Lecture 25: Diabetes Insipidus Case Flashcards Preview

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Flashcards in Lecture 25: Diabetes Insipidus Case Deck (71)
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What is the normal serum [Na+]?

135-145 mE/L


What are the 5 types of diabetes insipidus (3 names for first one and 2 for second one)?

1. Central = neurogenic = hypothalamic
2. Nephrogenic = renal
3. Gestational
4. Dipsogenic
5. Psychogenic


What is central/neurogenic diabetes insipidus due to? Overall and 4 main causes by order of incidence?

Inability to synthesize or secrete active vasopressin due to:
1. Hypothalamic lesions (40-50% of cases) due to tumor, sarcoidosis, or histiocytosis (langerhan's cell)
2. Neurosurgery damaging neurons around the base of the brain
3. Idiopathic (20-30% of cases) due to autoimmune inflammatory attack on posterior pituitary = lymphocytic infundibuloneurohypophysitis
4. Genetics (5% of cases)


What is nephrogenic diabetes insipidus due to? What can cause this (4 potential causes (2 types))?

Inability of kidney to detect vasopressin
1. Familial:
- V2 mutation: X-linked recessive
- AQP2 mutation: autosomal dominant
2. Acquired:
- Hypercalcemia (above 13)
- Hypokalemia (below 2.5)
- Drugs: lithium, demeclocycline


What is gestational diabetes insipidus due to?

Placenta secretes vasopressinase that degrades vasopressin


What is diabetes insipidus characterized by?

Large dilute urine volume


What are the 4 possible diseases that can cause polyuria?

1. Osmotic diuresis
2. Diabetes insipidus
3. Primary polydipsia
4. Osmoreceptor dysfunction


What is osmotic diuresis caused by? Example? Blood osmolarity?

Osmotic agent in the urine causing excessive urination
Eg: glucose in diabetics
Normal blood osmolarity because thirst regulation is intact


What are the 2 types of primary polydipsia?

1. Dipsogenic DI
2. Psychogenic DI


What is the most common cause of polyruria in Western countried?

Primary polydipsia


What does polydipsia mean?

Excessive water intake


What is dipsogenic DI? 4 causes?

Low thirst threshold caused by:
1. Mass lesions in posterior pituitary
2. Granulomatous diseases: inherited primary immunodeficiency disease which increase the body's susceptibility to infections caused by certain bacteria and fungi: masses of immune cells that form at sites of infection or inflammation
3. Aging
4. Idiopathic


What is psychogenic DI?

Excessive drinking due to psychiatric disorders or simply believing it's more healthy, not actual thirst


Describe osmoreceptor dysfunction. Blood concentration?

Osmoreceptors connected to and regulating AVP secretion and thirst have lesions or are destroyed so you are lacking AVP AND THIRST
Hyperosmolar blood


What is DI's incidence?

1 in 10-15,000 people


What % of DI compared to DM?



Has the DI incidence increased over the past 50 years?



What are the 2 types of body fluid homeostasis?

1. Osmotic
2. Volume


What is the normal range of blood osmolality?

280-295 mOsm/kg


What is the definition of osmolality?

Solute (mOsm) / water (kg)


What does total plasma osmolality primarily include? How do their concentrations relate to one another?

1. Na+
2. H2CO3-
3. Cl-

[Na+] = [H2CO3-] + [Cl-]


What is the equation to calculate plasma osmolality?

Plasma osmolality = 2 x[Na+] + glucose (mg/dL)/18 + BUN (mg/dL)/2.8


What does BUN stand for?

Blood urea Nitrogen


What is the effective osmotic pressure?

The osmolality of the impermeable particles that contribute to the osmotic pressure


What is the equation to calculate effective plasma osmolality?

Effective plasma osmolality = 2 x[Na+] + glucose (mg/dL)/18


Why is BUN not included in the equation for effective plasma osmolality?

Because nitrogen can freely diffuse through plasma membranes


Describe the genes that encode for AVP.

Genes encode a large precursor hormone, vasotocin, and the 9 AA at the N-terminal is AVP
The rest is secreted into the blood and has no biological effect


What are the 5 regulators of AVP secretion by hypo?

1. Blood hyperosmolality
2. Angiotensin II
3. Decreased atrial receptor firing = hypovolemia = increased AVP secretion
4. Sympathetic stimulation
5. Hypervolemia sensed by baroreceptors and natriuretic peptide in the brain: inhibition of AVP secretion


What 2 hypo nuclei is AVP secreted by?

1. Paraventricular
2. Supraoptic


What is the role of ADH?

Reabsorption of water in kidney tubules to decrease plasma osmolality and concentrate urine