Long term control of blood pressure Flashcards
Which organ is responsible for long term control of blood pressure ?
Control of plasma volume by the kidneys
What are the functions of the kidney ?
Excretion of waste products Maintainace of ion balance Regulation of pH Regulation of osmolarity Regulation of plasma volume
What is the effect of 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 achieved ?
Control over Na+ transport determines how big that osmotic gradient is
Control over the permeability of the collecting duct to water determines if water follows that osmotic gradient or not
Hence you can control how much water is lost in the urine, and how much is retained
Where is sodium pumped ?
Pumped outside of the distal tube - concentration of the solute therefore decreases significantly before it reaches the collecting duct
What will effect how big the conc gradient is ?
Modulating Na+ transport
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 (factor) and brain natriuretic peptide (factor)
Where is 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
(all of these are signs of low MAP)
What does renin do ?
Converts inactive angiotensinogen to angiotensin I
Which in turn converted by angiotensin converting enzyme to angiotensin II
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How does angiotensin II stimulate release of aldosterone from the adrenal cortex ?
increases Na+ reabsorption in the loop of Henle
Therefore reduces diuresis and increases plasma volume
How does angiotensin II increase release of ADH from the pituitary ?
Increases water permeability of the collecting duct
Therefore reduces diuresis and increases plasma volume and increases sense of thirst
How does angiotensin II increase TPR ?
It is a vasoconstrictor
Where is ADH produced ?
Synthesised in hypothalamus
Released from posterior pituitary
