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Kidneys and Renal functions > Blood Pressure & the Kidneys > Flashcards

Blood Pressure & the Kidneys Flashcards

1
Q

What is the relationship between salt intake and BP?

A

Higher Na intake excretion → Higher blood pressure

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2
Q

What is the major electrolyte of ECFV?

A

Na is the major electrolyte of the extracellular fluid volume (ECFV)

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3
Q

What fluid makes up the ECFV?

A

Interstitial fluid, plasma fluid, cerebrospinal fluid

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4
Q

Why does the ICFV have lower Na?

A

Intracellular volume has little Na – due to Na/K ATPase

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5
Q

How does a change in Na balance cause a change in ECFV?

A
  1. Change in Na balance
  2. Change in osmolarity
  3. ADH release
  4. Water moves through ADH stimulated aquaporin
    channels in CD
  5. Change in ECFV (and Blood volume)
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6
Q

How do we calculates BP?

A

BP = CO x TPR

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7
Q

What determines the cardiac output?

A

SV is a major determinant of CO (CO = HR x SV)

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8
Q

What is the effect of increased blood volume?

A

↑ Blood volume leads to ventricular filling and ↑ SV (Starling’s law)

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9
Q

What is the long term control of BP?

A

Regulating Na levels via the kidneys regulates blood volume – long-term control of blood pressure

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10
Q

What is the short term BP control?

A

Via baroreceptors (min to min)

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11
Q

What is the aim of CVS [Na] control?

A

Try to control Na output

- aim to conserve Na as we are a low Na diet species

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12
Q

Explain the control of [Na] via CVS

A
  1. Change in Na intake
  2. Change in ECFV
  3. Afferent pathways:
    • Cardiac volume receptors
    • Baroreceptors
    • Renal artery pressure
  4. Stimulates efferent pathways:
    • Neuronal: sym, nervous system
    • Hormonal: RAAS, ANP
    • Haemodynamic: Pressure natriuresis, GFR control
  5. Change in renal Na output
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13
Q

What is the significance of renin in RAAS?

A

Renin secretion is central to control [Na]

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14
Q

What are the major factors stimulating the release of renin?

A

↓ BP and ↓ BV - ↓ renal blood flow - afferent arteriole mechanoreceptors

↓ Na levels at macula densa

Sympathetic nerve activation of β1 adrenoreceptors

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15
Q

What causes the stimulation of Renin release in RAAS?

A

Due to changes in baroreceptors activity, and cardiac volume receptors

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16
Q

What is the macula densa?

A

Region of contact between afferent arteriole and distal tubule of same nephron

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17
Q

What are Renin secreting JGA cells?

A

Modified smooth muscle cells along the afferent arteriole

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18
Q

What is aldosterone?

A

steroid hormone synthesised in Zona glomerulosa of adrenal gland – released by action of Angiotensin II

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19
Q

Where does aldosterone produce its effects?

A

Aldosterone acts at steroid receptors inside cells

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20
Q

What are the effects of aldosterone?

A

increased expression of ENaC and Na/K pump
↑ Na reabsorption at distal tubular sites
Results in ↑ renal K excretion

21
Q

What is the consequence of too much aldosterone?

A

Excess aldosterone leads to hypokalaemia

22
Q

Which cardiac natriuretic peptides control? Na excretion

A

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)

23
Q

Where are cardiac natriuretic peptides found?

A

In specialised cardiac myocytes

24
Q

What causes the release of cardiac natriuretic peptides?

A

Released by ↑ cardiac filling pressures (↑ECFV)

25
Q

What are the renal effects of ANP?

A

Natriuresis (↑ Na excretion)

Diuresis (↑ H2O excretion)

26
Q

What effect does ANP have on the vasculature of the body?

A

Vasodilatation by stimulation of PKG in VSMCs - ↓ Systemic BP
(Drugs on VSM lecture)

27
Q

What hormonal effects does ANP produce?

A

↓ Renin secretion

↓ Aldosterone secretion

28
Q

Explain the relationship of the ANP and RAAS systems

A

ANP opposes RAAS system

29
Q

What effect does the renal artery pressure have on Na excretion?

A

Renal arterial pressure causes an increase in renal Na+ excretion

30
Q

Why does the renal arterial pressure not alter GFR?

A

Renal-arterial Autoregulation prevents GFR increasing due to renal arterial pressure

31
Q

What are the effects of increased capillary pressure in the medulla?

A

Increases fluid filtration and interstitial pressure

Prevent tubular reabsorption

32
Q

At what BP do we see hypertension?

A

Hypertension present when:

Systolic > 140 mmHg and/ or Diastolic > 90 mmHg

33
Q

How is hypertension classified?

A

Secondary (Identifiable cause ~ 5 - 10 % of cases )

Essential (Unknown cause, > 90 % of cases)

34
Q

What are some secondary causes of hypertension?

A

excess renal Na reabsorption and abnormalities in hormone secretion

35
Q

Name some clinical disorders causing hypertension

A

Liddle’s syndrome
Conn’s syndrome
Renal artery stenosis

36
Q

What may be a potential cause of essential hypertension?

A

Essential hypertension may involve abnormal handing of Na+ balance

37
Q

What is Liddle’s syndrome?

A

A rare genetic form of high BP associated in epithelial Na+ sodium channel (ENaC)

38
Q

What does Liddle’s syndrome cause?

A

Increase ENaC activity
Increase renal Na retention
Suppresses renin/aldosterone: ↑ECVF + ↑BP

39
Q

What is Conn’s Syndrome?

A

Overproduction of aldosterone by adrenal gland tumour (Adenoma) causing:
↑ ECFV
↓ Plasma potassium
↓ Plasma renin activity

40
Q

Explain the effects of Conn’s syndrome

A

Renal sodium reabsorption - ↑ ENaC
↑ ENaC / ↑ Na/K ATPase / ↑ K excretion
ECFV expansion - ↓ renin secretion

41
Q

Explain why Conn’s syndrome is a form of primary aldosteronism

A

Conn’s syndrome = Primary aldosteronism

High blood pressure due to low renin levels – High aldosterone

42
Q

What is the effect of insufficient aldosterone?

A

Addison’s disease, insufficient release of aldosterone, chronic Na loss, large ↓ ECFV, severe hypotension, leading to collapse and death
(in contrast to Conn’s)

43
Q

What is renal artery stenosis?

A

Abnormal narrowing of the renal artery

44
Q

How does renal artery stenosis affect Na retention?

A
  1. ↓Renal A pressure due to ↓ BF caused by the stenosis
  2. Causes renin secretion
  3. Forms angiotensin II
  4. ↑Aldosterone,
    ↑Vasoconstriction
  5. Na retention and ↑BP
45
Q

What are the causes of essential hypertension?

A

Causes unknown

But Genetic predisposition and environmental factors lead to intermediate phenotypes that lead to increased BP

46
Q

what environmental factors can cause essential hypertension?

A 
Life style (e.g. physical activity)
Diet (e.g. salt intake, alcohol, diabetes)
47
Q

What is the role of anti-hypertensive treatments?

A

Agents that decrease RAAS
e.g.
ACE inhibitors
Ang II receptor blockers

48
Q

What renal diseases cause an increase in BP?

A

Liddle’s syndrome
Conn’s syndrome
Renal stenosis

49
Q

Which renal disorders cause a drop in BP?

A

Addison’s disease

Cushing’s diseases

Kidneys and Renal functions (14 decks)

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