Chapter 3 Cells and Tissues Cell Physiology

Membrane Transport  Membrane Transport  Movement of substances into and out of the cell  Selective Permeability  The plasma membrane allows some materials to pass while excluding others  Transport is by two basic methods  Passive transport (no energy)  Active transport (requires energy)

Solutions and Transport  Solution  Homogeneous mixture of two or more components  Solvent – dissolving medium  Solutes – material being dissolved  Intracellular fluid  Fluid on the interior of the cell  Interstitial fluid  Fluid on the exterior of the cell

Passive Transport Processes  Diffusion  Particles tend to distribute themselves evenly within a solution  Movement is from high to low concentration, or down a concentration gradient

Passive Transport Processes  Movement is down a concentration gradient 5 Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)

Passive Transport Processes  Types of diffusion  Simple diffusion  Unassisted process  Solutes are lipid-soluble materials or small enough to pass through membrane pores

Passive Transport Processes  Types of diffusion  Osmosis – simple diffusion of water  Highly polar water easily crosses the plasma membrane  High water concentration to low water concentration 7 membrane H2OH2O

Passive Transport Processes  Osmosis – simple diffusion of water  Hypertonic – there is a higher concentration of solute/lower concentration of water outside the cell  A cell in a hypertonic environment will ALWAYS LOSE water (CELL SHRINKS)

Passive Transport Processes  Osmosis – simple diffusion of water  Hypotonic – there is a lower concentration of solute/higher concentration of water outside the cell  A cell in a hypotonic environment will ALWAYS GAIN water (CELL SWELLS)

Passive Transport Processes  Osmosis – simple diffusion of water  Isotonic – there is an equal concentration of solute and water inside and outside the cell  In an isotonic environment water will diffuse in & out at equal rates (CELL SIZE STAYS THE SAME)

Passive Transport Processes Cytolysis Plasmolysis H2O moved into cell H2O moved out of cell Hypotonic Hypertonic

Passive Transport Processes 12 Osmosis in Red Blood Cells Red Blood Cell in a Hypotonic Environment RBC swells & bursts (lyses)

Passive Transport Processes  Types of diffusion  Facilitated diffusion  Substances require a carrier protein for passive transport  Carrier protein changes shape to move materials across the membrane

Passive Transport Processes

 Filtration  Water and solutes are forced through a membrane by fluid, or hydrostatic pressure  A pressure gradient must exist  Example: Filtration occurs in the kidneys

Active Transport Processes  Requires energy  Transport substances that are unable to pass by diffusion  Too large  Unable to dissolve in the fat core of the membrane  Have to move against a concentration gradient  Two common forms of active transport  Solute pumping  Bulk transport

Active Transport Processes  Two common forms of active transport  Solute pumping  Bulk transport  Solute pumping  Ions are transported by solute pumps  ATP energizes protein carriers  Moves substances against concentration gradients  Example: Sodium – potassium pump in Nervous system

Active Transport Processes

19 Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

Active Transport Processes  Bulk transport  Exocytosis  Moving materials out of the cell by vesicle  Vesicle attaches to plasma membrane and is emptied  Example: hormones in the nervous system Inside Cell Cell environment

Active Transport Processes

 Bulk transport  Endocytosis  Extracellular substances are engulfed by being enclosed in a membranous vesicle  Types of endocytosis  Phagocytosis – cell eating  Pinocytosis – cell drinking  Receptor – mediated endocytosis

Active Transport Processes  Phagocytosis – cell eating (large)  Pinocytosis – cell drinking (small)

24 White Blood Cell Bacteria

Active Transport Processes  Receptor – mediated endocytosis  Some integral proteins on the plasma membrane have receptors that recognize and take in hormones, cholesterol, etc.