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Physiology 1 : renal > Blood flow and glomerular filtration > Flashcards

Blood flow and glomerular filtration Flashcards

1
Q

How much of the resting cardiac output do the kidneys receive?

A

→ nearly a quarter

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2
Q

What is the large blood flow to the kidneys related to?

A

→ metabolic needs of the kidney

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3
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 and Vit D

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4
Q

How long is the average nephron?

A

→ 4cm

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5
Q

What is the functional unit of the kidney?

A

→ nephron

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6
Q

What can the kidney not regenerate?

A

→ new nephrons

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7
Q

Why is the glomerulus unusual?

A

→ It enters and leaves as an artery

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8
Q

What do the blood vessels form around the tubule?

A

→ peritubular capillaries

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9
Q

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

A

→ Glomerulus

→ Peritubular capillaries

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10
Q

What are the 2 stages of urine formation?

A

→Glomeruli produce the liquid

→The tubules modifies its volume and composition

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11
Q

How much fluid is filtered through the glomerulus and how much is being excreted as urine?

A

→Nearly all of the fluid filtered through the glomerulus is reabsorbed back from the tubule into the blood
→with the remainder being excreted as urine at a rate of 1ml/min

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12
Q

What urine output equates to renal failure?

A

→ <5ml/day

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13
Q

Why is there such a high filtration rate?

A

→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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14
Q

What is the first stage of urine production?

A

→ Glomerular filtration

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15
Q

How is glomerular fluid formed?

A

→By passive ultrafiltration of the plasma across the glomerular membrane
→as described by Starling’s principle of capillary fluid filtration

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16
Q

What is the GFR set by?

A

→Autoregulation

→Renal sympathetic vasomotor nerve activity

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17
Q

What is the glomerulus enclosed by?

A

→ Completely enclosed by the epithelium of the BC, though they are specialised to form podocytes

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18
Q

What is a passive ultrafiltrate of plasma?

A

→ Plasma from which the proteins have been filtered out

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19
Q

What is the concentration of small solutes and plasma proteins in glomerular fluid?

A

→For small solutes, such as NaCl, glucose and urea
The concentration in glomerular fluid = the concentration in plasma

→For plasma proteins
The concentration in glomerular fluid = almost zero

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20
Q

What is proteinuria a sign of?

A

→Proteinuria is a sign of renal/urinary tract disease

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21
Q

What drives the ultrafiltration process?

A

→A net pressure drop across the glomerular membrane drives the ultrafiltration process
→imbalance of Starling forces

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22
Q

What does the glomerular membrane sieve out?

A

→ Solutes from Plasma by Molecular Size

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23
Q

What is the pressure like in the kidney capillaries?

A

→ The highest compared to arterioles in the body

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24
Q

What does high pressure in the kidney capillaries create?

A

→ An outward force

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25
Q

What are the 2 components opposing the outward force created by high pressure in the glomerular capillary?

A

→colloid osmotic pressure exerted by proteins in the blood (25mmHg)

→pressure in the Bowman’s Space (10mmHg)

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26
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

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27
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.

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28
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

29
Q

What is the relationship between net filtration force and net absorptive force and what does this result in?

A

→net filtration force is always more than the net absorptive force
→resulting in a glomerular filtration rate of 20% which is colossal compared to 1% elsewhere in the body

30
Q

What happens to starling force balances in peritubular capillaries?

A

→Starling force balance is reversed (absorption) in peritubular capillaries

31
Q

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

A

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

32
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 and the
→COP rises because fluid is lost from the capillaries, →protein is getting more concentrated
→ exerting a greater force driving fluid back from the tubule into the capillary

33
Q

What are the gaps called in the capillary membranes?

A

→The capillary membrane is not continuous but have gaps called fenestrae

34
Q

Why can blood not pass through fenestrae?

A

→Normally blood cannot pass through the fenestrae because the blood cells cannot fit and are trapped

35
Q

What can travel through the fenestrae?

A

→ Anything that dissolves in water

→ Through the basal lamina (glycocalyx)

36
Q

What is the size range of fenestrae?

A

→ 50-100nm

37
Q

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

A

→ The filtration slits are subdivided into much smaller pores that are 4nm wide
→ Made of nephrin and podocin
→ Albumin gets trapped here

38
Q

What is nephrotic syndrome?

A

→ Nephrin and podocin are not made

39
Q

What is myeloperoxidase?

A

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

40
Q

What does myeloperoxidase produce?

A

→black precipitate in a positive reaction

41
Q

How did they prove that albumin cannot pass into urine?

