Renal Function & Glomerular Filtration

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  • Created by: Becca
  • Created on: 26-12-13 18:30
What are the 2 types of nephron? Where are glomeruli found?
Cortical nephron (85%, cortex) & juxtamedullary nephron (15%, medulla). All glomeruli are found in the cortex!
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What is the structure of the nephron?
Afferent arteriole -> Glomerular capillaries (sit in Bownman's space of Bowman's capsule, renal corpuscle) -> Proximal convoluted tubule -> Descending limb loop of Henle -> Thin ascending limb -> Thick ascending limb -> Distal CT -> Collecting duct
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What is the function of the renal corpuscle? Where is the juxtaglomerular apparatus? What is its role?
Renal corpuscle: site of initial blood filtration. Juxtaglomerular apparatus: thick ascending loop of Henle, involved in autoregulation & renin release (salt and water balance)
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What is the role of the tubular system?
Tubular system (cortical & medullary) controls concentration & content of urine
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What are the two capillary beds of the nephron? What pressure are they under & what is their function?
Glomerular capillaries under high hydrostatic pressure, favours filtration (movement from blood to Bowman's space). 2nd capillary bed from branches of efferent arteriole -> peritubular capillary plexus, low pressure favors reabsorption & secretion
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What are the vasa recta?
Blood vessels branching off from the capillary plexus. They supply oxygen and nutrients to the juxtamedullary apparatus
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What is filtration?
Movement of fluid from blood to lumen of nephron in renal corpuscle
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What is reabsorption?
Movement of filtered material from lumen of nephron back into blood through peritubular capillaries
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What is secretion?
Removal of selected molecules from the blood & their addition to fluid in lumen of nephron
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What is excretion?
Removal of substances from the body
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How are filtration, reabsorption, secretion & excretion linked?
Urinary excretion = Filtered - Reabsorbed + Secreted
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How much plasma is filtered? What is this called?
Only about 20% of plasma entering glomerulus is filtered. This is the filtration fraction
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What is glomerular filtration?
Fluid driven from capillaries into Bowman's capsule, across "glomerular filter" by capillary hydrostatic pressure - driving force for filtrate formation
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Which has the smaller diamater, efferent or afferent arterioles? What is the purpose of this?
Efferent arterioles have a smaller diameter than afferent arterioles. This helps to maintain glomerular capillary hydrostatic pressure
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What is the glomerular filtration rate, GFR?
The volume of fluid entering the Bowman's capsule per unit time
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What is the structure of the glomerular filter?
Mesangial cells between capillaries (structural & regulate blood flow), single layer of endothelial cells separated from epithelial cells (podocytes) by basement membrane. Fenestration = gaps between endothelium, permeable to H20, repel proteins
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What is significant about podocytes?
Podocytes have filtration slit (slit pores) --> filtration barrier. Normally all constituents in plasma except plasma proteins & cells appear in filtrate (small amounts of protein in high BP)
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How does capillary hydrostatic pressure influence ultrafiltration?
Driving force from glomerular capillary to Bowman's space. Efferent arterioles contract, increase hydrostatic pressure -> increase GFR. Afferent constrict, decrease hydrostatic pressure -> decease GFR
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How does colloid osmotic pressure influence ultrafiltration?
Changes in protein metabolism outside kidney e.g. hypoproteinaemia. Increase osmotic pressure -> decrease GFR. Decrease osmotic pressure -> increase GFR
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How does acute obstruction of urinary tract influence ultrafiltration?
Changes Bowman's space pressure. Increase pressure -> decrease GFR. Decrease pressure -> increase pressure
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How does change in Kf (permeability of the glomerular capillary membrane, Kf = intrinsic permeability x filtration area) influence ultrafiltration?
Increase Kf (drugs causing vasodilation of glomerular capillary) -> increase GFR. Decrease Kf (diseases with decrease no. glomeruli or membrane thickness/pore area) -> decrease GFR
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What is the oncotic pressure in Bowman's space? Why?
Essential zero as glomerular filtrate is essentially protein free
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What is the purpose of measuring GFR?
GFR provides an estimate of how efficiently the kidney filters wastes from blood. Essential part of assessing patients with kidney disease, provides information on: severity/course of disease, approximate % function & influences drug prescriptions
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What is a good indicator of GFR? Why is this used?
Inulin: freely filtered (small), not reabsorbed/secreted/metabolised by kidney (not degraded or synthesised), no effect on renal function (non-toxic) & easily measured in urine. Mass filtered = mass excreted
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What is the equation used to measure GFR?
GFR = Ui x V/Pi (Urine concentration of inulin x urine flow rate / plasma concentration of inulin). Note UV/P is renal clearance of solute i.e volume of plasma that is cleared of substance per unit time
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What is used to measure eGFR (estimated GFR)? Why?
Creatinine clearance: easier to measure than inulin clearance, plasma creatinine concentration remains close to constant & no intravenous infusion necessary, timed urine collection & 1 serum collection (consider muscle mass/gender/weight/age)
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What is the equation to measure eGFR?
eGFR = ([U]CR x V)/[P]CR --> [U]CR = urine concentration of creatining, V = urine flow rate, [P]CR = plasma concentration of creatinine
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When should eGFR not be used?
In children, malnourished patients, in pregnancy, in acute renal failure or oedema
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Other cards in this set

Card 2

Front

What is the structure of the nephron?

Back

Afferent arteriole -> Glomerular capillaries (sit in Bownman's space of Bowman's capsule, renal corpuscle) -> Proximal convoluted tubule -> Descending limb loop of Henle -> Thin ascending limb -> Thick ascending limb -> Distal CT -> Collecting duct

Card 3

Front

What is the function of the renal corpuscle? Where is the juxtaglomerular apparatus? What is its role?

Back

Preview of the front of card 3

Card 4

Front

What is the role of the tubular system?

Back

Preview of the front of card 4

Card 5

Front

What are the two capillary beds of the nephron? What pressure are they under & what is their function?

Back

Preview of the front of card 5
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