Renal 4

Question 1

Tubular Reabsorption (3)

Answer 1

 High capacity & variable; 
very selective
 Many electrolytes and 
nutrients almost 
completely reabsorbed
 Most waste products 
poorly reabsorbed.

Question 2

Tubular Secretion (2)

Answer 2

 Variable
 Important for certain
electrolytes (K+, H+), drugs,
toxins.

Question 3

Once fluid is reabsorbed across the tubule epithelium

into the interstitial fluid, it enters

Answer 3

peritubular capillaries

via Bulk Flow

Question 4

Reabsorption =

Answer 4

Kf (Net Reabsorptive force)
= Kf (Reabsorptive Force)-(Filtration force)
=Kf ((πC + Pif) – (PC + πif))

Question 5

Normal rate of Peritubular Capillary Reabsorption =

Answer 5

124 ml/min (GFR?)

Question 6

Normal rate of Peritubular Capillary Reabsorption = 124 ml/min (GFR?)
Large: (2)

Answer 6

 Large Kf (high surface area and permeability)

 Large πC (due to volume lost during filtration)

Question 7

> —% of filtered sodium

reabsorbed

Answer 7

99

Question 8

> 99% of filtered sodium
reabsorbed
 All along —

Answer 8

nephron

Question 9

Sodium Reabsorption can

occur via both (2)

Answer 9

Transcellular

and Paracellular

Question 10

Transcellular pathways (2)

Answer 10

- Passive across apical and 
active across basolateral 
membranes
- Apical Na+ transport may 
be secondary active and 
tied to reabsorption of 
other substance (ex. 
Glucose)

Question 11

Transport maximum

Answer 11

Maximum rate some substances
can be transported across the
epithelium (absorption or
secretion)

Question 12

transport maximum is due to

Answer 12

saturation of transport

proteins

Question 13

Renal Threshold is the

Answer 13

plasma
concentration that saturates the
carrier (tubular load)

Question 14

Once the transport maximum is

reached for all nephrons,

Answer 14

further
increases in tubular load are not
reabsorbed and are excreted.

Question 15

examples of transport max (6)

Answer 15

glucose, amino acids,
phosphate, sulfate, urate,
(creatinine, PAH)

Question 16

As [Glucose] plasma increases, the [Glucose] filtrate —, Glucose tubular load —.

Answer 16

increases

increases

Question 17

Reabsorption of Water: Passive But Influences Many Solutes

 Strictly —

Answer 17

passive

Question 18

As Na+ reabsorbed, creates
gradient for — reabsorption via
osmosis

Answer 18

H2O

Question 19

Proximal tubule highly permeable

to —

Answer 19

H2O

Question 20

As H2O moves via osmosis: (2)

Answer 20

- Carries other solvents along = 
Solvent drag (size restricted)
- Creates gradients for the passive 
reabsorption of other solute (ex. 
Cl- and Urea)

Question 21

H2O Permeability varies as  move 
through nephron (2)

Answer 21

• Ex. Ascending limb of Loop of
  Henle (not permeable to H2O
• Collecting duct (regulated; ADH)

Question 22

PT Reabsorption of Na+, Cl-, Urea

and H2O exhibit

Answer 22

Gradient-Time

Transport

Question 23

The concentrations of solutes in different parts of the tubule depend on relative reabsorption of the solutes compared to water: (2)

Answer 23

 if water is reabsorbed to a greater extent than the solute, the solute will become more concentrated
in the tubule (e.g., creatinine, inulin)
 if solute is reabsorbed to a greater extent than
water, the solute will become less concentrated in the tubule (e.g., glucose, amino acids)

Question 24

Regional Tubular Transport (5)

Answer 24

1. Early Proximal Tubule (early PT or PCT) and
   Late Proximal Tubule (late PT or PST)
2. Loop of Henle
3. Early Distal Tubule (early DT)
4. Late Distal Tubule and Cortical Collecting
   Duct (Late DT and CCD)
5. Medullary Collecting Duct (MCD)

Question 25

Loop of Henle (3)

Answer 25

Thin descending limb Thin ascending limb Thick ascending limb

Question 26

Proximal Tubule | PT =

Answer 26

PCT + PST

Question 27

Cells have High capacity for Active | and Passive Reabsorption (4)

Answer 27

- Large # mitochondria - Large surface area on both apical and basolateral membranes - Large number of membrane proteins - High permeability for H2O.

