Long Term Control of Blood Pressure Flashcards
Which organ is responsible for long term control of blood pressure?
•Revolves around the control of plasma volume by the kidney
What are the functions of the kidney?
–Excretion of waste products
–Maintenance of ion balance
–Regulation of pH
–Regulation of osmolarity
–Regulation of plasma volume
What are the following areas labelled on this nephron?
What is the effect f the renal counter current system?
Creates a very high osmolarity outside the collecting duct
How is control over how much water is lost with urine acheived?
Osmotic gradient exists between the collecting duct and outside the collecting duct.
Na+ transport determines this gradient
•Control over the permeability of the collecting duct to water determines if water follows that osmotic gradient or not
Where is sodium pumped?
Pumped outside of the distal tube - concentration of the solute therefore decreases significantly before it reaches the collecting duct
What is the affect of varying the permeability of the collecting duct?
- Making the collecting duct very permeable to water will result in lots of water reabsorption, little urine, and conserve plasma volume
- Making the collecting duct very impermeable to water will result in little reabsorption, lots of urine (= diuresis), and a reduction in plasma volume
What are the three main hormones that regulate water reabsorption?
Renin - angiotensin - aldosterone system
Antidiuretic factor (ADH, vasopressin)
Atrial natriuretic peptide
Where is the 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
What is responsible for detecting a reduced delivery of sodium and chlorine ions?
Macula densa
Where do you find the macula densa?
The ascending loop of henle
(distal convulated tubule)
Where is renin produced?
In the juxtaglomerular of the kidneys - granule cells
What triggers renin production?
Signs of low mean arterial pressure:
- Activation of sympathetic nerves to the juxtaglomerular apparatus
- Decreased distension of afferent arterioles (renal baroreflex)
- Decreased delivery of sodium and chlorine through the tubule
What does renin do?
Converts angiotensinogen to angiotensin 1
Angiotensin converting enzyme
Angiotensin 2
How does angiotensin increase MAP?
Stimulates release of aldosterone from the adrenal cortex.
(this increases the amount of sodium reabsorption in the loop of henle - less diuresis and increased plasma volume)
Increases the release of ADH from the pituitary
(increases the permeability of the collecting duct, reduces diuresis. Increases sense of thirst)
Is a vasoconstrictor
(increases total peripheral resistance)
How is the formation of angiotensin 2 a form of negative feedback?
- Multiple mechanism detect any decrease in MAP
- Stimulates release of renin
- This evokes multiple mechanisms which increase MAP
Where is ADH produced?
–Synthesised in the hypothalamus
–Released from the posterior pituitary
What triggers ADH release?
A decrease in blood volume - (Baroreceptors from CVS relayed by medullary cardiovascular centres)
An increase in osmolarity in interstitial fluid (osmoreceptors in the hypothalamus)
Circulating angiotensin 2 (triggered by the renin-angiotensin-aldosterone system)
What is the effect of ADH?
Increases the permability of the collecting duct to H2O
Causes vasoconstriction (hence why it is sometimes known as vasopressin)
Why is the release of ADH classed as a negative feedback mechanism?
–Multiple mechanism detect any decrease in MAP
–Stimulates release of ADH
–This evokes multiple mechanisms which increase MAP
What does ANP stand for?
Atrial natriuretic peptide
Where is atrial natriuretic peptide formed?
Produced in and released from the myocardial cells in the atria
What triggers release of ANP?
Increased distension of the atrium ( a sign of increased MAP)
What does ANP do?
Increases the excretion of sodium (natriuresis) - (opposes the act of angiotensin 2 which causes lots of sodium to be reabsorbed by the loop of henle)
Inhibits the release of renin
Acts on the medullary CV centres to reduce MAP
Why is the release of ANP described as a negative feedback mechanism?
–A mechanism that detects any increase in MAP
–Stimulates release of ANP
–This evokes multiple mechanisms which reduce MAP
What percentage of hypertension cases are as a result of secondary (knoown) causes?
Only 5% to 10%
What are the rational drug treatments for hypertension?
–Ca2+ channel antagonists
–b-adrenoceptor antagonists – specifically beta 1 receptor antagonist – reduces cardiac output and blood pressure
–Thiazide diuretics – work in sodium transporter in kidney – stops build up of sodium gradient – makes you excrete more water
–Angiotensin converting enzyme inhibitors
–Angiotensin 2 antagonist
