ILA: SALT AND WATER BALANCE

Question 1

Total body water is distributed to three compartments (intracellular, interstitial and intravascular. How is the total body water distributed by volume?

Answer 1

28 L
11 L
3 L

Question 2

Which is the most common intracellular cation?

Answer 2

K+

Question 3

Osmolality can be measured directly in the laboratory. It can also be calculated from blood results. What are factors in calculated osmolality?

Answer 3

Na+ (2)
K+ (2)
Urea
Glucose

Question 4

Give an example of insensible fluid loss.

Answer 4

Sweating due to fever

Question 5

You examine a patient and notice he has lower leg pitting oedema. His albumin level is also low. Describe the relationship between albumin and oedema.

Answer 5

A low albumin causes a decrease in oncotic pressure and water diffuses from the blood into the interstitial fluid.

Question 6

What happens to ADH concentration in plasma as plasma osmolarity increases?

Answer 6

Increases

Question 7

What is the site of synthesis of aldosterone?

Answer 7

Adrenal cortex

Question 8

What is the site of synthesis of ADH?

Answer 8

Hypothalamus

Question 9

What is the principal site of renin production?

Answer 9

Juxtaglomerular cells

Question 10

What does renin do?

Answer 10

Converts angiotensinogen to angiotensin 1

Question 11

A healthy medical student drinks 2 litres of water in 5 minutes. What is her physiological response?

Answer 11

Osmolality falls –> ADH secretion stops –> increased urine volume

Question 12

A young patient has cranial diabetes insipidus (a disorder in which the pituitary gland fails to release ADH when stimulated to do so). She is referred for a water deprivation test during which she is nil by mouth. What will be her blood and urine osmolality after 3 hours of water deprivation?

Answer 12

Blood = 300 mOsm/Kg
Urine = 100 mOsm/g
Note: normal serum osmolality is 275-295 mOsm/Kg, where as urine osmolality varies from 50 to 1400 mOsm/Kg