Renal excretory function of kidney Flashcards
How many litres go through the kidney
180
How many litres are lost as urine
2
Describe the structure of the glomerulus from venous inward
Venous
Porous endothelium
Glomerular basement membrane
Podocytes (epithelial surface)
What gets through podocytes
Glucose
Water
Solutes
Low molecular weight proteins
Where does filtration begin
Ultrafiltration of plasma within Bowmans Capsule
Name the factors that determine filtrate
- Net filtration pressure
- Podocyte slit pores
- Size of molecule
- Charge of molecule
- Negative charge of GBM glycoproteins
What can get through the glomerulus
Water
Electrolytes
Urea
Amino
What is the cutoff of what can get through glomerulus
5200 daltons
What is the molecular weight of albumin? Can it get through?
69,000 daltons
No
What does albuminuria indicate
Problem at point of glomerulus because albumin shouldn’t be able to filter through
Define glomerular filtration rate
Total amount of fluid that is filtered through the glomeruls
What should normal GFR be
120ml/ min
What substance is used to measure GFR
Creatinine
Why is creatinine used to measure GFR
- Freely filtered by glomerulus and is not reabsorbed
Why is measuring creatinine for GFR not accurate
It overestimates true renal function from 10-20% because it is actively secreted from peritubular capillaries
Equation for creatinine clearance
(urine concentration * urine volume)/ plasma concentration
Method for measuring clearance of a substance
- Measure concentration of creatinine in the plasma
- Collect urine for fixed period to get urine flow
- Measure concentration of creatinine in the collected urine
What is the gold standard for measuring GFR
Nuclear medicine scan
What is commonly used to measure GFR
Estimated GFR
mdrd equation
What is required for MDRD equation
Sex
Age
Creatinine
Race
What shape is the curve on the graph showing relationship between GFR and creatinine
Bell shaped
What does the graph on the relationship between GFR and creatinine tell us
- Small changes in creatinine have large affect on GFR
- Large changes in creatinine have small effect on GFR
Why do muscular individuals have high serum creatinine
Because creatinine is produced by the muscle
Does eGFR over or underestimate true GFR in
a) muscular people
b) malnourished people
a) underestimate
b) overestimate
What is the use of the drug trimethoprin? What is the effect on plasma creatinine?
UTI treatment
Inhibits creatinine secretion from the peritubular capillary cells
Does the drug trimethoprin change GFR
No
What is the function of tight junction between tubular cells
Limits water and solute movement between cells
Maintains polarity between apical and baso-lateral
Where does primary active transport occur
Between tubular cell and interstitium
What is primary active transport pump
Na+/K+ pump
What is the sodium and potassium levels in tubular cell
10-20mmol/l sodium
140mmol/l potassium
What is the sodium and potassium levels in the interstitium?
Na= 140mmol/L Potassium= 4mmol/L
Where does secondary active transport occur?
On the basolateral end of tubular cell
What is pumped from tubular lumen to tubular cell in secondary active transport
Sodium
Phosphate
Glucose
Amino Acids
Describe the anatomy of the proximal tubule
Apical brush border contains microvilli
It is convuluted for the first two thirds and straight for the final third
What is the function of the proximal tubule
Bulk of reabsorption of solutes
What % of the following are reabsorbed at proximal tubule
a) solutes
b) water
c) amino acids
a) 80
b) 65
c) 100
How does sodium leave the loop of henle
Active transport
What leaves through the ascending loop
Water
How does osmolality change down the loop of henle
It increases
Is the ascending limb permeable to water
No
What does the distal nephron consist of
Distal tubule
Collecting tubule
Collecting duct
What is the function of the distal nephron
Potassium excretion
Regulation of sodium delivery
Urine acidification
How much sodium is left in filtrate when it reaches distal tubular cell
8%
What inhibits the sodium potassium cell at distal tubular cells
Thiazide diuretics
What determines the osmalality of urine in collecting tubule
ADH
What happens in the presence of ADH
- Aquaporins become permeable to water
- Passage of water from collecting tubule to interstitium down conc gradient
- Production of concentrated urine
What happens if there is a deficit of ADH secretion
Copious dilute urine
Diabetes insipidus
Define renal threshold
Concentration of substance dissolved in blood above which kidney begin to remove it into the urine
What happens when the renal threshold is exceeded
Reabsorption of substance by proximal renal tubule is incomplete and some of substance remains in the urine
What happens at plasma levels of about 10 mmol/L
Glucose appears in the urine because amount of glucose exceeds reabsorption capacity of tubules (all glucose carriers are saturated)
Define transport maximum for glucose/ Tmg
Constant maximal value of rate of glucose reabsorption
Define osmotic diuresis
If excess solute present in tubular fluid this will atrract water and increases urine volume
What does osmotic diuresis lead to
Polyuria
Why do diabetic people often complain of increased thirst
Polyuria leads to increase in plasma osmolality leading to thirst sensation
