Urinary System 4 - Tubular Function Flashcards Preview

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Flashcards in Urinary System 4 - Tubular Function Deck (26)
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1
Q

Define osmolarity

A

All the concentrations of the different solutes (measured in mmol/l) added together. separately

2
Q

Compare passive and active movement in reabsorption

A
  • As the concentration of lipophilic molecules increases, rate increases
  • Protein dependent transport reaches a peak
  • ATP dependent processes reach a peak
3
Q

How is water transported into filtrate?

A
  • Through tight junctions (paracellular)

- Through aquaporins

4
Q

How are passive uptake systems regulated?

A
  • Controlled by the number of protein channels present in the membrane
  • Channels can be stored in the cytoplasm
5
Q

Describe the process of protein reabsorption

A
  • Uptaken by endocytosis
  • pH causes a conformational change and the protein and receptor split
  • Receptor retaken to the membrane
6
Q

What is the transport maxima?

A
  • The maximum rate of reabsorption
  • Can vary between basal rate and stimulated rate depending on protein expression
  • Once surpassed, a substance will enter the urine
7
Q

Compare reabsorption in the different parts of the nephron

A
  • PCT 60-70% of all solute, all glucose, 65% Na, 90% bicarbonate
  • Loop of henle reabsorbs 25% Na
  • Distal convoluted tubule absorbs 8% Na
  • Collecting duct water only
8
Q

Describe the process of reabsorption in the proximal convoluted tubule

A
  • Sodium is coupled with chloride, glucose and amino acids
  • Protein is reabsorbed by endocytosis
  • Na/proton pump in the apical membrane
  • Urea, potassium and magnesium has paracellular pathways
  • Basolateral membrane as glucose and amino acid transporters, sodium potassium pump and cl-/HCO3- pump (Cl- into blood)
9
Q

Describe the reabsorption of bicarbonate ions in the early PCT

A
  • In the tubule, H+ from the sodium proton pump reacts with bicarbonate ions
  • Carbonic anhydrase converts carbonic acid into H2O and CO2
  • These diffuse into the cells of the proximal tubule, were carbonic anhydrase is made again and dissociates
  • Bicarbonate ions are reabsorbed into the blood, while protons are pumped back out through the same initial sodium, proton exchanger
10
Q

List the substances that undergo active reabsorption in the proximal convoluted tubule

A
  • Glucose
  • Amino acids
  • Sodium
  • Potassium
  • Calcium
  • Vitamin C
  • Uric acid
11
Q

List the substances that undergo passive reabsorption in the proximal convoluted tubule

A
  • Urea

- Water

12
Q

Why is secretion in the PCT important?

A
  • Route of excretion of some substances

- Some drugs enter the tubular fluid here to act further down the nephron

13
Q

What cells line the descending and ascending limbs of the loop of henle?

A
  • Descending limb is thin - squamous epithelium with a few mitochondria
  • Ascending limb is thick - Cuboidal with some microvilli and many mitochondria
14
Q

Compare the functions of the ascending and descending limbs of the loop of henle

A
  • Descending limb passively absorbs water, and sodium and potassium follow down the osmotic gradient
  • Ascending limb actively reabsorbs chloride, with sodium passively following, as well as bicarbonate. It is impermiable to water
15
Q

Describe the tubular fluid leaving the loop of henle

A
  • 85% water and 90% sodium has been reabsorbed

- The solution is hypo-osmolar compared to plasma

16
Q

Describe the ion movement in the ascending loop of henle

A
  • Sodium enters with chloride and potassium
  • Potassium diffuses into plasma through open channels
  • On the basal membrane, sodium potassium pump, potassium channels, and a potassium chloride transporter (out)
  • Chloride also has separate channels
  • Sodium, potassium, calcium and magnesium ions also diffuse via paracellular pathway
17
Q

Describe the cells lining the distal convoluted tubule

A
  • Cuboidal epithelim with some microvilli
  • Complex lateral membrane interdigitations with sodium pumps
  • Multiple mitochondria
18
Q

Describe the ion movement in the distal convoluted tubule

A
  • Sodium chloride pump at the apical membrane
  • Calcium channel too
  • Basolateral membrane, sodium calcium pump (3Na in 1Ca out), chloride and potassium channels + sodium potassium pump
19
Q

How do thiazides affect absorption in the distal convoluted tubule?

A
  • Thiazides are diuretics
  • They block the sodium-chloride channels on the apical membrane
  • This results in plasma calcium rising as sodium is still pumped out of the cell by Na/K ATPase, so the only other entry into the cell is through the Na/Ca pump on the basal membrane, which pumps calcium out
20
Q

What are principal cells?

A
  • Present in the distal tubule and collecting duct
  • They are affected by aldosterone
  • Important in sodium, potassium and water balance
  • Mediated by Na/K ATPase
  • Water reabsorption controlled by vasopressin
21
Q

What are intercalated cells?

A
  • Important in acid-base balance
  • Mediated by H+ ATP pump (pumps protons into tubular fluid)
  • Present in distal tubule and collecting duct
  • Basal membrane contains Cl-/HCO3- pump
22
Q

Why is there very little paracellular transport in the collecting duct?

A

Tight epithelium with strong tight junctions

23
Q

List the three single gene defects affecting tubular function

A
  • Renal tubule acidosis
  • Bartter syndrome
  • Faconi syndrome (dents disease)
24
Q

What is renal tubular acidosis?

A
  • Hyperchloremic metabolic acidosis
  • Impaired growth
  • Hypokalemia
  • Protons are not excreted in the kidney, or there may be issues with carbonic anhydrase (linked with proton production for excretion)
25
Q

What is bartter syndrome?

A
  • Excessive electrolyte secretion
  • Premature birth
  • Polyydramnios
  • Salt loss
  • Metabolic alkalosis
  • Hypokalemia
  • Renin and aldosterone hyper secretion
26
Q

What is Faconi syndrome?

A
  • Increased excretion of uric acid, glucose, phosphate and bicarbonate
  • Excretion of small proteins, associated with renal tubular acidosis as the protein isn’t separated from its membrane protein in the proximal tubules
  • Protons are pumped in to the cells, and the H+/Cl- pump is faulty and so a low enough pH can not be reached in the endosome for dissociation