Physiology - The proximal tubule and loop of Henle

Question 1

In normal physiological conditions what percentage of glucose is reabsorbed?
Same for urea
Same for creatinine

Answer 1

Glucose - 100%
Urea ~50%
Creatine - 0%

Question 2

What is the name for the original fluid found in Bowman’s capsule?

What is the difference between it and blood?

Answer 2

Glomerular filtrate

Lacks RBCs + large plasma proteins

Question 3

Where does the vast majority of reabsorption occur in the nephron?

Answer 3

Proximal convoluted tubule

Question 4

What are the two pathways that a substance can take for reabsorption?

Answer 4

transcellular - across tubular epi cells

paracellular - between tubular epi cells

Question 5

What is the difference between primary and secondary active transport?

Answer 5

Primary active transport - need a carrier to move the substance against concentration gradient

Secondary
- move with a carrier against concentration gradient but with another ion (normally Na+)

Question 6

Where is the only part of the nephron where Na+ is not reabsorped?

Answer 6

Descending loop of Henle

Question 7

How are glucose and AA reabosorbed?

Answer 7

Via secondary active transport into tubular capillary cell

(helps to drive Na+ reabsorption)

Then diffusion into interstitial fluid beside peritubular capillary/vasa recta

Question 8

In what situation would glucose be excreted?

Use scientific language

Answer 8

When rate of filtered glucose surpasses the transport maximum

(filtered glucose = plasma conc. x GFR - as plasma conc. increases rate of filtration increases)

This occurs in uncontrolled DM

Question 9

Draw a graph of filtration, reabsorption and excretion of glucose to plasma glucose conc.

Answer 9

Compare to graph in Onenote

Question 10

Only absorbed substances have a Tm (transport maximum). T/F?

Answer 10

F - same occurs for secreted substances

e.g. some substances can max

Question 11

What drives Na+ reabsorption?

Answer 11

Basolateral Na+K+ ATPase channels

this bit is important

Question 12

What part of the nephron is responsible for generating a cortico-medullary solute concentration gradient?

Why is this important?

Answer 12

Loop of Henle

Enables formation of HYPERTONIC urine

(hypertonic = low H2O = concentrated)

Question 13

Compare ascending and descending limb of loop of Henle in terms of:

• salt reabsorption
• water reabsorption

Answer 13

Descending limb

• no salt reabsorption
• water reabsorption

Ascending limb

• salt reabsorption
• no water reabsorption

Question 14

Why in the ascending limb of Henle when NaCl- is being reabsorbed does H2O not follow?

Answer 14

Tight junctions between tubular epi cells -> no paracellular diffusion of H2O can take place

Question 15

What is the difference in osmolality between the beginning and end of the proximal convoluted tubule?

Explain

Answer 15

There isn’t any

Although a lot of solutes are being absorbed e.g. glucose and AA - water is also following so osmolarity remains the same

Question 16

What part of the loop of Henle do loop diuretics act on?

Why can they cause a side effect on hypokalaemia?

Answer 16

Ascending loop of Henle

• prevent NaCl from being reabsorbed by blocking triple transporter
• lower NaCl in blood -> reduce BP

NaCl reabsorption requires the recycling of K+ ions (they are no longer reabsorbed in the same way)

Question 17

Where in the loop of Henle is the tubular fluid most concentrated/hypertonic/highest osmolality?

Where in the kidney does the intersitital fluid have the highest osmolarity/most concentrated/hyerptonic?

Answer 17

End of descending loop of Henle

Deepest in the medulla

Question 18

Explain why osmolality changes in the loop of Henle?

Answer 18

Increases as go down descending loop of Henle as losing water but not salt

Decreases as go up ascending limb of Henle as losing salts but not water

Question 19

How does the vasa recta work to maintain the medullary gradient within the loop of Henle?

Answer 19

Vasa recta has v leaky vessels

Hairpin pattern

Blood in vasa recta follows same osmolality pattern and means that no osmolality is washed away