The proximal tubule and the loop of Henle Flashcards Preview

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Flashcards in The proximal tubule and the loop of Henle Deck (38)
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1

where does most reabsorption occur?

Proximal tubule

2

how often is plasma filtered?

65 times per day

3

what do the kidneys reabsorb?

99% of fluid
99% of salt
100% of glucose
100% of amino acids
50% of urea
0% creatinine

4

Is reabsorption specific or non specific?

specific - unlike filtration which is non-specific

5

what is glomerular filtrate?

modified filtrate of blood- contains ions and solutes at plasma concentration but lacks RBCs and large plasma proteins

6

how does the osmolarity change between the fluid reabsorbed in the proximal tubule and the filtrate?

iso-osmotic - no change in osmolarity

7

what is reabsorbed in the proximal tubule?

Sugars
Amino acids
Phosphate
Sulphate
Lactate

8

what is secreted in the proximal tubule?

H+
Hippurates
Neurotransmitters
Bile pigments
Uric acid
Drugs
Toxins

9

what are the two membranes of the wall of the nephron?

apical membrane - faces tubular fluid and lumen
Basolateral membrane - faces interstitial fluid

10

what is paracellular reabsorption?

some substances are reabsorbed between adjacent epithelial cells through "leaky" tight junctions

11

what is essential for Na+ reabsorption?

An energy-dependent Na+-K+ ATPase transport mechanism at the basolateral membrane

12

what is iso osmotic fluid reabsorption across "leaky" proximal tubule epithelium due to?

(1) Standing Osmotic Gradient
(2) Oncotic Pressure Gradient

13

what causes oncotic drag of peritubular plasma?

After losing 20% plasma , the plasma protein concentration is higher in peritubular capillaries and so helps drag fluid from lateral space into the blood

14

what causes paracellular reabsorption of negative chloride ions?

the net movement of positive charge from the movement of Na+ from tubular fluid into blood through the transcellular route sets up an electrical gradient and so negative ions move

15

why does the osmolarity not change?

water follows reabsorbed salt and so salt and water are absorbed in equal proportions

16

how much glucose is reabsorbed in the proximal tubule?

100%

17

what happens to rate of filtration if you increase plasma concentration?

rate of filtration increases

18

why does reabsorption plateau?

Membrane transporter proteins are fully saturated with glucose

19

what is the function of the loop of henle?

-Generates a cortico-medullary solute concentration gradient
-This enables the formation of hypertonic urine

20

what is countercurrent flow?

opposing flow in two limbs

21

what do the loop and vasa recta establish together?

hyper-osmotic medullary interstitial fluid

22

what does the ascending limb reabsorb and what is its permeability to water?

-Along the entire length of the ascending limb Na+ & Cl- are being reabsorbed
-relatively impermeable to water

23

what does the descending limb reabsorb and what is its permeability to water?

-does not reabsorb NaCl -highly permeable to water

24

what does the selective permeabilities of the ascending and descending limbs enable?

an osmotic gradient to be established in the medulla

25

what is the triple co-transporter?

transporter that allows the movement of Na+, K+ and Cl- from the filtrate to the interstitial fluid

26

how is K+ recycled and what does this mean?

-Potassium is moved across both basolateral and luminal membranes so there is not net movement of potassium
-recycling means that NaCl is absorbed into the interstitial fluid

27

what blocks the triple co-transporter?

loop diuretics

28

why does water not cross the membrane?

the tight junctions are to small to fit water though and so water cannot follow the salt

29

what happens when the triple co-transporter pumps solute from the ascending limb?

1. Solute removed from lumen of ascending limb (water cannot follow)

2. Tubular fluid is diluted and osmolality of interstitial fluid is raised

3. Interstitial solute cannot enter the descending limb

4. Water leaves the descending limb by osmosis

5. Fluid in the descending limb is concentrated

30

what is the difference ins osmotic state from leaving proximal tube and entering distal tubule?

-its iso osmotic leaving the proximal tubule
-its hypo osmotic entering the distal tubule