1. Water Transport Osmosis, osmolarity, and osmotic pressure

2. Semipermeable membrane – allow some molecules to cross while restricting others Osmotic pressure – force associated with the movement of water Osmolarity – ability of solution to induce water to cross a membrane Figure 2.13

3. Osmolarity is reflective of the concentration of solute particles in a solution.

4. Relative Osmolarity Hypotonic solutions have a lower concentration of solutes than cytoplasm (ICF) swelling or even lysis

5. Hypertonic solutions have a higher concentration of solutes than cytoplasm crenation

6. Isotonic solutions concentration of solutes is the same as cytoplasm

7. Tonicity Hypotonic solutions have a lower concentration of solutes than cytoplasm Hypertonic solutions have a higher concentration of solutes than cytoplasm crenation lysis Isotonic solutions concentration of solutes is the same as cytoplasm

8. Bulk Transport Endocytosis 1. phagocytosis

9. Bulk Transport Endocytosis 2. pinocytosis

10. Bulk Transport Endocytosis can remove and store membrane proteins

11. Bulk Transport Exocytosis used to install membrane proteins secretion of products

13. Epithelial Tissue-Protection, Secretion, & Absorption A. Membranes (coverings and linings) 1. sheets of attached individual epithelial cells

14. 2. transport of substances across an epithelium can be active or passive

15. 3. epithelial cells packed tightly together by cell junctions and attached to underlying tissue at basement membrane

16. B. Gap junction (nexus) 1. circular intercellular connection

17. 2. electrical or metabolic couplings - ions or chemical signals

19. C. Tight junctions 1. often located nearest apical surface

20. C. Tight junctions 2. seal intercellular space 3. continuous band around cell

22. Tight junctions tend to be leaky in areas where large volumes are absorbed across the epithelium (leaky epithelium).

23. Epithelial Transport A. Transcellular pathway may use active transport. 1. substances crossing an epithelium must cross cell membrane at least twice

24. Epithelial Transport 2. differentiated membranes basal and apical membranes can have different functional properties

25. Epithelial Transport B. Water transport across an epithelial membrane - can be passive or can be “uphill” - there is no such thing as active transport of water - uphill movement of water is done via osmosis - is a secondary consequence of solute transport

26. Epithelial Transport standing-gradient hypothesis (solute-coupled water transport) a. tight junctions near apical surface b. leaves intercellular clefts c. active transport of salt out of cells d. water follows salt