Regulation Of Water Na And ECF Volume

Question 1

In adult animals what is the percentage of Intracelluar, extracellular, interstitial and intravascular fluid in accordance to body weight

Answer 1

Intracellular fluid = 40% body weight
Extracellular fluid = 20% body weight
Interstitial fluid = 15% body weight
Intravascular fluid = 5% body weight

Question 2

Where does normal fluid loss occur and at what rate

Answer 2

Through the kidneys at 1-2ml/kg/hour is a sensible loss

Question 3

Where does insensible fluid loss occur

Answer 3

Evaporation from the skin
Exhalation from the lungs
In the faeces

Question 4

What is normal fluid intake and normal urine output

Answer 4

Normal fluid intake = 50ml/kg/day through ingestion of liquids and moist food and metabolic synthesis of water. Polydipsia is more than 100mls/kg/day.

Normal urine output is 1ml/kg/hour. Polyuria is more than 50ml/kg/day

Question 5

Since there is no sensory receptors to directly monitor water and Na what do receptors respond to

Answer 5

Osmolarity
Plasma volume
Blood pressure

Question 6

What can kidneys do to maintain fluid volume

Answer 6

Regulate sensible water loss
Concentrate urine if animal dehydrated (up to a point)
Produce copious amounts of dilute urine when there is an excess of water

Question 7

How is ADH regulated

Answer 7

Osmolarity is monitored by osmoreceptors neuron’s in the hypothalamus - increase rate of firing to increase in osmolarity = increase release of ADH.
When plasma osmolarity drops below threshold value then neuron’s stop firing no ADH is released and dilute urine is produced

Question 8

At what percent of osmolarity increase is thirst stimulated

Answer 8

3%

Question 9

Is Na+ intake regulated

Answer 9

No all Na+ is ingested and absorbed
There is no direct sensor for Na compared to Ca and K

Question 10

How is Na regulated and what it is dependent on

Answer 10

It’s not
Na ingested must equal Na loss for ECF volume to be stable
Regulation of Na is dependent upon receptors for blood pressure and blood volume
Kidneys regulate ECF volume by adjusting excretion of Na

Question 11

Which three hormones regulate renal Na and Cl reabsorption and secretion

Answer 11

Angiotensin 2 and Aldosterone promote urinary Na and Cl reabsorption and water by osmosis when dehydrated
Natriuretic peptides promote excretion of Na and Cl followed by water excretion to decrease blood volume