Fluid, Electrolyte and Acid Base

Question 1

What is Intracellular Fluid (ICF) compartment?

Answer 1

This is essentially trillions of compartments put together, as this is made up of all of our Cells in the body.

It accounts for almost two-thirds of all of the fluid in the body

Question 2

What is Extracellular Fluid (ECF) compartment?

Answer 2

This comprises the Plasma - which is the fluid portion of the blood - and the Interstitial fluid - which is the fluid in between the tissue cells.

There are also many other examples of ECF that are distinct from plasma and interstitial fluid, and I introduced you to this as Transcellular fluid previously (e.g., CSF, fluid found in joints, and even lymph!) - but, to be honest, quite often this is just considered part of interstitial fluid.

Question 3

What is meant by water is our ‘universal solvent’?

Answer 3

Water in which Solutes are dissolved, and when solutes are dissolved into a solvent, you get a solution.

Question 4

What can solutes can be broadly classified into?

Answer 4

Electrolytes and Nonelectrolytes.

Question 5

What are Electrolytes?

Answer 5

Electrolytes are chemical compounds that dissociate into ions in water.

Typically, electrolytes are inorganic salts, both inorganic and organic acids and bases, and some proteins.

Question 6

What are Nonelectrolytes?

Answer 6

Nonelectrolytes, on the other hand, have bonds that prevent them from dissociating in a solution. Most nonelectrolytes are organic molecules such as glucose, lipids and urea, for example.

Question 7

Why do electrolytes contribute to osmotic activity of a fluid more than non-electrolytes?

Answer 7

When they dissociate what’s happening is they’re contributing more solute particles to the solution.
Regardless of the type of solute particle, water moves according to osmotic gradients (from an area of less osmolality to an area of greater osmolality), and so electrolytes have the greatest ability to cause fluid shifts in the body.

Question 8

What is difference between anion and cation?

Answer 8

A cation is an atom or a group of atoms bearing one or more positive electric charges. An anion is an atom or a group of atoms bearing one or more negative electric charges. Cations carry one or more positive charges. Anions carry one or more negative charges.

Question 9

What is the main cation in the Extracellular Fluid ECF?

Answer 9

Sodium (Na+)

Question 10

What is the main anion in the Extracellular Fluid ECF?

Answer 10

Chloride (Cl-)

Question 11

What is the main cation in Intracellular Fluid (ICF)?

Answer 11

Potassium (K+)

Question 12

What is the main anion in Intracellular Fluid (ICF)?

Answer 12

Hydrogenphosphate (HPO42-)

Question 13

Why are the concentrations of sodium and potassium ions are almost exactly opposite?

Answer 13

The concentrations of sodium and potassium ions are almost exactly opposite between the ECF & ICF, and this reflects the constant activity of the sodium-potassium ATP-dependent pumps which keep the intracellular Na+ concentrations low and K+ high, facilitating all sorts of processes (think: conducting nerve impulses [action potentials] and cardiac action potentials, etc.)

Question 14

How does fluid move among compartments?

Answer 14

Osmotic and Hydrostatic Pressures.

Question 15

Give an example of hydrostatic pressure?

Answer 15

(formation of lymph) When plasma is forced out of capillaries

Question 16

Give an example of colloid osmotic pressure?

Answer 16

(formation of lymph) The vast majority of plasma is reabsorbed back into the bloodstream as a result of colloid osmotic pressure, created by the large plasma proteins contained within it, and what isn’t returned is picked up by the lymphatic vessels and returned to the blood that way.

Question 17

How does fluid moves between the interstitial fluid and the ICF though?

Answer 17

The movement of water is almost continuous the movement of ions across the plasma membrane is more restricted.
Generally, therefore, ions move selectively either through active transport or via ion channels.

Question 18

What happens with a decreasing the ECF solute content?

Answer 18

The ECF becoming Hypotonic - would cause a shift in water into the cells, causing them to swell and potentially lyse cytolysis.

Question 19

What happens with a Increasing the ECF solute content?

Answer 19

The ECF becoming Hypertonic - would cause a shift in water out of the cells, causing cells to shrivel

Question 20

What would dehydration, caused by a lack of fluid intake, do to the osmolality of blood?

Answer 20

Blood would become more hypertonic.

Water volume has been lost and is not being replaced and the relative concentration of solutes is higher.

Question 21

What happens to the osmolality of blood if someone has severe vomiting and diarrhoea?

Answer 21

They will have isotonic dehydration because they will be losing fluid and salts in equal proportions.

Question 22

What happens to the osmolality of blood if someone has a fever?

Answer 22

They will have hypertonic dehydration because they will be losing more water than solutes through sweat.

Question 23

What would overhydration of water for someone running an endurance race do to the osmolality of blood?

Answer 23

Hypotonic dehydration because water volume has been increased and the relative concentration of solutes (particularly NA+ conc) is lower. When ECF NA+ conc decreases substantially - called hyponatremia - net movement of water is into the cells causing them to swell. This can be a life-threatening situation.

Question 24

What does euhydration mean?

Answer 24

Normal level of hydration

Question 25

What does sensible water loss mean?

Answer 25

water lost via urine output, ‘excess’ sweat (i.e., associated with exercise) and water lost in faeces. Sensible water loss accounts for ~60% of all water losses.

Question 26

What does insensible water loss mean?

Answer 26

Water losses that cannot be easily measured - general sweat

Question 27

What regulates the thirst mechanism?

Answer 27

The hypothalamic thirst centre, drives our fluid intake.

Question 28

What are the three stimuli for thirst mechanism?