A

→ Myeloperoxidase injected into plasma
→ Penetrates through basal lamina but piles up at filtration slits
→ None penetrates into urinary space

42
Q

What can the glomerular membranes be described as?

A

→3 sieves in series of increasing fineness

43
Q

What are changes in urine due to?

A

→ due to changes in tubular reabsorption

44
Q

What is the mechanism keeping GFR constant?

A

→The mechanism holding GFR constant is an internal

one called “autoregulation”

45
Q

What is held constant over a range of arterial blood pressures?

A

→GFR and Renal blood flow are held constant over a range of arterial pressure

46
Q

In the normal range of blood pressures what happens to GFR and what is this called?

A

→In the normal range of arterial pressure, even if BP changes up or down,
→GFR remains constant = AUTOREGULATION

47
Q

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

A

→If there was no autoregulation, then a relatively small increase in BP would cause a similar 25% increase in GFR

48
Q

What would happen if tubular reabsorption were to stay constant?

A

→then urine flow would increase by 30-fold

(the difference between GFR and tubular reabsorption), →depleting blood volume very quickly

49
Q

What is the Bayliss’ Myogenic response (BMR) and what does it prevent?

A

→Direct vasoconstriction of afferent arteriole with an increase in perfusion pressure
→Can prevent changes in response to BP fluctuations that occur in intervals greater than 3-4 seconds

50
Q

What is Tuboglomerular feedback (TGF) and what does it involve?

A

→Flow-dependent signal detected in macula densa, that alters the tone of the afferent arteriole
→The method likely involved adenosine/or ATP

51
Q

What does tuboglomerular feedback respond to?

A

→Responds to slower BP fluctuations, over intervals of 20 seconds or longer

52
Q

What do TGF and BMR do together?

A

→act in concert and stabilise renal function by preventing pressure-induced fluctuations in :
→RBF (Renal Blood Flow),
→GFR
→delivery of filtrate to the distal tubule (“Distal Delivery”)

53
Q

What does an increase in perfusion pressure lead to?

A

→immediate increase in vessel radius (few seconds only) →blood flow goes up briefly

54
Q

What happens if the blood pressure increases to keep the pressure in the bowmans capsule the same?

A

→vessels just upstream of the glomerular capillaries contract and increase the resistance
→resulting in a drop of pressure
→ keeping the pressure in the Bowman’s capsule (Pgc) still in the same range

55
Q

What is the equation for flow?

A

→ Flow = change in pressure / resistance

56
Q

What must autoregulation be mediated by?

A

→mediated in part by changes in afferent arteriolar resistance

57
Q

What happens as the systemic pressure rises?

A

→increase in afferent arteriolar tone prevents the elevation in pressure from being transmitted to the glomerulus
→allowing Pgc and GFR to remain unchanged

58
Q

Describe how GFR is decreased through TGF

A 
GFR increases
↓
Flow through tubule increases 
↓
Flow past macula densa increases (altering luminal NaCl and luminal osmolality)
↓
Paracrine diffuses from macula to afferent arteriole 
↓
Afferent arteriole contracts 
↓
Resistance in afferent increases 
↓
Hydrostatic pressure in glomerular decreases
↓
GFR decreases
59
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

60
Q

What nerves can reduce GFR?

A

→Renal sympathetic nerves (vasoconstrictor, noradrenergic) can reduce the GFR
→by re-setting autoregulation to a lower level

61
Q

What 3 situations is extrinsic control of GFR used?

A

→Standing upright (orthostasis)
→Heavy exercise
→Haemorrhage & other forms of clinical shock

62
Q

In shock what are sympathetic actions helped by?

A 
these sympathetic actions are aided by 
→circulating vasoconstrictor hormones 
→ adrenaline
→angiotensin
→ and vasopressin
63
Q

What is the role of extrinsic GFR?

A

→The role is to conserve body fluid during physical stress

64
Q

What are the 2 main clinical disorders of the GFR?

A

→Glomeruli too leaky to plasma protein:

→GFR too low (more common)

65
Q

What are the signs of nephrotic syndrome and what do they respond well to?

A

→Proteinuria
→Hypoproteinaemia
→Oedema
→respond well to steroids

66
Q

What are the signs of low GFR?

A

→Chronic glomerulonephritis

→Non-functioning glomeruli

67
Q

What value of GFR is chronic renal failure?

A

→When GFR < 30 ml/min, this is CHRONIC RENAL FAILURE

68
Q

What is chronic glomerulonephritis?

A

→The whole of the glomerulus is replaced by collagen
→ hence there is no blood flow or RBC
→so no glomerular filtrate

69
Q

What are gaps between podocytes called?

A

→ filtration slits

Physiology 1 : renal (13 decks)

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