Lecture 35 4/9/24 Flashcards
Which types of control mechanisms are in place around tubular reabsorption?
-nervous
-hormonal
-local
What is an important feature of tubular reabsorption?
reabsorption of some solutes can be regulated independently of others, esp. through hormonal control systems
What is glomerulotubular balance?
intrinsic ability of the tubules to increase their reabsorption rate in response to increased tubular load
Why does the percentage of GFR reabsorbed in the proximal tubule remain constant when filtered load increases?
because rate of reabsorption also increases
Besides the proximal tubule, which other segment of the nephron also sees a degree of glomerulotubular balance?
Loop of Henle
What is the overall goal of glomerulotubular balance?
prevent overloading of the distal tubular segments when GFR increases
Why is it important that glomerulotubular balance and tubuloglomerular feedback work together?
they both work to prevent changes in GFR from dramatically changing urine output
What percent of water and solutes is normally reabsorbed?
99%
What is the normal rate of peritubular capillary reabsorption?
124 ml/min
Which two determinants of peritubular capillary reabsorption are directly influenced by renal hemodynamic changes?
-hydrostatic pressure of the peritubular capillaries
-colloid osmotic pressure of the peritubular capillaries
How is peritubular capillary hydrostatic pressure influenced by arterial pressure?
increases in arterial pressure tend to raise peritubular capillary hydrostatic pressure and decrease reabsorption rate
How is peritubular capillary hydrostatic pressure influenced by afferent and efferent arteriole resistance?
increased resistance of the afferent or efferent arterioles reduces peritubular capillary hydrostatic pressure and increases reabsorption rate
Which factors influence the peritubular capillary oncotic pressure?
-systemic plasma colloid osmotic pressure
-filtration fraction
What are the characteristics of filtration fraction?
-the higher the filtration fraction, the greater the fraction of plasma filtered through glomerulus
-protein in the plasma left behind is more concentrated
What is filtration fraction?
GFR/RPF
How does angiotensin II raise filtration fraction?
by decreasing RPF
How do changes in the peritubular capillary physical forces influence tubular reabsorption?
by changing the physical forces in the renal interstitium
What is the net movement of water and solutes with the normal, high rate of peritubular capillary reabsorption?
net movement into the peritubular capillaries, with little back leak into the tubule lumen
What happens when peritubular capillary reabsorption is reduced?
-increased interstitial fluid hydrostatic pressure
-tendency for greater amounts of solute and water to leak back into tubular lumen
-reduced rate of net reabsorption
What is pressure natriuresis?
increased sodium excretion with increased arterial pressure