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Semester 3 - Urinary > Session 4 - Changes in Plasma Volume (Cells of the tubules) > Flashcards

Session 4 - Changes in Plasma Volume (Cells of the tubules) Flashcards

1
Q

What is in predominant in the ECF?

A

• Sodium

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2
Q

What ion is predominant in the ICF?

A

• Potassium

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3
Q

What occurs at the glomerulus?

A

• Filters of 180l/d (bulk filter)

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4
Q

What occurs at the PCT?

A
  • Freely permeable membrane
    • Reabsorbs electrolytes, glucose (100%), urea (50%) and amino acids (100%)
    • Reabsorbs large amount of fluid (66%)

Reduces water content

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5
Q

What occurs at the thin descending tube of the loop of henle?

A
  • High conc of sodium

* Concentrates filtrate due to loss of water

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6
Q

What happens at the thin ascending tube of the loop of henle?

A
  • Pulls Cl- and Na+ out of filtrate without H20

* Causes filtrate to become dilute

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7
Q

Why is the DCT special?

A

• Selective reabsorption

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8
Q

What happens at the DCT?

A
  • Reabsorbs water and concentrates urine via action of ADH
    • Reabsorbs Na and water as a result of aldosterone action
    • Secretes K+ as a result of aldosterone
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9
Q

What occurs in the collecting duct?

A
  • Permeability affected by ADH

* Absorbs or secretes K+, Na+, H+ and ammonia according to body’s needs

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10
Q

What are the excretory ranges of sodium?

A

• Low salt diet 0.5g/d

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11
Q

Why can’t we directly excrete water?

A
  • No water pump

* Must follow solute

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12
Q

Why is important to control the volume of the ECF?

A

• Includes the vascular system (blood pressure), the volume of which needs to be controlled within very tight limits

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13
Q

What is sodium balance?

A

The kidneys must match input of sodium with output

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14
Q

Why does ECF expansion occur

A
  • If Na+ excretion is less than intake, it is retained in the body in the ECF
    • This causes water to be drawn into the ECF from the nephron, causing increase in volume
    • Blood volume and arterial pressure increase
    • Oedema may follow
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15
Q

Why does ECF contraction occur?

A
  • If Na+ excretion is greater than intake (patient is in negative balance) the Na+ content decreases
    • Less water drawn out of nephron, so ECF volume decreases along with blood volume and arterial pressure
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16
Q

Does an increase in Na+ mean you get an increase in ECF osmolarlity?

A
  • If conc of Na+ in the ECF increases, then so does the volume
    • Increased volume gives increased CO, so increase Na+ excretion
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17
Q

State the % of Sodium filtered at each point of the nephron

A
  • PCT - 67%
    • Descending thin limb of Henle’s loop - 0%
    • Ascending thin and thick limb of Henle’s loop - 25%
    • Distal convoluted tubule - 5%
    • Collecting duct system - 3%
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18
Q

State the % of water filtered at each point

A
  • PCT - 65%
    • Descending thin limb of Henle’s loop - 10-15%
    • Ascending thin and thick limb of Henle’s loop - 0
    • Distal convoluted tubule - 0
    • Collecting duct system - 5 (>24% during dehydration)
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19
Q

How much Na+ is filtered in glomerulus?

A

• 100%

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20
Q

How much Na+ is reabsorbed in the PCT?

A

• 67%

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21
Q

What is glomerular tubular balance?

A
  • Reabsorption of sodium is always around 67%

* Blunts Na+ excretion response

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22
Q

What do all transporters depend on?

A

The action of Na+/K+ATPase

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23
Q

What are the two regions of the PCT?

A

• Section 1 (early)

Section 2 + 3(late)

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24
Q

Give one transporters found in the basolateral membrane of the S1 section of PCT

A

3Na-2K-ATPase

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25
Q

Give five transporters found in apical membrane of S1 of PCT

A
  • Co-Transported with glucose
    • Na-H exchange
    • Co-transport with AA/Carboxylic Acids
    • Co-transport with phosphate (increase with [PTH])
    • Aquaporin
26
Q

What happens to Urea and Cl- in S1 of the PCT?

A
  • Remain in filtrate, to counterbalance loss of glucose/AA/phosphate/HCO3
    • Gives conc grad for Cl-
27
Q

What is found in basolateral membrane of S2-S3?

A

• NaK/ATPase

28
Q

What drives reabsorption of Cl- in S2-S3?

A

• Conc gradient

29
Q

How is Cl- primarily reabsorbed in S2-S3?

A
  • Na-H exchanger
    • Paracelluar Cl- reabsorption
    • Transcellular Cl- reabsorption

Aquaporin

30
Q

Why is PCT known as a bulk transporter of water?

A

• Highly water permeable

31
Q

What is water-reabsorption in the PCT driven by?

A
  • Solute reabsorption

* ENa (Na+ in)

32
Q

What does the high water permeability of the PCT allow?

