BW&EH

Question 1

What are the main fluid compartments?

Answer 1

Intracellular (interstitial fluid, lymph), extracellular fluid compartment (Pleural fluid, pericardial fluid, CSF) and vascular (plasma)

Question 2

Which fluid compartment is used in routine measurements?

A. Intracellular fluid compartment
B. Extracellularfluid compartment
C. Vascular

Answer 2

C

Question 3

What percentage of the water is plasma?

Answer 3

Firstly 60% of body weight is water. Calculate water first 0.6xbody weight= water

But

0. 6xBWx0.083=plasma (L)
1. 3%

Question 4

Match the where the majority of specific electrolyes are most common in compartments.

A. ICF
B. ECF

1. Potassium
2. Sodium
3. Magnesium

Answer 4

A1,3

B2

Question 5

Why is there an increase in potassium during haemolysis?

Answer 5

Because the K can shoot up coming from ICF into the plasma, which is being measured

Question 6

Causes for raised anion gaps?

Answer 6

Increase in the unmeasured anions
- Lactate, Ketones and alcohols (ethanol)

Rarely decrease in umeasured cations
- Calcium, Magnesium

Question 7

Describe with example the importance of electrolytes in the correct compartment?

Answer 7

Sodium is required to be in the ECF to maintain blood pressure

Potassium have important roles in intracellular reactions

Thus, the two electrolytes relationship with compartment is maintained by the Na-K-ATPase

Question 8

Factors affecting water movement

Answer 8

Osmotic pressure
- Created by electrolytes and non-electrolytes

Oncotic pressure
- Created by proteins

Hydrostatic pressure
- Mechanical pressure generated by the heart

Question 9

What occurs in oncotic pressure?

Answer 9

Using vascular and extra vascular space.

Water is remained at the vascular space because the proteins are too big to cross the capillary walls, therefore controlling the amount of water in vascular and extravascular space

Question 10

Describe osmotic pressure.

Answer 10

High osmotic pressure refers to the amount of osmotically active particles in the space.
- Movement of water occurs low to high osmotic pressure in order to dilute the high osmotic pressure

Question 11

Difference between osmotic and oncotic pressure

Answer 11

Osmotic pressure is determined by the number for particles.
- E.g. more sodium particles in the ECF than there are protein particels. Therefore sodium exerts a greater effect than protein

Question 12

Define osmolality

Answer 12

The number of solute particles /kg of solvent

Question 13

Define osmolarity

Answer 13

Number of particles /L of solution

• Affected by temperature
• Includes the solute space

Question 14

Define omsolarity/osmolality

Answer 14

Conc of solutes in a solution that contribute to the osmotic pressure

Question 15

Why is osmolality more frequently used as a measurement rather than osmolarity?

Answer 15

It is not affected by solute space or temp changes

In water: osmolarity=osmolality

In plasma some of the volume is occupied by proteins/lipids making water volume less than 6% total volume

Question 16

What is measured osmolality?

Answer 16

Measures the amount of osmotically active particles present in the plasma

Question 17

What is calculated osmolality?

Answer 17

Calculate the expected osmolality using other measured analytes
=(2xNa) + K + urea + glucose (if abnormal)

Question 18

How is the osmolar gap calculated?

Answer 18

Difference between measured and calculated osmolality

Question 19

Importance of water retention in cells?

Answer 19

• No water= shrivel up
• Blood needs appropriate pressure to ensure the blood can keep circulating and supply the heart and organs with essentials
• To do this, water moves when required. Controlled by different forces

Question 20

Describe cerebral dehydration.

Answer 20

Describes the process where water moves from brain cell (low solute) to dehydrated vasculature (higher solute)

• This causes the brain cell to shrink - cerebral dehydration
• Blood vessels may tear (haemorrhage)
• Can cause central pontine myelinosis

Question 21

Mechanism to limit cerebral dehydration

Answer 21

The brain cell is able to synthesis osmolytes to raise its osmolality and prevent water loss to vasculature.

