Fluids and Electrolytes

Question 1

Name the body fluid compartments and the volume of total water in each.

Answer 1

• Intracellular fluid 40% of body weight (25 Litres)
  
  • Extracellular fluid is interstitial fluid (between cells/ within tissues) and plasma combined. This makes up 20% of body weight of 15 Litres

Question 2

The role of ADH is to __________. a. increase water reabsorption b. decrease water reabsorption c. produce dilute urine d. lower blood pressure

Answer 2

a. increase water reabsorption

Question 3

The most rapid response to a fall in pH of the blood involves what?

Answer 3

Chemical buffer systems

Question 4

The amount of water carried by the body changes throughout the lifespan. What are the average percentages of water for infants, adults and elderly?

Answer 4

Infants- 70% Adults- 60%men 60%women Elderly- 50-55%

Question 5

Water is referred to as the ________ solvent.

Answer 5

universal

Question 6

Why don’t non-electrolytes dissolve in water?

Answer 6

Because non-electrolytes have bonds preventing them from dissociating in water and so therefore carry no net electrical charge.

Question 7

What happens to electrolytes in water?

Answer 7

They dissociate into ion particles in water.

Question 8

Electrolytes freely dissociate in water to ions (charged particles able to conduct electric current). Include inorganic salts, acids and bases, and some proteins. Electrolytes also have greater osmotic power. Why?

Answer 8

This is because once they dissociate in water they contribute at least two particles to the solution.

Question 9

What is the electrolyte makeup of the ECF and ICF?

Answer 9

• ECF (plasma and interstitial fluid): - Similar composition, except higher protein content of plasma - Major cation: Na+ - Major anion: Cl– - ICF (inside cells): - Low Na+ and Cl– - Major cation: K+ - Major anion HPO42–

Question 10

There is a continuous exchange and mixing of body fluids between fluid compartments. Wht factors regulate this exchange?

Answer 10

This is regulated by osmotic and hydrostatic pressures.

Question 11

what is Osmosis?

Answer 11

Osmosis is the term used to describe the diffusion of water across a semi-permeable membrane as it moves down its concentration gradient.
Water moves through membranes more readily than solutes.

Question 12

If tere was an area of high sugar concerntration and an area of low sugar concertration separated by a membrane. In wich direction would water move?

Answer 12

Water would move towards the area where solute concerntration is higher as it wants to dilute it.

Question 13

What is osmotic pressure?

Answer 13

- Osmotic pressure measures the tendency of water to move across membranes.

• Higher osmotic pressure = Lower water concentration.
• So the concentration of solute particles determines the osmotic pressure of a body fluid.

Question 14

What are osmolality and osmolarity a measure of and what is the difference between the two?

Answer 14

• Are measures of total concentration of all dissolved particles in solution.
• Osmolality refers to number of milliosmoles per kg of water.
• Osmolarity refers to number of milliosmoles per litre of solution.

Question 15

What is tonicity?

Answer 15

Tonicity is a term used in describing osmotic pressure.
•Describes fluid surrounding cells.

Question 16

Describe the folowing terms in relation to the cells in the body Isotonic, Hypertonic and Hypotonic.

Answer 16

- Isotonic.
•Fluid surrounding the cells is said to be isotonic where the concentrations of solutes and concentrations of water are the same inside the cell as outside the cell. There will be no net movement of water into or out of the cell.
- Hypertonic.
•Cells in a fluid environment which has a higher concentration of solutes and so a lower concentration of water (i.e. a higher osmotic pressure) will tend to lose water to the environment. Cells will shrink.
- Hypotonic.
•Cells in a fluid environment which has a lower concentration of solutes and therefore a higher concentration of water (so lower osmotic pressure) will tend to gain water from this environment. Cells will swell and even burst. This environment is said to be hypotonic.

Question 17

The bodies fluid has a relatively low concentration of solutes the difference between osmolality and osmolarity is negligable and the two terms are often used interchangeably in clinical practice. What is the osmolarity of the ICF and ECF?

Answer 17

The osmolarity of the ICF and ECF is about 300 milliosmoles/L equivalent to 0.9% NaCl.

Question 18

If you eat salty potatoe chips, without drinking water what happens to the volume of your extracellular fluid?

Answer 18

The volume if your extracellular fliud willl increase. The is becasue the osmolarity of the plasms rises therefore water moves out of the cells and intot the extracellular fluid causing the calls to shrink. This also causes the vloume of plasma to rise as well as blood pressure.

Question 19

Why is a low salt diet recommended for people suffering from hypertension?

Answer 19

Becasue the more salf in a persons diet the more fluid that moved into the extracellular fluid and the more fluid the body retains. The more fluid the body retains the higher the blood pressure.

Question 20

Whilst running a marathon, George, suffers from hypernatremia. What has casue hypernatremia?

Answer 20

Profound sweating has casued dehydration which leads to an increase in Sodium concerntration in the plasma (hypernatremia).

