6. Cardiovascular System Flashcards
What is the purpose of the cardiovascular system?
Transport system for materials on which the cells of the body depend upon (CO2, O2, Hormones and Heat). This allows the maintenance of homeostasis and survival.
Name the 4 main components of blood.
Plasma, Erythrocytes (RBCs), Leukocytes (WBCs) and Platelets
Name the 5 types of blood vessel.
Arteries, Arterioles, Capillaries, Venules and Veins.
What vessel goes the the right side of the heart to the lungs?
Pulmonary Artery
What is the role of the aorta?
Transport blood from heart to organ systems.
What brings blood back to the heart from the organ systems?
Vena Cava
Which side of the heart has a thicker ventricular wall?
Left side
Where does the superior vena cava come from?
Head to Heart
Name the two valves of the heart
Semilunar and Atrioventricular
Name the 4 components of the conduction system involved in the origin of the heart rate.
Sinoatrial Node (SAN), Atrioventricular Node (AVN), Bundle of His and Pukinje Fibres.
What is the threshold potential of the SAN?
-40mV
What causes the initial slow depolarisation to threshold?
Na+ entry through a voltage gated sodium channel only found in cardiac pacemaker cells. If (funny) channels open when membrane hyperpolarised. Net inward movement of Na+ current so membrane potential moves towards threshold. K+ flow out of cell slows to prevent further reduce in potential
What happens when If (funny) channels close?
Transient Ca2+ channels open before membrane reaches threshold. Brief influx of Ca2+ further depolarises membrane bringing it to threshold. Then the T type Ca2+ channels close
Describe the rising phase after the potential reaches threshold in SAN AP
L type Caa2+ channels open resulting in a large influx of Ca2+
Describe the falling phase after the potential reaches 0mV.
L-type Ca2+ channels close, voltage gated K+ channels open, causing efflux of K+ which reduces the charge back to -60mV
How long is the AVN delay?
0.1s to allow enough time for ventricles to fill before contraction.
What is the role of SAN?
Triggers heart beat
What is the frequency of AP generation in SAN?
70/min
What happens when SAN becomes dysfunctional?
AVN determines heart rate (50/min)
What happens if Purkinje Fibres determine heart rate?
30/min ventricular rate, very sedentary existence (comatosed) - need a artificial pacemaker.
Does cardiac action potentials differ from SAN action potentials?
Yes
Describe the rising phase of cardiac muscle AP.
Activation of voltage-gated Na+ channels causes fast movement of Na+ in raising the potential from -90 to 30mV.
What is threshold potential of cardiac AP?
-70mV
What does the opening of T type K+ channels cause?
Fast limited efflux to give a brief small reploarisation.
How is the plateau phase formed?
Activation of slow L-type Ca2+ channels allows slow influx of Ca2+ preventing further decrease in potential
Describe the rapid falling phase of a cardiac AP.
Voltage gated K+ channels open to restore -70mV. They close and then leaky K+ channels open to get to -90mV
What initiates Ca2+ release from the sacroplasmic reticulum in cardiac muscle?
L-type Ca2+ channels in the T tubules open to allow small amount of Ca2+ to enter and stimulate release from sacroplasmic reticulum
What does a long refractory period prevent?
Tetanus of cardiac muscle. Protective. Allows filling and emptying for normal function
How long is the plateau phase of cardiac muscle?
250ms
How long is the contraction phase of cardiac muscle?
300ms
Name the two parts of the cardiac cycle.
Diastole and Systole
Describe phase 1 of the cardiac cycle.
Diastole: Blood flows through atria to ventricles (AV are open) Pressure in veins sufficient to drive blood into heart. Semilunar valves are closes. Ventricular pressure is lower than the aorta and pulmonary arteries. End phase 1 is when atria contract which drives blood into ventricles.
Describe phase 2 of the cardiac cycle.
Systole: Ventricles contract, ventricles pressure exceeds atrial pressure causing AV valves to close. Semilunar valves are closed as ventricular pressure not high enough to force it open. No blood flowing into or out of ventricle which keeps volume constant. By the end of this phase ventricular pressure is great enough to force open the semilunar valves.
Describe phase 3 of the cardiac cycle.
