Water Transport Osmosis, osmolarity, and osmotic pressure
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
Osmolarity is reflective of the concentration of solute particles in a solution.
Relative Osmolarity Hypotonic solutions have a lower concentration of solutes than cytoplasm (ICF) swelling or even lysis
Hypertonic solutions have a higher concentration of solutes than cytoplasm crenation
Isotonic solutions concentration of solutes is the same as cytoplasm
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
Bulk Transport Endocytosis 1. phagocytosis
Bulk Transport Endocytosis 2. pinocytosis
Bulk Transport Endocytosis can remove and store membrane proteins
Bulk Transport Exocytosis used to install membrane proteins secretion of products
Epithelial Tissue-Protection, Secretion, & Absorption A. Membranes (coverings and linings) 1. sheets of attached individual epithelial cells
2. transport of substances across an epithelium can be active or passive
3. epithelial cells packed tightly together by cell junctions and attached to underlying tissue at basement membrane
B. Gap junction (nexus) 1. circular intercellular connection
2. electrical or metabolic couplings - ions or chemical signals
C. Tight junctions 1. often located nearest apical surface
C. Tight junctions 2. seal intercellular space 3. continuous band around cell
Tight junctions tend to be leaky in areas where large volumes are absorbed across the epithelium (leaky epithelium).
Epithelial Transport A. Transcellular pathway may use active transport. 1. substances crossing an epithelium must cross cell membrane at least twice
Epithelial Transport 2. differentiated membranes basal and apical membranes can have different functional properties
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
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