Question 28

PT Reabsorbs (2)

Answer 28

– ~ 65% of filtered Na+, Cl-, HCO3-, and K+ – All filtered glucose and amino acids.

Question 29

PT Secretes (3)

Answer 29

- metabolic waste products such as H+ ions , organic acids, and bases such as: bile salts, oxalate, urate, and catecholamines - Harmful drugs or toxins - Para-Aminohippuric Acid (PAH)

Question 30

Early PT (3)

Answer 30

Paracellulary  Passive down ΔEC  Solvent drag

Question 31

Late PT (4)

Answer 31

 Transcellular  Apical 2° active Formate/Cl- antiporter  Basolateral facilitated diffusion  Paracellularly

Question 32

*SGLT2 inhibitors used in | treatment of

Answer 32

T2DM (ex. | Glifozins; Invokana).

Question 33

``` Δ in [Solute] as Filtrate Passes through Proximal Tubule Tx = [solute] in filtrate Px = [solute] in plasma (4) ```

Answer 33

``` Na+ and H2O - Isotonic Solution Reabsorbed Proximal portions reabsorb all Glucose, Amino Acids and 65% HCO3- Distal Portion reabsorbs more Cl- and urea Creatinine not actively reabsorbed ```

Question 34

1. Thin Descending Limb (tDL) (3)

Answer 34

```  High H2O permeability (Contain AQP-1 channels): major role in concentration/dilution of urine  No active solute transport  Urea secretion via facilitated diffusion ```

Question 35

2. Thin Ascending limb (tAL) (3)

Answer 35

 does not reabsorb significant amounts of any solutes  impermeable to water  Urea secretion via facilitated diffusion

Question 36

3. Thick Ascending Limb (TAL) (4)

Answer 36

 Impermeable to H2O and Urea  Major site of Na+, K+, Cl- reabsorption, H+ secretion  By end of Loop of Henle, more solute reabsorbed than H2O  Distal End of TAL forms part of JG apparatus

Question 37

Early Distal Tubule (6)

Answer 37

```  Parallels TAL in that it absorbs solute w/out H2O  Impermeable to H2O (and urea).  Reabsorbs ions  Na+-Cl- co-transporter in apical membrane moves Na+ and Cl- into cells from tubule lumen  Na+-K+-ATPase transports Na+ into interstitium.  Cl- diffuses into the interstitium through channels in basolateral membrane. ```

Question 38

 Reabsorbs ions (3)

Answer 38

- 5% of Na+ & Cl- – Further dilutes filtrate – Diluting Segment

Question 39

Late Distal/Cortical Collecting Duct (CCD) | Two Cell Types

Answer 39

1. Principal Cells | 2. Intercalated Cells

Question 40

1. Principal Cells (4)

Answer 40

``` 60-70% of cells Site of Aldosterone and ADH action –Reabsorb Na+ and H2O –Secrete K+ ```

Question 41

``` Late Distal/Cortical Collecting Duct (CCD) These segments are completely impermeable to --- ```

Answer 41

Urea

Question 42

``` 2. Intercalated Cells cell types (2) ```

Answer 42

Alpha Intercalated Cells | Beta Intercalated Cells

Question 43

Alpha Intercalated Cells (4)

Answer 43

``` Function important during acidosis Secrete H+ Reabsorb K+ and HCO3- 1° Active Transport of H+ across apical membrane can secrete H+ against a great ΔC (1000:1) ```

Question 44

Beta Intercalated Cells (3)

Answer 44

Function important during alkalosis Secrete K+ and HCO3- Reabsorb H+

Question 45

Medullary Collecting Duct (MCD) (4)

Answer 45

```  Processes < 10% of Na+ and H2O but very important (10% of 180 L).  Site of Aldosterone and ADH action  Urea reabsorbed via facilitated diffusion  Secretes H+ using same mechanism as α-intercalated cells. ```

Question 46

Regional Tubular Transport | Tx/Px) (5

Answer 46

``` 1. Proximal Convoluted Tubules (PCT) 2. Loop of Henle 3. Early Distal Convoluted Tubules (DCT) 4. Late Distal Tubule and Cortical Collecting Duct 5. Medullary Collecting Duct (CT) ```