09 Diabetes Insipidus Harieg Flashcards
What are the two main physiologic mechanisms that regulate body water?
Thirst. Antidiuretic Hormone (ADH)
How does thirst work?
Controlled by hypothalamus. Two stimuli are true thirst based on water need: 1) cellular dehydration caused by an increase in extracellular osmolality, 2) a decrease in blood volume, which may or may not be associated with a decrease in serum osmolality
What do Osmoreceptors do?
Sensory neurons which are located in or near the thirst center in the hypothalamus, respond to changes in extracellular osmolality by stimulating the sensation of thirst
Where is ADH stored?
Pituitary gland
Where is ADH made?
Its a hormone made in the hypothalamus, stored in the pituitary gland and released into the blood stream when necessary
What are ADH levels controlled by?
Extracellular volume and osmalality
How does ADH work?
ADH direct kidneys to concentrate the urine by reabsorbing the filtered water to the bloodstream –> less urine. When this system for regulating the kidney’s handling of fluids is disrupted can cause diabetes insipidus
What is Diabetes Insipidus?
Deficiency of or a decreased response to ADH also known as arginine vasopressin (AVP). Unable to concentrate urine during periods of water restriction. Excrete large volumes of urine, usually 3-20 L/day
What are the similarities in signs and symptoms between DM and DI?
Excessive thirst and excessive urination
What are the signs and symptoms of DI?
Polyuria. Nocturia. Thrist. Mild daytime fatigue/somnolence
When monitoring urine output, what is considered polyuria?
> 50 ml/kg daily
What is urine osmolality like in DM?
A urine osmolality of 300 mOsmol/L or more plus a high serum glucose level
What is urine osmolality like in DI?
If the urine osmolality is less than 300 mOsmol/L in the presence of polyuria
What is urine osmolality like in Renal Disease?
High urine osmolality plus high serum uria
What are the two types of DI?
Neurogenic/Central (Defect in synthesis or release of ADH). Nephrogenic (Kidneys do not respond to ADH)
ADH normally promotes reabsorption of water in the collecting duct of nephrons. If urine osmolality does not increase after injection of exogenous ADH, what might the patient have?
Nephrogenic DI
Increased plasma osmolality normally stimulates release of ADH. If urine osmolality remains lower than plasma osmolality during fluid restriction, what might the patient have?
Central DI
When does Central DI occur?
In both sexes equally and affects all ages, with the most frequent age of onset between 10 and 20 years. Vasopressin (ADH) missing or very low level due to malfunction of hypothalamus or posterior pituitary gland (impaired synthesis, transport, and release of ADH)
What can Central DI be caused by?
Head injury. Tumors. Neurosurgical manipulations. Infections. Bleeding. There is usually a loss of 75-80% of ADH secretory neurons before polyuria becomes evident