Reabsorption Along The Tubule Flashcards
What sets the diffusion gradient?
Sodium potassium ATPase
What is central diabetes insipidus?
Impaired ADH synthesis or secretion by hypothalamus
Causes of central diabetes insipidus
Damage to hypothalamus or pituitary gland due to:
- brain injury
- tumour
- sarcoidosis or TB
- aneurysm
- forms of meningitis
Treatment of central diabetes insipidus
- administering ADH desmopressin
- clinically by ADH injection or nasal sprays
What is nephrogenic diabetes insipidus?
Acquired insensitivity of kidney to ADH
Causes of nephrogenic diabetes insipidus
- mutations in genes coding for V2 receptors
- chronic pyelonephritis
- polycystic kidneys
- drugs e.g. lithium
Treatment of nephrogenic diabetes insipidus
- low salt + low protein diet > reduces urine output
- thiazide > increase Na+ excretion
Differentiate between central and nephrogenic diabetes insipidus
Central:
- impaired ADH synthesis or secretion
- little ADH levels in plasma
Nephrogenic:
- acquired insensitivity of kidney to ADH
- plasma ADH levels are normal
In both water is inadequately reabsorbed > large quantity of urine
What is SIADH?
Syndrome of inappropriate ADH secretion
excessive release of ADH
Causes of SIADH
- stroke
- malignancy
- lung disease
- drugs e.g. opiates
- metabolic disease e.g. porphyria, hypothyroidism
Symptoms of SIADH
- hyponatremia + low plasma osmolality
- concentrated urine
- inappropriate Na+ excretion
- weight gain
When should SIADH be considered?
In hyponatremic patients with an absence of a condition that can impair water excretion
e.g. hypovolaemia, oedema, endocrine dysfunction, renal failure + drugs
Presentation of diabetes insipidus
- polyuria
- thirst
- dehydration
- dilute urine
- dry mucous membranes
What is SIADH characterised by?
- Dilutional hyponatraemia
- in which plasma Na+ conc is lowered and total body fluid is increased
What is Tm?
The maximum tubular resorptive capacity for a solute
