Physiological Fluids

Question 1

Bodily fluids are essentially weak solutions of what in water?

Answer 1

Salts.

Question 2

Are urine, gut contents and hormones physiological fluids?

Answer 2

No! Only intracellular and extracellular fluids are physiological fluids.

Question 3

What is a molar solution?

Answer 3

The molecular weight of a substance in grammes, dissolved in one litre of water.

Question 4

What is 1M, defined as the molecular weight of a substance in grammes, dissolved in one litre of water?

Answer 4

A molar solution.

Question 5

What is a millimolar solution?

Answer 5

The molecular weight of substance in grammes/1,000, dissolved in one litre of water.

Question 6

What is 1mM, define as the molecular weight of a substance in grammes/1,000, dissolved in one litre of water?

Answer 6

A millimolar solution.

Question 7

How does the composition of extracellular fluids reflect the origins of life in shallow, warm seas?

Answer 7

The ionic composition of extracellular fluid is similar to that of the seas where life originated.

Question 8

Which has a higher concentration of Na+ in its extracellular fluid? Terrestrial animals, or those that live in salt water?

Answer 8

Animals that live in salt water have a higher concentration of Na+ in its extracellular fluid.

Question 9

What are the specialised systems that animals have developed to enable them to live on land and maintain an ‘internal sea’?

Answer 9

A waterproof covering, means of water intake and excretion, fluid circulation and a monitoring system for osmotic pressure and volume.

Question 10

Extracellular fluids are, in terms of dissolved ions, weak solutions of what dissolved in water?

Answer 10

NaCl, sodium chloride or common salt.

Question 11

What is the concentration of NaCl in extracellular fluid?

Answer 11

150mM - around 9g of salt dissolved in one litre of water.

Question 12

Intracellular fluids are, in terms of dissolved ions, weak solutions of what dissolved in water?

Answer 12

KCl - potassium chloride.

Question 13

Of the 60% of a vertebrate’s body weight that is water, what proportion is extracellular fluid, and how much is intracellular fluid?

Answer 13

40% is intracellular fluid and 20% is extracellular fluid.

Of the intracellular fluid, 16% is interstitial fluid and 4% is plasma (lymph and transcellular fluid are negligible).

Question 14

The total volume of ……………. in humans is 2.8 litres, which is vital!

Answer 14

Plasma.

Question 15

Loss of how much body fluids can result in death?

Answer 15

Just 10%!

Question 16

Which fluid bathes cells?

Answer 16

Extracellular fluid.

Question 17

Why, in terms of the capillary wall, are the components of interstitial fluid and plasma very similar?

Answer 17

The capillary wall is leaky, meaning that the composition of interstitial fluid and plasma end up being very similar.

Question 18

What cannot cross the ‘leaky’ capillary wall?

Answer 18

Large proteins.

Question 19

How do exchange proteins get across the capillary wall?

Answer 19

By vesicular transport.

Question 20

How can small, water-soluble substances get across the capillary wall?

Answer 20

Via water-filled pores in the membrane.

Question 21

How do lipid-soluble substances cross the capillary cell walls?

Answer 21

They can pass through the endothelial cell because they are lipid-soluble.

Question 22

Is plasma inside or outside cells?

Answer 22

Inside.

Question 23

Is interstitial fluid inside or outside cells?

Answer 23

Outside.

Question 24

What can be described as semi-premeable and phospholipid, with specific channels for water and ions?

Answer 24

The cell membrane.

Question 25

Can the cation K+ an the anion Cl- move freely across the membrane?

Answer 25

Yes, they can.

Question 26

Is K+ a cation or an anion?

Answer 26

A cation.

Question 27

Is Cl- a cation or an anion?

Answer 27

An anion.

Question 28

What is meant by daily water balance?

Answer 28

The maintenance of fluid in the body because water is lost in urine, sweat and faeces.

Question 29

True or false? Kidneys can adapt to extreme conditions by retaining more water.

Answer 29

True.

Question 30

True or false? Different animals' kidneys function differently, according to their environment.

Answer 30

True. Some animals' kidneys have adapted to the conditions in their environment to maintain water homeostasis.

Question 31

How does the bannertail kangaroo rat thrive in a desert environment?

Answer 31

It has adapted so that it gets all of the water it needs as a product of metabolism.

Question 32

Where does the majority (90%) of water enter the body? Where does the rest come from?

Answer 32

Through the gut. The remaining 10% is generated chemically during energy use.

Question 33

Ultimately, which two things regulate total water in the body?

