S4) Blood Pressure and The Kidney Flashcards
What is the formula for calculating blood pressure?
mean arterial BP = CO x TPR
What is the formula for calculating cardiac output?
CO = SV x HR
Explain the 2 actions which allow for the short term regulation of blood pressure
Baro-receptor reflex:
- Adjust sympathetic and parasympathetic inputs to the heart to alter CO
- Adjust sympathetic input to blood vessels to alter TPR
Describe the long term regulation of blood pressure
Neurohormonal response to affect salt and water balance
Identify 4 processes which act on the kidney to regulate blood pressure
- Renin-angiotensin-aldosterone system
- Sympathetic nervous system
- Prostaglandins
- ADH
Describe the events which occur in RAAS
Identify 3 factors which stimulate renin release from the JGA cells in the kidney
- Reduced NaCl delivery to macula densa in distal tubule
- Reduced perfusion pressure in the kidney (detected by baroreceptors in afferent arteriole)
- Sympathetic stimulation to JGA increases release of renin
What are the direct effects of Angiotensin II on the kidney?
- Vasoconstriction of efferent arteriole (AA > EA)
- Enhances Na+ reabsorption at the PCT (stimulates Na-H exchanger in apical membrane)
Angiotensin II stimulates aldosterone release from the adrenal cortex.
Identify 2 of its actions on the kidney
Acts on principal cells of collecting duct:
- Stimulate Na+ and water reabsorption by increasing expression of the apical Na+ channel (ENaC)
- Increases basolateral Na+ extrusion via Na/K/ATPase
How does the sympathetic nervous system act on the kidney?
- Reduce renal blood flow (vasoconstriction of renal artery)
- Stimulates Na+ reabsorption (NHE3 & Na/K ATPase) in PCT
- Stimulates renin release from JGA
In normal situations, prostaglandins have little effect.
Regardless, how does it act in RAAS?
- Vasodilates the afferent arteriole
- Enhances renin release
What stimulates the release of prostaglandins?
Release stimulated by vasoconstrictors:
- Angiotensin II
- Noradrenaline
- ADH
Prostaglandins and RAAS interact to stimulate each other.
What is the net effect of both of these substances?
- Systemic vasoconstriction
- Vasoconstriction of the efferent arteriole
- Vasodilation of afferent arteriole
- Preservation of GFR
What is the main role of ADH?
- Increases water reabsorption in distal nephron (AQP2) in order to control plasma osmolarity through water retention
- Concentrated urine formed
What stimulates the release of ADH?
- Plasma osmolarity
- Severe hypovolaemia
ADH is also called arginine vasopressin.
Why is this?
ADH also causes vasoconstriction
Atrial Natriuretic Peptide acts in the opposite direction of other neurohormonal regulators.
What are its 2 main actions?
- Causes vasodilation of afferent arteriole, increasing GFR
- Inhibits Na+ reabsorption especially in collecting duct, causing natriuresis
What stimulates the release of ANP and what inhibits its release?
- Low circulating blood volume = inhibits ANP release
- High circulating blood volume = stimulates ANP release
In terms of evolution, why is hypertension an anticipated problem?
- Mechanisms which increase/maintain BP are stronger than the mechanisms which reduce BP when it is too high
- Hence, volume depletion (dehydration or blood loss or sepsis) is more of a risk than hypertension
What is hypertension?
Hypertension is a persistent increase in blood pressure
Identify 2 pathological processes involving RAAS
- Secondary hypertension
- Secondary hyperaldosteronism (oedema)
Identify 4 clinical conditions resulting in secondary hypertension
- Renovascular hypertension
- Coarctation of the aorta
- Primary hyperaldosteronism (Conn’s syndrome)
- Cushing’s syndrome
Describe the pathophysiology of renovascular disease
- Renal artery stenosis
- 1/both kidneys affected
- Due to atheroma (75%) or fibromuscular dysplasia (25%)
Identify 5 endocrine causes of hypertension
- Primary hyperaldosteronism (Conn’s syndrome)
- Cushing’s syndrome
- Liquorice
- Phaeochromocytoma
- Hyperthyroidism / Hypothyroidism
What is apparent mineralocorticoid excess syndrome?
AME is a condition resulting in an excess amount of aldosterone and cortisol in the distal nephron of the kidney due to excessive liquorice ingestion
What is oedema?
Oedema is the accumulation of excessive salt/water in the interstitium
Identify 5 causes of generalised oedema
- Heart failure
- Chronic kidney disease
- Nephrotic disease
- Liver disease
- Pregnancy
What is Chronic Kidney Disease?
- CKD is a condition leading to the inability to excrete excess salt and water due to reduced kidney function (↓ GFR)
- It results in hypertension and oedema
Which 2 underlying processes lead to Nephrotic syndrome?
- Reduced oncotic pressure causing reduced perfusion pressure and activation of RAAS / SNS / ADH
- Alterations in sodium and water excretion due to reduced kidney function (hypertension & reduced GFR)
Identify 3 symptoms of Nephrotic Syndrome
- Proteinuria > 350 mg/mmol (>3.5 g / 24 hr)
- Hypoalbuminaemia
- Oedema
