Kidney pathophysiology Flashcards
Diuretics definition and purpose
Drugs that increase urine flow
Mainly given to cause loss of water and salts
Main clinical uses of diuretics
Cardiac failure
Oedema
Hypertension
Liver disease and some types of kidney disease
Overdose or poisoning to help excretion
Abuse- eating disorders patients to lose weight
Body fluid compartments (at least 70% of body = water)
Extracellular fluid (30% of body)
5% in plasma
20% in interstitial fluid (bathes the cells)
5% as transcellular fluid (between cells)
Intracellular fluid (40% of body)
Ion content of extracellular fluid
Cations: Na+ 135 K+ 3.5 Ca++ 4.0 Anions: Cl- 100 HCO3- 28
Ion content of intracellular fluid
Cations: K+ 160 Na+ 10 Ca++ 1.0 Anions: HPO4- 100 Protein 65
Characteristics of ideal diuretic
Removes sodium and other electrolytes in proportion to conc in ECF
Once oedema is eliminated there should be no further electrolyte loss
May be necessary to continue diuretic to prevent recurrence of oedema
Interrelated regulation of body fluid composition and volume
Internal osmotic pressure- mainly via ADH
Internal volume- mainly via aldosterone
Osmotic regulation
Increase in osmotic pressure in blood e.g. after sweating
Blood goes to hypothalamus (osmo-receptors)
Travels down nerve tract to
Posterior pituitary- increases ADH, increases permeability of distal tubule, increases water resorption
Volume regulation
Reduction is vascular volume leads to a decrease in renal blood flow
Leads to the renin-angiotensin cascade, releasing aldosterone from the adrenal cortex
Causes sodium and water retension leading to oedema
Oedema is caused by
An alteration of the balance between volume of fluid in blood capillaries and tissue spaces
Cardiac oedema
Two components (Starling)- backward failure theory and forward failure theory
Backward failure theory
Right side of heart fails, unable to clear returning blood
Increase in venous pressure causes increase in transudation of fluid into interstitial spaces
Decreases plasma volume
Leads to renin-angiotensin cascade and the renal retention of sodium and water
Forward failure theory
Failure of cardiac left side leads to back pressure in the pulmonary artery
Causes pulmonary oedema and reduction in respiratory function
Hepatic oedema
Caused/ aggravated by cirrhosis of the liver Metabolism of aldosterone is impaired Increased sodium retention Causes excess fluid in peritoneum Increased intra-abdominal pressure Increased venous pressure in lower limbs
Nephrotic oedema
More prevalent in childhood and young adults
Inflammation and increased glomerular permeability to plasma proteins which are lost in urine
Causes reduced colloid oncotic pressure
Discourages water osmosis into plasma
