Cardiovascular System- Applied Flashcards
1)Relate the events of the cardiac cycle to the electrocardiodiagram (ECG)
2) define the heart rate, cardiac output, stroke volume, tachycardia, bradycardia and sinus rhythm
Heart rate- speed of the heart contractions, beats per minute (bpm)
Cardiac output- the amount of blood ejected from each ventricle every minute. Expressed in litres per minute and is calculated: SV X HR
Stroke volume (SV)- volume of blood pumped out of the ventricles with each heart beat (70ml)
Sinus tachycardia- a normal sinus rhythm above 100 bmp when the individual is at rest. It accompanies exercise and anxiety but is also seen in some disorders e.g. fever, hyperthyroidism and some cardiac conditions.
Sinus bradycardia- a normal sinus rhythm below 60bpm. This may occur during sleep and is common in athletes. It is abnormal when it follows myocardial infarction or accompanies raised intracranial pressure.
(A normal cardiac cycle gives rise to normal sinus rhythm, which has a rate of between 60-100 bmp)
Define the terms blood pressure and peripheral resistance
Blood pressure: is the force or pressure that the blood exerts on the walls of blood vessels. It maintains the essential flow of blood through the body organs and ensures adequate venous system.
The force of your blood pushing against the walls of your arteries is what is measured during BP.
BP= CO X TPR
Total peripheral resistance (TPR): amount of force exerted on the circulating blood by the vasculature of the body.
3 factors affect the TPR
1) autonomic activity- the sympathetic system (leads to vasoconstriction)
2) blood viscosity- increased thickness of blood leads to increased TPR
3) Medications- vasoconstrictor and vasodilator drugs
Explain how cardiac output and peripheral resistance generates blood pressure
-blood pressure is determined by cardiac output and peripheral resistance
-change in either of these tends to later systematic blood pressure, although the body’s compensatory mechanism usually adjust for any significant change
-blood pressure = CO X TPR
-an increase in CO raises both systolic and diastolic pressures. An increase in SV increases systolic pressure more than diastolic.
-TPR: if there is a high degree of systemic vasoconstriction, the resistance to blood blood and the blood pressure increases. Vasodilation, reduces TPR and blood pressure. Age related stiffening to the arterial walls increases TRP and blood pressure.
Outline the location and role of baroreceptors and the medullary cardiovascular centre in the control of blood pressure
The cardiovascular centre (CVC) is a collection of interconnected neurones responsible for control or cardiac output and blood pressure located in the medulla and pons within the brain stem.
The CVC receives, integrates and coordinates inputs from: baroreceptors, chemoreceptors and higher centres in the brain.
The CVC send sympathetic and parasympathetic nerve impulses to the heart and blood vessels. Activity in these nerves slows down or speeds up the heart rate and dilates or constricts blood vessels, essential for control of blood pressure.
Within the wall of the carotid sinuses are barorecptors, nerve endings sensitive to stretch.
They continuously feed info to the CVC regarding the degree of stretch in the arterial walls, which directly reflects the pressure in the vessel.
A rise in blood pressure in these arteries stretches the vessel wall and stimulates the baroreceptors, increasing their input to the CVC . The CVC responds by increasing parasympathetic nerve activity to the heart, slowing it down.
At the same time, the CVC inhibits sympathetic stimulation to the blood vessels, causing vasodilation.
The net result is a fall in systemic blood pressure to reverse the initial rise
Define the terms of hypertension, hypotension, normotension and postural hypotension
-hypertension means high blood pressure. Stage one is 140-159/90-99. Stage 2 is 160-179/100-119. Severe hypertension is >180/>120.
-hypotension means low blood pressure.
-normotension is blood pressure within the normal range (ideally 120/80 for an adult)
-postural hypotension is an abrupt fall in blood pressure on standing up suddenly from a sitting to lying position. It is most common in older people, whose barorecptor reflex does not respond quickly enough to maintain blood pressure during sudden changes of body position.
Outline the role of the renin-angiotensin-aldosterone system and atrial natriuretic peptide in controlling blood volume
Renin is produced in the nephrons within the kidneys and increases blood pressure by acting on angiotensinogen.
The release of renin is inhibited by atrial natriuretic peptide (ANP), which is released in response to increases in blood pressure.
Renin acts on angiotensinogen, which is made in the liver and converts into angiotensin. Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II. Angiotensin II raises blood pressure by constricting blood vessels. It also triggers the release of anti-diuretic hormone (ADH) from the hypothalamus, leading to water retention in the kidneys. It acts directly on the nephrons and decreases glomerular filtration rate.
