Membrane Dynamics

Phys

What is osmosis?

movement of water across semi-permeable membrane into more concentrated solution to reach equilibrium

What is osmotic pressure?

pressure required to oppose osmosis

What is osmolarity?

number of osmotically active particles in solution

In human physiology, are ‘osmolarity’ and ‘osmolality’ interchangeable?

yes

What is the normal osmolarity value for the human body?

280-296 milliosmoles

What is tonicity?

how a cell responds in solution based on its solute permeability and concentration

What is hypertonicity?

There is more solute outside the cell than inside the cell, causing water to leave the cell, and the cell shrinks.

What is isotonicity?

The concentration is about the same inside and outside of the cell, causing no change in cell size.

What is hypotonicity?

There is more solute inside than outside the cell. To dilute the concentration, water moves inside the cell, which causes the cell to swell.

What does tonicity always describe?

The relationship between the cell and the solution which it is placed.

Can osmolarity predict tonicity?

No.

In the real world, why is tonicity crucial?

It is crucial in deciding which IVs to give to patients.

What is distinguishing about penetrating solutes?

They can cross the membrane.

What is distinguishing about non-penetrating solutes?

They cannot cross the membrane.

What is the most important non-penetrating solute in the human body?

NaCl (salt)

What is bulk flow?

most general flow of transport; gases and liquid move down pressure gradient; higher pressure to lower pressure

What is an example of bulk flow?

blood flows from areas of higher pressure in arteries to lower pressure in veins

What is passive transport?

requires no energy, moving down concentration gradient

What is active transport?

requires energy, moving up against concentration gradient

What are the aspects of diffusion?

1. passive process

2. high concentration to low

3. net movement until concentration is equal

4. rapid over short distances

5. directly related to temperature

6. inversely related to molecular weight and size

7. in open system or across a partition

Do ions move by diffusion?

NO — ions are influenced by electrochemical gradients

What does Fick’s Law of Diffusion mean?

Diffusion rate is directly proportional to:

1. surface area of membrane (more room for things to move)

2. concentration gradient (bigger difference = faster rate)

3. membrane’s permeability (molecular size, lipid solubility, composition of lipid bilayer)

What is facilitated diffusion?

passive process that uses carrier protein to transport another lipophobic or electrically charged particle down the gradient

What is active transport?

requires ATP to move things against concentration gradient

What are the 4 major function of membrane potentials?

1. Structural proteins (cell junctions, connecting membrane to cytoskeleton, cell shape)

2. Membrane enzymes (help catalyze reactions)

3. Membrane receptor proteins (help with chemical signaling and communication

4. Membrane transport proteins (channel and carrier proteins)

What are the 4 types of channel proteins?

Water, ion, open, and gated channels

What are the 3 types of gated channels?

chemically gated channel, voltage gated channels, and mechanically gated channels

Both sides of ____ protein are never open at the same time.

carrier

symport carrier proteins

move all things in same direction

antiport carrier proteins

move things in opposite directions

uniport

1

co-transporters

more than 1

What are GLUT transporters?

move glucose in/out of cells by facilitated diffusion decrease

Carrier-mediated transport is dictated by ___

specificity, competition, and saturation

What is phagocytosis?

cell eating; seek and destroy threat to cell; vesicle engulfs phagosome

What is endocytosis?

bringing something into the cell; something the cell needs; membrane indents and smaller vesicle brings inside the necessity

What is exocytosis?

exports large molecules and waste from lysosomes

What are the 5 types of epithelial transport?

absorption, secretion, paracellular transport, transcellular transport, and transcytosis

What does absorption consist of?

moves from lumen to ECF to be absorbed by body and into bloodstream

What does secretion consist of?

moves from ECF to lumen

What does paracellular transport consist of?

occurs in junction between epithelial cells

What does transcellular transport consist of?

goes through cells, meaning it has to cross 2 membranes in the epithelial tissue

What does transcytosis consist of?

endocytosis + vesicular transport + exocytosis; allows transported materials to remain intact

What is the value of resting membrane potential?

-70 millivolts

What is resting membrane potential?

the state of electrical disequilibrium that all living cells exist in; inside the cell is slightly more negative than the outside

What is the most important ion in establishing resting membrane potential?

potassium

What is depolarization?

membrane potential is less negative than resting membrane potential

What is repolarization?

membrane potential returns to resting membrane potential

What is hyperpolarization?

membrane potential becomes more negative than resting membrane potential

What is the cause of cystic fibrosis?

a faulty transporter — CFTR