Long Term Control of Blood Pressure Flashcards
Long term control of blood pressure revolves around what?
control of plasma volume by the kidneys
Outline the three hormone systems involved in blood pressure control.
- Renin-angiotensin-aldosterone system
- Antidiuretic factor (ADH, vasopressin)
- Atrial natriuretic peptide
What are the functions of the kidneys? (5)
- Excretion of waste products
- Maintenance of ion balance
- Regulation of pH
- Regulation of osmolarity
- Regulation of plasma volume
Controlling plasma volume is used to regulate ______.
MAP
What determines how big the osmotic gradient outside the collecting duct is?
Control over Na+ transport
Control over the _________ of the collecting duct to water determines if water follows that ________ ________ or not.
permeability
osmotic gradient
Making the collecting duct very permeable to water will result in…
(3)
- lots of water reabsorption
- little filtrate/urine
- conserve plasma volume
Making the collecting duct very impermeable to water will result in…
(3)
- little reabsorption
- lots of urine
- reduction in plasma volume
What is the clinical term for lots of urine output?
diuresis
If there is little urine output (diuresis), what will happen to the plasma volume, and why?
it will increase, due to increased water.
How permeable will the collecting duct be if there is a hypo-osmotic urine output?
very impermeable
large volume (low conc.)
How permeable will the collecting duct be if there is a hyper-osmotic urine output?
What volume of urine will be produced?
very permeable
small volume (high conc.)
If there is watery urine, there will be ________ plasma volume?
reduced
The kidney/hormonal regulation systems are all what type of mechanisms?
negative feedback
Renin-angiotensin-aldosterone system
Where is renin produced?
From the juxtaglomerular (= granule cells) of the kidney
Renin-angiotensin-aldosterone system
What triggers renin production?
(3)
- Activation of sympathetic nerves
- Decreased distension of afferent arterioles (the “renal baroreflex”)
- Decreased delivery of Na+/Cl- through the tubule (low BP = less filtrate being produced)
In the ‘Renin-angiotensin-aldosterone system’, how are all the mechanisms signalling renin production activated?
low MAP (BP)
Which part of the nephron detects the decreased Na+ and Cl- ion concentration which causes the release of renin?
macula densa
What does renin do?
2
- Converts inactive angiotensinogen to angiotensin I
- angiotensin I is converted by an enzyme to angiotensin II
What is the name of the enzyme which converts angiotensin I to angiotensin II?
angiotensin converting enzyme (ACE)
Briefly, what does angiotensin II do?
3
- Stimulates the release of aldosterone from the adrenal cortex
- increases the release of ADH from the pituitary
- acts as a vasoconstrictor
Describe what the hormone, aldesterone, does?
4
- Increases Na+ reabsorption in the loop of Henle
- reduces diuresis (urine output)
- Increases plasma volume
- Increases MAP
What is ADH? (1)
What does an increase in ADH from the pituitary gland do? (5)
Antidiuretic hormone
- Increases permeability of the collecting duct
- reduces diuresis
- increases plasma volume
- increased MAP
- It also increases the sense of thirst.
How does renin being a vasoconstrictor affect MAP? (1)
- increases TPR
- increasing MAP
(MAP = CO x TPR)
Where is ADH synthesised and released from?
2
- synthesised in the hypothalamus
- released from the posterior pituitary gland
Outline what triggers the release of ADH.
3
- low plasma volume
- circulating angiotensin II
- increase in interstitial fluid osmolarity
Where is a low plasma volume detected in order for ADH to be released?
(2)
- cardio-pulmonary baroreceptors
- relayed via the medullary cardiovascular centres
Where is an increase in interstitial fluid osmolality detected in order for ADH to be released?
(2)
- osmoreceptors
- in the hypothalamus
What is common about all the triggers which release ADH?
Therefore, what outcome should we anticipate from the release of ADH?
They are all a result of low plasma volume/MAP
An increase in MAP
Why is ADH also called vasopressin?
It is a vasoconstrictor
What does ADH do?
- Increases permeability of collecting duct
- reduces diuresis
- increases plasma volume
- vasoconstriction
- increases MAP
What is ANP?
Where is it produced?
Atrial natriuretic peptide
myocardial cells in the atria
Where is brain natriuretic peptide (BNP) released from?
The myocardial cells of the ventricles
What triggers the release of ANP and BNP?
ANP - increased distension in the atria.
BNP - increased distension in the ventricles.
i.e. increased plasma volume, increased MAP.
What is the clinical term for the increased secretion of Na+ in the urine?
natriuresis
What do ANP do?
3
- Increases excretion of Na+ (natriuresis)
- Inhibits the release of renin (opposite)
- Acts on medullary CV centres to reduce MAP
How is the release of ANP different to the release of ADH and renin? (2)
How are they the same? (1)
ANP - for MAP reduction
renin/ADH - for MAP increase
They are all negative feedback systems.
What is the difference between primary and secondary hypertension?
primary - idiopathic
secondary - known cause
What are some classes of anti-hypertensive drugs? (4)
- Ca2+ channel blockers
- B1 antagonists (beta blockers)
- thiazide diuretics
- angiotensin converting enzyme inhibitors
Briefly outline how Ca2+ channel blockers work in treating hypertension?
(3)
- target Ca channels in heart and in some smooth muscle,
- reduces SV/CO
- reduces BP
Briefly outline how thiazide diuretics work in treating hypertension?
(4)
- Na+ transporters
- reduces size of Na+ gradient in kidneys
- reduces PV
- reduces BP
