Physiological Fluids Flashcards
Bodily fluids are essentially weak solutions of what in water?
Salts.
Are urine, gut contents and hormones physiological fluids?
No! Only intracellular and extracellular fluids are physiological fluids.
What is a molar solution?
The molecular weight of a substance in grammes, dissolved in one litre of water.
What is 1M, defined as the molecular weight of a substance in grammes, dissolved in one litre of water?
A molar solution.
What is a millimolar solution?
The molecular weight of substance in grammes/1,000, dissolved in one litre of water.
What is 1mM, define as the molecular weight of a substance in grammes/1,000, dissolved in one litre of water?
A millimolar solution.
How does the composition of extracellular fluids reflect the origins of life in shallow, warm seas?
The ionic composition of extracellular fluid is similar to that of the seas where life originated.
Which has a higher concentration of Na+ in its extracellular fluid? Terrestrial animals, or those that live in salt water?
Animals that live in salt water have a higher concentration of Na+ in its extracellular fluid.
What are the specialised systems that animals have developed to enable them to live on land and maintain an ‘internal sea’?
A waterproof covering, means of water intake and excretion, fluid circulation and a monitoring system for osmotic pressure and volume.
Extracellular fluids are, in terms of dissolved ions, weak solutions of what dissolved in water?
NaCl, sodium chloride or common salt.
What is the concentration of NaCl in extracellular fluid?
150mM - around 9g of salt dissolved in one litre of water.
Intracellular fluids are, in terms of dissolved ions, weak solutions of what dissolved in water?
KCl - potassium chloride.
Of the 60% of a vertebrate’s body weight that is water, what proportion is extracellular fluid, and how much is intracellular fluid?
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).
The total volume of ……………. in humans is 2.8 litres, which is vital!
Plasma.
Loss of how much body fluids can result in death?
Just 10%!
Which fluid bathes cells?
Extracellular fluid.
Why, in terms of the capillary wall, are the components of interstitial fluid and plasma very similar?
The capillary wall is leaky, meaning that the composition of interstitial fluid and plasma end up being very similar.
What cannot cross the ‘leaky’ capillary wall?
Large proteins.
How do exchange proteins get across the capillary wall?
By vesicular transport.
How can small, water-soluble substances get across the capillary wall?
Via water-filled pores in the membrane.
How do lipid-soluble substances cross the capillary cell walls?
They can pass through the endothelial cell because they are lipid-soluble.
Is plasma inside or outside cells?
Inside.
Is interstitial fluid inside or outside cells?
Outside.
What can be described as semi-premeable and phospholipid, with specific channels for water and ions?
The cell membrane.
Can the cation K+ an the anion Cl- move freely across the membrane?
Yes, they can.
Is K+ a cation or an anion?
A cation.
Is Cl- a cation or an anion?
An anion.
What is meant by daily water balance?
The maintenance of fluid in the body because water is lost in urine, sweat and faeces.
True or false? Kidneys can adapt to extreme conditions by retaining more water.
True.
True or false? Different animals’ kidneys function differently, according to their environment.
True. Some animals’ kidneys have adapted to the conditions in their environment to maintain water homeostasis.
How does the bannertail kangaroo rat thrive in a desert environment?
It has adapted so that it gets all of the water it needs as a product of metabolism.
Where does the majority (90%) of water enter the body?
Where does the rest come from?
Through the gut.
The remaining 10% is generated chemically during energy use.
Ultimately, which two things regulate total water in the body?
Thirst and anti-diuretic hormone (AVP).
When is anti-diuretic hormone released?
Anti-diuretic hormone is released when receptors in the hypothalamus detect a change in blood osmolarity.
What happens when receptors in the hypothalamus detect a change in blood osmolarity?
Anti-diuretic hormone (AVP) is released.
Approximately how much fluid is lost daily in urine?
1.5l. This can be regulated if there are large fluid losses elsewhere, for example excess sweating or haemorrhage.
What is the difference between thirst and appetite for water?
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.
Which of these is a physiological description of water requirement, and which is an individual behaviour?:
a. Thirst.
b. Appetite for water.
a. Thirst - physiological requirement for water.
b. Appetite for water - individual behaviour.
Why must animal cells regulate their volume carefully?
To avoid bursting or losing water.
Define osmosis.
The movement of water across cell membranes, from where particle concentration is lowest to where it is highest.
What is osmotic concentration (mOsm)?
A measurement of the number of particles in osmosis.
Why is osmotic concentration used instead of solute concentration when measuring osmosis?
Some solutes dissociate into multiple ions, so the number of particles, rather than the amount of solute, needs to be measured.
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’.
Osmosis.
How does water move across the cell membrane?
Through aquaporins.
Aquaporins and energy from Brownian motion of solutes and water are key in…?
…osmosis.
How do charged solutes, such as Na+ molecules and the electrostatic charge on the area of aquaporins near the membrane surface cause osmosis?
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.
If cells are in a solution of 150mM NaCl, why is the osmotic concentration 300mOsm?
NaCl dissociates into two ions.
What does the term tonicity mean? What two factors determine tonicity?
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.
The reflection coefficient is used to indicate…?
…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.
What does a reflection coefficient of 1 tell us about a solute?
What if a solute has a reflection coefficient of 0?
A solute with a reflection coefficient of 1 is totally impermeant.
A solute with a reflection coefficient of 0 is freely permeant.
How does the effective osmotic concentration of an isotonic solution compare to the effective osmotic concentration of intracellular fluid?
An isotonic solution has the same effective osmotic concentration as intracellular fluid.
What would happen to cells placed in an isotonic solution, assuming that the solutes are largely impermeable?
Nothing!
What is a hypertonic solution? What happens to cells placed in such a solution?
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.
Define a hypotonic solution. What are the consequences of cells being placed in such a solution.
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.
Isotonic, hypertonic and hypotonic principles largely apply if the solutes are largely impermeable. What happens if the solutes are PERMEABLE?
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.
