Chapter 8 Measurements of renal function Flashcards
What measurements of renal function are used?
glomerular filtration rate
creatinine
creatinine clearance
What is glomerular filtration rate?
volume of plasma filtered by the glomerulus per unit of time
How is glomerular filtration rate measured?
1) formal assessment : looking at inulin that in injected intravenously
2) estimated from serum creatinine measurements: (applicable to adults with stable creatinine levels) done by applying a formula:
(a) Cockcroft-Gault formula (overestimates (looks at CrCl).
(b) modification of diet in renal disease study equation (underestimates).
(c) CKD-EPI: most commonly used, more accurate
How is creatinine produced?
end product of mm breakdown
What does creatinine levels tell you?
rough guide of GFR, as freely filtered at glomerulus but is secreted by the renal tube
How is creatine clearance measured (CrCl)?
2) what is a drawback?
measure serum creatinine and 24hr urine collection, then calculated using following equation
CrCl= (urine conc*volume)/serum creatinine
2) impracticle
3) estimate GFr using CKD-EPI equation (has 4 variables)
Control of acid-base balance is aided by kidneys how?
1) regentate bicarbonate and reasbsorb filtered bicarbonate from the urine (in proximal tubule)
2) achieves net excretion by generating and excreting NH4+
3) also excretes protons bound to other buffer
Kidneys regulate body fluid volume and composition how?
modifies concentration of Na+ and Cl-, through excretion or reabsorbtion, helping control extraceullar volume as sodium and cl- ions are major extracellular ions and thus determinants of extracellular volume.
Kidneys extrete drugs, how is this relevant to dose in prescriptions?
when kidney function is reduced , the dose of water-soluble drugs that are cleared via kidneys must be reviewed and reduced.
How are kidneys relevant to endocrine activity?
1) form active metabolite Vitamin D3 that is calcitriol.
2) kidneys produce the hormone erthyropoietin
what are the systemic affects on the body due to the kidney forming calcitriol?
normocalcaemic and adequate bone mineralisaiton:
1) acts on gut= increase Ca and phosphate uptake
2) suppresses parathyroid hormone= therefore reducing osteoclast activity (osteoclasts eat bone).
how are the kidneys relevant to blood pressure control?
1) regulates salt and water balance
2) JGA produces renin, which via the renin-angiotensin-aldosterone system = angiotensin2 binding to AT1 and AT2 receptors.
AT1 binding= vasoconstriciton, aldosterone release and vasopressin relesae, salt and water retention in the kidneys , and sympathetic NS activaiton
AT2 binding= involved in antiproliferative and remodelling effects, which are thought to be important in the many cardioprotective and renoprotective effects of the renin– angiotensin blockade.