Question 22

Describe the rehydration process of cerebral dehydration

Answer 22

Rehydration must occur slowly. If it occurs quickly then the osmolytes will not clear quickly enoguh from the brain cells

• Causes the ECF to be significantly more dilute than the brain
• Water rush into the brain cells causing cerebral oedema

Question 23

What is water overload?

Answer 23

When the kidneys excretion rate of up to 20mL/min is exceeded

Question 24

What is cerebral oedema?

Answer 24

• Describes when water moves to area of higher conc. Overloaded vasculature -> brain cell
• Brain cells swells, cerebral oedema

Question 25

Protective mechanims against cerebral oedema?

Answer 25

Achieved by reducing concentration gradient. Step 1 - Brain cells lose sodium Step 2 - Brain cells synthesis and lose osmolytes

Question 26

How would correction of cerebral oedema occur?

Answer 26

Correction must be slowly administered. 1. Brain cell has lost osmolytes and sodium 2. Therefore rapid increase in vasculature osmolality will cause water to rush out the brain cell resulting in cerebral dehydration

Question 27

Describe the sodium and water relationship.

Answer 27

Sodium is the major ECF electrolye and exerts majority of the osmotic effect. Sodium balance is therefore inextricably linked to water balance - water follows sodium

Question 28

Describe the axis that regulate sodium regulation. (Draw for extra points)

Answer 28

Sodium levels are regulated by the renin-angiotensin-aldosterone axis. The axis is stimulated by low Na, low aterial pressure, low ECF volume, sympathetic NS stimulation. - Liver is stimulated to release angiotensinogen which is cleaved by renin (from the kidney) to cleave angiotensin I. - Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE) - Angiotensin II stimulate ADH and the adrenal cortex to release aldosterone. - Aldosterone act on kidney to reabsorb sodium and excrete potassium

Question 29

Describe sodium regulation in the distal tubule.

Answer 29

Principal cells - aldosterone - Aldosterone binds to its receptor to stimulate reabsorption - Generates an electrochemical gradient to allow K+ and H+ excretion - One H+ or K+ for each Na+ reabsorbed

Question 30

By what hormones are potassium regulated by?

Answer 30

Aldosterone, insulin, catecholamines

Question 31

Describe effect of aldosterone on potassium regulation.

Answer 31

Aldosterone promotes sodium reabsorption and potassium excretion in the distal convoluted tubule

Question 32

Describe effect of insulin on potassium regulation.

Answer 32

Has a direct interaction with the Na/K ATPase, independent of glucose - Drives potassium intracellularly - Hypercalcaemia in plasma

Question 33

Describe effect of catecholamines on potassium regulation.

Answer 33

Adrenaline drives potassium intracellularly | Noradrenaline allows potassium to leave cells

Question 34

Match the following hormone with effect to potassium regulation A. Aldosterone B. Noradrenaline C. Insulin D. Adrenaline 1. Allows potassium to leave cells 2. Drives potassium intracellularly 3. Excrete potassium in the distal convoluted tubule 4. Drives potassium intracellularly by Na/K-ATPase interaction

Answer 34

A3 B1 C4 D2

Question 35

Describe the control of water balance

Answer 35

System between the collecting duct and ADH. - Draw the axis - Stored in pPituitary - Release of ADH

Question 36

What are some osmotic factors stimulating ADH?

Answer 36

Osmoreceptors in the hypothalamus - Swell/shrink in response to omsolality - Dehydration - contract - ADH release - Hydration - swell -ADH inhibited

Question 37

What are some non-osmotic factors stimulating ADH?

Answer 37

Nausea, ECF hypovolaemia, hypotension, certain drugs

Question 38

Describe the specific actions of ADH

Answer 38

The luminal cells lining the collecting ducts are impermeable to water. During rehydration, channels (aquaporin II) are inserted into the membrane to allow water reabsorption - ADH binds V2 on basolateral surface, which allows insertion of aquaporin 2 channels into the luminal membrane - to enable water reabsorption

Question 39

What is the effects of aldosterone on electrolyte composition in DCT?

Answer 39

Stimulates Na+ absorption by actions of the aldosterone receptor - Generates a gradient to allow H+ and K+ to leave