Tubular Function

Question 1

How much filtrate can a healthy individual produce?

Answer 1

180L/day

Question 2

What is the renal tubule composed of?

Answer 2

PCT, loop of Henle, DCT, collecting ducts

Question 3

What is the primary site of reabsorption?

Answer 3

PCT - proximal convoluted tubule

Question 4

What structure of the PCT allows reabsorption?

Answer 4

it is long, convoluted and has microvilli allowing for larger surface area and more absorption

Question 5

What are all portions of the nephron closely associated with?

Answer 5

peritubular capillaries (vasa recta)

Question 6

When substances are reabsorbed what is their pathway of travel?

Answer 6

tubule lumen > tubule wall > interstitial space > peritubular capillaries

Question 7

When substances are secreted what is their pathway of travel?

Answer 7

peritubular capillaries > interstitial space > tubule wall > tubule lumen

Question 8

What substances are reabsorbed?

Answer 8

Sodium Chloride Calcium Phosphate Potassium Bicarbonate, Water Glucose Amino acids, Urea (sometimes)

Question 9

What substance is always secreted?

Answer 9

creatinine

Question 10

How does water move across the membrane?

Answer 10

via protein pores in the phospholipid bilayer (aquaporins)

Question 11

How do amino acids and glucose move down their concentration gradient?

Answer 11

via sodium co-transporters

Question 12

How much filtrate is passively reabsorbed?

Answer 12

50% (90L)

Question 13

Where is the sodium potassium pump located?

Answer 13

basolateral membrane of epithelial cells

Question 14

Where do the sodium co-transporters get energy?

Answer 14

secondary active transport from energy generated by Na+/K+ pump

Question 15

How does the sodium/potassium pump allow reabsorption of the remaining filtrate?

Answer 15

• Water follows Na+ wherever it goes - osmosis
• Glucose and amino acids co-transported with Na+
• Chloride and negative ions follows Na+

Question 16

What happens to glucose reabsorption in diabetic patients?

Answer 16

high levels of glucose in lumen overwhelm the co-transporters therefore not all of the glucose would be reabsorbed and ultimately cause the glucose to be excreted from the body via the urine

Question 17

What % of nutrients are reabsorbed at the PCT?

Answer 17

100%

Question 18

What % of water is reabsorbed at the PCT?

Answer 18

65%

Question 19

What % of negative ions are reabsorbed at the PCT?

Answer 19

65%

Question 20

What is the remaining filtrate that travels to the loop of Henle?

Answer 20

60L

Question 21

What are the 3 sections of the loop of Henle?

Answer 21

thick ascending limb
thin ascending limb
thin descending limb

Question 22

Where are the aquaporin channels in the loop of Henle?

Answer 22

thin descending limb - epithelial cells

Question 23

Where is water impermeable in the loop of Henle?

Answer 23

thick ascending limb
thin ascending limb

Question 24

Where is there sodium/potassium pumps in the loop of Henle?

Answer 24

thick ascending limb

Question 25

Why can water not follow sodium?

Answer 25

no aquaporin channels in thick ascending limb

Question 26

What pump in the thick ascending limb transports Cl-, Na+, 2 K+?

Answer 26

NKCC2 Transporter

Question 27

Where does the NKCC2 get energy?

Answer 27

secondary active transport via sodium/potassium pump

Question 28

What is the interstitial space in the loop of Henle?

Answer 28

medulla

Question 29

Where does anti-durietic drug furosemide work?

Answer 29

binds to NKCC2 pump and inhibits it

Question 30

What conditions are created in the medulla as sodium is actively reabsorbed from the filtrate? (water prevented from following)

Answer 30

medulla becomes highly salty causing water in the descending limb to leak into medulla through aquaporin channels following rules of osmosis

Question 31

What happens to the concentration of the filtrate as it descends the thin descending limb?

