Long Term Control of Blood Pressure Flashcards
What are the functions of the kidneys?
Excretion of waste, maintenance of ion balance, regulation of osmolarity and regulation of plasma volume
What can be controlled to regulate MAP?
Plasma volume
How is long term control of blood pressure mediated?
Kidneys
Not mediated by the arterial baroreflex
How does the kidneys create osmotic gradient?
Renal counter-current system creates a very high osmolarity outside collecting duct
Control over Na+ transport do determines osmotic gradient
Control over permeability to water determines if water follows osmotic gradient
How then control how much water in urine is lost or retained
What happens if the collecting duct is very permeable to water?
Lots of water reabsorption
Little urine and conserves plasma volume so increase MAP
What happens if the collecting duct is impermeable to water?
Little reabsorption so lots of urine = diuresis
Reduction in plasma volume which decreases MAP
What is the feedback system that senses disturbances in PV and MAP?
Renin-angiotensin-aldosterone system (RAAS)
Where is renin produced?
From the juxtaglomerular (=granule cells) of the kidney
What triggers the production of renin?
Activation of sympathetic nerves to juxtaglomerular apparatus
Decreased distension of afferent arterioles (renal baroreflex)
Decreased delivery of Na+/Cl- through the tubule
What causes sympathetic innervation signals being released?
Reduced MAP
BP is low
Describe high BP and filtration?
If high BP then more filtration so more Na+ and Cl- going out into proximal tubule so more Na+/Cl- delivered to Macula densa
Describe low BP and filtration?
Less filtration and less delivery of Na+/Cl- so signals reduction in MAP and triggers release of renin
What does renin do?
Converts inactive angiotensinogen to angiotensin I
Is then converted to angiotensin II by angiotensin converting enzyme
What does angiotensin II do?
Stimulates release of aldosterone from adrenal cortex
Increases release of ADH from the pituitary
Is a vasoconstrictor
Is a negative feedback system
How is RAAS a negative feedback system?
Multiple mechanisms detect any decrease in MAP, stimulates renin release and evokes multiple mechanisms which increase MAP
What does release of aldosterone from adrenal cortex cause?
Increases Na+ reabsorption in the loop of Henle
Reduces diuresis and increases plasma volume as bigger osmotic gradient
What does release of ADH from the pituitary cause?
Increases water permeability of collecting duct so less water excreted
Which reduces diuresis and increases plasma volume
Increases sense of thirst
Where is ADH produced?
Synthesised in the hypothalamus
Released from the posterior pituitary into bloodstream
What triggers ADH release?
A decrease in blood volume
An increase in osmolarity of ISF
Circulating angiotensin II
These show signs of low plasma volume and/or MAP
Where is a decrease in blood volume sensed?
By cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres
Where is an increase in osmolarity in ISF sensed?
By osmoreceptors in the hypothalamus
What does ADH do?
Increases the permeability of the collecting duct to H2O therefore reduces diuresis and increases plasma volume - more H2O reabsorbed and less excreted
Causes vasoconstriction causing increase MAP as increase in TPR
Explain how Antidiuretic hormone is a negative feedback system?
Multiple mechanisms detect any decrease in MAP, stimulates release of ADH and evokes multiple mechanisms which increase MAP
What is ANP and BNP?
Atrial natriuretic peptide and brain natriuretic peptide
Where are ANP and BNP produced?
ANP is produced and released from myocardial cell in the atria
BNP is produced and released from ventricles
What triggers a release of ANP and BNP?
Increased distension of the atria and ventricles - sign of increased MAP
What does ANP and BNP do?
Increase excretion of Na+ (natriuresis)
Inhibit release of renin
Act on medullary CV centres to reduce MAP
Aim is to decrease MAP
Explain ANP and BNP as a negative feedback system?
A mechanism detects any increase in MAP, stimulates release of ANP and BNP, and evokes multiple mechanisms which reduce MAP
What are some drugs used for treatment of hypertension?
Ca2+ channel antagonist
B-adrenoceptor antagonist
Thiazide diuretics
Angiotensin converting enzyme inhibitors
Angiotensin II antagonists
