Renal Flashcards
What percentage of the bodies blood supply does the kidney receive?
20-25%
What two factors affect the permeability of a molecule in the kidneys?
Size and charge
What is average (textbook) GFR?
125ml/min
How does each nephron regulate it’s own GFR?
Constricting/dilating afferent and efferent capillaries
How would a nephron reduce it’s own GFR?
Constricting afferent and dilating efferent
Where does reabsorption mostly occur in the nephron?
The PCT (proximal convoluted tubule)
In the PCT what two ways are substances reabsorbed across cells?
Paracellular - in-between cells
Transcellular - Through cells
What substances are reabsorbed in the PCT? (4)
Electrolytes such as Na+, Cl- and K+
Glucose, amino acids
Proteins, urea
Some water
What are the two types of nephron, their differences?
Which is more common?
Cortical - Glomeruli in outer cortex of kidney, and loop of henle descends into outer medulla (most common)
Juxtamedullary Nephrons have their glomeruli near the cortex-medulla boundary and their loops of henle descend into the deep medulla.
Why is the reabsorption of water in the loop of henle not coupled the the reabsorption of solutes?
The descending limb is only permeable to water (due to presence of aquaporins)
Briefly, in steps, how does the loop of henle function?
- Na+ and Cl- efflux from the thick ascending limb (pumped out) makes the interstitium hyperosmolar
- Because the descending limb is permeable to water, it is drawn out of the loop into the interstitium.
- As the fluid in the loop reaches the thin ascending limb Na+ and Cl- diffuse out (as the interstitium is less concentrated)
- In the thick ascending limb Na+ and Cl- are actively pumped out.
Where does aldosterone act and what does it do?
In the DCT, it regulates Na+ and K+ balance and the acid/base balance.
How does ADH regulate water balance in the DCT?
Increased amounts of ADH inserts aquaporins in the DCT meaning water diffuses out of the lumen.
Why are Creatinine and Urea used as markers for kidney clearance?
Constantly produced and filtered at constant rates so the only reason for their clearance to change would be due to a change in the kidney.
Why is there a 10% discrepancy in the textbook GFR and actual GFR of creatinine?
The excretion exceeds the filtration due to a small amount of secretion in the proximal tubule.
What three things does the Creatinine formation in the body depend on?
Muscle mass, Age and Gender
What two factors affect the plasma urea levels?
Protein turnover (more protein intake = more urea)
Hydration status
Why is the Urea:creatinine ratio useful?
As both are constantly produced and filtered if the GFR naturally falls then both would be expected to fall in parallel.
Is urine output more likely to be reduced in chronic or acute kidney Injury?
In acute, in chronic there may be compensation.
What can changes in urinary pH indicate?
High pH may indicate certain urinary tract infections
Low pH may indicate metabolic acidosis
What might increased Na+ in the urine indicate?
Tubular kidney problems, due to an inability to reabsorb Na+ (as it is freely filtered)
What is specific gravity?
The weight of a solution compared to pure water (similar to osmolality but not as accurate)
What does a high specific gravity and normal osmolality indicate?
The presence of large molecules, e.g. protein and glucose
If glucose appears in the urine what does that indicate? Why does glucose appear in the urine?
Indicative of uncontrolled diabetes
Blood glucose levels are high and the glucose transporters in the PCT are saturated.
Apart from glucosuria what else in a dipstick test can be indicative of diabetes?
Ketoacidosis
Three types of proteinuria?
Glomerular proteinuria (Increased glomerular permeability)
Tubular proteinuria (Impaired reabsorption)
Overflow proteinuria (Overproduction of small proteins)
