Chapter 3 Cells and Tissues Cell Physiology. Membrane Transport Membrane Transport Movement of substances into and out of the cell Selective Permeability

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


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)


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)


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)


CytolysisCytolysis PlasmolysisPlasmolysis

H2O moved into cell

H2O moved out of cell

HypotonicHypotonic HypertonicHypertonic


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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)


Facilitated diffusion

Substances require a carrier protein for passive transport

Carrier protein changes shape to move materials across the membrane



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 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


Phagocytosis – cell eating (large)

Pinocytosis – cell drinking (small)

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White Blood Cell

Bacteria


Receptor – mediated endocytosis

Some integral proteins on the plasma membrane have receptors that recognize and take in hormones, cholesterol, etc.

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Chapter 3 Cells and Tissues Cell Physiology. Membrane Transport Membrane Transport Movement of substances into and out of the cell Selective Permeability