Session 5-Control Of Blood Pressure Flashcards
What is the equation for cardiac output?
CO=SV x HR
Cardiac output=stroke volume x heart rate
What is the mechanism for short term regulation of blood pressure?
Baroreceptor reflex
Which nerve endings are sensitive to stretch?
Those in the carotid sinus and aortic arch
True or false: decreased arterial pressure stretches baroreceptors
FALSE - increased pressure stretches
True or false: baroreceptor reflex works well to control acute changes in BP (up to 15 minutes)
TRUE
Why does the baroreceptor reflex not control sustained changes in BP?
The threshold for baroreceptor firing resets
What are medium and longer term controls of BP directed at?
Controlling sodium balance and thus extracellular fluid volume
What controls plasma volume?
Control of extracellular fluid volume - water follows sodium therefore controlling total body sodium levels controls plasma volume
What are the four neurohumoral pathways controlling circulating volume and therefore BP?
1) Renin-angiotensin-aldosterone system (RAAS)
2) Sympathetic nervous system
3) Antidiuretic hormone (ADH)
4) Atrial natriuretic peptide (ANP)
Which cells release renin?
Granular cells of juxtaglomerular apparatus (JGA)
Which factors stimulate renin release? (3)
1) reduced NaCl delivery to distal tubule
2) reduced perfusion pressure in kidney causes release of renin
3) sympathetic stimulation to JGA increases release of renin
Which reaction does renin catalyse?
Angiotensinogen -> angiotensin
Which enzyme catalyses the conversion of angiotensin I to angiotensin II?
Angiotensin converting enzyme (ACE)
How does angiotensin II affect the body? (3)
1) vasoconstriction
2) stimulates Na+ reabsorption at kidney
3) stimulates aldosterone from adrenal cortex which then stimulates no. 2)
What are two types of angiotensin II receptors?
Angiotensin 1 (AT1) Angiotensin 2 (AT2)
True or false: the main actions are via AT1 receptor which is a GPCR
TRUE
What action do the angiotensin II receptors have at the following sites:
1) sympathetic nervous system
2) hypothalamus
1) vasoconstriction
2) increases thirst sensation (stimulates ADH release-antidiuretic)
What are the actions of aldosterone? (4)
1) acts one principal cells of collecting ducts
2) stimulates Na+ and therefore water reabsorption
3) activates apical Na+ channel and apical K+ channel
4) increases basolateral Na+ extrusion via Na/K ATPase
What is the apical Na+ channel called?
ENaC (Epithelial Na Channel)
True or false: bradykinin, found in the lung, has vasoconstrictor actions
FALSE - vasodilator
What does angiotensin converting enzyme break bradykinin into?
Peptide fragments
What effect does the breakdown of bradykinin have?
Vasoconstriction effects of angiotensin II are augmented because ACE breaks bradykinin down (has vasodilator effects)
What is a side effect of ACE inhibitors?
Dry cough
Complete the sentence:
High levels of sympathetic stimulation ___________ renal blood flow as there is ___________________ of arterioles. It also ________ glomerular filtration rate (GFR).
Reduces
Vasoconstriction
Decreases
What does stimulation of the sympathetic nervous system release and what does this lead to?
Renin from juxtaglomerular cells
Increased angiotensin II levels and therefore increased aldosterone levels
What is the main role of antidiuretic hormone? (ADH)
Formation of concentrated urine by retaining water to control plasma osmolarity
What stimulates the release of antidiuretic hormone (ADH)? (2)
1) Increases in plasma osmolarity
2) Severe hypovolaemia
True or false: ADH also stimulates Na+ reabsorption
TRUE
What does atrial natriuretic peptide (ANP) promote?
Na+ excretion
Complete the sentences:
Atrial natriuretic peptide (ANP) is synthesised and stored in _________ _____________ and are released in response to ________. Reduced circulating blood volume ___________ the release of ANP as there is less _________.
Atrial myocytes
Stretch
Inhibits
Stretch
What are the actions of atrial natriuretic peptide (ANP)? (4)
1) vasodilation of afferent arteriole
2) increases blood flow (increases glomerular filtration rate)
3) inhibits Na+ reabsorption along nephron
4) causes natriuresis (loss of sodium in urine)
What do prostaglandins act as?
Vasodilators
True or false: prostaglandins act as a buffer to excessive vasoconstriction produced by parasympathetic nervous system and RAAS
FALSE - sympathetic nervous system, not parasympathetic
What does dopamine cause? (3)
1) Vasodilation
2) Increases renal blood flow
3) Reduces reabsorption of NaCl
What is hypertension?
Sustained increase in blood pressure
What BP measured in a clinic is classified as stage 1 mild hypertension?
> /= 140/90 mmHg
What BP measured in a clinic is classified as stage 2 moderate hypertension?
> /= 160/100 mmHg
What BP measured in a clinic is classified as severe hypertension?
> /= 180/110 mmHg
What is the difference between primary and secondary hypertension?
Where the cause of hypertension can be defined, it is referred to as secondary hypertension. Where the cause is unknown, it is referred to as primary hypertension
What are some causes of hypertension?
Renovascular disease
Chronic renal disease
Hyperaldosteronism
Cushing’s syndrome
How can renovascular disease cause secondary hypertension?
Occlusion of renal artery (renal artery stenosis) abuses fall in perfusion pressure in kidney -> increased renin production -> activation of RAAS -> vasoconstriction and Na+ retention at other kidney
What can happen in later stages of renal parenchymal disease?
Na+ and water retention due to inadequate glomerular filtration
How can Cushing’s syndrome lead to hypertension?
Excess secretion of glucocorticoid cortisol - at high concentration acts on aldosterone receptors -> Na+ and water retention
How can phaeochromocytoma lead to hypertension?
Tumour of adrenal medulla -> secretes catacholamines (noradrenaline, dopamine and adrenaline)
What can hypertension lead to?
Heart failure
MI
Stroke
Renal failure
How can hypertension lead to heart failure?
Increases afterload -> LV hypertrophy
How can hypertension lead to myocardial ischaemia and MI?
Increased afterload -> increased myocardial oxygen demand
OR
Arterial damage -> atherosclerosis
How can hypertension lead to cerebro-vascular disease/stroke, aneurysm, renal failure and retinopathy?
Arterial damage -> atherosclerosis and weakened vessels
How is secondary hypertension treated?
Treat primary cause
What are the non-pharmacological approaches to treating hypertension?
Exercise
Diet
Reduced Na+ intake
Reduced alcohol intake
How can the RAAS be targeted to treat hypertension?
1) ACE inhibitors
2) Angiotensin II receptor antagonists -> vasodilator and diuretic effects
True or false: L-type Ca channel blockers can be used to treat hypertension
TRUE - reduce Ca2+ entry to vascular smooth muscle cells so they relax
How can beta blockers be used to treat hypertension?
Block beta1 receptors in the heart, reducing effects of sympathetic output and reduce heart rate and contractility
