Blood Pressure & the Kidneys Flashcards
What is the relationship between salt intake and BP?
Higher Na intake excretion → Higher blood pressure
What is the major electrolyte of ECFV?
Na is the major electrolyte of the extracellular fluid volume (ECFV)
What fluid makes up the ECFV?
Interstitial fluid, plasma fluid, cerebrospinal fluid
Why does the ICFV have lower Na?
Intracellular volume has little Na – due to Na/K ATPase
How does a change in Na balance cause a change in ECFV?
- Change in Na balance
- Change in osmolarity
- ADH release
- Water moves through ADH stimulated aquaporin
channels in CD - Change in ECFV (and Blood volume)
How do we calculates BP?
BP = CO x TPR
What determines the cardiac output?
SV is a major determinant of CO (CO = HR x SV)
What is the effect of increased blood volume?
↑ Blood volume leads to ventricular filling and ↑ SV (Starling’s law)
What is the long term control of BP?
Regulating Na levels via the kidneys regulates blood volume – long-term control of blood pressure
What is the short term BP control?
Via baroreceptors (min to min)
What is the aim of CVS [Na] control?
Try to control Na output
- aim to conserve Na as we are a low Na diet species
Explain the control of [Na] via CVS
- Change in Na intake
- Change in ECFV
- Afferent pathways:
- Cardiac volume receptors
- Baroreceptors
- Renal artery pressure
- Stimulates efferent pathways:
- Neuronal: sym, nervous system
- Hormonal: RAAS, ANP
- Haemodynamic: Pressure natriuresis, GFR control
- Change in renal Na output
What is the significance of renin in RAAS?
Renin secretion is central to control [Na]
What are the major factors stimulating the release of renin?
↓ BP and ↓ BV - ↓ renal blood flow - afferent arteriole mechanoreceptors
↓ Na levels at macula densa
Sympathetic nerve activation of β1 adrenoreceptors
What causes the stimulation of Renin release in RAAS?
Due to changes in baroreceptors activity, and cardiac volume receptors
What is the macula densa?
Region of contact between afferent arteriole and distal tubule of same nephron
What are Renin secreting JGA cells?
Modified smooth muscle cells along the afferent arteriole
What is aldosterone?
steroid hormone synthesised in Zona glomerulosa of adrenal gland – released by action of Angiotensin II
Where does aldosterone produce its effects?
Aldosterone acts at steroid receptors inside cells
What are the effects of aldosterone?
increased expression of ENaC and Na/K pump
↑ Na reabsorption at distal tubular sites
Results in ↑ renal K excretion
What is the consequence of too much aldosterone?
Excess aldosterone leads to hypokalaemia
Which cardiac natriuretic peptides control? Na excretion
Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)
Where are cardiac natriuretic peptides found?
In specialised cardiac myocytes
What causes the release of cardiac natriuretic peptides?
Released by ↑ cardiac filling pressures (↑ECFV)
What are the renal effects of ANP?
Natriuresis (↑ Na excretion)
Diuresis (↑ H2O excretion)
What effect does ANP have on the vasculature of the body?
Vasodilatation by stimulation of PKG in VSMCs - ↓ Systemic BP
(Drugs on VSM lecture)
What hormonal effects does ANP produce?
↓ Renin secretion
↓ Aldosterone secretion
Explain the relationship of the ANP and RAAS systems
ANP opposes RAAS system
What effect does the renal artery pressure have on Na excretion?
Renal arterial pressure causes an increase in renal Na+ excretion
Why does the renal arterial pressure not alter GFR?
Renal-arterial Autoregulation prevents GFR increasing due to renal arterial pressure
What are the effects of increased capillary pressure in the medulla?
Increases fluid filtration and interstitial pressure
Prevent tubular reabsorption
At what BP do we see hypertension?
Hypertension present when:
Systolic > 140 mmHg and/ or Diastolic > 90 mmHg
How is hypertension classified?
Secondary (Identifiable cause ~ 5 - 10 % of cases )
Essential (Unknown cause, > 90 % of cases)
What are some secondary causes of hypertension?
excess renal Na reabsorption and abnormalities in hormone secretion
Name some clinical disorders causing hypertension
Liddle’s syndrome
Conn’s syndrome
Renal artery stenosis
What may be a potential cause of essential hypertension?
Essential hypertension may involve abnormal handing of Na+ balance
What is Liddle’s syndrome?
A rare genetic form of high BP associated in epithelial Na+ sodium channel (ENaC)
What does Liddle’s syndrome cause?
Increase ENaC activity
Increase renal Na retention
Suppresses renin/aldosterone: ↑ECVF + ↑BP
What is Conn’s Syndrome?
Overproduction of aldosterone by adrenal gland tumour (Adenoma) causing:
↑ ECFV
↓ Plasma potassium
↓ Plasma renin activity
Explain the effects of Conn’s syndrome
Renal sodium reabsorption - ↑ ENaC
↑ ENaC / ↑ Na/K ATPase / ↑ K excretion
ECFV expansion - ↓ renin secretion
Explain why Conn’s syndrome is a form of primary aldosteronism
Conn’s syndrome = Primary aldosteronism
High blood pressure due to low renin levels – High aldosterone
What is the effect of insufficient aldosterone?
Addison’s disease, insufficient release of aldosterone, chronic Na loss, large ↓ ECFV, severe hypotension, leading to collapse and death
(in contrast to Conn’s)
What is renal artery stenosis?
Abnormal narrowing of the renal artery
How does renal artery stenosis affect Na retention?
- ↓Renal A pressure due to ↓ BF caused by the stenosis
- Causes renin secretion
- Forms angiotensin II
- ↑Aldosterone,
↑Vasoconstriction - Na retention and ↑BP
What are the causes of essential hypertension?
Causes unknown
But Genetic predisposition and environmental factors lead to intermediate phenotypes that lead to increased BP
what environmental factors can cause essential hypertension?
Life style (e.g. physical activity) Diet (e.g. salt intake, alcohol, diabetes)
What is the role of anti-hypertensive treatments?
Agents that decrease RAAS
e.g.
ACE inhibitors
Ang II receptor blockers
What renal diseases cause an increase in BP?
Liddle’s syndrome
Conn’s syndrome
Renal stenosis
Which renal disorders cause a drop in BP?
Addison’s disease
Cushing’s diseases