Question 21

Whilst running a marathon, George, suffers from hypernatremia. he is feeling very thirsty. What stimuli triggers the thirst mechanism?

Answer 21

As George in dehydrated he had less fuild running through his veins and therefore a lowered blood pressure. A reduced blood pressure triggeres baroreceptors constrication of blood vessels and increase heart rate (Sympathetic) in creasing stroke volume. Changes in osmotic pressure of the plasma which is detected by osmoreceptors in the hypothalamus cause thirst. A reduction of saliva also causes thirst. Furthermore a drop in BP also causes gramular cells to release renin which is turned into angiotensin –> ACE—> Angiotensin II —> increased water retention, hypothaus thirst, vasoconstriction, increased water retention ADH- aquaporins.

Question 22

What is the marjor stimulus for the release of ADH?

Answer 22

An increase in ECF osmolarity and changes in blood or plasma volume which causes either a rise or fall in blood pressure.

Question 23

What is the direct effect of ADH?

Answer 23

• increased water reabsorption (aquaporins) and constriction of blod vessels

Question 24

What effect with the release of ADH have of the plasma volume and osmolarity?

Answer 24

It will increase the plasma volume and decrease osmolarity.

Question 25

At the end of a marathon George quenches his thirst with a bottle of water. What feedback mechanisms operate to control his thirst?

Answer 25

Saliva and streach receptors in the stomach.

Question 26

At the end of a marathon Goerge quenches his thirst with a bottle of water. If the thirst feedback mechanism fails what will happen?

Answer 26

George will continue to drink water with will reduce osmolarity. This leads to a shift of fluid back into the cells causing them to swell. If he continues to drink water it will lead to the cells swelling so much they may burst in particular the neurons which is water intoxication.

Question 27

You arrive at the scene of a car accident to find Sally haemorrhaging from multiple lacerations as a result of being thrown through the widscreen. As a result of th accident what changes will occur in her: ECF volume, ECF osmolarity, ICF volume, BP, GFR and urine volume?

Answer 27

decreased ECF volume, Same ECF osmolarity, Same ICF volume as there is not osmolarity change, Reduce BP, Reduced GFR and unrine volume.

Question 28

A person with a long history of smoking (reduced rate and depth of breathing) has now developed emphysema, resultig in hypoventilation. How might you expect this to affect their blood pH levels?

Answer 28

This would reduce the ph level of their blood because hypoventilation causes CO2 levels to rise this causes a rise in H+ ions and therefore a rise in pH. Respiratory acidosis.

Question 29

A person with a long history of smoking (reduced rate and depth of breathing) has now developed emphysema, resultig in hypoventilation. This causes a rise in H+ iorn and therefore pH. What happens to the excess H+ iorns produced?

Answer 29

They are excreted in urine, as carbin dioxide by the lungs, Chemical buffers (rapid first line of defence) and renal mechanisms, this can take hours to take effect however it is the most potent mechanism.

Question 30

JOanne, a diabetic patient, is at the mergency department with acidosis due to the production of ketnes. Would you expect her ventilation to be increased or decreased? why?

Answer 30

An increase in H+ iorns shifts the buffer equation to the left, this causes an increase in CO2, an increase in CO2 increases the rete and depth of breathing. This person does not have an issue with braething but they will be breathing faster and deeper.

Question 31

• Remember that the total number of particles is the same inside the cell and outside the cell, but the proportions of types of particular ions will differ, however.
• It is the concentration of water that is most significant. So a solution such as 0.9% NaCl is considered isotonic to the cells. This does not mean that the cells contain 0.9% NaCl, it means the concentration of water inside the cells is the same as the concentration of water in the 0.9% NaCl solution.

Question 32

What recptors directly monitor fluid and electrolyte levels and casue a response?

Answer 32

There is no receptor that directly monitors fluid oe electrolye levels. Response is to changes in plasma volume or osmotic concentrations.

Question 33

All water moves passively in response to ______________?

Answer 33

osmotic gradients

Question 34

If ECF becomes hypertonic relative to ICF, where does what move?

Answer 34

water moves from ICF to ECF

Question 35

Sf ECF becomes hypotonic relative to ICF where does water flow?

Answer 35

from ECF into cells

Question 36

There two modes of transport across capillary walls, what are they?

Answer 36

difussion and filtration

Question 37

What is the major difference between intravascular and interstitial fluid?

Answer 37

The presence of proteins in the plasma, within the intravascular space. The water concentration within the plasma is therefore lower. Its osmotic pressure is higher.

Question 38

Fluid shifts between compartments are due to what?

Answer 38

Diffusion- differences in osmotic pressure.
Filtration- differences in hydrostatic pressure.

Question 39

At the capillary bed there is a slight excess in ________ pressure over _______ pressure.

Answer 39

At the capillary bed there is a slight excess in hydrostatic pressure over osmotic pressure.

