How does water move in the body?

1. 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

2. Distribution of solutes in the body fluid compartments plasma Interstitial fluid Intracellular fluid

3. Distribution of solutes in the body fluid compartments Ions and solutes are in disequilibrium

4. Ions and solutes are in disequilibrium • Water can cross the cell membrane Na+ K+ Na+ K+ proteins

5. Osmosis • water moves along its concentration gradient across a semi-permeable membrane • Water moves to dilute a solute

6. Osmosis

7. Osmotic pressure is pressure exerted to counter the movement of water to dilute something

8. 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

9. 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-

10. 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) Compare the osmolarity of 2 solutions:

11. 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)

12. 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

13. Osmosis, the diffusion of water across the cell membrane, has consequences on cells • After water leaves a cell, the volume changes (it can shrink)

14. Tonicity • Describes how the cell volume will change in a solution

15. P is penetrating solute N is nonpenetrating solute

18. Water moved into the cell to dilute the solutes.

19. Cell gains volume in a hypotonic solution • Cell looses volume in a hypertonic solution • Cell keeps the same volume in an isotonic solution.

20. 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

21. 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