Systole: Blood is ejected into aorta and pulmonary arteries through semilunar valves and ventricular volume falls. Ventricular pressure rises then declines to below aortic pressure in which semilunar valves close ending ejection.
Describe phase 4 of the cardiac cycle.
Ventricular myocardium relaxes. All valves close so volume of ventricles remains constant. Ventricular pressure low so atrioventricular valves open and blood enters returning the cycle to phase 1.
How long does diastole and systole occur?
Diastole = 0.5s Systole = 0.3s
What is the average heart beat rate?
72/min
Does blood enter aorta during diastole?
No
Define Pulse Pressure
Difference between systolic pressure and diastolic pressure in aorta.
Define Mean Arterial Pressure
Average pressure occurring in the aorta during one cardiac cycle.
How would you work out the mean arterial pressure (MAP)?
MAP = Diastolic Pressure + 1/3(Systolic Pressure - Diastolic Pressure)
How would you calculate blood pressure (BP)?
Systolic Pressure/Diastolic Pressure.
What does end diastolic volume (EDV) represent?
Volume of blood in the ventricle at end of diastole which is the maximum ventricular volume attained during the cardiac cycle, which is reached just before the start of ejection.
What does end systolic volume (ESV) represent?
Volume of blood in the ventricle at the end of systole which is the minimum ventricular volume, which is attained just after ejection
Define Stroke Volume (SV)
Volume of blood in ventricles just before ejection minus the volume of blood just after ejection (SV = EDV-ESV)
Define Ejection Fraction (EF)
Ration volume ejected in one beat to volume contained in ventricle immediately prior to ejection (EF = SV/EDV) Tells us if the heart is pumping efficiently
When is the lub sound produced?
Phase 2 (AV close)
When is the dup sound produced?
Phase 4 (SL close)
Which heart sound is louder sharper and higher pitched?
Dup
What causes the heart sounds?
Turbulent blood flow as valve narrow not by the valves snapping shut.
What is the function of an electrocardiogram (ECG)
Non invasic way of monitoring electrical activity of the heart. They record overall spread of electrical current through the heart as a function of time during the cardiac cycle. They can discover abnormal electrical activity
On the ECG, what does the P wave represent?
Atrial Contraction
On the ECG, what does the QRS complex represent?
Ventricular Contraction
Which part of an ECG represents ventricular repolarisation?
T wave
Which part of an ECG represents AV nodal delay?
PR Segment
On an ECG, what does the ST segment represent?
Ventricle completely depolarised, ventricular activation is complete and are contracting and emptying
On an ECG, what does the TP segment represent?
Heart muscle completely repolarised, at rest and ventricles filling
How can you determine the heart rate from an ECG?
Determine the HR by dividing 60 seconds by the R-R interval (time between two heart beats)
Define Cardiac Output.
Volume of Blood pumped out bby each ventricle per minute
Does the volume of blood flowing in the pulmonary circulation equal the volume of blood flowing systemic circulation?
Yes - means that the cardiac outputs of each ventricles are normally the same.
What are the two determinants of the cardiac output?
Heart rate and stroke volume.
CO = HR x SV
Define stroke volume
Volume of blood pumped per beat
What determines the heart rate?
Autonomic influences on SAN.
What nerves are involved in parasympathetic and sympathetic pathways in the heart?
Parasympathetic: Vagus nerve to atria, SAN and AVN
Sympathetic: Cardiac sympathetic nerve to atria, SAN, AVN and ventricles.
Does sympathetic stimulation increase or decrease the heart rate?
Increase
Name two hormones that increase HR
Adrenaline and Noradrenaline
At rest does sympathetic or parasympathetic stimulation dominate?
Parasympathetic
What determines stroke volume?
Extent of venous return (intrinsic control) and by sympathetic activity (extrinsic control) .
What effect does increased end-diastolic volume have on stroke volume?
Increases stroke volume. As more blood returns to the heart, the heart pumps out more blood.
What does the optimal length of cardiac muscle fibre result in?
Maximum Stroke Volume.
What does noradrenaline and adrenaline trigger?
Increased release of Ca2+ for increased stroke volume.
What are the two variables on a Frank-Starling Curve?
