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SGUL - Physiology 1 > Renal Blood Flow and Glomerular Filtration > Flashcards

Renal Blood Flow and Glomerular Filtration Flashcards

1
Q

Why is there such a huge filtration rate (namely 180 litres a day)?

A

High rate of formation of glomerular fluid is needed to wash out the waste products fast enough to keep their blood level low

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2
Q

Generally, how is glomerular fluid formed?

A

Passive ultrafiltration of plasma across the glomerular membrane

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3
Q

What is the glomerular rate (GFR) set by?

A
  • autoregulation
  • renal sympathetic vasomotor nerve activity.
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4
Q

What does the glomerulus consist of?

A

Capillaries and the Bowman’s capsule.

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5
Q

What are the key features of glomerular filtration for small solutes?

A

Concentration in the glomerular fluid is equal to the concentration in the plasma

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6
Q

What are the key features of glomerular filtration for plasma proteins?

A

Concentration in the glomerular fluid should be almost zero

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7
Q

What is proteinuria?

A

Presence of proteins within the urine

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8
Q

What is proteinuria a sign of?

A

Renal/ urinary tract disease

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9
Q

What drives ultrafiltration?

A

Net pressure drop across the glomerular membrane

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10
Q

On what basis does the glomerular membrane sieve out solutes?

A

Molecular size

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11
Q

What drives glomerular fluid formation?

A

Imbalance of Starling’s forces

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12
Q

What are the three forces that contribute to glomerular fluid formation?

A

Pc - capillary blood pressure - around 50 mmHg.
πp - plasma colloid osmotic pressure - around 25 mmHg.
Pu - pressure in the Bowman’s space - 10 mmHg.

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13
Q

What are podocytes?

A

Cells in the Bowman’s capsule that wrap around the capillaries of the glomerulus.

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14
Q

Describe the filtration slits in between the podocytes.

A
  • Glomerular fluid emerges through slit.
  • Slit is about 30 nm wide.
  • Central spine with lateral rungs
  • Subdivides the filtration slit into pores that are 4 nm wide.
  • Made of the proteins nephrin and podocin.
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15
Q

What do nephrin and podocin deficiency cause?

A

Nephrotic syndrome.

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16
Q

The glomerular membrane is 3 sieves in series of increasing fineness.
What are they?

A
  • Fenestrated capillary
  • Basement membrane
  • Filtration sites of podocytes
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17
Q

Describe the fenestrated capillaries.

A
  • Blocks big structures like RBCs
  • Allow smaller molecules through, such as albumin, fibrinogen, and water.
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18
Q

Describe the basement membrane.

A
  • Allow albumin and water through
  • Block molecules like fibrinogen
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19
Q

Describe the filtration sites of podocytes.

A
  • Allow small molecules through, such as water, glucose, NaCl, urea, creatinine
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20
Q

Why is GFR usually held constant? Why doesn’t it fluctuate?

A
  • Usually held constant at 120 ml/min.
  • Allows tubules to reabsorb filtrate and not be overwhelmed by excessive GFR.
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21
Q

What internal mechanism determines GFR?

A

Autoregulation

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22
Q

What are changes in urine production caused by?

A
  • Changes in tubular reabsorption
  • NOT by changes in GFR
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23
Q

What happens to renal plasma flow and GFR when blood pressure rises?

A

They stay relatively constant due to autoregulation.

24
Q

What 2 mechanisms are responsible for the intrinsic control of GFR?

A

BAYLISS MYOGENIC RESPONSE
TUBULOGLOMERULAR FEEDBACK (TGF)

25
Q

Describe the Bayliss Myogenic response.

A
  • Increase in the perfusion pressure leads to an immediate increase in vessel radius
  • Blood flow rises briefly
26
Q

How does the myogenic response affect autoregulation?

A

Changes in diameter of the afferent arteriole alters the resistance, maintaining autoregulation.

27
Q

Describe tubulo-glomerular feedback.

A
  • Increased distal tubular sodium chloride concentration
  • Causes basolateral release of adenosine from the macula densa cells.
  • ATP signal leads to a contraction of afferent arterioles.
28
Q

Describe how TGF controls the GFR and renal blood flow (RBF). PART 1

A
  • Change in the RBF/ GFR
  • Change in the NaCl delivery to the DCT
  • Macula densa sense the change
29
Q

Describe how TGF controls the GFR and renal blood flow (RBF). PART 2

A
  • Affect afferent arterioles via paracrine/vasoactive agents
  • Arterioles change diameter and resistance
  • Restores RBF/ GFR
30
Q

Describe the extrinsic control of GFR.

