PHYSIOLOGY - Renal Function (Reabsorption and Secretion)

Question 1

Where does reabsorption and secretion occur in the nephron?

Answer 1

Renal reabsorption occurs within the renal tubular system

Question 2

What is tubular reabsorption?

Answer 2

Tubular reabsorption is the movement of filtered substances within the filtrate into the peritubular capillaries

Question 3

What are the two methods of tubular reabsorption?

Answer 3

Transcellular (active or passive)
Paracellular

Question 4

What are the two structures that allow for paracellular reabsorption?

Answer 4

Zonary occludens and claudens present at the paracellular junctions

Question 5

What is the basolateral membrane?

Answer 5

The basolateral membrane is the tubular membrane closest to the peritubular capillaries

Question 6

What is the apical membrane?

Answer 6

The apical membrane is the tubular membrane closest to the filtrate

Question 7

Isosmotic reabsorption occurs at the level of the proximal convoluted tubule (PCT). What does this mean?

Answer 7

Isosmotic reabsorption in the proximal convoluted tubule is the interdependence of solute and water reabsorption into the peritubular capillaries (i.e. as solutes are reabsorbed, water is also reabsorbed)

Question 8

What are the ten solutes reabsorbed at the level of the proximal convoluted tubule (PCT)?

Answer 8

Na+, K+, Ca2+, Cl-, PO4-, HCO3-, sulphates, glucose, citrates, amino acids

Question 9

Which solutes are reabsorbed by paracellular transmission at the level of the proximal convoluted tubule (PCT)?

Answer 9

Ca2+, Cl-, K+

Question 10

(T/F) Within the renal tubular system, sodium potassium ATPase pumps are only located on the basolateral membrane

Answer 10

TRUE

Question 11

What is the role of the sodium potassium ATPase pump in tubular reabsorption?

Answer 11

The sodium potassium ATPase pump establishes a concentration gradient with a high concentration of extracellular sodium and a high concentration of intracellular potassium

Question 12

What are the three Na+ transport systems present on the apical membrane of the proximal convoluted tubule?

Answer 12

• Na+ specific channels
• Na+/H+ counter transport systems
• Na+/solute (PO4-, sulphates, glucose, citrates) co-transport systems

Question 13

How is PO4-, sulphates, glucose and citrates reabsorbed at the level of the proximal convoluted tubule (PCT)?

Answer 13

PO4-, sulphates, glucose and citrates are reabsorbed with Na+ via a co-transport system on the apical membrane

Question 14

How are low molecular weight proteins reabsorbed into the peritubular capillaries at the level of the proximal convoluted tubule (PCT)?

Answer 14

Low molecular weight proteins undergo endocytosis from the filtrate into the proximal convoluted tubule (PCT) where they are broken down into amino acids and reabsorbed into the peritubular capillaries

Question 15

The apical membrane of the proximal convoluted tubule (PCT) is impermeable to bicarbonate (HCO3-). How is HCO3- reabsorbed into the peritubular capillaries at the level of the proximal convoluted tubule?

Answer 15

Carbonic anhydrase tethered to the apical membrane of the proximal convoluted tubule (PCT) which catalyses the reaction between HCO3- and H+ to form H2CO3 which readily dissociates into H2O and CO2 which can diffuse into the proximal convoluted tubule (PCT). Free floating carbonic anhydrase within the proximal convoluted tubule catalyses the reaction between H2O and CO2 back into HCO3- and H+. H+ returns to the filtrate via an Na+/H+ counter transport system on the apical membrane and HCO3- enters the peritubular capillaries via an Na+/HCO3- co-transport system on the basolateral membrane

Question 16

Why are excess solutes that cannot be reabsorbed at the level of the proximal convoluted tubule (PCT) excreted in the urine?

Answer 16

The proximal convoluted tubule is a saturable system due to having lots of carrier proteins which will become saturated leading to the excretion of excess solutes in the urine

Question 17

What is absorbed at the level of the thin descending loop of Henle?

