RENAL PHYSIOLOGY: WATER REGULATION -- Pathophysiology

PATHOPHYSIOLOGY OF WATER BALANCE

Basic Condition	Example	Cause
ANURIA
Low glomerular filtration pressure	Shock	Reduced systemic arterial pressure
	Renal artery stenosis	Reduced post-restriction arterial pressure
Reduced renal blood flow; also reduced GFR	Diabetic nephropathy	Alteration of glomerular blood vessels and increased filtration barrier
High tubular hydrostatic pressure	Renal stone	Increased Bowman’s capsule and tubular hydrostatic pressure
Reduced number of functioning nephrons	Renal degenerative disease	Reduced area available for exchange
Inappropriately high ADH secretion	Syndrome of Inappropriate ADH (SIADH)	Pituitary pathology

POLYURIA
Inability of pituitary to secret ADH	Diabetes insipidus (pituitary)	Reduced H2O reabsorption in distal tubule and collecting ducts
Inability of the distal tubule and collecting ducts to respond to ADH	Diabetes insipidus (nephrogenic)	Reduced H2O reabsorption in distal tubule and collecting ducts
Note: Diabetes insipidus (any cause) is termed a water diuresis (excretion of a large volume of dilute urine)
Lack of nocturnal increase in ADH release	Nocturnal enuresis	Excess volume in bladder
Excess filtered load of osmotically active particles		Reduced osmotic gradient for water reabsorption
high blood glucose	Diabetes mellitus
ingestion of non-reabsorbed particles	Mannitol, NH4+
Reduced tubular reabsorption of Na+	Most clinical diuretics	Reduced osmotic gradient for water reabsorption
Note: above two result in an osmotic diuresis (excretion of a large volume of concentrated or iso-osmotic urine)
Excess water ingestion	Primary polydipsic diabetes insipidus	Psychogenic