A
  • Extrinsic control of neurohormonal.
  • Renal sympathetic nerves (vasoconstrictor, noradrenergic) can reduce the GFR by resetting the autoregulation to a lower level.
31
Q

When may renal sympathetic nerves alter GFR?

A
  • standing upright (orthostasis)
  • heavy exercise
  • haemorrhage
32
Q

What is the role of extrinsic GFR control?

A

Conserve body fluid during physical stress.

33
Q

What aids the renal sympathetic nerves in extrinsic GFR control?

A

Circulating vasoconstrictor hormones such as adrenaline, angiotensin, and vasopressin.

34
Q

Describe the two major clinical disorders of the GFR. PART 1

A

Nephrotic Syndrome
- Filtration slit disordered by nephrin deficiency
- Glomeruli too leaky to plasma protein:
- Cause proteinuria, hypoproteinaemia and oedema.
- Respond well to steroids.

35
Q

Describe the two major clinical disorders of the GFR. PART 2

A

LOW GFR
Chronic glomerulonephritis - non-functioning glomeruli.
When the GFR gets to <30 ml/min, this is considered chronic renal failure.

36
Q

The 2 kidneys, which make up about 0.5% of the body weight, receive nearly a quarter of the resting cardiac output.

Why?

A
  • Large blood flow is not related to the metabolic needs of the kidney
  • Function of the role that the kidneys play in the regulation of the ECF and blood volume regulation and rapid waste disposal.
37
Q

What are the 4 main functions of the kidney?

A

→Control volume & composition of body fluids
→To get rid of waste material from the body
→Acid-Base balance
→As an endocrine organ – EPO, Renin

38
Q

What can the kidney not regenerate?

A

→ new nephrons

39
Q

What are the 2 sets of capillaries that a nephron has?

A

→ Glomerulus
→ Peritubular capillaries

40
Q

What are the 2 stages of urine formation?

A

→Glomeruli produce the liquid
→The tubules modifies its volume and composition

41
Q

What urine output equates to renal failure?

A

→ <5ml/day

42
Q

What is the net effect on glomerular capillaries as a result of the forces acting on it?

A

→net effect is an outward force of approximately 15mmHg
→drives fluid out of the capillary into the BC

43
Q

What happens as blood flows through the capillary with respect to pressure?

A

→As the blood flows through the capillary, there is a slight drop in pressure from the afferent end to the efferent end.

44
Q

What happens to the plasma as the blood flows along?

A

→ plasma also gets more concentrated as the blood flows along due to fluid loss

45
Q

What is the relationship between net filtration force and net absorptive force?

A

→net filtration force is always more than the net absorptive force

46
Q

What is the blood pressure entering the glomerulus and what does this result in?

A

→The blood pressure in the afferent arteriole is higher than the colloid osmotic pressure (COP) entering the glomerulus
→ resulting in a net filtration pressure out of the capillaries into the tubule.

47
Q

What is the blood pressure like as you exit the glomerulus and what does this result in?

A

→As we travel out of the glomerulus into the efferent arteriole, the pressure begins to drop.
→COP rises because fluid is lost from the capillaries
→ exerting a greater force driving fluid back from the tubule into the capillary

48
Q

Why can blood not pass through the fenestrae?

A

Blood cells cannot fit and are trapped

49
Q

What can travel through the fenestrae?

A

→ Anything that dissolves in water
→ Passes through the basal lamina (glycocalyx)

50
Q

Why does albumin not appear in the urine even though it can fit through the fenestrae and podocytes?

A

Trapped in the 4nm pores

51
Q

What is myeloperoxidase?

A

→ Albumin sized protein which is held up at the filtration slits

52
Q

What does myeloperoxidase produce?

A

→black precipitate

53
Q

What is myeloperoxidase used to prove?

A

→ Myeloperoxidase injected into plasma
→ Penetrates through basal lamina but piles up at filtration slits
→ Same size as albumin so albumin cannot pass into urine

54
Q

What would happen to GFR if there were no autoregulation and an increase of BP occurred?

A

→Relatively small increase in BP would cause a similar 25% increase in GFR

55
Q

What do TGF and the myogenic response do together?

A

→stabilise renal function by preventing pressure-induced fluctuations in RBF (Renal Blood Flow) and GFR
→delivery of filtrate to the distal tubule

56
Q

What must autoregulation be mediated by?

A

→mediated by changes in afferent arteriolar resistance

57
Q

What does an increase in osmolality and NaCl in the juxtaglomerular apparatus result in?

A

→results in a release of ATP
→ leads to a contraction of the afferent arteriole
→ contributes to the maintenance of pressure in the Bowman’s capsule

SGUL - Physiology 1 (68 decks)

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