Cell Membrane: Transport, Osmosis, and Body Fluids

Question 1

Membrane Transport

Answer 1

Cell membranes are selectively permeable

Question 2

What are the two properties that influence whether they can permeate the cell membrane without assistance?

Answer 2

1. Relative solubility of particle in lipid
2. Size of the particle

Question 3

Two forces are involved in accomplishing transport

Answer 3

1. Passive forces (no energy required)
2. Active forces (energy/ATP required)

Question 4

Diffusion

Answer 4

Depends on the random movement of molecules.
Establishes equilibrium without energy.
Molecules move from areas of high concentration to low concentration.
Occurs across a permeable membrane.
Is crucial to survival of every cell.

Question 5

Facilitated Diffusion

Answer 5

Molecule binds and causes conformational change in order to release through membrane

Ex: GLUT 1 (glucose transporter in erythrocytes) is needed for cellular respiration

Question 6

Non-permeable membrane

Answer 6

When a solute is too large or too hydrophilic to move through membrane

Question 7

Channel-mediated transport

Answer 7

Gated ion channel that is specific to one type of ion.
Opens in response to stimulus and lets many ions in at once

Question 8

Primary Active Transport

Answer 8

Ex: The Na+/K+ ATPase
Utilized ATP for a switch of Na and K (3 Na out and 2 K in)
Critical for survival

Question 9

Secondary Active Transport

Answer 9

ATP is not directly used

Ex: Glucose transport (SGLT1): Na provides energy, glucose is moved against concentration gradient

Question 10

Osmosis

Answer 10

Net diffusion or movement of water down its concentration gradient

Water moves by osmosis to the area of higher solute concentration

Question 11

Relationship between solute and water concentration in solution

Answer 11

Higher the solute concentration, the lower the concentration of water

Question 12

Channels

Answer 12

Water is small enough to permeate the plasma membrane
The driving force for movement is the concentration gradient

Ex: aquaporins

Question 13

Permeable Membrane

Answer 13

Membrane allows both water and solute to pass

Question 14

Semi-permeable membrane

Answer 14

Membrane allows water to pass but not solute

Ex: water will move (osmosis) to balance out solute concentration

Question 15

Hydrostatic Pressure

Answer 15

Solute can’t move across membrane thus water has to move and creates a lower level of fluid where water moves from and higher level where water moved to.

The difference is called hydrostatic pressure difference

Question 16

Osmolarity (mOsm/L) / Osmolality (mOsm/kg)

Answer 16

Total amount of particles per amount of solution
The intracellular and extracellular fluid is essentially identical (~290 mOsm)

Question 17

Higher concentration of impermeable substance in a cell:

Answer 17

Water is forced to move and cell volume and shape change

Question 18

Tonicity

Answer 18

Ultimate effect a solution has on cell volume which determines whether cell size remains the same, swells, or shrinks when a solution surrounds the cell

Question 19

Effective osmolarity

Answer 19

refers to the osmolarity of non permeable particles in solution

controls the actual movement of water

Question 20

Isotonic

Answer 20

No net movement of water; no change in cell volume

Intracellular osmolarity = extracellular osmolarity

Question 21

Hypotonic

Answer 21

Water diffuses into cells; cell swells

Question 22

Hypertonic

Answer 22

Water diffuses out of cells; cells shrink

Question 23

Clinical Signs of Hydrations Status

Answer 23

1. Skin turgor (elasticity after tenting)
2. Mucous membranes (pink and moist)
3. Capillary Refill time (should be quick)
4. Eyes (normal vs. sunken)
5. Hematocrit; more quantifiable, more reliable

Question 24

Intracellular fluid

Answer 24

Fluid contained within the cells

Question 25

Extracellular fluids

Answer 25

fluid outside the cells (plasma, interstitial fluid, minor ECF components)

Question 26

Total Body Water (TBW)

Answer 26

ICF + ECF = ICF + ISF + Plasma
Total plasma protein (g/dL)

Question 27

Hematocrit

Answer 27

Fraction of plasma occupied by red blood cells (RBC) after centrifugation

Question 28

Body Water Dynamics: Basic Principles

Answer 28

-Water shifts between compartments to maintain equality
-Electrolytes, such as Na, do not cross cell membranes and are confined to ECF
-Any loss or gain of water and/or electrolytes must initially occur in the ECF
-Changes in TBW, total plasma protein and hematocrit may occur