solution B
• 2 OsM glucose
• B is hyperosmotic to C
• (B has more particles/L than A)
Compare the osmolarity of 2 solutions:
• Solution A
• 1 OsM glucose
• A is isosmotic to C
• Solution C
• 1 OsM NaCl
• C is isosmotic to A
Osmosis, the diffusion of water across the cell membrane, has consequences on cells
• After water leaves a cell, the volume changes (it can shrink)
Tonicity
• Describes how the cell volume will change in a solution
P is penetrating solute
N is nonpenetrating solute
Water moved into the cell to dilute the solutes.
• Cell gains volume in a hypotonic solution
• Cell looses volume in a hypertonic solution
• Cell keeps the same volume in an isotonic solution.
Tonicity indicates how the cell volume will change in a solution
• In a hypotonic solution, the cell has a higher concentration of a nonpenetrating solute than the solution, water moves in.
• In a hypertonic solution, the cell has a lower concentration of nonpenetrating solute than the solution, water leaves the cell
During intavenous injection:
• 0.9% (normal) saline isotonic
• D5--.9% saline (5% dextrose) isotonic
• D5W hypotonic
• 0.45% saline hypotonic
• Vs dehydration hypotonic
• Vs blood loss isotonic