Diffusion, osmosis, tonicity

Question 1

Diffusion

Answer 1

Allows for the passive movement of molecules across various biological borders from an area of high concentration to low concentrations resulting in an equal distribution

No energy required

Can occur in gasses, liquids, solids

Question 2

Types of diffusion

Answer 2

1. paracellular transport
2. transcellular transport

Question 3

Paracellular transport

Answer 3

movement across barrier in between cells

driven by gradients

Question 4

What regulates paracellular transport?

Answer 4

Regulated by tight and adherens junctions between endothelial cells. The number of junctions on the lateral surface of the epithelial cells can greatly influence regulation (can be tight or leaky)

Question 5

Transcellular transport

Answer 5

Movement across cells. Driven by active processes such as transport proteins, pumps, and receptors

Question 6

Factors influencing rate of diffusion

Answer 6

Based on Fick’s Law.

Directly proportional factors
* Concentration gradient
* Surface area where diffusion occurs

Inversely proportional
* Solvent viscosity (thickness)- the thicker the particles, the slower diffusion will be
* Radius of diffusing particles- larger the particles, slower the diffusion

Question 7

Oxygen transport

Answer 7

Passive diffusion. Oxygen will move from areas of high partial pressure to areas of low partial pressure.

Reason why hemoglobin picks up oxygen in RBCs so that more oxygen will come inside the cells

Question 8

Hydrated shells of ions

Answer 8

Ions become hydrated when surrounded by water in solution. Diffusion is affected by ion size, and their hydrated shells might be even larger.

Ex. K ions are larger than Na ions, BUT Na attract more water than K. So Na is larger in the long run and is slower to diffuse

Question 9

Electrochemical gradient

Answer 9

Determines ion movement.

Ions will move from high to low concentrations AND towards opposite charges.

When both of these gradients are working together, diffusion will be much faster.

Question 10

Osmosis

Answer 10

Diffusion describing the movement of water from high to low concentration across a semi-permeable membrane.

Question 11

Osmotic pressure

Answer 11

The amount of solutes within the water which determine which way water will move.

The higher the solutes in water, the higher the osmotic pressure. Water will move towards the area with the most solutes.

This is because if there are more solutes taking up space then there would be less water.

Question 12

Osmosis in the blood

Answer 12

• Hydrostatic pressure pushes water out to interstitial space
• Osmotic pressure draws water into interstitial space

Question 13

Effective osmolarity or Tonicity

Answer 13

The ability of a solution to initiate water movement.

Depends on impermeable solutes or effective osmoles.

Question 14

Effective osmoles

Answer 14

sodium, glucose in diabetic patients

Question 15

Ineffective osmoles

Answer 15

urea (very permeable so when cells are very active, the urea will move out of bloodstream)

Question 16

Using NaCl in IV fluids

Answer 16

NaCl is used because cells are generally impermeable to Na because there isn’t enough transport for it which means that Na will stay in the bloodstream. Then since Na is higher in the bloodstream, the osmotic pressure is higher, and water will move into the bloodstream

Question 17

Tonicity of a solution

Answer 17

Describes the concentrations of impermeant solutes compared to normal plasma

3 options: hypertonic, isotonic, hypotonic

Question 18

Isotonic solution

Answer 18

equal amounts of impermeable solutes compared to plasma

Question 19

Hypotonic solution

Answer 19

contains less impermeable solutes compared to plasma

Question 20

Hypertonic solution

Answer 20

contains more impermeable solutes compared to plasma

Question 21

RBCs in hypotonic solution

Answer 21

More impermeable solutes inside cell, RBC will expand, as fluid is drawn inside the cell

Question 22

RBCs in hypertonic solution

Answer 22

more impermeable solutes outside the cell, RBC will shrink as fluid is drawn outside the cell

Question 23

RBCs in isotonic solution

Answer 23

RBC will stay the same

Question 24

Osmosis in the blood

Answer 24

• Osmotically active particles draw water into the blood vessels from the interstitial space
• Hydrostatic pressure pushes water out into the interstitial space

Question 25

Osmolal gap in the blood

Answer 25

Looks at the plasma osmolarity in the blood.

Osmolal gap= measured-calculated osmolality
Normal < 10mOsm/kg
High > 10 mOsm/kg

The body will sense changes in tonicity via osmoreceptors. These receptors will tell the body to release enzymes and bring the osmotic pressure back to baseline.