* L11-Volume regulation Flashcards
What volume is measured and changed by the body’s volume regulation systems?
The effective circulating volume
What are the two main cell types in the juxtaglomerular apparatus?
granular cells in the afferent arteriole
macular densa cells in the thick ascending limb
What is a mechanism in the distal tubule for triggering the renin-angiotensin system?
Low Na+ in the distal tubule is characteristic of hypovolaemia and is detected by the macula densa cells of the TAL. This then signals to the granular cells of the afferent arterioles that stimulate renin production.
What is the effect of renin?
Renin causes conversion from angiotensinogen to angiotensin 1 which is then converted by ACE in the endothelial cells of the lungs to angiotensin II which causes vasoconstriction and increased na+ reabsorption in the proximal tubule. It also stimulates aldosterone production that causes increased sodium reabsorption in the distal tubule and collecting duct.
What are the two main physiological triggers for aldosterone release?
Angiotensin II and hyperkalcaemia
What are the 4 different locations that the RAAS can be inhibited to control blood pressure? Give examples of drug names
ACE inhibitors (captopril) Angiotensin 1 receptor antagonists (ATII acts on these receptors- candesartan) Aldosterone receptor antagonists (spironolactone) Renin inhibition (aliskiren)
Why are AT1 antagonists prescribed over ACE inhibitors despite being more expensive?
They don’t have the side effect of a dry cough that ace inhibitors have.
What are the 5 key actions of angiotenin II to increase circulating volume?
Vasoconstriction
Increase Na+ uptake from the proximal tubule hence causing water reabsorption
Increase aldosterone release from the adrenal cortex
Cause ADH release
Casuses thirst
Which cells sense a fall in blood pressure and cause increased renin release?
The Granular cells of a the juxtaglomerular apparatus in the afferent arteriole.
What are the three actions of sympathetic innervation to the afferent arteriole?
Vasoconstriction upstream of the granule cells, this further amplifies the fall in pressure sensed by the granular cells.
Increased stimulation of renin release by the granular cells.
Afferent arteriole vasoconstriction drops glomerular
hydrostatic pressure to the glomerulus and hence
lower s GFR
How does a fall in sodium to the distal tubule occur with low blood volume to cause an increase in renin release?
Decreased blood volume causes decreased pressure in the vasa recta. This increases the uptake of fluid from the tubules and hence causes a fall in sodium to the distal tubule.
Why does hyponatraemia acutely often follow haemorrhage?
The ADH acts to increase plasma volume by increasing water reabsoption however this will dilute the Na+ in the blood.
What is the role of atrial natriuretic peptide?
It is released from the heart in reponse to increased atrial filling from hypervolaemia. It is a powerful vasodilator and inhibits RAAS. It decreases water reabsorption at the kidneys by decreasing Na+ reabsorption.
What does dopamine do?
Increases Na+ excretion
What kind of molecule is ADH?
A polypeptide
