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Flashcards in LOOP OF HENLE Deck (28)
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1

what is the role of the loop of henle?

concentrates urine by creating a region of hypertonicity to extract the water osmotically
- more Na+ reabsorption
- urinary dilution
- generation of medullary hyperosmoticity via counter-current multiplication

2

what is the permeability of the descending limb of the loop of henle like?

water permeable
impermeable to solutes

3

what is the permeability of the ascending limb of the loop of henle like?

water impermeable
permeable to solutes

4

what is counter-current multiplication in the loop of henle?

• Urinary concentration and generation of hyperosmotic
interstitium to aid collecting duct in water reabsorption (when ADH is present)
• Fluid enters the loop from proximal CT flows down descending limb then up the ascending limb, these opposing flows are counter-currents

5

what is the role of the thick ascending limb of the loop of henle in counter-current multiplication?

• Driving force is Na/K ATPase in basolateral membranes of cells in
ascending limb which keep intracellular Na+ concentrations low
to allow more reuptake
• The NKCC2 uses the gradient (secondary active transport) and
pumps Na+ out of the lumen in the thick ascending tubule
• K+ is recycled on apical membrane back into lumen through
ROMK channels
• Cl– leaves cells through CLCK A channels (CLCK B in inner
medulla) on basolateral membrane
• Process creates a negatively charge tubule lumen which repels
Ca2+, Mg2+ and Na+ and they move paracellularly with the aid
of proteins in the tight junctions (paracelin or claudin XVI)
• Creates hyperosmotic interstitium, creates a gradient of 200
mOsm/L between lumen and interstitium

6

what is the driving force of counter-current multiplication in the thick ascending limb of the loop of henle?

Na+/K ATPase in the basolateral membranes of cells in the ascending limb
they keep intracellular Na+ concentrations low to allow more reuptake

7

how is Na+ reabsorbed in the ascending limb of the loop of henle?

The NKCC2 uses the gradient (secondary active transport) and pumps Na+ out of the lumen in the thick ascending tubule along with K+
• K+ is recycled on apical membrane back into lumen through ROMK channels

8

how is Cl- ions reabsorbed in the ascending limb of the loop of henle?

• Cl– leaves cells through CLCK A channels (CLCK B in inner
medulla) on basolateral membrane

9

what happens to Ca2+, Mg2+ and Na+ in the ascending limb of the loop of henle in counter current multiplication?

• Process creates a negatively charge tubule lumen which repels
Ca2+, Mg2+ and Na+ and they move paracellularly with the aid
of proteins in the tight junctions (paracelin or claudin XVI)

10

what is the role of the descending limb of the loop of henle in counter current multiplication?

• Only permeable to water which flows out due to osmotic
pressure, concentration of interstitium matches concentration in
descending limb
• As fluid moves down loop it gets more concentrated; the longer
the loop the greater the gradient which is created
• Tubule flow means that the concentration gradient starts from a
higher baseline than before it

11

what is the role of the thin ascending limb of the loop of henle in counter-current multipication?

Salt pumped passively

12

what is the role of urea in counter-current multiplication in the loop of henle?

urea is osmotically active and cant move in or out of loop of henle otherwise the counter-current system would collapse
it aids the urine concentration in the loop of henle

13

what is the blood supply to the loop of henle?

vasa recta supply O2 and nutrients to deep structures

14

what happens to blood as it descends into the medulla?

as blood descends Na+ and Cl- flow into blood and water out
as the blood ascends again water flows in again

15

what happens to the volume of blood in the vasa recta in the kidney?

the volume doubles when it leaves the vasa recta
this is due to extra salt and water being reabsorbed from both loop of henle and collecting duct

16

how is Na+ concentration regulated by the kidney?

- low total body Na+ leads to low plasma volume
- plasma volume is detected by baroreceptors
- there is a decrease in BP which initiates reflexes to decrease GFR and increase Na+ reabsorption

17

what is the short term regulation of Na+ in the kidney?

changes in GFR

18

what is the long term regulation of Na+ in the kidney?

RAAS

19

where does Na+ reabsorption take place in the kidney?

proximal tubule = 60%
loop of henle = 25%
distal tubule = 10%
collecting duct = 4%

20

what is the direct effect of increased GFR?

from arterial blood pressure
a reduced BP results in reduced filtration pressure
blood osmolality and oncotic pressure play a role

21

what is the indirect effect of increased GFR?

from sympathetic nerves
reflex of arterials - in response to increased stretch, the vessels respond by constricting
it mainly effects the afferent arterioles reducing blood entry into the glomerulus

22

how is GFR increased?

neuroendocrine inputs (aldosterone) result in reabsorption of Na+ to increase plasma volume (negative feedback loop)

23

where is the majority of K+ reabsorbed in the kidney?

90% in the proximal tubule

24

what are the factors that affect K+ secretion in the kidney?

- high K+ diet
- aldosterone

25

what is the effect of a high K+ diet on K+ secretion in the kidney?

increases plasma K+ concentration
there is enhanced uptake of K+ via the Na/K ATPase

26

what is the effect of aldosterone on K+ secretion in the kidney?

increased intake of K+ leads to increased extracellular K+ conc - directly stimulates aldosterone production
increased aldosterone increases K+ secretion and eliminates excess K+ from body

27

what is the juxtaglomerular apparatus?

located in afferent arteriole and DCT
macula densa cells in DCT - detect changes in Na+
granular cells in afferent arteriole - secrete renin

28

what is the action of the juxtaglomerular apparatus in response to low Na+ concentration?

If filtration is slow then more Na+ will be absorbed and the macula densa cells send a signal to reduce the afferent arteriole resistance and increase glomerular filtration
• Macula densa cells release prostaglandins in response to a reduction in Na+. This stimulates granular cells to secrete renin