Endocrine

Question 1

What is the role of ADH in the body?

Answer 1

Antidiuretic hormone - prevents diuresis; the thalamus stimulates the pituitary gland to release ADH which then acts on the kidneys to increase water reabsorption + reduce water loss

Water reabsorption dilutes the blood and increases its volume.

Question 2

What is Diabetes Insipidus?

Is it related to Diabetes mellitus?

Answer 2

Diabetes Insipidus = water loss

Cranial DI is where ADH is not being secreted or not being secreted enough by the pituitary gland.

Nephrogenic DI is where the kidneys are not responsive to ADH secretion. Usually due to ADH receptor mutations.

RESULTS in reduced water REABSORPTION and increased DIURESIS.

Not exactly related to Diabetes mellitus but symptoms are similar = Polyuria & Polydypsia (thirst)

Question 3

What drug is given to treat Central Diabetes Insipidus?

Answer 3

Desmopressin

Desmopressin is the synthetic form of vasopressin (ADH); Nephrogenic Diabetes Insipidus is treated with thiazide diuretics which results in decreased Na reabsorption and water excretion & increased water reabsorption *

Question 4

(…) diabetes insipidus is characterized by low levels of ADH

Answer 4

Central diabetes insipidus is characterized by low levels of ADH

Question 5

(…) diabetes insipidus is characterized by normal or high levels of ADH

Answer 5

Nephrogenic diabetes insipidus is characterized by normal or high levels of ADH

Question 6

Desmopressin has high affinity for ADH-activated (…) receptors

Answer 6

Desmopressin has a high affinity for ADH-activated V2 receptors

Vasopressin is ADH - V for V2

Question 7

Desmopressin may be used to treat central diabetes insipidus & night (..)

Answer 7

Desmopressin may be used to treat central diabetes insipidus & night enuresis (bed wetting)

Question 8

What adverse effect may desmopressin have on sodium levels?

Answer 8

hyponatremia = seizures, confusion, dizziness, falls & coma

Desmopressin (synthetic ADH) acts on kidney receptors to increase water REABSORPTION therefore it DILUTES the blood and its contents.

Question 9

One class of drugs that may treat nephrogenic diabetes insipidus is (…), which enhances the uptake of NaCl and H2O in the proximal tubule

Answer 9

Thiazide diuretics

confusing mechanism: thiazide diuretics decrease reabsorption of NaCl in the early DCT -> increased urinary excretion of Na+ -> decreased ECF volume -> increased proximal Na+ and H2O reabsorption -> decreased urine output

Where most of the reabsorption occurs = PCT

Question 10

Desmopressin is a long-acting synthetic analog of (…) and its doses are arranged in a way that allows for diuresis to occur every now and then to avoid fluid overload

Answer 10

Desmopressin is a long-acting synthetic analog of ADH and its doses are arranged in a way that allows for diuresis to occur every now and then to avoid fluid overload

Question 11

What is the likely diagnosis in a patient with diluted urine (more water) that improves significantly following water deprivation and administration of desmopressin?

Answer 11

Central diabetes insipidus

Water deprivation test: Patient does not take in any water, Desmopressin is given intranasally; if urine output is concentrated then the likely diagnosis is Central DI because concentrated urine means that water is being reabsorbed in response to Desmopressin (synthetic ADH) - therefore less likely to be a problem with ADH receptors as seen in Nephrogenic DI.

Question 12

In syndrome of inappropriate antidiuretic hormone (SIADH) too much ADH is being released resulting in increased (…) reabsorption

Answer 12

water reabsorption

As a result, the body’s RAAS system is deactivated as it senses an increase in blood volume (ADH causes water reabsorption which dilutes the blood -> hyponatremia) thus promoting Na and H20 loss as a way to combat this change in blood volume which further leads to Hyponatremia

Question 13

Syndrome of inappropriate ADH (SIADH) may be treated with water restriction, with (…first-line treatment…), or with a tetracycline such as demeclocycline

Answer 13

Syndrome of inappropriate ADH (SIADH) may be treated with water restriction, with tolvaptan, or with a tetracycline such as demeclocycline

fluid restriction prevents reabsorption; drug treatment aims to BLOCK V2 RECEPTORS and correct hyponatremia caused by SIADH

Question 14

What endocrine pathology is treated with demeclocycline?

Answer 14

SIADH

Question 15

In SIADH, urinary sodium levels are (…increased/decreased…)

Answer 15

increased

RAAS system deactivates in response to increase blood volume (water reabsorption in response to increased ADH release) promoting Na and H20 loss via urine

Question 16

Why is it important to avoid rapid correct of hyponatremia?

Answer 16

Rapid correction of hyponatremia => osmotic demyelination of nerve cells in the brain (destroys myelin sheath) => problems with the brain’s nervous system