cardiovascular week 2 Flashcards
What is the function of the arterial system?
to distribute blood from the heart to the capillary beds throughout the body
What are the three types of arteries?
elastic
muscular
arterioles
Describe elastic arteries
major distributing vessels including the aorta, brachiocephalic trunk, common carotid and subclavian arteries and most of the large pulmonary arterial vessels
Describe muscular arteries
main distributing branches of the arterial tree - radial, femoral, coronary and cerebral arteries
Descrive arterioles
the terminal branches of the arterial tree which supply the capillary beds
Describe the general trends in the structure of arteries
there is a gradual transition in structure and function between the three types of arterial vessel rather than an abrupt demarcation.
In general, the amount of plastic tissue decreases as the vessels become smaller and the smooth muscle component assumes relatively greater prominence
What is blood pressure?
the force exerted by the blood against any unit area of the vessel wall
What does blood pressure depend on?
cardiac output X total peripheral resistance
Describe the roll of the autonomic nervous system of controlling BP
the sympathetic is most important in controlling circulation
the parasympathetic contributes importantly to regulation of heart function
What does innervation of the small arteries and arterioles allow?
sympathetic stimulation to increase resistance to blood flow to the tissues
What does the innervation of the large vessels (particularly veins) allow?
sympathetic stimulation decreases the volume of the vessels. This can push more blood to the heart
what action does the sympathetic NS have on the heart?
increased heart rate and contractility
What action does the parasympathetic NS have on the heart?
decreased heart rate and contractility
Where is the vasomotor centre located?
bilaterally mainly in the reticular substance of the medulla and the lower third of the pons
Where are parasympathetic impulses carried?
Through the vagus nerve
Where are sympathetic impulses carried?
through the spinal cord and peripheral sympathetic nerves to virtually all arteries, arterioles and veins of the body
What is sympathetic vasoconstrictor tone?
continuous partial constriction of the blood vessels
What role does the hypothalamus have on regulating BP?
it can exert powerful excitrory or inhibitory effects on the vasomotor centre
Simulation of the motor cortex, for example, excites the vasomotor centre
What effect does sympathetic stimulation have on the adrenal medullae?
causes the medullae to secrete both adrenaline and noradrenaline into the circulating blood.
What are the actions of adrenaline and noradrenaline?
they act directly on all blood vessels, usually to cause vasoconstriction.
In a few types of tissue adrenaline causes vasodilation because it also has a beta adrenergic receptor stimulatory effect, which dilates rather than constricts certain vessels
How is blood pressure raised rapidly?
most arterioles of the systemic circulation are constricted, which greatly increases the TPR
The veins are especially strongly constricted to displace blood back to the heart, thus increasing the volume of blood in the heart chambers. the stretch of the heart then causes the heart to pump with increasing force and increases arterial pressure.
Strong sympathetic stimulation also increases heart rate and contractility of the heart, thereby increasing cardiac output and therefore increasing BP.
Where are the main baroreceptors located?
the carotid sinus and the aortic arch
What are some vasoconstrictor agents involved in the humoral control of BP?
noradrenaline
adrenaline
angiotensin II
ADH
Describe angiotensin II
powerful vasoconstrictor substance
powerfully constricts small arterioles and therefore increases TPR
Also decreases sodium and water excretion by the kidneys, thereby increasing arterial pressure
Where is ADH formed?
nerve cells in the hypothalamus and is transported down by nerve axons to the pituitary gland and from there is secreted into the blood
What are the major functions of ADH?
powerful vasoconstrictor
greatly increases water resorption from the renal tubules
What are some of the results of high blood pressure?
premature vascular disease leading to cerebrovascular events, iscahemic heart disease and peripheral vascular disease
How many people are affected by high BP?
20-30% of the population
What are some of the causes of hypertension?
genetic factors - runs in families fetal factors - low birth weight environmental factors - obesity alcohol intake sodium intake stress - relationship with chronic stress uncertain
What happens to resistance vessels as result of hypertension?
structural changes
increased wall thickness
reduction in lumen diameter
What happens to the large vessels as a result of hypertension?
thickening of the media
increases in collagen and deposition of calcium
loss of arterial compliance
What effects does hypertension have on the heart?
increased peripheral resistance leads to increased ventricular load which may lead to left ventricular hypertrophy
What are the main ways that medications can lower blood pressure?
block effects of the sympathetic nervous system - reduces effect on heart B1, reduce effects on blood vessels a1 receptors, reduce renin release from kindney b1 blockers.
Kidney - reduce blood volume - diuretics
hormones - inhibit renin-angiotensin- aldosterone system (ACE inhibitors and angiotensin receptor blockers)
vasodilation of peripheral resistance arterioles (ca2+ channel blockers)
Give examples of beta blockers
propranolol (1 and 2)
atenolol (1 selective)
Describe the action of beta blockers
competitive reversible antagonists
lower BP by blockade of B1 sympathetic tone of heart and reduction of renin release from kidney
lowers heart rate and force of contraction
decreases CO
What are the adverse effects of beta blockers?
exacerbate asthma
intolerance to exercise
hypoglycaemia
vivid dreams
Give examples of alpha blockers?
phentolamine (1 and 2)
doxazosin, prozosin (1 selective)
Describe the action of alpha blockers
competitive reversible antagonists
lower BP via decrease in sympathetic tone in arterioles, decreases TPR
What are the adverse effects of alpha blockers?
postural hypotension
reflex tachycardia
increased closure of internal sphincter of the bladder
Give examples of ACE inhibitors
captopril
enelapril
Describe the mechanism of ACE inhibitors
lowers BP by reduced formation of angiotensin II, loss of stimulated release of aldosterone, reduction in renal resorption of sodium and water
What are the adverse effects of ACE inhibitors?
sudden hypotension on first dose
persistant irritant cough due to break down of bradykinin (a peptide that activates sensory neurons on the lungs)
Give examples of angiotensin II receptor blockers
losartan and candesartan
Describe the action of angiotensin II receptor blockers
mediates vasoconstriction and aldosterone releasing actions of angiotensin II
What is the advantage of angiotensin II receptor blockers?
No irritant cough as seen in ACE inhibitors
Give an example of a diuretic
bendroflumethiazide
Describe the action of diuretics
lower BP by reducing blood volume
mechanism through reduced renal resorption of sodium and water
additional vasodilator action may contribute
What are the adverse effects of diuretics?
decrease in plasma K+ concentration - can cause arrhythmia
reactions with other drugs
Give example of calcium channel blockers
verapamil (primary effect on cardiac muscle)
diltazem and nifedipine (primary effect on vascular smooth muscle)
Describe the action of calcium channel blockers
reduce Ca2+ into vascular smooth muscle by blocking L-type voltage operated calcium channels
either by open channel block, allosteric modulation (nifedipine)
reduces BP by reducing peripheral resistance / decreasing CO
What are the adverse effects of calcium channel blockers?
headaches
constipation
cardiac dysrythmias
What are the NICE guidelines for hypertension treatment?
Under 55 - ACE inhibitor or angiotensin II receptor blocker
Over 55 or African / caribbean origin - Ca2+ blockers
Then add ACE inhibitor or angiotensin II blocker and Ca2+ blocker
Then add diuretic
Then add alpha or beta blocker
What happens when a person stands up in relation to their blood pressure?
arterial pressure in the head and upper part of the body falls markedly
this could lead to unconsciousness
However, the falling pressure is detected by the baroreceptors and initiates an immediate reflex, resulting in strong sympathetic discharge throughout the body which minimises the decrease of pressure in the head and upper body