Answer 31

no active sodium pumps in descending limb therefore urine becomes more concentrated

Question 32

What happens to the concentration of the filtrate as it ascends the thick ascending limb?

Answer 32

concentration of (sodium) filtrate decreases

Question 33

What is the process in which urine is concentrated called?

Answer 33

counter current multiplication

Question 34

Where does the reabsorbed water (and salt) go in the medulla?

Answer 34

return to bloodstream via the vasa recta

Question 35

What is the role of the DCT?

Answer 35

Fine-tuning - site of fluid volume and electrolyte regulation

Question 36

Where is the target site for several hormones that regulate water and sodium levels?

Answer 36

the DCT

Question 37

What hormones work in the DCT and what is their role?

Answer 37

* Anti-diuretic hormone (ADH) – Increases water reabsorption * Aldosterone – Increases Na+ reabsorption * Atrial natriuretic hormone (ANH) – Promotes Na+ secretion

Question 38

Why is filtrate hypotonic as it enters the DCT?

Answer 38

it has more water and solute than surrounding interstitium (100mosmoles vs 3000mosmoles in normal bodily fluids)

Question 39

Is there aquaporin channels in DCT?

Answer 39

No aquaporins present (in the absence of hormonal regulation)

Question 40

What happens to urine in the DCT in the absence of external hormonal regulation?

Answer 40

In the absence of external hormonal regulation a large volume of dilute (hypotonic) urine is produced

Question 41

What does low fluid, low blood volume cause?

Answer 41

low blood pressure

Question 42

What detects this change?

Answer 42

pituitary gland

Question 43

Where does ADH (vasopressin) act?

Answer 43

epithelial cells lining DCT and collecting ducts

Question 44

What does ADH cause?

Answer 44

Insertion of aquaporins allows water to be reabsorbed from the filtrate small volume of concentrated urine produced

Question 45

What is the vasopressin receptor?

Answer 45

AVPR2 (vasopressin receptor 2)

Question 46

Once vasopressin binds, what occurs?

Answer 46

activates signal transduction within cell signal enters nucleus and stimulates transcription factors which translate proteins that create aquaporin channels that are inserted into membrane and allow water to leave filtrate, pass through tubule wall and into interstitial space to eventually return back to blood

Question 47

What hormone can a fall in blood volume also stimulate?

Answer 47

aldosterone

Question 48

What is the action of aldosterone?

Answer 48

Aldosterone acts on distal and collecting tubules Upregulates activity and insertion of Na+K+ pumps and channels small volume of concentrated urine produced

Question 49

Why does water leave due to Na+ pump activity?

Answer 49

osmosis

Question 50

Where does aldosterone bind?

Answer 50

diffuses through cell membrane and binds directly to transcription factors that up regulate activity and insertion of Na+/K+ pumps

Question 51

When is ANP released?

Answer 51

increase in blood pressure

Question 52

How does ANP work?

Answer 52

counteracts effects of ADH and aldosterone by removing aquaporin channels and decreasing activity and insertion of Na+/K+ pumps

Question 53

What urine is produced in ANP?

Answer 53

large volume of dilute urine

Question 54

What % of liquid is excreted as urine?

Answer 54

1-2%

Question 55

What fraction is reabsorbed in the PCT?

Answer 55

2/3

Question 56

The kidney uses sodium handling in various different ways to support reabsorption of a large volume of filtrate. In which section of the kidney is the majority of sodium reabsorbed?

Answer 56

Proximal convoluted tubule

Question 57

In the Loop of Henle, the thin descending limb......

Answer 57

Is freely permeable to water

Question 58

What is the primary purpose of counter current multiplication?

Answer 58

water reabsorption

Question 59

What cellular response does ADH signalling have on epithelial cells lining the distal convoluted tubule?

Answer 59

Insertion of aquaporins

Question 60

By what process is sodium reabsorbed across the basolateral surface of epithelial cells lining the proximal convoluted tubule?

Answer 60

active transport