Reabsorption & secretion

Question 1

Renal threshold is defined as

Answer 1

plasma threshold at which saturation occurs

Question 2

Mechanisms that substances are reabsorbed from the nephron back into the blood

Answer 2

Carrier mediated transport proteins

Question 3

What is Tm

Answer 3

maximum transport capacity

-transport rate at saturation

Question 4

If maximum transport capacity (Tm) is exceeded, what happens to the excess substrate

Answer 4

excreted in urine

Question 5

Renal plasma threshold for glucose is

Answer 5

> 10mmol/l

-beyond this, glucose will appear in the urine

Question 6

Plasma glucose is reabsorbed up to what conc. (i.e. beyond, this glucose conc., it cannot be reabsorbed as renal plasma threshold for glucose is reached)

Answer 6

10mmol/l

Question 7

Appearance of glucose in the urine of diabetic patients is due to the failure of what; NOT THE KIDNEY

Answer 7

insulin

Question 8

What mechanism by the kidney regulates the levels of ions like sulphate and phosphate

Answer 8

Tm (maximun transport capacity) mechanism
-Tm is at a conc. where normal plasma conc. causes saturation of the carrier proteins so any increase above the normal level is excreted

Question 9

What % of sodium filtered is reabsorbed + what percentage of this is reabsorbed mostly in the PCT

Answer 9

99.5%

75%

Question 10

Unlike sulphate and phosphate ions which are reabsorbed by the kidney by a maximum transport capacity (Tm) mechanism, how is Na+ reabsorbed by the kidney

Answer 10

By Na/K pump expressed in the tubule membrane which actively transports Na+ back into the plasma

Question 11

High Na+ conc. in tubule lumen and low Na+ conc. in the proximal tubule cells means sodium moves across the luminal membrane into the proximal tubule cells by…

then Na+ in the proximal tubule cells are reabsorbed into the ECF by

Answer 11

passive transport

active transport - Na/K pump

Question 12

Na+ is not usually freely permeable at cell membranes (needs carrier proteins), so how can Na+ passively move from tubule lumen into proximal tubule cells

Answer 12

proximal tubule cells have a higher permeability to Na+ ions than most other membranes in the body because of the enormous surface area offered by the microvilli and the large number of Na+ ion channels, which facilitate the passive diffusion

Question 13

Active transport of Na+ out of the tubule followed by Cl- creates an … … drawing … out of the tubules as well

Answer 13

osmotic force

water

Question 14

H2O removed by osmosis from the tubule filtrate concentrates all the substances left in the tubule as fluid volume decreases which creates

Answer 14

outgoing conc. gradients of these remaining substances

Question 15

Reabsorption of Na+ by active transport into the ECF creates a … gradient which drives … reabsorption as well, e.g. …

Answer 15

electrochemical

anion

Cl-

Question 16

What are anions

Answer 16

negatively charged ions

Question 17

Does PTH increase or decrease reabsorption of phosphate

Answer 17

decrease

increases it excretion in urine

Question 18

Explain the significance of the active reabsorption of Na+ ions at the proximal tubule.

Answer 18

key to the reabsorption of the other components of the filtrate in the tubule as it establishes gradients for which other ions, water and solutes move down passively

Question 19

Name some substances that are coupled to Na+ transport, i.e. share the same carrier protein (symporter)

Answer 19

Glucose

Amino acids

Question 20

Apart from filtration and reabsorption, the final renal process is secretion - what exactly does this entail

Answer 20

Secretory mechanisms transport substances from the peritubular capillaries into the tubule lumen so providing a second route into the tubule, if didn’t get in through the glomerulus initially

Question 21

Secretion of what substances from the peritubular capillaries into the tubule lumen is significant

Answer 21

Proteins/protein bound substances because glomerulus restricts the filtration of proteins into the tubule

Question 22

K+ ions are primarily reabsorbed where in the nephron

Answer 22

proximal tubule

Question 23

What are cations

Answer 23

positive ions

Question 24

Major cation in the body

Answer 24

K+

Question 25

Normal plasma K+

Answer 25

4mmol/l

Question 26

Hyperkalaemia occurs when plasma K+ rises to
+
what effect does this have on resting membrane potential of excitable cells + consequence on these cells

Answer 26

5.5mmol/l

Decreases it so excessively depolarises cells which can cause ventricular fibrillation

Question 27

Hypokalaemia occurs when plasma K+ lowers to
+
what effect does this have on resting membrane potential of excitable cells + consequence on these cells

Answer 27

<3.5mmol/l

Increases it so hyperpolarises cells like cardiac muscle –> arrhythmia

Question 28

Increase dietary K+ has what effect on urine

Answer 28

Increased urinary loss to excrete K+

Question 29

Although most K+ filtered through the kidneys is reabsorbed in the proximal tubule, its regulation occurs mostly where in the renal system

Answer 29

Collecting duct

Question 30

What hormones increase K+ loss in urine

Answer 30

Aldosterone

ADH

Question 31

Increase in ECF K+ conc. stimulates what hormone to be released and circulated to the kidneys to stimulate K+ secretion in urine

Answer 31

Aldosterone

Question 32

Aldosterone promotes Na+ reabsorption where

Answer 32

Distal tubule