chapter 3 cells and tissues cell physiology. membrane transport membrane transport movement of...
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Chapter 3
Cells and Tissues
Cell Physiology
Membrane TransportMembrane 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 TransportSolutions 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 ProcessesPassive 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 ProcessesPassive Transport Processes Movement is down a concentration gradient
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Cell membrane
Solute moves Solute moves DOWNDOWN concentration concentration gradient gradient (HIGH to LOW)(HIGH to LOW)
Passive Transport ProcessesPassive Transport Processes Types of diffusion
Simple diffusion
Unassisted process
Solutes are lipid-soluble materials or small enough to pass through membrane pores
Passive Transport ProcessesPassive 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
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membrane
H2O
Passive Transport ProcessesPassive 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 ProcessesPassive 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 ProcessesPassive 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 ProcessesPassive Transport Processes
CytolysisCytolysis PlasmolysisPlasmolysis
H2O moved into cell
H2O moved out of cell
HypotonicHypotonic HypertonicHypertonic
Passive Transport ProcessesPassive Transport Processes
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Osmosis in Red Blood CellsOsmosis in Red Blood Cells
Red Blood Cell in a Hypotonic EnvironmentRBC swells & bursts (lyses)RBC swells & bursts (lyses)
Passive Transport ProcessesPassive 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 ProcessesPassive Transport Processes
Passive Transport ProcessesPassive 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 ProcessesActive 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 ProcessesActive 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 ProcessesActive Transport Processes
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Sodium-Potassium PumpSodium-Potassium Pump
3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential
Active Transport ProcessesActive 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 CellCell environment
Active Transport ProcessesActive Transport Processes
Active Transport ProcessesActive 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 ProcessesActive Transport Processes
Phagocytosis – cell eating (large)
Pinocytosis – cell drinking (small)
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White Blood Cell
Bacteria
Active Transport ProcessesActive Transport Processes
Receptor – mediated endocytosis
Some integral proteins on the plasma membrane have receptors that recognize and take in hormones, cholesterol, etc.