Answer 17

Water

Question 18

Hyposmotic reabsorption occurs at the level of the this descending loop of Henle. What does this mean?

Answer 18

The thin descending loop of Henle has a lower osmolarity than the filtrate so water is reabsorbed into the loop of Henle and into the peritubular capillaries

Question 19

What are the five solutes reabsorbed at the level of the thick ascending loop of Henle?

Answer 19

Na+, K+, Ca2+, Cl-, Mg2+

Question 20

Which solutes are reabsorbed by paracellular transmission at the level of the thick ascending loop of Henle?

Answer 20

Na+, Ca2+, Mg2+

Question 21

How is water reabsorbed at the level of the thick ascending loop of Henle?

Answer 21

Water is reabsorbed at the level of the thick ascending loop of Henle by paracellular transmission

Question 22

Describe how Na+ is reabsorbed at the level of the thick ascending loop of Henle

Answer 22

Na+ is reabsorbed via the Na+/K+/2Cl- co-transporter system on the apical membrane. Na+ is moved from the thick ascending loop of Henle into the peritubular capillaries via the sodium potassium ATPase pump on the basolateral membrane

Question 23

Describe how Cl- is reabsorbed at the level of the thick ascending loop of Henle

Answer 23

Cl- is reabsorbed via the Na+/K+/2Cl- co-transporter system on the apical membrane. Cl- is moved from the thick ascending loop of Henle into the peritubular capillaries via Cl- specific channels and Cl-/K+ co-transporter systems on the basolateral membrane

Question 24

Describe how K+ is reabsorbed at the level of the thick ascending loop of Henle

Answer 24

K+ is reabsorbed via the Na+/K+/2Cl- co-transporter system on the apical membrane. K+ is moved from the thick ascending loop of Henle into the peritubular capillaries via Cl-/K+ co-transporter systems on the basolateral membrane. Some of the K+ is recycled back into the filtrate by leaky K+ channels on the apical membrane

Question 25

What repels Na+, Ca2+ and Mg2+ from the filtrate allowing these solutes to undergo paracellular reabsorption at the level of the thick ascending loop of Henle?

Answer 25

The movement of K+ out of the thick ascending loop of Henle via leaky K+ junctions on the apical membrane repels Na+, Ca2+ and Mg2+ from the filtrate

Question 26

What are the five solutes reabsorbed at the level of the distal convoluted tubule (DCT)?

Answer 26

Na+, K+, Ca2+, Cl-, Mg2+

Question 27

(T/F) Na+, K+ and Cl- are reabsorbed at the level on the distal convoluted tubule (DCT) by the same mechanism as the thick ascending loop of Henle

Answer 27

ALMOST TRUE. Except both the basolateral and apical membrane of the distal convoluted tubule (DCT) has leaky K+ channels

Question 28

How are Ca2+ and Mg2+ reabsorbed at the level of the distal convoluted tubule (DCT)?

Answer 28

Ca2+ and Mg2+ are repelled from the filtrate by the recycled K+ to drive carrier mediated trans cellular reabsorption of Mg2+ and Ca2+ into the peritubular capillaries

Question 29

What are the two types of cell involved in reabsorption within the collecting ducts?

Answer 29

Principle cells
Intercalated cells

Question 30

What are the three solutes reabsorbed by the principle cells?

Answer 30

Na+, K+, Cl-

Question 31

What are the two solutes reabsorbed by the intercalated cells?

Answer 31

K+, Cl-

Question 32

What is tubular secretion?

Answer 32

Movement of non filtered substances from peritubular capillaries or tubular cells into the filtrate

Question 33

What is secreted at the level of the proximal convoluted tubule (PCT)?

Answer 33

Protein bound organic ions, endogenous waste, exogenous drugs

Question 34

What is secreted at the level of the collecting ducts?

Answer 34

K+