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Ch. 26 Fluid, Electrolyte, and Acid-Base Balance
Chapter 25, Problem 20

Mr. Jessup, a 55-year-old man, is operated on for a cerebral tumor. About a month later, he appears at his physician's office complaining of excessive thirst. He claims to have been drinking about 20 liters of water daily for the past week and says he has been voiding nearly continuously. A urine sample is collected and its specific gravity is reported as 1.001. What is your diagnosis of Mr. Jessup's problem? What connection might exist between his previous surgery and his present problem?

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Step 1: Identify the symptoms presented by Mr. Jessup, which include excessive thirst (polydipsia) and excessive urination (polyuria).
Step 2: Note the specific gravity of the urine sample, which is 1.001. This indicates very dilute urine, suggesting the kidneys are not concentrating urine effectively.
Step 3: Consider the possible causes of these symptoms. One common condition that matches these symptoms is diabetes insipidus, which is characterized by an inability to concentrate urine, leading to excessive urination and thirst.
Step 4: Connect Mr. Jessup's recent cerebral tumor surgery to his current symptoms. Surgery in the brain, particularly near the pituitary gland or hypothalamus, can lead to central diabetes insipidus if these areas are damaged, as they are responsible for the production and release of antidiuretic hormone (ADH).
Step 5: Conclude that Mr. Jessup's symptoms and recent surgery suggest a diagnosis of central diabetes insipidus, likely due to damage to the hypothalamus or pituitary gland during the tumor removal.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Diabetes Insipidus

Diabetes Insipidus (DI) is a condition characterized by excessive thirst and the excretion of large amounts of dilute urine. It occurs due to a deficiency of the antidiuretic hormone (ADH), which regulates water balance in the body. In Mr. Jessup's case, his symptoms of excessive thirst and low urine specific gravity suggest that he may be experiencing DI, potentially as a complication following his cerebral surgery.
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Cerebral Surgery Complications

Cerebral surgery can lead to various complications, including damage to the hypothalamus or pituitary gland, which are crucial for hormone regulation. If the surgery affected areas responsible for ADH production or release, it could result in DI. Understanding the anatomical and functional relationships in the brain helps explain how surgical interventions can lead to endocrine disorders.
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Urine Specific Gravity

Urine specific gravity is a measure of the concentration of solutes in urine, indicating the kidney's ability to concentrate urine. A normal specific gravity ranges from 1.005 to 1.030. Mr. Jessup's urine specific gravity of 1.001 indicates very dilute urine, which aligns with the symptoms of DI, as the kidneys are unable to concentrate urine due to insufficient ADH.
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