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Urinary > Week 3 - Clearance and filtration > Flashcards

Week 3 - Clearance and filtration Flashcards

1
Q

What is the difference between cortical and juxtamedullary nephrons?

A
  • Cortical have shorter loops of henle with peritubular capillaries and a high concentration of renin
  • Juxtamedullary had long loop of henle which penetrates deep into medulla and capillaries arranged in vasa recta and no renin
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2
Q

Where are the glomeruli of all nephrons found?

A

-Cortex only

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3
Q

What is the filtration faction?

A

-Only 20% of blood passing through afferent arteriole filteres at any one time. 80% exits via efferent arteriole

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4
Q

What is the difference between plasma and ultra-filtrate?

A

-Identical apart from ultra-filtrate doesnt contain cells or large proteins

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5
Q

What makes up the filtration barrier?

A
  • Fenestrated capillary endotheium
  • Shared basement membrane
  • Visceral peritoneum forming podocytes
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6
Q

What is the basement layer made of and why is this helpful?

A
  • Acellular gelatinous layer of collagen and glycoproteins

- Glycoproteins have a negative charge which repel proteins which have a negative charge (improves selectivity)

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7
Q

What infers the size limitation of the filtration barrier?

A

-Filtration slits formed by psuedopodia

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8
Q

What effect does the negative charg of the basement membrane have on protein filtration?

A
  • Negative proteins are repelled and thus less filtered regardless of size
  • Positive proteins are pushed through BM which allows slightly bigger proteins to be filtered
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9
Q

What physical forces drive filtration? Which exerts the most force?

A
  • Hydrostatic pressure in capillary (the push) (50mmHg)
  • Hydrostatic pressure in bowman’s capsule (15mmHg)
  • Oncotic pressure in afferent arteriole(25mmHg)
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10
Q

What is the result of the hydrostatic pressure in the gomeruli capillaries?

A

-Drives filtrate through the filter

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11
Q

Why is the hydrostatic pressure in glomerular capillaries high?

A

-Afferent arteriole is wider than efferent arteriole

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12
Q

What effect does oncotic pressure of capillaries have on filtration?

A

-Draws filtrate back into the capillary

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13
Q

Why is there hydrostatic pressure in the bowman’s capsule and what effect does this have on filtration?

A
  • Generated by the filtrate that is being filtered

- Pushes filtrate back into the capillaries

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14
Q

Describe autoregulation in the kidneys

A
  • Autoregulation is a myogenic response which occurs in response to stretch of the smooth muscle and aims to maintain GFR within normal limits despite small changes in blood pressure
  • If bp increase, smooth muscle stretched ->vasoconstriction of afferent occurs in order to maintain bloodflow and thus GFR.
  • If bp decreases -> smooth muscle relaxes -> vasodilation occur in afferent arteriole to maintain bloodflow and GFR to remain the same. Vasoconstriction of efferent arteriole to increase hydrostatic pressure
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15
Q

What is tubulo-glomerular feedback?

A
  • Mechanism to reduceGFR
  • Occurs when there are changes in tubular flow rate as a result of changes in GFR
  • Changes NaCl in DCT due to an change in filtered load
  • Detected by macular densa in juxtaglomerular apparatus which stimulates the afferent arteriole to release either adenosine for vasoconstriction or prostaglandins for vasodilation
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16
Q

What is the TGF response if GFR increases?

A
  • Increased GFR
  • Increased NaCl in DCT
  • Rise in concentration detected by MD cells of JGA
  • JGA causes release of adenosine
  • vasoconstriction of afferent arteriole
  • Decreased GFR
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17
Q

In what limits does autoregulation of the kidneys work?

A

-80-180mmHg

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18
Q

What is bulk transport?

A

-Major reabsorption in PCT

19
Q

What drives reabsorption of solutes and water in PCT?

A
  • NaKATPase on basolat generates Na gradient which cotransports other molecules with it (secondary active transport)
  • Water follows down osmotic gradient
20
Q

What happens to the solutes that move into tubular cells?

A

-Diffuse into capillaries

21
Q

Name the Na transporters on the apical membrane of the following segements:

i) PCT
ii) LoH
iii) Early DCT
iv) Late DCT and CD

A

i) Na:H antiporter or Na:glucose symporter
ii) NKCC2
iii) NCCT
iv) ENaC

22
Q

Describe glucose reabsorption in PCT

A
  • uses energy from Na gradient to drive reabsorption
  • 2 mols of Na per glucose
  • glucose passes through interstitium to peritubular capillary down its gradient by facilitated diffusion
23
Q

What happens if transport maximun of glucose is reached?

A

-Rest of glucose spills over into urine causing glycosuria and polyuria

24
Q

Is reabsorption always transcellular?

A

-No can be paracellular

25
Q

What happens to the K inside the tubule cells if NaKATPase on basolat?

A

-Diffuses down its conc gradient via romK back into interstitium

26
Q

What is meant by secretion in the tubules?

A

-Solutes secreted from the peritubular capillaries to lumen of PCT

27
Q

What substances are commonly secreted into tubular fluid?

A

-H+, K+ and organic cat/anions

28
Q

Describe organic anion/cation secretion in PCT

A
  • Entry into tubular cell through facilitated diffusion from capillary
  • Na:H exchanger generate H gradient from tubule cell to lumen
  • Secretion into lumen by H:OC exchanger using H gradient
29
Q

What is the normal GFR in males and females?

A
  • Males = 115-125ml/min

- Females 90-100ml/min

30
Q

What characteristics must a substance have in order to be used to calculate GFR

A
  • Freely filtered
  • Not secreted
  • Not reabsorbed
31
Q

What is average renal blood flow?

A

-1.1L/min

32
Q

What is renal plasma flow?

A

-Plasma is approx 55% of blood and thus 1.1Lx0.55=605ml/min of plasma

33
Q

How much of the renal plasma flow is filtered?

A

-20% (125ml (GFR))

34
Q

What is renal clearance?How do you calculate renal clearance?

A
  • The volume of plasma that is completely cleaned of the substance by the kidneys per unit time
  • (conc in urine x urine volume)/conc in plasma
35
Q

When are renal clearance tests used?

A

-Determine GFR

36
Q

What two substances are used to measure GFR?

A
  • Inulin

- Creatinine

37
Q

What would a clearance value higher than GFR indicate?

A

-The substance is secreted

38
Q

What is eGFR?

A

-calculation to calculate adjusted GFR which takes into account mass, age, sex and ethnicity

39
Q

How do you calculate filtered load?

A
  • Work out how many mg/ml in plasma

- Times this by GFR

40
Q

What is renal threshold?

A

-The plasma concentration of a substance at which transport maximum is reached and the substance starts spilling into urine

41
Q

What is Tm for glucose?

A
  • 375 mg/min in males

- 300mg/min in females

42
Q

Which nephron is most dominant cortical or juxtamedullary?

A

-Cortical (90%)

43
Q

What type of reabsorption occurs in pct?

A

-Isomotic

44
Q

In addition to glucose, what else uses secondary active transport in PCT for reabsorption?

A
  • Amino acids and water-soluble vitamins (B and C)

- Lactate, ketones and acetate

Urinary (21 decks)

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