1: Physiology 4 & 5

Question 1

Where does the majority of reabsorption occur?

Answer 1

Proximal tubule

Question 2

What is a normal healthy GFR?

Answer 2

125 ml/min

Question 3

Why is reabsorption specific?

Answer 3

Specific transport proteins

Question 4

What is the osmolarity of the fluid at the start of the proximal tubules compared to that at the end?

Answer 4

The same

no change in osmolarity

Question 5

Which process mainly occurs in the proximal tubule?

Answer 5

Reabsorption

Question 6

Does secretion occur in the proximal tubule?

Answer 6

Some secretion

Question 7

By which two means can substances be reabsorbed into peritubular capillaries?

Answer 7

Transcellular (through cell membranes)

Paracellular (through tight junctions)

Question 8

What is primary active transport?

Answer 8

Energy used to transport a substance against its concentration gradient using a carrier

Question 9

What is secondary active transport?

Answer 9

Active transport of a substance by carriers COUPLED to the concentration gradient of another ion

Question 10

Secondary active transport usually occurs using the concentration gradient of which ion?

Answer 10

Sodium

Question 11

What is facilitated diffusion?

Answer 11

Passive transport WITH A CARRIER

Question 12

Where is 2/3rds of filtered sodium reabsorbed?

Answer 12

Proximal tubules

Question 13

Where are NaKATPases found on the tubular cells of the proximal tubules?

Answer 13

Basolateral

empties into capillaries

Question 14

What is the function of NaKATPases on the basolateral membrane of the tubular cells?

What does this achieve?

Answer 14

Active transport of 3 Na OUT and 2 K IN

Maintains concentration gradient of sodium

So it can diffuse in (be reabsorbed) at the apical membrane

Question 15

Where do sodium ions go once they have been secreted OUT of tubular cells by NaKATPase?

Answer 15

Peritubular capillaries

leaving conc gradient from filtrate to tubular cells

Question 16

The transport of sodium from the filtrate to the capillaries sets up which types of gradient?

Answer 16

CONCENTRATION GRADIENT FOR SODIUM (so more is reabsorbed from proximal tubules)

OSMOTIC GRADIENT FOR WATER (following sodium)

ELECTROCHEMICAL GRADIENT FOR CHLORINE (so it’s reabsorbed by the PARACELLULAR route)

Question 17

By which routes are sodium and chlorine reabsorbed?

Answer 17

Sodium - transcellular

Chlorine - paracellular

Question 18

Why doesn’t the osmolarity of the proximal tubules decrease as you go along?

Answer 18

Water and salt reabsorbed equally

Question 19

By which means does glucose leave proximal tubules?

Answer 19

Co-transport with sodium (SGLT2)

Question 20

How does glucose leave the tubular cells by the basolateral membrane?

Answer 20

FACILITATED DIFFUSION down its concentration gradient

GLUT2?

Question 21

How does water follow sodium and glucose into the peritubular capillaries?

Answer 21

Paracellular reabsorption

Question 22

Which two substances are reabsorbed via the paracellular route?

Answer 22

Water

Chloride ions

Question 23

What proportion of glucose is reabsorbed in the proximal tubules?

Answer 23

100% normally

Question 24

What is the equation for rate of filtration?

Answer 24

Rate of filtration = [substance]_plasma x GFR

Question 25

Does the **rate of reabsorption** of glucose increase in proportion with its **rate of filtration**?

Answer 25

**Yes, up to the point where all the carriers are saturated**

Question 26

Which transporter is saturated when the rate of filtration of glucose is too high?

Answer 26

**SGLT2** co-transporter

Question 27

Which rate starts to increase if you pass the maximum rate of reabsorption of glucose?

Answer 27

**Rate of excretion** glycosuria

Question 28

What is the **T_M** of glucose?

Answer 28

**Transport maximum of glucose** RATE OF FILTRATION AFTER WHICH YOU START TO EXCRETE GLUCOSE **2 mmol/min**

Question 29

What is the a) **rate of filtration** b) **plasma concentration** of glucose after which you start to get glycosuria?

Answer 29

**a) 2 mmol/min**, transport maximum **b)** Around **12** **mmol/L**

Question 30

After you reach the transport maximum for glucose, glucose is excreted by the kidneys, producing which sign?

Answer 30

**Glycosuria**

Question 31

What value is a) inulin/creatinine b) PAH used to determine?

Answer 31

**a) GFR** (because their clearance = GFR) **b) Renal blood flow** (because its clearance = RBF)

Question 32

**100%** of which substances are reabsorbed in the proximal tubules?

Answer 32

**Glucose** **Amino acids**

Question 33

What is the **osmolarity** of the proximal tubules all the way along it? Why?