Answer 33

Thirst and anti-diuretic hormone (AVP).

Question 34

When is anti-diuretic hormone released?

Answer 34

Anti-diuretic hormone is released when receptors in the hypothalamus detect a change in blood osmolarity.

Question 35

What happens when receptors in the hypothalamus detect a change in blood osmolarity?

Answer 35

Anti-diuretic hormone (AVP) is released.

Question 36

Approximately how much fluid is lost daily in urine?

Answer 36

1.5l. This can be regulated if there are large fluid losses elsewhere, for example excess sweating or haemorrhage.

Question 37

What is the difference between thirst and appetite for water?

Answer 37

Thirst is a physiological description of water requirement, associated with a dry, tacky feeling in the mouth. It is one of the first signs of dehydration. Appetite for water is an individual behaviour. Animals drink to satiety in a few minutes, too short a time for physiological mechanisms to control their behaviour.

Question 38

Which of these is a physiological description of water requirement, and which is an individual behaviour?: a. Thirst. b. Appetite for water.

Answer 38

a. Thirst - physiological requirement for water. b. Appetite for water - individual behaviour.

Question 39

Why must animal cells regulate their volume carefully?

Answer 39

To avoid bursting or losing water.

Question 40

Define osmosis.

Answer 40

The movement of water across cell membranes, from where particle concentration is lowest to where it is highest.

Question 41

What is osmotic concentration (mOsm)?

Answer 41

A measurement of the number of particles in osmosis.

Question 42

Why is osmotic concentration used instead of solute concentration when measuring osmosis?

Answer 42

Some solutes dissociate into multiple ions, so the number of particles, rather than the amount of solute, needs to be measured.

Question 43

What process does this describe?: 'The movement of water across a cell membrane from the side where particle content is lowest to the side where particle concentration is highest'.

Answer 43

Osmosis.

Question 44

How does water move across the cell membrane?

Answer 44

Through aquaporins.

Question 45

Aquaporins and energy from Brownian motion of solutes and water are key in...?

Answer 45

...osmosis.

Question 46

How do charged solutes, such as Na+ molecules and the electrostatic charge on the area of aquaporins near the membrane surface cause osmosis?

Answer 46

As the charged solute particles randomly interact with the electrostatic charge of the aquaporins, they are repelled move water molecules out of the way, which are immediately replaced by other water molecules from within the aquaporin channel. Hence there will be more interactions on the side where there are most solutes, so water will move to that side.

Question 47

If cells are in a solution of 150mM NaCl, why is the osmotic concentration 300mOsm?

Answer 47

NaCl dissociates into two ions.

Question 48

What does the term tonicity mean? What two factors determine tonicity?

Answer 48

Animal cells can vary in their permeability, tonicity refers to their response of cells in a solution. Tonicity is determined by osmotic concentration AND the permeabilty of the membrane to specific solutes.

Question 49

The reflection coefficient is used to indicate...?

Answer 49

...the permeability or ability of a solute to cross a cell membrane. It is dependent on the particle and the membrane it is trying to pass through.

Question 50

What does a reflection coefficient of 1 tell us about a solute? What if a solute has a reflection coefficient of 0?

Answer 50

A solute with a reflection coefficient of 1 is totally impermeant. A solute with a reflection coefficient of 0 is freely permeant.

Question 51

How does the effective osmotic concentration of an isotonic solution compare to the effective osmotic concentration of intracellular fluid?

Answer 51

An isotonic solution has the same effective osmotic concentration as intracellular fluid.

Question 52

What would happen to cells placed in an isotonic solution, assuming that the solutes are largely impermeable?

Answer 52

Nothing!

Question 53

What is a hypertonic solution? What happens to cells placed in such a solution?

Answer 53

A hypertonic solution has a HIGHER effective osmotic concentration than intracellular fluid. Cells placed in such a solution would lose water and shrivel when placed in such a solution if the solutes are largely impermeable.

Question 54

Define a hypotonic solution. What are the consequences of cells being placed in such a solution.

Answer 54

A hypotonic solution has a LOWER osmotic concentration than intracellular fluid. Cells placed in a hypotonic solution would swell and may burst, assuming that the solutes are largely impermeable.

Question 55

Isotonic, hypertonic and hypotonic principles largely apply if the solutes are largely impermeable. What happens if the solutes are PERMEABLE?

Answer 55

If the concentration of permeable solutes is higher outside the cell, the solute will move into the cell and have a hypotonic effect, irrespective of osmolarity.