USMLE Step 1 Neuroanatomy Review 26 06 Hypothalamus (4_6)

USMLE Step 1 Neuroanatomy Review 26 06 Hypothalamus (4_6)


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Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3 26 06 Hypothalamus (4_6) Below

Begin 26 06 Hypothalamus (4_6) Transcription

Student doctor, what particular condition would be the result of a lesion to the paraventricular and supraoptic nuclei?

  • This would be diabetes insipidus.

What two symptoms are characteristic of both diabetes insipidus and diabetes mellitus, especially in the initial presentation of the patients?

  • Both polyuria, which is frequent, excessive urination, and polydipsia, which is frequent, excessive thirst.

Now in both cases, the polyuria is a type of diuresis. What type of diuresis is going on with diabetes mellitus?

  • A hyperosmolar diuresis.

And what is the osmolar agent?

  • Glucose.

What is the type of diuresis is the cause of diabetes insipidus?

  • An insufficiency of ADH.

Now, actually we need to qualify that. The insufficiency of ADH is due to what type of diabetes insipidus?

  • Neurogenic diabetes insipidus, that is when a lesion to the paraventricular and supraoptic nuclei of the supraoptic region is involved. The result of this lesion in terms of ADH is simply that ADH is not being produced.

Now what is the other type of diabetes insipidus where there is plenty of ADH and the supraoptic region is actually not affected?

  • This would be nephrogenic diabetes insipidus, where the nephrons are not responsive to ADH.

Now there are many causes to those conditions and the picture gets rather complicated from this point on. But there are two simple distinctions that we can make as long as you keep in mind that there are complexities behind these simplifications. In very general terms, what is the most likely cause of a nephrogenic diabetes insipidus?

  • This would be genetic, this would be an inherited condition.

What is the inheritance of nephrogenic diabetes insipidus when it is genetic in origin?

  • This is x-linked inheritance.

And what is the expression in males?

  • Full expression.

And the expression in females?

  • Partial expression if the female is heterozygous. If she is homozygous of course, then there’s full expression just as in the males.

If the diabetes insipidus is neurogenic in origin, what are the two most likely causes?

  • Either trauma in the region or a tumor in the region.

Finally, what psychological condition can mimic diabetes insipidus?

  • Psychogenic polydipsia.

By the way, what type of diuresis is involved in the polyuria associated with psychogenic polydipsia?

  • This simply is a water diuresis.


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