Control of blood pressure Flashcards
How is pressure calculated?
Pressure = flow x resistance
How is blood pressure calculated?
maBP = CO x TPR
What are the two timeframes that blood pressure is regulated during?
Short-term
Long-term
What is the short-term regulation of blood pressure?
Baroreceptor reflex
What are baroreceptors sensitive to?
Are sensitive to stretch
Where are baroreceptors located?
Aortic arch
Carotic sinus
How do baroreceptors detect an increase in pressure?
Arterial walls are stretched
Stretches nerve endings of baroreceptors
What do baroreceptors do once stretched?
Increase frequency of action potentials fired
Which nerve carries action potentials from baroreceptors in aortic arch?
Vagus nerve - cranial nerve 10
Which nerve carries action potentials from baroreceptors in carotid sinus?
Glossopharyngeal nerve - cranial nerve 9
Where are action potentials from the baroreceptors carried to?
Medulla oblongata
How does the medulla oblongata relate to the cardiovascular system?
Is the cardiovascular control centre
How does the medulla oblongata respond to the increased frequency of action potentials via afferent nerves?
Decrease in sympathetic output
Parasympathetic output is increased
What is the result of decreased sympathetic output and increased parasympathetic output? What is the overall result?
Reduced CO - reduced heart rate, force of contraction, SV
Reduced TPR - vasodilation
Reduced maBP - reduced CO, TPR
How do baroreceptors detect a decrease in blood pressure?
Less stretching of arterial walls
Less stretching of baroreceptor nerve endings
What do baroreceptors do when they’re no lonnger being stretched?
Decrease frequency of action potentials to medulla oblongata via
vagus nerve - aortic arch
glossopharyngeal nerve - carotid sinus
How does the medulla oblongata respond to the decreased frequency in action potentials via afferent nerves?
Increases sympathetic output
Decreases parasympathetic output
What is the result of an increased sympathetic output and a decreased parasympathetic output? What is the overall result?
Increased CO - increased heart rate, force of contraction, SV
Increased TPR - vasoconstriction
Increased maBP - increased CO, TPR
What type of feedback does the baroreceptor reflex involve? Explain how
Negative feedback loop
change in blood pressure results in blood pressure being restored back to normal
Why are baroreceptor reflexes not involved in the long-term control of blood pressure?
Threshold for baroreceptor firing action potential is reset
to the new blood pressure
What type of pathways are involved in the medium-long term control of blood pressure?
Neurohumeral pathways - ANS and circulating factors
What are the four neurohumeral pathways involved in medium-long term control of blood pressure?
Renin-angiotensin aldosterone system (RAAS)
Sympathetic nervous system (SNS)
Anti-diuretic hormone (ADH)
Atrial natriuretic peptides (ANP)
What do all the four neurohumeral pathways involved in medium-long term control of blood pressure have in common?
All affect sodium retention
How does controlling sodium retention affect blood pressure?
Sodium retention affects water reabsorption
Extracellular fluid volume
Plasma volume
Blood volume
Affects filling of ventricle in diastole, EDV, SV, CO
And finally blood pressure
What are the factors that cause the release of the renin?
Reduced perfusion pressure in kidneys
Sympathetic stimulation of JGA
Reduced NaCl deliverty to distal tubule, macula densa
How do the kidneys detect reduced perfusion pressure?
Have baroreceptors
in afferent arterioles
Where is renin released from in the kidneys?
Granular cells of afferent arteriole
of juxtaglomerular apparatus (JGA)
What is the function of renin?
To cleave angiotensinogen to angiotensin 1
Where is angiotensinogen released from?
Liver
What does ACE stand for?
Angiotensin converting enzyme
Where is ACE released from?
Epithelial cells in lungs
What is the role of ACE?
Convert angiotensin 1
into angiotensin 2
Break down bradykinin protein
into peptide fragments
What does angiotensin 2 bind to?
Angiotensin 2 receptors - AT
What are the types of angiotensin 2 receptors?
Type 1 - AT1
Type 2 - AT2
What type of angiotensin 2 receptor does angiotensin 2 mostly bind to?
AT1
What type of receptor is AT1?
GPCR
Where are AT1 receptors located
Arterioles
Kidneys
Adrenal cortex
Sympathetic NS
Hypothalamus
What effect does angiotensin 2 binding to AT2 in the arterioles cause? How does this affect blood pressure?
