Long term control of blood pressure Flashcards
how is blood pressure controlled in the long term?
control of plasma volume by the kidney
what is not involved in the long term control of blood pressure?
arterial baroreflex
what 3 hormone systems are involved in the control of blood plasma
Renin-angiotensin-aldosterone system
Antidiuretic factor (ADH, vasopressin)
Atrial natriuretic peptide
what are some functions of the kidney? (5)
Excretion of waste products Maintenance of ion balance Regulation of pH Regulation of osmolarity Regulation of plasma volume
what happens if the collecting duct is very permeable to water?
results in lots of water reabsorption, little urine, and conserve plasma volume
what happens if the collecting duct is very impermeable to water?
little reabsorption, lots of urine (= diuresis), and a reduction in plasma volume
Describe how the kidney regulates plasma volume
the kidney is made up of 1000s of units called nephrons that filter waste and fluid out of the blood
Blood is filtered under pressure in the glomerulus out into Bowman’s capsule.
the waste, nutrients, H20 etc move through the proximal tubueles to the loop of Henle, the distal tubule and finally into the collecting duct that leads to the bladder for excretion
What does blood enter and leave the glomerulus through?
afferent and efferent arterioles
what happens with Na+ and H20 in the loop of Henle?
Na+ can move across through transporters on thick ascending tubule
this causes water to move across thin descending tubule due to decrease in H20 conc as Na+ displaces it (increase in osmolarity). H20 moves from high to low conc.
continuous shuttling of high conc filtrate in and low conc filtrate out until max conc of 1200 is reached
this is called the counter current system
what is the max concentration that can be reached in medulla
1200 mOsM
what does the counter current system do
it creates a very high osmolarity outside the collecting duct
what does the counter current system do
it creates a very high osmolarity outside the collecting duct (high Na+ and H20 conc)
define osmolarity
total number of particles in solution both penetrating and non-penetrating
what control can you have over the counter current system?
you can control Na+ transport which determines how big the osmotic gradient is
or control over the permeability of collecting duct to H2O which determines if H2O follows the osmotic gradient or not
a very permeable collecting duct results in small volume of…
hyper-osmotic urine (ie low H20 conc, high Na+ conc) ie small vol of very concentrated urine
a very impermeable collecting duct results in small volume of…
hypo-osmotic urine (ie high conc H20, low Na+ conc)
where is renin produced
from the juxtaglomerular (granule cells) of the kidney on the side of the afferent arteriole near bowman’s capsule
what triggers renin production
Activation of sympathetic nerves to the juxtaglomerular apparatus
Decreased distension (dilation) of afferent arterioles (the “renal baroreflex”)
Decreased delivery of Na+/Cl- through the tubule
the three triggers of renin production are signs of what?
low mean arterial pressure/low BP
what does angiotensin II do?
Stimulates release of aldosterone from the adrenal cortex
which increases Na+ reabsorption in the loop of Henle and therefore reduces diuresis (too much fluid in urine) and increases plasma volume
increases release of ADH from the pituitary - which increases water permeability of the collecting duct therefore reduces diuresis and increases plasma vol and increases sense of thirst
is a vasoconstrictor therefor increases TPR
define tubular reabsorption
process by which the nephron removes water and solutes from the tubular fluid (pre-urine) and returns them to the circulating blood
how is the Renin-angiotensin-aldosterone system a negative feedback system?
Multiple mechanism detect any decrease in MAP
Stimulates release of renin
This evokes multiple mechanisms which increase MAP
where is ADH antidiuretic hormone synthesised
in the hypothalmus
where is ADH antidiuretic hormone released from
posterior pituitary
what triggers ADH release?
A decrease in blood volume (as sensed by cardioplumonary 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 are signs of low plasma volume or MAP
what does ADH do?
Increases the permeability of the collecting duct to H2O, therefore reduces diuresis and increases plasma volume - increases MAP
Causes vasoconstriction (hence its alternative name, vasopressin), therefore increasing MAP
How is ADH release involved in a negative feedback system
Multiple mechanism detect any decrease in MAP
Stimulates release of ADH
This evokes multiple mechanisms which increase MAP
where is atrial natriuretic peptide produced?
produced in and released from myocardial cells in the atria
what triggers ANP release?
increased distension (dilation) of the atrium ie atrium expanding ie when MAP increases
what does ANP do?
Increases excretion of Na+ (natriuresis) - decrease in plasma volume
Inhibits the release of renin
Acts on medullary CV centres to reduce MAP
how is ANP involved in a negative feeback system
A mechanism that detects any increase in MAP
Stimulates release of ANP
This evokes multiple mechanisms which reduce MAP
what 2 hormone systems work to increase MAP
Antidiuretic hormone system
Renin-angiotensin-aldosterone system
which hormone system results in a reduced MAP
atrial natriuretic peptide hormone system
common drugs/treatment for hypertension
Ca2+ channel antagonists
beta adrenoceptor antagonists
Thiazide diuretics - increase water and salt in urine - increased calcium re-absorption into the blood - lower blood pressure though as lower plasma volume
Angiotensin converting enzyme inhibitors