Answer 33

**300 mosmol/L** Same volumes of water and NaCl reabsorbed, so osmolarity doesn't change

Question 34

What are the two parts of the Loop of Henle?

Answer 34

**Descending limb** **Ascending limb**

Question 35

What is the function of the **Loop of Henle**?

Answer 35

Generates **solute concentration gradient** between the renal cortex and medulla

Question 36

The Loop of Henle allows for the production of **(hypertonic / hypotonic)** urine which is **(dilute / concentrated)** in solute.

Answer 36

**hypertonic** **high solute concentration** (concentrated)

Question 37

What process occurs in the Loop of Henle to produce concentrated urine?

Answer 37

**Countercurrent multiplication**

Question 38

Which blood vessel, found in **juxtamedullary** nephrons, help concentrate the urine along with the Loop of Henle?

Answer 38

**Vasa recta**

Question 39

What is **reabsorbed** in the **descending limb** of the Loop of Henle?

Answer 39

**WATER** NOT NaCl

Question 40

What is **reabsorbed** in the **ascending limb** of the Loop of Henle?

Answer 40

**NaCl** NOT WATER

Question 41

The descending limb reabsorbs \_\_\_. The ascending limb reabsorbs \_\_\_.

Answer 41

**descending limb** = WATER **ascending limb** = NaCl

Question 42

What transporter is found at the basolateral membrane of every cell in the body?

Answer 42

**NaKATPase**

Question 43

Which transporter, found on the luminal membrane of the cells of the ascending limb, transports ions across the membrane?

Answer 43

**Na-K-2Cl co-transporter**

Question 44

Does water follow salt into the tubular cells in the ascending limb?

Answer 44

**No** **Can't, tight junctions won't let it through**

Question 45

What ions are absorbed into the interstitial fluid, then the capillaries at the ascending limb?

Answer 45

**Na** **Cl**

Question 46

Which drugs block the triple transporter in the ascending limb?

Answer 46

**Loop diuretics** e.g furosemide

Question 47

As a result of the action of the triple transporter and NaCl reabsorption in the ascending limb, what happens to the osmolarity of the ascending limb?

Answer 47

**Osmolarity decreases**

Question 48

**Interstitial fluid osmolarity (increases / decreases)** as a result of NaCl reabsorption by the ascending limb.

Answer 48

**increases**

Question 49

What happens when osmolarity of a compartment increases?

Answer 49

**Osmosis of water from another compartment**

Question 50

As a result of osmosis into the **interstitial space** from the DESCENDING LIMB, what happens to the descending limb's osmolarity?

Answer 50

**Increases** runs round into ascending limb, NaCl reabsorbed, ascending limb's osmolarity decreases, interstitium's osmolarity increases so water reabsorbed from descending limb, descending limb's osmolarity increases... accumulates and accumulates, concentrating tubular fluid many many times

Question 51

What process occurs in the Loop of Henle?

Answer 51

**Countercurrent multiplication** Distal tubule's fluid has a much higher osmolarity compared to proximal tubule Establishes **concentration gradient** between cortex and medulla

Question 52

What **three** substances contribute to the **concentration gradient** between the renal cortex and medulla?

Answer 52

**Water** **NaCl** by countercurrent multiplication in Loop of Henle **Urea recycling**

Question 53

Which part of the kidney has the higher osmolarity?

Answer 53

**Renal medulla** where countercurrent multiplication occurs

Question 54

Which hormone requires there to be a **concentration gradient** between the renal cortex and medulla?

Answer 54

**ADH**

Question 55

What is the purpose of ADH?

Answer 55

**Controls water concentration by changing permeability of collecting ducts to water** **Altering urine output and concentration** **Allowing kidneys to produce hypertonic, concentrated urine if dehydrated** or **hypotonic, dilute urine** **if overloaded**

Question 56

Keeping in mind the osmolarities of the renal **cortex** and **medulla**, what happens to the osmolarity of the vasa recta as it goes **down** into the medulla **back up** into the cortex?

Answer 56

**down** - osmolarity INCREASES (water diffuses out down conc gradient, solute diffuses in down conc gradient) **up** - the opposite, as osmolarity of interstitium DECREASES going back up to cortex

Question 57

How is the vasa recta adapted so it doesn't take up solute and urea and wash it out of the adrenal medulla?

Answer 57

**Hairpin loops** **Endothelium** is freely permeable to NaCl and H20 **Low volume blood flow**

Question 58

What two structures maintain the concentration gradient between the renal cortex and medulla?

Answer 58

**Loop of Henle** (via countercurrent multiplication and urea cycle) **Vasa recta**