Question

A 28 year old male complained of excessive thirst and an increase in urinary volume. Lab results showed the following

urine specific gravity (relative density) was less than 1.005 (normal: 1.040 - 1.050)

urine osmolarity (concentration) was less than 200 mOsm/L (normal: 500 - 800 mOsm/L)

urinary volume was 15 L/day (normal: 1.5 to 3.0 L)

serum sodium was 145 mEq/L (normal: 136 - 145 mEq/L)

serum potassium was 2.8 mEq/L (normal: 3.6-5.1 mEq/L)

Water deprivation and hypertonic saline infusion did not cause a significant reduction in urinary volume or urinary osmolarity:

a urine specific gravity (relative density) of 1.009

a urine osmolarity (concentration) of 225 mOsm/L

However, there was a significant increase in the concentration of the urine and decrease in urinary output following administration of ADH.

1)What condition is the patient suffering from

2)Why did the water deprivation and hypertonic saline infusion not result in a concentrated urine?

3)Describe the location of the disorder in this individual. Is the defect related to the lack of receptors or the lack of hormone; explain your answer?

4)How might the patient be treated for his condition, explain your answer

5)Draw out the negative feedback pathway for the hormone involved

Answer 1

1. The patient is suffering from Diabetes Insipidus. He is having  Polydipsia as he is complaining of excessive thirst. He is also suffering from Polyurea as he is producing large volume of urine as urine volume is 15L/day against the normal value of 1.5 to 3.0L.

2. Because of lack of ADH.

3. The location of this disorder is Posterior pituitary and Hypothalamus.

The disorder is related to the lack of hormone, because urine concentration is increased and urine output is

decreased when ADH hormone is administered. So, the hormone receptors in kidney are working properly.

4. The patient should be given Desmopressin, a synthetic analog of vasopressin. As it is a peptide hormone, it

can not be given orally. because then it will be digested by the normal process of digestion. So, it will be given

as nasal spray. Then it will be absorbed in the blood of the capillary network of nose.

5. When blood osmotic pressure is lowered and blood volume is increased, ADH secretion decreases. This is negative feedback.