Cellular Physiology: Membrane Transport

requires ATP, transports particles up concentration gradient

Active transport

Osmosis: channel proteins in cell membrane

Aquaporins

bulk transport into a cell

Endocytosis

Eliminating or secreting material from cell and replacement of plasma membrane

Exocytosis

Movement of particles through a selectively permeable membrane by hydrostatic pressure

Filtration

Mechanisms considered to be passive

Filtration Simple diffusion Facilitated diffusion Osmosis

referred to as "cell drinking" non-selective constitutive process

Fluid-phase pinocytosis

Simple Diffusion: If the plasma membrane is present

Gated-channels open & close in response to stimuli: -ligand-regulated gates -voltage-regulated gates - voltage-regulated gates (4)

cells in this solution would lose water and shrivel (crenate)

Hypertonic solution

has high concentration of nonpemeating solutes (low water concentration)

Hypertonic solution

cells in this solution would absorb water, swell and may burst (lyse)

Hypotonic solution

has low concentration of nonpermeating solutes (high water concentration)

Hypotonic solution

Simple Diffusion: If the plasma membrane is present

Important in nerve signal and muscle contraction (5)

Water Movement: Three terms used to describe tonicity

Isotonic Hypotonic Hypertonic

cell will neither swell nor shrink when placed in this solution

Isotonic solution

has same concentration of nonpermeating solutes as the cell

Isotonic solution

low-density lipoproteins

LDL's

Diffusion of water through a selectively permeable membrane

Osmosis

Transport Mechanisms are classified as either being

Passive or Active

requires no ATP, movement of particles across selectively permeable membrane, down concentration gradient

Passive transport

Active Transport: A protein embedded in the membrane (a pump) is used to move a specific substance against its concentration gradient.

Primary Active Transport

Active Transport: The substance to be transported binds to the pump and is moved across the plasma membrane. Ex. iodine pump, Na+K+ pump

Primary Active Transport

Mechanisms considered to be active

Primary active transport (pumps) Secondary active transport Bulk transport (endocytosis and exocytosis)

The transport mechanism itself is passive, but depends on the concentration gradient established by an active transport mechanism ex. intestinal absorption of glucose.

Secondary Active Transport

3Na+ bind to receptor, carrier phosphorylated, changes conformation, releases Na+ in ECF, binds 2K+, releases Pi, resumes conformation, releases K+

Sodium-Potassium Pump

Simple Diffusion: If the plasma membrane is present

Some channels are constantly open (3)

Diffusion rates are influenced by the following factors: difference, rate

Steepness of conc.gradient

Active Transport: Primary Active Transport

The energy to fuel the pump is supplied directly by ATP.

Receptor-Mediated Endocytosis

This occurs in the uptake of LDL's by endothelium of blood vessels

Receptor-Mediated Endocytosis: uses this process to move a substance across a cell

Transcytosis

Simple Diffusion: If the plasma membrane is present

a integral protein channel or pore may be utilized. Ions move into and out of cells using these channels (2)

Facilitated Diffusion: Passive transport of a solute down its concentration gradient, across membrane, with

aid of a carrier

a carrier that transports solutes in opposite directions ex. Na+/K+ pump

antiport

Transport of large particles and fluid droplets through the membrane, using vacuoles or vesicles

bulk transport

Water Movement: Tonicity - ability of a solution to affect fluid volume and pressure within a cell depends on

concentration and permeability of solute

Carriers often function in

cotransport

When a carrier transports 2 different solutes simultaneously, or within one transport cycle

cotransport

phase pinocytosis

fluid in bulk transport

Osmosis: Diffusion of water through a selectively permeable membrane

from an area of more water ( side B = less dissolved solute) to an area of less water (side A = more dissolved solute)

Facilitated Diffusion: Used by larger solutes like

glucose

Filtration: In capillaries, blood pressure forces water, salts, nutrients and solutes into tissue fluid, while larger particles like blood cells and protein are

held back

Osmosis

increase in aquaporins increases rate of osmosis

Simple Diffusion: bind to chemical messenger

ligand-regulated gates

Simple Diffusion: Simple diffusion does not always involve a

membrane

Diffusion rates are influenced by the following factors: permeability, rate

membrane permeability

Diffusion rates are influenced by the following factors: area, rate

membrane surface area

Diffusion rates are influenced by the following factors: larger molecules move slower

molecular weight

Receptor-Mediated Endocytosis: Receptors on membrane bind to specific molecules in ECF, cluster together, then sink in, become coated with a

peripheral protein, clathrin, and pinch off into cell as clathrin-coated vesicle

engulfing large particles by pseudopods

phagocytosis

mediated endocytosis

receptor in bulk transport

the movement of particles as a result of their constant, random motion

simple diffusion

Simple Diffusion: If the plasma membrane is present

small, nonpolar, uncharged substances may diffuse directly across the phospholipid bilayer ex. oxygen, carbon dioxide, steroids, fat-soluble vitamins, alcohol. (1)

a carrier that transports both solutes in the same direction ex. Na+/glucose transporter

symport

Diffusion rates are influenced by the following factors: temp., motion of particles

temperature

Filtration: Hydrostatic pressure

the force exerted on the membrane by water

Water Movement: ability of a solution to affect fluid volume and pressure within a cell

tonicity

Receptor-Mediated Endocytosis: insulin absorbed into endothelial cell from blood by RME, then

transported out into tissues

Simple Diffusion: gates:physical stress such as stretch and pressure

voltage-regulated gates

Simple Diffusion: potential changes across plasma membrane

voltage-regulated gates

Facilitated Diffusion:Solute binds to carrier

, carrier changes shape and releases solute on other side of membrane

the two basic forms of bulk transport

-Endocytosis -Exocytosis

Three forms of endocytosis are:

-phagocytosis -fluid -receptor

Functions of Sodium-Potassium Pump

. Regulation of cell volume cell swelling stimulates the Na+- K+ pump: (down) ion concentration, (down osmolarity and cell swelling 2. Heat production 3. Maintenance of a membrane potential Na+- K+ pump keeps inside of membrane negative, outside of membrane positive 4. Secondary active transport