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WEEK 4:
Renal function: glomerular filtration and its control:
| Question | Answer |
|---|---|
| functions of kidneys | regulate electrolyte balance, regulation of body fluid, excretion of metabolic waste + foreign substances, conservation of useful substances (glucose etc), production + secretion of hormones, gluconeogenesis, and blood pressure maintenance |
| how do the kidneys regulate body fluid (3) | Osmolality* (water balance), Volume/BP (Na+ balance) and Acid base balance (H+ and bicarb balance) |
| main hormones used in endocrine function of kidney | erythropoietin, renin (angiotensin), and 1,25-dihydroxy vitamin D3 |
| role of erythropoietin | erythrocyte RBC production |
| function of renin (angiotensin) | its production/release Na+ balance and hence ECF volume and cardiovascular regulation |
| function of 1,25- dihydroxy vitamin D | calcium balance |
| basic processes for urine formation (4) | Filtration of plasma, Reabsorption of substances from and secretion into filtrate, Final urine and Micturition |
| movement of tubule lumen to blood is called | reabsorption |
| movement of blood to tubule lumen is called | secretion |
| removal from body is called | excretion |
| arterial blood supply for kidneys | renal artery |
| at rest, what % of cardiac output delivered to kidneys | 25% |
| blood from kidneys is drained via | renal veins |
| blood enters glomerulus from | interlobular artery (branch of renal artery) |
| blood enters what arteriole | afferent at high pressure |
| when blood enters leaky glomerular capillaries what % of plasma is forced out | 15-20% |
| blood drains/exits into what arteriole | efferent arteriole |
| from efferent arteriole the blood goes where | peritubular capillary |
| how many nephrons in each kidney | 1x10^6 |
| types of nephrons | cortex and medulla |
| where is the glomerulus | cortex of kidney |
| renal corpuscle | site of initial blood filtration (filtrate, ultrafiltrate tubular fluid) |
| tubular system consists of (2) | cortical and medullary |
| tubular system function | controls concentration and content of urine |
| renal corpuscle contains (2) | bowmans capsule + glomerulus together |
| proximal convoluted tubule contains many | mitochondria - therefore are thick structures |
| juxtaglomerular apparatus includes (2) | autoregulation and renin release (salt and water balance) |
| capillary beds in series (2) | Glomerulus – high hydrostatic pressure (60 mmHg) – filtration and Peritubular capillaries - low pressure (20 mmHg) - reabsorption, secretion |
| pressure in glomerulus | high hydrostatic pressure (60mmHg) |
| function of glomerulus | filtration |
| function of peritubular capillaries | reabsorption and secretion |
| pressure in peritubular capillaries | low pressure (20mmHg) |
| urinary excretion = | filtered - reabsorbed + secreted |
| what % of plasma entering glomerulus is filtered | 20% |
| how much plasma enters glomerulus via the afferent arteriole | around 600ml/min plasma |
| how much plasma is filtered/ ultrafiltered | 120ml/min (180L/day) |
| what % of fluid is reabsorbed | >19% |
| how much urine produced | 1ml/min urine/ 1.5L (<1% volume excreted) |
| what initiates glomerular filtration | fluid driven from capillaries into Bowman's capsule across glomelular filter by capillary hydrostatic pressure |
| function of differences in arteriole diameter | efferent arterioles have smaller diameter than afferent to maintain glomerular capillary hydrostatic pressure |
| glomerular filter consists of (3) | Endothelial cells, Basement membrane and Podocytes |
| negatively charged glycoproteins on surface of endothelium of glomerulus and basement membrane do what | repel anionic proteins eg albumin |
| endothelium fenestrated and freely permeable to | water |
| what appears in filtrate | all parts of plasma except plasma proteins as too big |
| fenestrations filter | red and white blood cells, platelets |
| basement membrane filter | large plasma proteins |
| filtration slits filter | medium sized proteins |
| glomerular filtration rate (GFR) refers to | rate of filtration from plasma to bowman's space |
| GFR governed by | starling forces |
| why does ultrafiltration occur | because starling forces drive fluid from lumen of glomerular capillaries across the filtration barrier into bowmans capsule space |
| effect of constriction of afferent arteriole | increases renal vascular resistance which reduces renal plasma flow (RPF) and decreases intraglomerular pressure and decrease GFR |
| effect of constriction of efferent arteriole | lowers RPF but increases intraglomerular pressure and GFR |
| GFR can reflect | severity and course of kidney disease, and approximate % kidney function (influences how much of drug you can prescribe and is also required if patient is receiving any form of imaging that requires IV contrast) |
| fall in GFR indicates | disease is progressing |
| rise in GFR indicates | at least partial recovery from disease |
| symptoms of kidney disease (4) | Hypertension (RAAS overdrive), Oedema (Sodium balance, and/or protein losing nephropathy), Proteinuria (problem with filter) and Haematuria (problem with filter or bleeding downstream, UTI, TCC etc) |
| can GFR be measured directly | no |
| how is GFR measured | indirectly from plasma clearance (kidneys ability to clear plasma of a given substance and then excrete it in urine) |
| what substance is used to measure GFR | substances which are freely filtered, do not affect GFR, and are not further secreted or reabsorbed eg inulin or creatinine |
| inulin for measuring GFR needs | infusing and tagging |
| creatinine for measuring GFR depends on | two errors cancelling - some secreted in PT but assay underestimates amount in urine by same amount |
| PI . GFR = | UI .V |
| GFR = | UI .V/PI |
| UI | urine concentration of inulin (mmol/L) |
| V. | urine flow rate (ml/min) |
| units for GFR | ml/min |
| Pi | plasma concentration of inulin (mmol/L) |
| UV/P is | renal clearance of solute (volume of plasma cleared of substance per unit time) |
| total blood flow = | effective blood flow / 0.9 |
| effective blood flow = | effective plasma flow / (1-Hct) |
| UV/P (for PAH) = | effective plasma flow |
| UV/P (for creatinine or inulin) = | GFR |
| estimate GFR using | serum creatinine measurement |
| creatinine | waste product of creatine (small non ionic waste molecule that diffuses out of cell) |
| creatine produced where (3) | liver, muscle, and other high energy cells |
| creatinine function | acts as buffer for phosphate during energy release (via enzyme creatine kinase) and allows for rapid regeneration of ATP |
| creatine is irreversibly hydrolysed into | creatinine via non enzymatic reaction |
Created by:
22tango
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