Long term control of Blood pressure Flashcards
How does the kidneys affect blood pressure?
Kidneys have main control over long term blood pressure.
They do this because they have large control over the plasma volume.
The way they control plasma volume is through the “counter current system”, osmolality increases significantly on the downward tube of the U and then decreases again on the way back up, the osmotic gradient is determined by the transport of Na+, and control over the permeability of the collecting duct to water determines if water follows that osmotic gradient or not (key in absorption/reabsorption). Hence you can control how much water is lost in the urine, and how much is retained.
What receptors are involved in sensing plasma volume?
Afferent arteriole entering kidney - Decreased distension signals reduced MAP
Macula densa cells - Reduced delivery of Na+/Cl+ signals reduced MAP
Sympathetic innervation signals reduced MAP
All signal to Juxtaglomerular (=granular) cells to RELEASE RENIN
What are the reflex pathways in controlling plasma volume?
Renin-angiotensin-aldosterone
Antidiuretic hormone
Atrial Natriuretic factor
Name the 3 stimuli for and explain the
Renin-angiotensin-aldosterone system
Afferent arteriole entering kidney - Decreased distension (stretch) signals reduced MAP
Macula densa cells (one if the tubules nearly leaving kidneys (after U) - Reduced delivery of Na+/Cl+ signals reduced MAP
Sympathetic innervation signals reduced MAP eg by baroreceptors in the aorta detecting low MAP
All signal to Juxtaglomerular (=granular) cells to RELEASE RENIN
What is the macular densa?
Sensory cells on one of the tubules of the kidney
What does angiotensin II do and how?
A lot to increase BP!
Think: Kidneys, Heart, vessels and pituitary!
STimulates adlosternone release from adrenal cortex in kidneys - increases Na+ resprtion in kidneys and therefore reduces diuresis and increases plasma volume
Increases Heart hypertrophy - increases Strength of contraction, increasing MAP
Is a Vasoconstrictor, increases TPR, increasing MAP
ADH release from pituritary, reduces diuresis by increasing water permiability in collecting duct in the kidney (more water into plasma), increasing MAP.
What is diuresis?
Urination of water (getting rid of water), filtration from the kidney
Where can ADH be found? What is it triggered by and what does it do?
Synthesised in the hypothalamus
Released from the posterior pituitary
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)
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
What is natriuresis?
Sodium excretion through the urine
Primary vs secondary hypertension?
Primary is mainly of unknown cause, secondary Only 5-10% is due to a known cause
Explain what Atrial Natriuretic factor is and what effects it has(where re ANP and BNP produced?) and what do they do?
Produced in, and released from myocardial cells in the atria & (despite the name), the ventricles respectively
Triggered by Increased distension of the atria & ventricles
Increase excretion of Na+ (natriuresis)
Inhibit the release of renin
Act on medullary CV centres to reduce MAP
Aim is to decrease BP and vol.
