10 - Tubular Reabsorption and Secretion PPT (QUIZ 3)

Question 1

How is urine formed?

Answer 1

Via glomerular filtration and tubular reabsorption/secretion

Question 2

How many times is our entire plasma volume filtered a day?

Answer 2

60 times!

Question 3

Define reabsorption.

Answer 3

The retention of substances contained in filtrate back into peritubular capillary blood.

Question 4

What is Filtration Only?

Answer 4

• NO reabsorption
• Metabolism products like urea and creatinine get filtered out
• Foreign substances like drugs (crack) get filtered out

Question 5

What is Filtration with Partial Reabsorption?

Answer 5

• Electrolytes like sodium and bicarbonate get reabsorbed easily
• Some partial reabsorption and some secretion (I love that the ppt says “maybe”)

Question 6

What is Filtration with Complete Reabsorption?

Answer 6

• Nutritional substances like glucose and AAs get completely reabsorbed

Question 7

What is Secretion?

Answer 7

• NO reabsorption
• Stuff like organic acids gets secreted into tubular acid to become urine

Question 8

What is the filtration rate of glucose through the kidneys dependent on?

Answer 8

Plasma glucose concentration

Question 9

Where does glucose reabsorption mainly occur?

Answer 9

Proximal convoluted tubule (PCT)

Question 10

What are the two steps of glucose reabsorption?

Answer 10

1. Glucose moves across the apical membrane into the brush border cells
2. Glucose diffuses across the basolateral membrane into the peritubular capillaries

Question 11

How is glucose moved across the apical membrane?

Answer 11

Sodium/glucose transporters use energy from the existing sodium conc. gradient to move glucose against its conc. gradient

Question 12

What type of diffusion does glucose utilize to enter the peritubular capillaries?

Answer 12

FACILITATED diffusion with GLUT1 and GLUT2

Question 13

What happens during normal plasma glucose levels (less than 200mg/dl)?

Answer 13

Glucose reabsorption matches with filtration

Question 14

What happens during high plasma glucose levels (more than 200mg/dl)?

Answer 14

The limited number of glucose transporter proteins prevents reabsorption from keeping up filtration

Question 15

What happens during higher (highest) plasma glucose levels (more than 350mg/dl)?

Answer 15

Glucose transport proteins are fully saturated and reabsorption cannot go any faster, thus reaching the TRANSPORT MAXIMUM!

Question 16

Where is excess glucose excreted?

Answer 16

Da urine

Question 17

What is the threshold concerning the glucose titration curve?

Answer 17

Threshold: the plasma glucose level at which glucose excretion starts

Question 18

What is splay concerning the glucose titration curve?

Answer 18

Splay is the initial, nonlinear increase in urine excretion

Question 19

What’s glycosuria?

Answer 19

Glucose excreted in urine due to:
- Diabetes (decreased insulin, increased plasma glucose)
- Pregnancy (hormonal changes resulting in increased renal blood flow and filtration

Question 20

What’s PAH?

Answer 20

Para-aminohippuric acid

Question 21

PAH is an organic acid (destined for urine). How much of PAH gets cleared from the plasma?

Answer 21

90%

Question 22

(TRUE/FALSE): PAH can be used for diagnostics due to its high clearance rate.

Answer 22

(TRUE)

Question 23

(TRUE/FALSE): There’s always renal absorption of PAH.

Answer 23

(FALSE): There is NO renal absorption of PAH

Question 24

Where does PAH secretion occur?

Answer 24

PCT

Question 25

How does PAH secretion relate with PAH concentration during low plasma PAH?

Answer 25

It’s linear, so if PAH concentration increases so will its secretion.

Question 26

During higher plasma PAH, what prevents all the PAH from being secreted despite its increasing concentration?

Answer 26

Carrier proteins prevent the increase of secretion, so some PAH will be left behind.

Question 27

Whether filtered or secreted, the body is unbiased against PAH- where is it excreted?

Answer 27

URINE!

Question 28

What can PAH be used as a diagnostic for?

Answer 28

Calculating renal plasma flow ([PAH entering]=[PAH leaving])

Question 29

If you know the renal plasma flow, what can you calculate for?

Answer 29

Renal blood flow (thanks PAH!)

Question 30

What is urea?

Answer 30

A waste byproduct of AAs

Question 31

Is urea freely filtered or partially filtered across the glomerular capillaries?

Answer 31

Freely filtered

Question 32

What does urea recycling help establish?

Answer 32

The corticopapillary gradient, which reabsorbs water from the kidney back into blood

Question 33

Here we go again… what’re the four steps to urea recycling?

Answer 33

1. 50% of urea is reabsorbed by simple diff. in PCT, the rest gets left with water
2. Urea from the medullary interstitium gets secreted back into the DCT tubule for a whopping 110% of initial urea present at the bottom of the loop of Henle (because of the higher urea concentration in the medullary intersitium)
3. The thick ascending limb of the loop of Henle and early DCT are impermeable to urea/water so urea lvls stay the same
4. 70% of initial urea gets reabsorbed into the late DCT interstitium and collecting duct, 40% gets excreted (ADH induces water reabsorption through aquaporin channels)

Question 34

Sorry for that whopper of a flashcard about urea recycling. Not much left!

Urea contributes to how much of the renal medulla’s osmolarity?

Answer 34

40-50%

Question 35

ADH being present makes a more ___________ urine because of more ____________________.

Answer 35

1. concentrated
2. water reabsorption

Question 36

ADH causes the body to reabsorb more of what in the collecting duct?

Answer 36

UREA

Question 37

More urea reabsorbed in the collecting duct increases the…

Answer 37

… osmolarity of the medulla.

Question 38

What does higher medullary osmolarity cause the nephron to do?

Answer 38

Reabsorb more water