Renin-angiotensin system Flashcards
What happens when blood pressure falls (immediate response)
Immediate activation of baroceptosr in major blood vessels and heart
What do baroceptors do
Increase sympathetic outflow from the CNS to produce immediate mechanisms to raise blood pressure
What is long term restoration of blood determined by
Kidney
What happens in the kidney
Lots of blood is filtered in the kidney and most is reabsorbed. We have mechanisms that control how much is reabsorbed
What does the juxtaglomerular apparatus do
Regulates salt and fluid balance
What do the cells in afferent arteriole do
Sample blood to kidney
What are the macula dense sensitive to
Alterations in salt concentrations
What do the granular cells do
cells in the kidney that synthesize, store, and secrete the enzyme renin
What happens when the volume of blood is low
Cells of juxtaglomerular apparatus sense volume and release renin
What are the stimuli for renin release
- Decreased renal perfusion pressure (detected by granular cells)
- Decrease NaCl concentration (detected at macula densa)
- INcreased sympathetic nerve activity (via action of beta1 adrenoceptors)
What happens in the angiotensin system
1) angiotensin made by liver
2) Renin (enzyme) breaks down angiotensin
3) Converted into angiotensin 1
4) angiotensin 1 converted to angiotensin 2 by angiotensin converting enzyme found in lungs
5) This causes the release of hormone andosterone
6) andosterone controls volume regulation
What does andosterone do
Increase retention of sodium and water
What are the actions of angiotensin 2
- VAsoconstrictor (increase peripheral resistance and hence blood pressure)
- Enhances sympathetic nerve function
- Increase release of aldosterone
- Release vasopressin (ADH)
Action of vasopressin
- vasoconstriction
- Increases fluid retention
Why does ADH increase fluid retention
Increases number of aquaporin-2 channelise the distal tubes/collecting duct of the kidney
Action of aldosterone
Increase expression of sodium channels
Activates the sodium potassium pump
Results in retention of sodium and water in body
What can be a stimulus for renin release
Decrease in cardiac output (heart failure)
Renal stenosis or aortic stenosis (narrowing of renal artery or aorta)
produces renin-induced hypertension
Hypotensive shock
What Is hypotension
Low blood pressure
Causes of hypotensive shock
BP= cardiac output total peripheral resistance
therefore low BP can be due to low CO and/or peripheral vasodilation
Examples of causes of low blood pressure
- Heaemorrhagic shock (blood loss, low CO)
- Cardiogenic shock
- Endotoxic shock
- Anaphylactic shock
How does cardiogenic shock cause a decrease in BP
Myocardial infarction causing loss in myocardial power
How does endotoxic shock cause a decrease in BP
Bacterial toxins cause marked peripheral vasodilation
How does anaphylactic shock cause a decrease in blood pressure
Histamine release caused vasodilation and increased capillary permeability
How to restore blood pressure after an increase in sympathetic activity
1) increase in heart rate
2) increase in stroke volume
3) therefore an increase In cardiac output
4) Blood pressure is restored
How else to restore blood pressure after an increase in sympathetic activity
1) vasoconstriction
2) increase in peripheral resistance
3) Blood pressure restored
How to restore a decrease in blood pressure because of a decrease in renal blood flow
1) decreased renal blood flow
2) Renin released so increase in angiotensin 2 and vasopressin
3) angiotensin increases salt and water retention which increases cardiac output which restores blood pressure
4) Both angiotensin 2 and vasopressin cause vasoconstriction which increases peripheral resistance and so blood pressure is restored
Why is the renin-angiotensin mechanism bad when there is heart failure
Heart failure causes a decrease in blood pressure so renin-angiotensin system increases pressure so the heart has to work harder to pump the blood as there is a higher pressure
therefore renin increases the speed of mortality when there is heart failure
