14. Long Term Control of BP Flashcards
Is long term control of BP mediated by arterial baroreflex?
No
What does long term control of BP revolve around primarily?
revolves around the control of plasma volume by the kidney
What 3 hormone systems are involved in long term control of BP?
- renin-angiotensin- aldosterone system
- antidiuretic factor (ADH, vasopressin)
- atrial natriuretic peptide
What organ is primarily involved in long term control of BP?
kidneys
What are main functions of the kidney? (5)
- excretion of waste products
- maintenance of ion balance
- regulation of pH
- regulation of osmolarity
- regulation of plasma
Control of what is used to regulate MAP?
control of PLASMA VOLUME
What arteriole carries blood to the Bowman’s capsule?
afferent arteriole
Where does pressure filtration occur in the nephron? (filtration of blood to lumen)
in the Bowman’s capsule (in the glomerulus) which is under pressure from the heart
Where does reabsorption and secretion occur in the nephron? (3)
- proximal tubule
- distal tubule
- collecting duct (eventually leading to bladder for excretion)
Where does reabsorption occur? (lumen to blood) in the nephron?
in the loop of Henle
What does the kidney do in terms of long term control of BP?
regulates plasma volume
What does the renal system create outside the collecting duct in terms of osmolarity?
creates high osmolarity outside the collecting duct
What determines how big the osmotic gradient is?
control over Na tranport
What determines if the water follows that osmotic gradient or not?
control over the permeability of the collecting duct to water
Therefore what can kidneys regulate in terms of water? (2)
- control how much water is lost (in urine)
2. control how much water is retained (reabsorbed)
As filtrate moves through nephron where does Na concentration increase?
outside the collecting duct (Na is pumped out when it reaches last tube) as filtrate is lower in conc as you move along nephron
How can a size of conc. gradient be modified?
by modifying permability of collective duct
What is the filtrate osmolarity at the start and end of nephron in mOsm?
start: 300mOsm
end: 50mOsm
By making the collecting duct very permeable to water, what effect will this have on:
- water reabsorption
- urine
- plasma volume
- lots of water reabsorption from body capillaries and other vessels back into blood
- little urine
- plasma volume conserved (remans high)
By making the collecting duct very impermeable to water, what effect will this have on:
- water reabsorption
- urine
- plasma volume
- little reabsorption into the surrounding vessels (more liquid retained)
- lots of urine (diuresis)
- plasma volume reduced
What effect will a very permeable collecting duct have on hyper-osmotic urine?
small volume of hyper-osmotic urine produced only (not much at all and not very watery)
What conc. of urine is found when collecting duct is very permeable?
High conc. of urine (because lots of water crossing over back into body which means less urine made)
What conc. of urine is found when collecting duct is impermeable?
Low conc. of urine (because less water crosses over and more is retained which means urine is more diluted)
What effect will a very impermeable collecting duct have on hypo-osmotic urine?
large volume of hypo-osmotic volume
Where is renin (hormone) produced?
fro the juxtaglomerular of the kidney (granule cells)
What triggers renin production? (3)
- activation of sympathetic nerves to the juxtaglomerular apparatus
- decreased distension (expanding) of afferent arterioles (the renal baroreflex) triggers renin production
- decreased delivery of Na/ CL through the tubule
What is the renin production a sign of?
all of these are signs of low MAP
Where are granule cells found in a nephron?
found on afferent arterioles
What 3 things triggers release of renin? (signals reduced MAP)
- Reduced delivery of Na/CL signals reduced MAP in macula densa just before Loop of Henle
- Decreased distension signals reduced MAP in afferent arteriole
- Sympathetic innervation signals reduced MAP
What does renin do?
- converts inactive angiotensinogen to angiotensin I
- this is in turn converted by angiotensin converting enzyme (ACE) to angiotensin II
(therefore it’s a precursor)
What is the main hormone which “does stuff” in the angiotensin pathway?
angiotensin II
What does angiotensin do?
- stimulates release of aldosterone from the adrenal cortex
- increases release of ADH from the pituitary
- is a vasoconstrictor
What does aldosterone do? (3)
- stimulates synthesis of more Na pumps, creating a bigger conc. gradient so more Na reabsorption in loop of Henle
- reduces diuresis
- increases plasma volume
What does ADH do?
- increases water permeability of the collecting duct
- MORE water reabsorbed
- less urine produced
- increased thirst
What effect does vasoconstriction have on TPR?
increases TPR
Is renin-angiotensin-aldosterone system a negative feedback system?
yes
What are the primary functions of negative feedback system? (3)
- multiple mechanism detects any decrease in MAP
- stimulates release of renin
- it evokes multiple mechanisms which increase MAP
Where is ADH produced?
- synthesised in the hypothalamus
Where is ADH released from?
released from posterior pituitary gland
What 3 things stimulate ADH release?
- decrease in blood volume (sensed by cardiopulmonary baroreceptors and relayed via medullary cardiovascular centres)
- increase in osmolarity of interstitial fluid (as sensed by osmoreceptors in the hypothalamus)
- circulating angiotensin II (triggered by renin-angiotensin- aldosterone system)
When is ADH released? (relating to plasma volume and/or MAP)
when signs of LOW plasma volume and LOW MAP
What is the link between osmolarity and plasma volume?
- high osmolarity means low plasma volume
- low osmolarity means high plasma volume
What does ADH do in order to specifically increase MAP?
- increases permeability of collecting duct to water (more reabsorption) which reduces diuresis and increases plasma volume
- causes vasoconstriction (hence name vasopressin) which increases MAP
What does diuresis mean?
Urination increase
Is the ADH system a negative feedback system?
Yes
What are the 3 main features of ADH hormone system?
- multiple mechanism detects any decrease in MAP
- stimulates release of ADH
- this evokes multiple mechanism which increases MAP
Where are ANP (atrial natriuretic peptide) and BNP (brain natriuretic peptide) produced and released?
produced and released from myocardial cells in the atria
What causes ANP and BNP release?
increased distension (expansion) of the atrium
What does a distension/ expansion of atrium indicate about the MAP?
it means it’s a sign of increased MAP
What do ANP and BNP do? (3)
Plans to DECREASE MAP by:
- increase excretion of Na (natriuresis)
- inhibits release of renin
- acts as medullary CV centres to reduce MAP
Is the ANP and BNP hormone system a negative feedback system?
yes
What are 3 primary features of ANP and BNP system?
- a mechanism that detects any increase in MAP
- stimulates release of ANP
- this evokes multiple mechanisms which reduce MAP
What is primary hypertension?
hypertension of unknown cause
What is secondary hypertension?
hypertension due to a known cause
What percentage of hypertension is classed as secondary?
only 5-10% (most are vastly due to unknown cause)
What are drugs for managing hypertension targeted at?
targeted at kidney function
What types of drugs are given for treatment of hypertension? (5)
- Ca channel antagonists
- b1 adrenoreceptor antagonists
- thiazide diuretics (stop Na transport)
- angiotensin converting enzyme inhibitors
- angiotensin II antagonist
What does long term control of MAP revolve around?
revolves around hormones acting on the kidney to control plasma volume
When is renin-angiotensin-aldosterone system stimulated and what does it do?
- stimulated when decrease in MAP
- it aims to increase MAP
When is ADH (vasopressin) system stimulated and what does it do?
- stimulated when decrease in MAP
- it aims to increase MAP
When is ANP and BNP system stimulated and what does it do?
- stimulated when increase in MAP
- it aims to decrease MAP