Stroke Volume (Y) and End-dastolic volume (X)
What effect does heart failure have on the contractility of the heart?
Decreases it
What does the kidney do to expand blood volume (and hence EDV) during heart failure?
Conserves salt/water
What receptors detect extreme in arterial blood pressure?
Arterial Baroreceptors
What is the function of negative feedbacks?
Allows extremes in a factor to be returned to its normal level to maintain an optimum environment in the body.
Describe the structure and location of Baroreceptors.
They are sensory non encapsulated nerve endings located in adventitial layer arteries in the aortic arch and carotid sinus.
What do the mechanoreceptors respond to in arteries?
Stretch of artery wall not pressure.
What is the response to increased ABP?
Causes individual baroreceptor fibre to fire bursts of action potentials
What is the response to decreased ABP?
Causes individual baroreceptors to fall silent and then renew activity at a slower rate.
What decreases during a haemorrhage?
Stroke Volume, Cardiac Output and Mean Arterial Pressure
What would happen if a baroreflex was to increase the ABP to the initial value after a haemorrhage?
Baroreceptors reflex would shut off once reached so ABP would fall again so keeping a slighly lower ABP keeps reflex activated and compensates for blood loss.
Describe the structure of an artery.
Large Diameter, Thick highly elastic walls to withstand high pressure. High amount of smooth muscle and collagen fibres.
Describe the function of an artery
Serve as a rapid-transmit passageway to organs and as a pressure reservoir.
What is the role of the elastic tissue in arteries?
During systole when a greater volume of blood flows into arteries from the heart, the elastic tissues expand to hold this excess volume which stores the pressure energy in the walls. When in diastole, the stretched walls passively recoil exerting pressure on the blood in order to push it into downstream vessels ensuring flow.
What is the function of arterioles?
Primary resistance to blood due to small diameter and determines distribution of cardiac output. Causes marked drop in mean arterial pressure across the vessels and maintains flow to end organs. Converts pulsatile systolic-to-diastolic pressure swings into nonfluctuating pressure in capillaries.
Describe the structure of the arterioles?
Highly muscular (thick layer of smooth muscle), well innervated walls with small diameter. Little elastic fibres.
What is vasoconstruction and vasodilation?
Smooth muscle contraction and relaxation respectively.
What is the function of capillaries?
Exchange materials between blood and tissue cells, branch extensively to bring blood within the reach of essentially every cell.
Describe the structure of capillaries.
No carrier-mediated transport systems, thin walled, narrow diameter, extensive network, contains pores.
Is the velocity of flow fast or slow in capillaries?
Slow
Velocity of flow is inversely proportional to what in vessels?
Total cross sectional area of all the vessels.
is the flow rate different in different vessels?
No, it is the same!
Describe the structure of veins.
Thin walled compared to arteries, highly distensible, large diameter. Contains smooth muscle, elastic and fibrous connective tissue. Has one way valves in peripheral veins to transport blood to heart. Contain more blood than arteries.
What is the function of veins?
Passageway to the heart from the organs and is a blood volume reservoir.
Define blood pressure.
Force exerted by the blood against a vessel wall. Depends upon the volume of blood and compliance of the vessel.
Is the compliance higher in veins or arteries?
Veins
What is the main driving force for blood flow?
Mean Arterial Pressure (MAP)
What two factors determine blood flow?
Pressure gradient and vascular resistance.
Vascular Resistance is inversely proportional to what?
Flow rate or vessel radius
What is the equation for blood flow?
Flow = Change in Pressure divided by resistance.
Name the two factors that are directly proportional to resistance.
Viscosity of the blood and vessel length.
Define the total peripheral resistance.
Combined resistance of all organs, including blood vessels
Which vessel contains 60% of the total peripheral resistance?
Arterioles
What effect does resistance have on the mean arterial pressure?
Increased resistance increases mean arterial pressure
MAP = CO x TPR
What two pressures need to be considered in Bulk Flow of the Capillaries?
Hydrostatic pressure and colloid osmotic pressures between plasma and interstitial fluid.
What happens at the arteriole end of the capillary?
Ultra filtration of molecules (water, oxygen) - not RBCs, WBCs, Large Proteins.
What happens at the venule end of the capillary?
Reabsorption of water and other molecules.
