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Anaesthetic FRCA Primary - eLFH Physiology > eLFH - Renal Physiology Part 3 > Flashcards

eLFH - Renal Physiology Part 3 Flashcards

1
Q

Trigger for activation of Renin-Angiotensin-Aldosterone System (RAAS)

A

Fall in BP and thus fall in renal blood flow

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2
Q

Overview of RAAS

A

Fall in BP detected by juxtaglomerular apparatus

Juxtaglomerular apparatus secretes renin

Renin stimulates conversion of angiotensinogen to angiotensin

Angiotensin causes vasoconstriction + Aldosterone secretion from adrenal cortex

Aldosterone causes Na+ and water reabsorption

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3
Q

Juxtaglomerular apparatus structure and components

A

Macula Densa

Juxtaglomerular cells

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4
Q

Macula Densa

A

Specialised epithelial cells

Increase renin release in response to low levels of delivered sodium due to fall in GFR or increase in proximal convoluted tubule reabsorption of Na+

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5
Q

Location of Macula Densa

A

Wall of first part of distal convoluting tubule

Abuts the afferent and efferent arterioles

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6
Q

Juxtaglomerular cells role

A

Secrete renin from granules

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7
Q

Location of juxtaglomerular cells

A

Wall of afferent arteriole (in the media)

Just before arteriole enters the glomerulus

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8
Q

Triggers for juxtaglomerular cells to secrete renin

A

Hypovolaemia

Increased sodium concentration in blood

Sympathetic stimulation

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9
Q

Features of Renin

A

Glycoprotein hormone

Formed from pro-renin and pre-pro-renin

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10
Q

Half life of renin

A

80 mins

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11
Q

Control of renin secretion

A

Renal sympathetic nerves

Intrarenal baroreceptors

Angiotensin II

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12
Q

Factors which increase renin secretion

A

Hypovolaemia
Cardiac failure
Cirrhosis
Renal artery stenosis
Catecholamines acting on beta 1 receptors

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13
Q

Factors which decrease renin secretion

A

Angiotensin II
Vasopressin
Beta blockers

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14
Q

Actions of renin

A

Cleaves Angiotensin I from Angiotensinogen

Angiotensin I converted to Angiotensin II by ACE in lungs / capillary endothelium

Angiotensin II converted to Angiotensin III in many tissues by aminopeptidase

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15
Q

Actions of angiotensin II

A

Vasoconstrictor including afferent and efferent arterioles in kidney
Greater effect on efferent arteriole than afferent arteriole - increases GFR

Aldosterone release

Potentiates sympathetic activity

Release of ADH

Thirst by direct effect on hypothalamus

Stimulates Na+/H+ antiporters in proximal convoluting tubule to cause Na+ and water retention

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16
Q

Triggers for aldosterone release from zona glomerulosa of adrenal cortex

A

Reduced renal blood flow via RAAS

Stress and trauma via ACTH release

Hyperkalaemia

Hyponatraemia

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17
Q

Time of onset of aldosterone action and why

A

Hours

As works via protein synthesis

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18
Q

Actions of aldosterone on distal convoluting tubules and collecting ducts

A

Increases sodium reabsorption and thus water reabsorption

Potassium and hydrogen ions are lost in exchange for Na+

Increases production of distal nephron transport mechanisms

19
Q

Site of ADH synthesis

A

Hypothalamus

20
Q

Site of ADH secretion

A

Posterior pituitary

21
Q

Factors which lead to ADH secretion

A

Baroreceptor and Osmoreceptor reflexes

22
Q

Inactivation site for ADH and half life

A

Inactivated in liver and kidney

Half life 18 mins

23
Q

Action of ADH on renal tubule

A

Inserts protein channels for water (aquaporins) into luminal membrane

Acts via cyclic AMP

24
Q

Action of ADH on arteriolar smooth muscle

A

At high concentrations of ADH, it causes arteriolar smooth muscle contraction

Reduces renal blood flow and GFR

Also increases MAP, hence use as second line vasopressor

25
Q

Role of ANP (atrial natriuretic peptide)

A

Secreted in response to atrial stretch

Increases renal excretion of Na+ and water

26
Q

Mechanism of action of ANP

A

Afferent arteriolar dilatation and efferent arteriolar constriction - increases net filtration pressure and renal blood flow

Inhibition of renin secretion and therefore inhibition of aldosterone release

Direct action on collecting ducts to decrease sodium reabsorption

27
Q

Site of ANP release

A

Atrial myocytes

28
Q

Diagram with whole RAAS illustrated

A
29
Q

Glomerular filtration rate definition

A

Flow rate of filtered fluid through the kidneys

30
Q

Normal value for adult GFR

A

180 L/day

aka

125 ml/min

31
Q

Renal Clearance definition

A

Volume of plasma completely cleared of that substance by the kidneys per unit time (ml/min)

32
Q

Use of clearance

A

Help quantify:
- Excretory function of kidney
- Rate of blood flow through kidneys
- Basic functions of the kidneys

Clearance of certain substances can be used to approximate GFR

33
Q

Clearance equation

A
34
Q

Substances used to measure GFR

A

Inulin

Creatinine

35
Q

Features of Inulin including molecular weight

A

Polysaccharide
Molecular weight 5200 Daltons

36
Q

Reasons Inulin is used to measure GFR

A

Freely filtered but not reabsorbed

Not toxic, metabolised or protein bound - therefore rate of excretion is equal to filtration rate

37
Q

Issues with using inulin

A

Not endogenous and needs IV administration

38
Q

Features of creatinine

A

By product of muscle metabolism - therefore endogenous
Almost entirely cleared by glomerular filtration

Therefore creatinine clearance can estimate GFR

39
Q

Issues with using creatinine

A

Small amount is secreted

Therefore amount of creatinine excreted slightly exceeds amount filtered

Therefore overestimates GFR

40
Q

Renal plasma flow estimation

A

If a substance is completely cleared from the plasma, clearance of that substance should equal renal plasma flow

GFR is only 20% of renal plasma flow

41
Q

Substance used to estimate renal plasma flow and why

A

Para-aminohippuric acid (PAH)

It is 90% cleared by kidneys from plasma

42
Q

Renal plasma flow estimate equation

A
43
Q

Renal blood flow equation

A

Renal Blood flow = Renal Plasma flow / (1 - Haematocrit)

Anaesthetic FRCA Primary - eLFH Physiology (13 decks)

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