Flashcards in Renal Excretory Function Deck (18):
What is the glomerulus?
Structure enclosed by Bowman's capsule filtering plasma
What is the significance of the afferent and efferent arterioles?
To the glomerulus
- afferent arteriole has large diameter
- efferent has a smaller diameter
- this generates a filtration pressure
- means fluid can be forced through the endothelium
What are podocytes?
cells that cover the capillaries of the glomerulus allowing filtration of selected material
How is does selective filtration occur in the glomerulus?
- fenestrated capillaries
What is proteinuria, how does it occur?
Proteins enter urine due to swollen podocytes
What factors determine filtrate?
Net filtration pressure
Podocyte slit pores
Size of molecule
Charge of molecule
How does charge and size of a molecule affect its filtration?
Negatively charged large proteins will not allowed through
Which molecules can easily be filtered in the glomerulus?
- free movement of small solutes/molecules (water, electrolytes, urea, amino acid)
- restriction of larger solutes (proteins)
What is GFR?
Total amount of fluid filtered through the glomerulus
- normally 120ml/min when CO is 1.2L/min
- parameter of kidney function
How is GFR measured?
- measure creatinine clearance
- this is the amount of substance cleared from the plasma ending up in the urine and can be compared to plasma concentration as it is completely filtered and none is reabsorbed
What is creatinine?
- breakdown product of creatine phosphate in muscle
- completely filtered and none reabsorbed but actively secreted = overestimation of 10-20%
How is creatinine clearance calculated?
- (urine conc x urine volume)/plasma concentration
What other methods of measuring GFR are there and why might you use them instead?
- creatinine clearance often takes place over a 24 hour period which can be difficult
- gold standard: nuclear medicine scan
- estimated GFR
How does creatinine change GFR?
- small changes in creatinine lead to large changes in GFR
Why may using creatinine to measure GFR be confusing?
- GFR fall decreases creatinine filtration so you get a proportional rise in creatinine
- misleading in muscular individuals (increased serum creatinine), malnourished individuals (low serum creatinine), drugs (inhibit tubular secretion of creatinine)
What is the renal threshold?
concentration of substance dissolved in blood above which the kidneys begin to remove it from the urine
- if exceeded reabsorption in the PCT is incomplete so the substance remains in the urine
What is the glucose threshold?
- greater than 10mmol/L
- appears in the urine as the amount of glucose exceeds reabsorption capacity of tubules and all glucose carriers are saturated