Question 40

At the capillary bed there is a slight excess in hydrostatic pressure over osmotic pressure.
This means that there is an overall nett loss of fluid from the ________ to the ______ ____.
This excess fluid is managed by the _________ ______ and eventually returned to the bloodstream.

Answer 40

At the capillary bed there is a slight excess in hydrostatic pressure over osmotic pressure.
This means that there is an overall nett loss of fluid from the bloodstream to the interstitial fluid.
This excess fluid is managed by the lymphatic system and eventually returned to the bloodstream.

Question 41

What are the obligatory water losses of the body (uncontrollable) ?

Answer 41

Insensible water losses include losses from the lungs, the skin and the digestive tract.
Also the kidneys must excrete wastes each day and some water must accompany them.

Question 42

Water Balance: Homeostasis is the multitude of processes occurring within the body facilitating maintenance of the composition of interstitial fluid within the narrow set points. These processes ensure a constancy within the bodies internal environment.
Maintenance of homeostasis includes two major tasks… What are they and how are they achieved?

Answer 42

1 Maintaining water balance within the cells (ICF). This ensures adequate functioning of cells.
2 Maintaining water balance in the plasma. This ensures the tissues of the body are adequately perfused.
- Both are achieved by maintaining the correct level of water in the ECF.

Question 43

What is the driving force of water intake?

Answer 43

Thirst mechanism

Question 44

What stimulates the osmoreceptors to activate the hypothalmic thirst centre?

Answer 44

An increase in plasma osmolarity.

Question 45

What factors stimulate the hypothalamic thirst centre? And what are their feedback mechanisms?

Answer 45

-A drop in plasma volume by 10-15%
-An increase in plasma osmolality by 1-2%
-By baroreceptor inputs or activation by angiotensin II
Feedback mechanisms that inhibit the thirst centre include
-Moistening of the mucosa of the mouth and throat
-Activation of stretch receptors of the stomach and intestine.

Question 46

Where is ADH produced, when is it roduced and what is its primary role?

Answer 46

• ADH is made by hypothalamus and stored in and released from posterior pituitary.
• The primary role of ADH is to decrease the amount of water lost at the kidneys.
• ADH will also cause constriction of peripheral blood vessels.
• The secretion of ADH is promoted or inhibited by changes in ECF osmolarity (detected by osmoreceptors) and by large changes in blood or plasma volume leading to changes in blood pressure (detected by baroreceptors).

Question 47

What is dehydration?

Answer 47

What fluid output exceed fluid intake.

Question 48

What happends during dehydration and what are some of the long and short term symptoms?

Answer 48

• Water depletion exceeds sodium depletion (esp in diarrhoea, diabetes insipidus, but NOT in haemorrhage). This leads to hypernatraemia (a high plasma Na+ concerntration) (NOT in haemorrhage).
• Early symptoms & signs include dry mucous membranes, thirst, dry flushed skin, decreased skin turgor, and decreased urine output.
• Later symptoms & signs include weight loss, fever and mental confusion.
• If prolonged leads to hypovolaemia, decreased circulating blood volume, and hypovolaemic shock (esp in haemorrhage).

Question 49

In dehydration fluid is lost from the ECF. What happends in order to try and balance the osmolarity of the ECF and hte ICF.

Answer 49

Osmotic movement of water from cells to ECF follows in an attempt to equalize osmolarity of ECF and ICF. Water movies fromt the ICF to the ECF and the cells become dehydrated.

Question 51

what are the pricipal effects of aldesterone?

Answer 51

To diminish urine output and increase blood volume

Question 52

What does changes in ECF potassium concerntration effect?

Answer 52

Resting membrane potential of cells in neurons and muscle cells.
Cardiac muscle tissue particularly sensitive to changes in K+ levels.

Question 53

How are potassium levels regulated?

Answer 53

• An increase in K+ levels stimulates the release of aldosterone through the renin-angiotensin mechanism.
• Aldosterone stimulates K+ secretion (and Na+ reabsorption) by DCT cells of the kidney.
• When K+ is low secretion is kept to minimum.

Question 54

What happens if potassium levels are too high or too low and what re these conditions called?

Answer 54

• Hyperkalaemia, if severe, can mean ventricular fibrillation and cardiac arrest. (- Increase potassium in ECF means restin membrane potential is less negative. Initially increased responsiveness, but decrease in K+ gradient means repolarisation and so refractory period prolonged therefore reduced excitability of cells.)
• Hypokalaemia results in muscle weakness and possible cardiac arrythmias. (Dereased potassium in ECF means RMP more negative. Means hyperpolarization and nonresponsiveness.)
  both conditions are able to disrupt electrical conduction in the heart and lead to sudden death.

Question 55

Which of the following is Calcium not important for:

a) Neuromuscular excitability
b) Blood clotting
c) pH balance
d) cell membrane permeability

Answer 55

c) pH balance

Question 56

What pH does a persons blood have to be at for it to be consdered alkalosis and acidosis?

Answer 56

• Above pH 7.45 considered alkalosis.
• Below pH 7.35 acidosis.