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Flashcards in Exploding Cells And Acid Trouble Deck (20):
1

What causes necrotic cells to swell and burst?

- Sodium can no longer leave the cell
- Concentration of solutes within the cell is higher than outside the cell (low water potential)
- Water moves in by osmosis
--> cell lysis

2

What is an osmole?

Osmoles = number of moles of osmotically acting particles in a solution

3

What is osmolaLity?

Osmalality = number of osmoles of solute per kg of solvent (osmol/kg)

Note = used clinically (more than osmalarity)

4

What is osmolaRity?

Osmalarity = number of osmoles of solute per L of solvent (osmol/L)

5

What is freezing-point depression and what can it be used for?

- Freezing-point depression is the process in which adding a solute to a solvent decreases the freezing point of the solvent. - - Examples include salt in water, alcohol in water, or the mixing of two solids such as impurities in a finely powdered drug.
- Used to test for serum/urine osmolality

6

What is normal plasma osmolality?

Normal plasma osmolality is 290 mOsmol/kg as measured by freezing point depression.

The range is 285-295 mOsmol/kg

7

If a patients plasma concentration is:
– Sodium is 140 mOsm/L
– Potassium is 5 mOsm/L
– Urea is 5mOsm/L
– Glucose is 5 mOsm/L
What is their calculated osmolality?

- Because sodium and potassium are as ions they need to be attached something (e.g. NaCl)
- Na+ and K+ osmalality will be double
= 2(140) + 2(5) + 5 + 5
= 280 + 10 + 5 + 5 = 300
Therefore, the calculated osmolality is close to the measured (290 mOsm/kg)

8

What is the Osmol gap?

- OG = measured serum osmolality − calculated osmolality
- A normal osmol gap is < 10 mOsm/kg

9

What can you say about a patients hydration from their serum osmolality?

Increase = Dehydration
Decrease = Overhydration

10

The molecular weight (molar mass) of glucose is 180 g/mol. How many moles in 1 litre of a 5% solution? How many millimoles in 1 litre of a 5% solution? What is the calculated osmolality therefore of a 5% dextrose solution?
(1% solution = 1g per 100ml )

5% solution = 5g per 100ml = 50g per litre
g/mol = 180 = 50/mol
50/180 = mol = 0.280 mol = 280mmol

Therefore, calculated osmolality = 280 mOsmol/kg

11

How does albumin contribute to oncotic pressure in the capillaries?

- Albumin levels are much higher in the capillary than in the interstitial space (4x)
- Cirrhosis (due to alcohol) --> low abulmin = decrease oncotic pressure = water leaves and goes into interstitial space = Ascites (abnormal accumulation fluid in the abdominal (peritoneal) cavity)

12

What is oncotic pressure?

Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that usually tends to pull water into the circulatory system. It is the opposing force to hydrostatic pressure.

13

How do levels of potassium and sodium ions compare in the blood plasma and intracellularly?

Plasma = Na+ 140 / K+ 5

Intracellular = Na+ 14 / K+ 160

Due to Na+K+ pump

14

What is pH?

pH = - log [H+]

'Power of hydrogen'

15

How do you measure blood pH?

Blood gas analysis

16

What does it mean to say that pH is a logarithmic scale?

Each one-unit change in the pH scale corresponds to a ten-fold
change in hydrogen ion concentration

17

What is normal blood pH? What is the limit of survival?

Normal plasma pH is 7.36 - 7.44

6.8 - 7.8 are the limits to survival

18

What is caused by abnormal plasma pH?

- Abnormal plasma pH nearly always results from major organ
dysfunction.
- The common organs that lead to pH abnormality are lungs, kidneys and liver.
- However the other common cause of a low pH is poor tissue perfusion – shock

19

What is 'shock'?

- Shock is defined as as a state of global cellular and tissue hypoxia due to reduced oxygen delivery, this is most commonly due to hypoperfusion. The commonest types of shock are cardiogenic, hypovolaemic and septic shock

20

Why is lactic acid production/regulation important ?

When tissues are poorly perfused anaerobic glycolysis leads to lactic acid production and lactic acidosis which lowers pH. This acidosis itself impairs cardiac function – a vicious downwards spiral!

• Normal plasma lactate is less than 1.6 nMol/L
– 2.0 – 4.0 reflects a significant underlying illness
– >4.0 – reflects a very serious underlying illness