A

Reabsorption to be isoosmotic with plasma

33
Q

What is the reabsorption of water in the PCT driven by? (3)

A
  • Osmotic gradient established by sodium reabsorption
    • Hydrostatic forces in interstitium
    • Oncotic force in the peritubular capillaries - 20% of filtrate lost a glomerulus, but cells and proteins remain in the blood
34
Q

Give three methods of autoregulation

A
  • Myogenic action
    • Tubulo-glomerular feedback
    • Glomerulotubular balance
35
Q

What is glomerulotubular balance?

A
  • Glomerulotubular balance is the balance between glomerular filtration rate and the rate of reabsorption of solutes
    • PCT can adjust the amount of sodium it reabsorbs (67%) in order to regulate any changes in glomerular filtration rate
36
Q

How is more Na+ excreted if ECF volume increases?

A
  • Increase in ECF volume causes
    • Increase in cardiac output

Increase in GFR

37
Q

How does Glumerulotubular balance work?

A
  • Macula densa in JGA detect low osmolarity of Na+
    • AG2 or prostaglandins release which act as a vasoconstrictor of afferent arterioles
    • Reduces GFR
38
Q

How are the descending limb and ascending limb of the loop of Henle different?

A
  • Descending limb reabsorbs water but on NaCl

* Ascending limb reabsorbs NaCl but not water

39
Q

What occurs in thin descending limb?

A

• Aquaporins secrete water from lumen to interstitium down conc grad provided by excretion of ions by thick ascending limb into interstitium

40
Q

Give a structural features of the thin descending limb which facillitates the movement of water

A

• No tight junctions between cells, which allows paracellular reuptake

41
Q

Give two transporters found in luminal side of thick ascending limb?

A
  • NaKCC2

* ROMK (K+ out down conc grad)

42
Q

Why is ROMK necessary on luminal aspect of thick ascending limb?

A

• To drive NaKCC2, which requires K+

43
Q

What is NaKCC2 the target of, and what condition does this cause?

A
  • Loop diuretics

* Increased loss of K+ in the urine causes hyperkalaemia

44
Q

Give two transporters found in the ECF membrane of thick ascending limb

A
  • Cl- transporters

* Na/K+ ATPase

45
Q

Why is thick ascending limb particularly sensitive to hypoxia?

A

Uses more energy than anywhere else in nephron

46
Q

Describe changes in concentration of filtrate from thin descending limb to the thick ascending limb

A
  • Normal filtrate enters TDL
    • Lots of water lost
    • High conc
    • Tal excretes large amount of ions
    • Hypo-osmotic filtrate produced
47
Q

Why is the thick ascending limb of the loop of henle known as the diluting segment?

A
  • NaCl leaves filtrate without removal of water

* Tubule fluid leaving loop is hypo-osmotic compared to plasma

48
Q

What is water reabsorption of early DCT based on?

A
  • Active Na+ reabsorption

* Actively transported by NaCC transporter, driven by 3NaK+-ATPase

49
Q

What is water permeability like in the Distal Convoluted Tubule?

A

• Fairly low

50
Q

What major ion is reabsorbed in the early DCT?

A

• Ca2+

51
Q

Outline the two transporters on the luminal side of early DCT

A

• NaCC transporter (Na+ in as well as Cl-)

Ca2+

52
Q

Give three transporters found on ECF side of early DCT

A
  • Cl-
    • NCX (Ca2+ into ECF, Na+ in)
    • Na+/K+ ATPase
53
Q

What part of DCT is sensitive to thiazide diurectics?

A

NCC transporter

54
Q

What drives reabsorption of Ca2+ in early DCT?

A

Parathyroid hormone

55
Q

How does the fluid entering the DCT compare to the ECF?

A

Hypo-osmotic

56
Q

What is water reabsorption in late DCT and collecting duct driven by?

A

Water permeability dependent on ADH

57
Q

What are the two cell types found in late DCT and early collecting tubule?

A
  • Principle cells (reabsorption of Na+ via Enac)

* Type B intercalated cells (active reabsorption of Chloride)

58
Q

How is Na+ reabsorbed in collecting duct?

A
  • Na+ pumped out into ECF by Na+/K+ATPase

* Drives eNaC (epithelial Na+ channel)

59
Q

What are the two transporters found on luminal side of principle cells in late DCT and early collecting tubule?

A
  • eNa (sodium in)

* ROMK (K+ out)

60
Q

What proportion of collecting duct cells are principle?

A

• 70%

61
Q

What is the main feature of principle cells?

A 
• Produce lumen charge
		○ Electrical gradient for paracellular Cl- absorption 
		○ K+ secretion into lumen
	• Variable uptake through aquaporin 2
		○ Dependent on ADH
62
Q

What do intercalated cells do?

A
  • Active reabsorption of chloride

* Secrete H+ ions or HCO3-

Semester 3 - Urinary (33 decks)

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