Answer 28

1. Osmoreceptors - detect ECF osmolality. Changes of only 1-2% activates these osmoreceptors.
2. Dry mouth - salivary glands produce less saliva when the osmotic pressure of blood is increased, as happens with dehydration
3. Decreased blood volume or pressure - as could happen with a haemorrhage. A change in blood volume or pressure of ~5-10% is detected by baroreceptors that directly active the thirst centre by the Angiotensin II.

Question 29

What is a chemical buffer?

Answer 29

system that resists changes in pH when a strong acid or base is added to it - think about homeostasis; we have a narrow range in which we need to keep our blood pH to ensure a stable internal environment, and if something is added to it to make it more acidic or alkaline, then we need a mechanism (or three!) to help stabilise it.

Question 30

What are the are three major chemical buffer systems in the body?

Answer 30

Bicarbonate, Phosphate, and Protein buffers

Question 31

What are the key principles of the Bicarbonate buffer system?

Answer 31

A mixture of H2CO3 (Carbonic Acid; which is a weak acid) and salts of HCO3- (Bicarbonate ions; which are a weak base). It is the main buffer operating in the ECF, but it also operates in the ICF.

Question 32

Which organs regulate the Bicarbonate ion (HCO3-) concentration?

Answer 32

The kidneys

Question 33

The bicarbonate ion (HCO3-) concentration in the ECF is normally around?

Answer 33

25mEq/L.

Question 34

Carbonic acid (H2CO3-) concentration is closely regulated by the?

Answer 34

respiratory system.

Question 35

The concentration of carbonic acid (H2CO3) is

Answer 35

1 mEq/L

Question 36

How is carbonic acid (H2CO3) produced?

Answer 36

It is created from the CO2 released during cellular respiration.

Question 37

Once created, HCO3- moves quickly from within the RBCs to the plasma - how

Answer 37

chloride shift

Question 38

What is chloride shift?

Answer 38

is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3−) and chloride (Cl−) across the membrane of red blood cells (RBCs).

Question 39

Net retention of CO2 hypoventilation will lead to?

Answer 39

Acidosis

When respiratory system problems cause the pH imbalance, we call this respiratory acidosis.

Question 40

Net elimination of CO2 hyperventilation will lead to?

Answer 40

Alkalosis

When respiratory system problems cause the pH imbalance, we call this respiratory alkalosis.

Question 41

The partial pressure of carbon dioxide (PCO2) is the measure of carbon dioxide within arterial or venous blood. When the respiratory system is functioning normally the PCO2 is between?

Answer 41

35 and 45 mmHg.

Question 42

If the partial pressure of carbon dioxide (PCO2) is above 45 mmHg it indicates?

Answer 42

respiratory acidosis because CO2 is an acid it will make the blood more acidic

Question 43

If the partial pressure of carbon dioxide (PCO2) is below 35 mmHg it indicates?

Answer 43

respiratory alkalosis because there is now less CO2 than ‘normal’, so blood will become more alkaline.

Question 44

What is the main way kidneys adjust acid-base balance?

Answer 44

By adjusting the amount of available bicarbonate ions, either by generating new HCO3- or by excreting HCO3- ions.

Question 45

How do the kidneys works to conserve bicarbonate ions that have been filtered - while at the same time get rid of excess H+ ions, that are making our blood more acidic?

Answer 45

as one hydrogen leaves the tubule cell and enters into the filtrate, one bicarbonate ion leaves the filtrate - combined with either Na+ or in exchange for Cl- - and enters the cell. Therefore, it is a one-for-one exchange.

When large amounts of H+ ions are secreted correspondingly large amounts of HCO3- enter the blood, which has the effect of raising blood pH.

Question 46

How is acid removed via Ammonium Ion (NH4+) Excretion?

Answer 46

Via glutamine metabolism.

Glutamine is the most abundant and versatile amino acid in the body. The breakdown of Glutamine (via deamination, oxidation and acidification by combining with H+) we get two Ammonium ions (NH4+) and two Bicarbonate ions (HCO3-)
The result is that more bicarbonate enters the blood plasma and the NH4+ is excreted in the urine, both of which help to reduce the overall acidity of the blood.

Question 47

What happens when the body is in alkalosis?

Answer 47

Bicarbonate Ion Secretion
There are specialised cells in the collecting ducts of the kidney that secrete HCO3- ions whilst reclaiming H+ ions.

However, it is important to understand that the predominant process in the nephrons and collecting ducts is to reabsorb HCO3- ions, and even during alkalosis, much more HCO3- is conserved than excreted.

Question 48

In a hyperventilating person, acidosis is caused by high PCO2 - how will the kidneys respond?

Answer 48

Renal compensation will occur through the kidneys retaining HCO3 - to offset the acidosis

Question 49

In a hyperventilating person alkalosis is caused by low PCO2. How will the kidneys respond?

Answer 49

Renal compensation will occur through the kidneys failing to retain HCO3- or by actively excreting it to offset the alkalosis.

Question 50

Metabolic acidosis is indicated by?

Answer 50

low blood pH and HCO3- concentration. There are several potential causes, including: Excess alcohol intake, excess loss of HCO3- (e.g., via chronic diarrhoea), starvation or uncontrolled diabetes mellitus (both as a result of ketosis), and the accumulation of lactic acid during exercise or shock.

Question 51

Metabolic alkalosis is indicated by?

Answer 51

rising blood pH and HCO3- levels. This is much less common than metabolic acidosis, but typical causes are: vomiting the acidic contents of the stomach (or having the stomach suctioned), or excess intake of base (e.g., too much antacid).