Ganong 24e chapter 37 - Renal (1) Flashcards
How much of the cardiac output goes to the kidneys?
20-25%, which equates to about 1200mL/min.
What is meant by the term “filtration fraction”?
This is the fraction of plasma reaching the kidneys that actually gets filtered at the glomerulus. It is the ratio of the GFR to the Renal Plasma Flow. The filtration fraction is usually about 0.20 or 20%.
What is a normal GFR?
About 125mL / min
What is a normal Renal Plasma Flow?
About 600mL / min
What is the difference between Renal Plasma Flow and Renal Blood Flow? What are their usual measurements?
Renal Plasma Flow = 0.55 x Renal Blood Flow (assuming that Haematocrit = 0.45)
RPF = approx 600mL/min. RBF = approx 1200mL/min
What happens to renal blood flow and GFR as the systemic BP changes?
Both renal blood flow and glomerular filtration remain constant between systolic BP of 70-210, thanks to autoregulation.
Where are the juxtaglomerular cells?
In the walls of the afferent arteriole.
Where is the macula densa?
These are specialized cells in the wall of the distal convoluted tubule, in close contact with the afferent and efferent arterioles of the glomerulus.
What are the two mechanisms of autoregulation of renal blood flow?
- Myogenic control (increased transmural pressure at the afferent arterioles causes the smooth muscle of the arterioles to constrict)
- Tubuloglomerular feedback (Na+ levels at the DCT are sensed by the macula densa cells, which release adenosine, causing vasoconstriction of the afferent arterioles.
How do you calculate the GFR using inulin?
GFR = Clearance of inulin.
Clearance of inulin = (concentration in urine) x (urine flow) / (concentration in plasma)
Complete this sentence: The descending limb of the Loop of Henle is permeable to _______ but impermeable to ________. The ascending limb is permeable to _______ but impermeable to ________ .
Complete this sentence: The descending limb of the Loop of Henle is permeable to _water_ but impermeable to _urea_. The ascending limb is permeable to _urea_ but impermeable to _water_ .
How does anti-diuretic hormone work?
It opens aquapores in the collecting ducts, so that water is reabsorbed.
How does aldosterone affect the kidneys?
It increases tubular reabsorption of sodium (by adding Na+ channels), and water follows by osmosis. Sodium ions are exchanged for H+ and K+ ions, so aldosterone also causes increased excretion of H+ and K+, potentially causing hypokalaemia and a metabolic alkalosis.
What is p-amino-hippuric acid useful for measuring?
It is called PAH, and used to measure renal plasma flow, because it has a high extraction ratio (ER). The ER is the proportion of renal arterial concentration of PAH that is removed by the kidneys, and therefore not reflected in renal venous concentration of PAH. The ER for PAH is 0.9.
This means that almost all of plasma PAH (90% of it) is removed by the kidneys in one pass through the nephron. PAH is filtered at the glomerulus and secreted by the tubules. The clearance of PAH is therefore approximately equal to the Renal Plasma Flow. (The actual RPF is obtained by dividing the clearance of PAH by 0.9)
Show the equation used to calculate renal clearance of a substance, for example PAH.
where UPAH = urinary concentration of PAH, PPAH = arterial plasma concentration of PAH, V = urine flow, ERPF = effective renal plasma flow (because the extraction ratio of PAH is as high as 0.9)
