3. Solutions and Concentrations

Question 1

What are the symptoms of dehydration?

Answer 1

Sunken eyes

Lack of skin turgor

Low blood pressure

Concentrated Urine

Weight loss

Dry mouth

Rapid pulse

Refusing fluids

Question 2

What causes dehydration?

Answer 2

Vomiting

Diarrhoea

Excessive sweating

Low water intake

Drainage from burns

Damage to thirst mechanism

Question 3

Why do we need H2O?

Answer 3

Universal solvent

Chemical reactions occur in water

Found as major component of plasma and cells.

Lubricant of joints, organs

High ability to absorb and retain heat as stays in liquid state over broad range (0-100 0C) of temperature

Large amount of heat required to increase­ its temperature (this stabilises body temperature plus sweating carries a lot of heat away from body)

Question 4

Where does our body water come from?

Answer 4

Drinks 1500ml

Food 750ml

Water of metabolism 250ml

Question 5

How much water is in our body?

Answer 5

32-40L approx 60%

Question 6

Where do we lose water from our bodies?

Answer 6

Urine 1500ml

Stools 100ml

Sweat 200ml

Respiratory loss 700ml

Question 7

Where is the water in the body?

Answer 7

Intracellular fluid 25L=2/3=66%

Extracellular fluid/Interstitial fluid 12L=30%

Plasma 3L=7.5%

Joints, CSF 0.7L

Question 8

What are aquaporins?

Answer 8

Semi-permeable membranes

Question 9

Define simple diffusion?

Answer 9

Movement from an area of high concentration to an area of low concentration through a semi-permeable membrane.

This is passive.

Question 10

Define defusion?

Answer 10

Allows substances to move in and out of cells e.g. organelles, large proteins, blood etc

Question 11

What factors affect diffusion rate?

Answer 11

Temperature i.e. Increased temperature increases motion of particles

Molecular weight i.e. Larger molecular weight means particles move slower

Steepness of conc. gradient i.e. increased difference, increased rate

Membrane surface area i.e. increased area increased rate

Membrane permeability i.e. increased permeability, increased rate

Question 12

Define osmosis?

Answer 12

Movement of water down its concentration gradient accross a semipermiable membrane

This is passive

Question 13

What is a solution?

Answer 13

A homogenous mixture of one or more dissimilar substances

Usually a liquid (solvent) and a solute (electrolyte - dissolved particle)

Question 14

What are the three types of solutions?

Answer 14

Aqueous solutions

Colloids

Suspensions

Question 15

What is an aqueous solution?

Answer 15

Small molecules dissolve

Ionic compounds dissociate into anions (-ve) and cations (+ve)

Electrolytes are soluble inorganic molecules whose ions conduct electricity in solution

Question 16

What is a colloid?

Answer 16

A solution where proteins or other large molecules as solute e.g. plasma or albumin

Question 17

What is a suspension?

Answer 17

A solution with even larger molecules than colloid solutions

Particles settle if undisturbed

Question 18

What is pH?

Answer 18

A low pH is acidic with a high amount of H+ ions, a high pH is basic with a high amount of OH- ions

The body has a pH of 7.35

Question 19

What is osmotic pressure?

Answer 19

The pressure exerted by water in a solution

OR

Exerted by solutes drawing water into area of low water

OR

The force (thrust) of water movement into the higher concentration solution

OR

The amount of hydrostatic pressure required to stop osmosis

OR

Pull of fluid from high -> low concentration

e.g. NA has high osmotic pressure as it pulls water across semi permeable membrane

Question 20

How can the concentration of solutions be measured?

Answer 20

1. ) g/L - weight per volume
2. ) % - weight in grams per 100ml
3. ) Moles of solute per litre i.e. 1 mole = Number of atoms/molecules present in a sample equal to the molecular weight in grams

so 1 mole H2=1 mole O2=1 mole NaCl same concentration

Question 21

Why use moles?

Answer 21

Gives better ability to comare as number of molecules in solution is more important

Question 22

What is osmolarity?

Answer 22

Number of osmoles/L solution (H20)

Dependent on number of particles dissolved rather than the weigh of the molecule

Question 23

What is osmolality?

Answer 23

Number of osmoles/kg (H20)

Question 24

How do you measure osmotic concentration?

Answer 24

Osmoles/L or Kg

Question 25

What is 1 osmole?

Answer 25

1 mole of dissolved particles i.e. 1 mole of NaCl contains 1 mole of Na+ ions and 1 mole of Cl- ions = 2 osmoles/L

Question 26

What does iso-osmotic mean?

Answer 26

Having the same osmotic pressure e.g. 300 mosmol Glucose, 300 mosmol NaCl, 300 mosmol Plasma Same osmolarity so isoosmotic to each other mosmol=milli osmol=1/1000 osmol

Question 27

Define tonicity?

Answer 27

Ability of a solution to affect the cell Depends on concntration and permeability of the membrane to the solutes

Question 28

What does isotonic mean?

Answer 28

Same tonicity

Question 29

What does hypotonic mean?

Answer 29

Having a lower tonicity than a particular fluid

Question 30

What does hypertonic mean?

Answer 30

Having a higher tonicity than a particular solution

Question 31

What is the tonicity inside and outside the cell?

Answer 31

Isotonic Concentration of electrolytes outside the cell is equal to that inside the cell No water movement No change in cell shape

Question 32

What do hypotonic solutions in the body do?

Answer 32

Has low concentration of solutes that do not cross the membrane High Water content (more water, less solute) Cell absorbs water, swells and may burst (lysis) NOT IDEAL

Question 33

What do hypertonic solutions in the body do?

Answer 33

Low water concentration and high concentration of solutes that do not cross the membrane Water moves out of cell to try and balance water/ion concentation Cells lose water and shrivel up NOT IDEAL

Question 34

How does the body tell us we need more water?

Answer 34

Thirst

Question 35

What happens in the body when body water decreases?

Answer 35

Osmoreceptors sense changing conc. Baroreceptors sense changing pressure These are communicated to thirst centre in hypothalamus Hypothalamus tells posterior pituitary to release ADH to reabsorb more water from urine and sends message to make mouth drier which makes you feel thirsty and makes you drink This is negative feedback

Question 36

What are the treatments for dehydration?

Answer 36

Fluid therapy Gelofusine (plasma expander, increases volume of fluid, isotonic to replace blood loss) 0.9% saline (0.9g saline in 100ml of water) 5% glucose/dextrose solution (5g glucose in 100ml of water)

Question 37

What two problems can result from overhydration?

Answer 37

Hyponatraemia (low sodium) Water intoxication e.g. ecstasy - take too much water, dilutes body fluids, cell swell, lysis

Question 38

What is hydrostatic pressure?

Answer 38

The force exerted on the membrane by water/fluid In a resting cell this will be stable as intracellular=interstitial

Question 39

What influences water movement?

Answer 39

Hydrostatic pressure Movement of fluid between compartments through a selectively permeable membrane driven by hydrostatic pressure

Question 40

What effect does fluid movement have?

Answer 40

Any fluid movement results in a change in osmotic pressure (electrolytes on one side of membrane) therefore cell will change size Water will always follow salts