Long term control of blood pressure Flashcards
What mediates long term control?
Probably not mediated by the arterial baroreflex
It is a kidney thing
What are the functions of the kidneys?
Excretion of waste products
Maintenance of ion balance
Regulation of pH
Regulation of osmolarity
Regulation of plasma volume
How does plasma affect MAP?
more plasma- higher MAP
less plasma- lower MAP
How does kidney’s counter current system work?
Counter-current system- builds up a big sodium gradient in the extracellular fluid in the loop of henle.
When water comes into collecting duct, by controlling the permeability , can allow water to follow that osmotic gradient or not.
Controls how much water is lost in urine and how much is retained.
How do kidneys counter current system work in more detail?
modulating Na+ transport will affect how big the osmotic gradient is in the first place and how big it is.
can make the collecting duct very permeable to water and will result in lots of water moving out of collecting duct , small volume of concentrated urine , plasma vol will increase and MAP will increase.
What does Renin-angiotensin-aldosterone system detect?
feedback system that senses disturbances in plasma volume and mean arterial pressure. It produces hormones to produce an appropriate response.
Where is renin produced?
From the juxtaglomerular (= granule cells) of the kidney
What triggers renin production?
Activation of sympathetic nerves to the juxtaglomerular apparatus
Decreased distension of afferent arterioles (the “renal baroreflex”)
Decreased delivery of Na+/Cl- through the tubule- if blood pressure is higher there will be more filtration and more sodium and chloride going out into the proximal tube- more delivered to macula densa.
-all signs of of low MAP
What does renin do?
Converts inactive angiotensinogen to angiotensin I
Which is in turn converted by angiotensin converting enzyme to angiotensin II
What does angiotensin II do?
Stimulates release of aldosterone from the adrenal cortex (steroid hormone):
Increases Na+ reabsorption in the loop of Henle
Therefore reduces diuresis and increases plasma volume
Increases release of ADH from the pituitary:
Increases water permeability of the collecting duct
Therefore reduces diuresis and increases plasma volume
And increases sense of thirst
Is a vasoconstrictor
Therefore increases TPR
i.e. this is a negative feedback system
Multiple mechanisms detect any decrease in MAP
Stimulates release of renin
This evokes multiple mechanisms which increase MAP
Where is Antidiuretic hormone produced?
Synthesised in the hypothalamus
Released from the posterior pituitary into bloodstream
What triggers ADH release?
A decrease in blood volume (as sensed by cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres)
An increase in osmolarity of interstitial fluid (as sensed by osmoreceptors in the hypothalamus)
Circulating angiotensin II (triggered by the renin-angiotensin-aldosterone system)
- all these are signs of low plasma volume and /or MAP
What does ADH do?
Increases the permeability of the collecting duct to H2O, therefore reduces diuresis and increases plasma volume
Causes vasoconstriction (hence its alternative name vasopressin), therefore increasing MAP
-both of these tend to increase MAP
Where are ANP (Atrial natrieutic peptide) and BNP (brain) produced?
Produced in and released from myocardial cells in the atria and (despite the name), the ventricles respectively (where BNP produced)
What triggers ANP and BNP release?
Increased distension of the atria and ventricles
-sign of increase MAP
What do ANP and BNP do?
Increase excretion of Na+ (natriuresis)- urine produced will have larger vol of less concentrated urine. Decrease plasma vol and MAP
Inhibit the release of renin- increases MAP
Act on medullary CV centres to reduce MAP
What classes of drugs do we use for management of hypertension?
Ca2+ channel antagonists
β-adrenoceptor antagonists
Thiazide diuretics
Angiotensin converting enzyme inhibitors
Angiotensin II antagonists
