Tubular Function

Question 1

What is osmolarity?

Answer 1

A measure of the solute concentration in a solution that depends on the number of dissolved solutes present

Question 2

What is osmolarity dependent on?

Answer 2

Number of particles in a solution, not the nature of the particles.

Question 3

How is osmolarity calculated?

Answer 3

Calculated by all the concentrations of different solutes added together measured in mmol/l and each ion counted separately

Question 4

What is the normal plasma osmolarity?

Answer 4

285-295 mosmol/l

Question 5

What is the normal urine osmolarity?

Answer 5

50-1200mosmol/l

Question 6

How can molecules be passively transported through the kidneys? What is the rate and solute concentration relationship using these forms of transport?

Answer 6

Protein independent transport - lipophilic molecules have a linear rate to solute conc relationship
Protein dependent transport - hydrophilic molecules has a curved rate to solute conc

Question 7

What does secretion do in tubular functions?

Answer 7

Moves substances from peritubular capillaries to tubular lumen, constituting a pathway into the tubule.

Question 8

How can secretion occur in the tubules

Answer 8

Diffusion

Transcellular mediated transport

Question 9

What are the most important substances secreted in the tubules?

Answer 9

H+ and K+

Question 10

What drugs are secreted in the tubules?

Answer 10

Choline
Creatine
Penicillin + others

Question 11

Where are most solutes reabsorbed in the kidney nephron thingys, what percentage is that?

Answer 11

Proximal convoluted tubule - 60-70%
100% glucose
65% Na
90% bicarb

Question 12

What drugs regulate collecting duct absorption?

Answer 12

Aldosterone and vasopressin

Question 13

What is found in the inner medulla of the kidney?

Answer 13

Loop of henle thin descending limb

Question 14

What is found in the outer medulla of the kidney?

Answer 14

Loop of Henle thick ascending limb

Question 15

What is found in the cortex of the kidney?

Answer 15

Proximal and distal convoluted tubules
Glomerulus
Collecting duct

Question 16

What happens in the basolateral membrane?

Answer 16

Na/K pump keeps intracellular Na low and K high

Large conc and electrical gradients favour Na movements into the cell - occurs in most nephron segments

Question 17

What happens in the early PCT?

Answer 17

Na+ entry down a large electrochemical gradient can bring about the uphill entry of glucose and aas and exit of H+
Carbonic anhydrase activity leads to Na+ reabsorption and increased urinary activity

Question 18

What is passively reabsorbed in the PCT?

Answer 18

Urea

Water

Question 19

What is actively reabsorbed in the PCT?

Answer 19

Glucose
Amino acids
Sodium
Potassium
Calcium
Vit C
Uric acid

Question 20

Why is a net secretion by the PCT important?

Answer 20

It is a route of excretion for some substances

Some drugs enter the tubular fluid here and act further down the nephron

Question 21

What kind of epithelium does the descending loop of henle have? What happens here?

Answer 21

Squamous epithelia with few mitochondria
Water passively reabsorbed, draws in Na and K
THIN limb

Question 22

What kind of epithelium does the ascending limb of loop of henle have?

Answer 22

Cuboidal epithelium with few microvilli but many mitochondria
THICK limb

Question 23

What happens in the ascending limb of the loop of henle?

Answer 23

Chloride actively reabsorbed
Sodium passively reabsorbed with it
Bicarbonate reabsorbed
Impermable to water

Question 24

How much water and sodium is reabsorbed by the point of reaching the end of the loop of Henle?

Answer 24

85% of water

90% of sodium

Question 25

What is the tubular fluid that leaves the loop of Henle like?

Answer 25

Hypo-osmolar with respect to plasma | Because more salt than water has been reabsorbed so the loop is hypo-osmolar with repect to plasma

Question 26

What is the distal convoluted tubule epithelium like? (structure)

Answer 26

Cuboidal with few microvilli. Complex lateral membrane interdigitations with Na+ pumps Numerous large mitochondria

Question 27

What happens in the distal convoluted tubule?

Answer 27

Na+ and Cl- co transporter linked to Ca2+ reabsorption

Question 28

How are Na+ and Cl- reabsorbed in the distal convoluted tubules?

Answer 28

By a channel sensitive to thiazides. Thiazides cause a rise in plasma Ca2+

Question 29

What happens at the macula densa of the distal convoluted tubule, what is the macula densa?

Answer 29

Part of juxtaglomerular apparatus, detects changes of Na+ conc of filtrate

Question 30

What happens in the distal part of distal covoluted tubule and cortical collecting duct?

Answer 30

Fine tuning of the filtrate to maintain homeostasis DCT - sodium reabsorbed (dependent on aldosterone) CT - sodium reabsorbed (dependent on aldosterone) Adjustment of Na/K/H/NH4 Water reabsorbed under control of ADH

Question 31

What is special about distal part of nephron and water?

Answer 31

Distal part of nephron impermable to water without ADH

Question 32

What does the principal cell do in the collecting duct and distal part of distal tubule?

Answer 32

Important in Na/K/water balance mediated with Na/K ATP pump

Question 33

What does the intercalated cell do in the collecting duct and distal part of distal tubule?

Answer 33

Important in acid base balance mediated by H+/ATP pump

Question 34

What is special abou the cortical collecting duct principle cell epithelium

Answer 34

Very tight epithelium, very little paracellular transport

Question 35

What are single gene defect conditions that affect tubular function?

Answer 35

``` Renal tubule acidosis Bartter syndrome Fanconi syndrome (dent's disease) ```

Question 36

What happens in renal tubular acidosis?

Answer 36

Hypercholermic metabolic acidosis Impaired growth Hypokalemia

Question 37

What happens in Bartter syndrome?

Answer 37

Excessive electrolyte secretion Antenatal Barterr sydrome: premature birth, polyhydroamnios, severe salt loss, moderate metabolic alkalosis, hypokalemia, renin and aldosterone hypersecretion

Question 38

What happens in Fanconi syndrome?

Answer 38

Increased excretion of uric acid, glucose, phosphate and bicarbonate Increased excretion of low MW proteins Disease of proximal tubules associated with renal tubular acidosis