Causes vasoconstriction
Increase in TPR, maBP
What effect does angiotensin 2 binding to AT2 receptors in the kidneys cause? How does this affect blood pressure?
Stimulates sodium reabsoprtion
Water follows
Increased BV, filling of ventricles, EDV, SV, CO, maBP
What effect does angiotensin 2 binding to AT2 receptors in the adrenal cortex cause?
Stimulates release of aldosterone
What effect does angiotensin 2 binding to AT2 receptors in the sympathetic NS cause?
Increased release of NA
What effect does angiotensin 2 binding to AT2 receptors in the hypothalamus cause?
Stimulates release of ADH
Which cells does aldosterone affect?
Principal cells of collecting ducts
in kidneys
What does aldosterone do?
Increases activity of Na+ K+ ATPase on basolateral domain
Activates ENaC on apical domain
What are the effects of aldosterone?
Increased Na+ efflux from cell into blood by Na+ K+ ATPase
Sets up Na+ conc. gradient
Na+ reabsorbed into cell through ENaC
What effect does bradykinin have?
Vasodilation
What is the purpose of ACE breaking down bradykinin?
Reduced vasodilation
Increase in TPR, maBP
How does sympathetic activity affect renal blood flow?
Reduce renal blood flow
by vasoconstriction of arterioles
How does reduced renal blood flow affect sodium retention?
Decreases GFR
Decreases Na+ excretion
How does sympathetic activity affect ion transporters in cells?
Increases activity of Na+ K+ ATPase on basolateral domain
Activates Na+ H+ exchanger on apical domain
How does sympathetic activity affect sodium retention?
Increased Na+ efflux from cell into blood by Na+ K+ ATPase
Creates Na+ conc. gradient
Na+ is reabsorbed into cell by Na+ H+ exchanger
Where in the kidney does the sympathetic nervous sytem affect ion transporter activity?
Proximal convoluted tubule
How does sympathetic activity affect renin?
Stimulates renin release from granular cells of afferent arteriole in juxtaglomerular apparatus
What is another name for ADH?
Arginine vasopressin
What causes the release of ADH?
Increase in plasma osmolarity
Severe hypovolaemia
What are the functions of ADH?
Increase sodium retention
Increase water reabsorption
Cause vasoconstriction
How does ADH increase sodium retention?
Stimulates Na+ K+ Cl- transporter
Na+ reabsorbed into cell
How does ADH increase water reabsorption?
Through increasing Na+ retention
Also by increasing aquaporin2
water reabsorbed through it
Where does ADH stimulate the Na+ K+ Cl- transporter?
Thick ascending limb
Where does ADH increase aquaporin2?
Distal nephron
How are atrial myocytes related to ANP?
Atrial myocytes synthesise, store and release ANP
What causes the release of ANP?
Stretch of atria
due to increased blood volume
What is the effect of ANP?
Natriuresis - loss of sodium in urine
How does ANP affect sodium retention?
Vasodilation of afferent arteriole
Increased GFR
Increased excretion of Na+
Inhibits Na+ reabsorption along nephron
What type of receptors are located in the atria?
Volume receptors
are low-pressure baroreceptors
How do atrial volume receptors detetch volume of blood?
Increased volume of blood causes stretching of atria
Stretching of baroreceptor nerve endings
Is ANP released when blood volume is low?
No
Reduced filling of heart
Less stretching of atria
Less ANP released
What is an effect of prostaglandins?
Vasodilation
How do prostaglandins affect sodium retention?
Local prostaglandins in kidney
cause vasodilation of afferent arteriole
increase GFR
increased Na+ excretion
How do prostaglandins have a protective function?
Buffer excessive vasoconstriction caused by RAAS, SNS
preventing damage to blood vessels
How is dopamine formed in the kidneys?
From circulating L-DOPA
Where are dopamine receptors present in the kidneys?
Renal blood vessels
Proximal convoluted tubule cells
Thick ascending limb cells
What are the effects of dopamine binding to its receptor?
Vasodilation
Reduced retention of sodium, water
How does dopamine decrease sodium retention?
Inhibits Na+ H+ exchanger
Inhibits Na+ K+ ATPase
Which cells does dopamine affect?
Principal cells in proximal convoluted tubule
And thick ascending limb