Flashcards in Cardiovascular System Deck (325):
What are the two circuits of the cardiovascular system?
Pulmonary and systemic
What are the differences in resistance and pressure between the pulmonary and systemic circuit?
Pulmonary: Medium resistance and medium pressure
Systemic: High resistance and high pressure
What is special about the the liver?
It has a dual supply of blood. One supply is from the gut via the hepatic portal vein. One supply is from the systemic arteries.
What percentage of blood volume is in each of the pulmonary circuit, heart and systemic circuit?
Where does most blood sit?
In the systemic veins
Why is an outlet valve essential for a ventricle?
When the ventricle is filling, it prevents arterial blood from returning to the pump.
Why is an inlet valve necessary?
To prevent high-pressure blood in the pumping chamber from returning to the veins.
What are the two phases that ventricles undergo?
What is an atrium? What is its purpose?
A reservoir upstream of the pump. During the ejection phase, it accumulates venous blood which can enter the ventricle quickly during the filling phase.
Why is it advantageous for the inlet and outlet of the ventricle lie close together?
The walls of the pumping chamber can shorten in length as well as in width.
How does an appendage (auricle) improve the heart?
Increases the capacity of the atrium.
How are the two ventricles separated?
Anterior and posterior interventricular sulcus
What is the heart's job?
To repressurise blood.
What are the peak pressures of the left and right atrium and ventricle?
Right atrium: 5 mmHg
Left atrium: 8 mmHg
Right ventricle: 27 mmHg
Left ventricle: 120 mmHg
What are the names of the valves between the left atrium and ventricle and the right atrium and ventricle?
Left atrium and ventricle: Mitral/bicuspid valve
Right atrium and ventricle: Tricuspid valve
What is below each valve to hold it in place?
Are atria effective pumps?
What type of tissue are valves made from?
Fibrous connective tissue
What are the Chordae tendineae?
Tendinous cords which tether the atrioventricular valves, thus preventing them from bursting upwards into the atrium during systole.
What is another name for atrioventricular valves?
Ventricular inlet valves
What forms the core of the heart?
The left ventricle
What are the open ends of the ventricles each subdivided into?
An inlet and outlet.
What must be the diameter of the inlets? Why is this?
Must be of a large diameter in order to admit blood at low pressure
Why do the outlets have a small diameter?
Blood leaves the ventricles at high pressure
What are the names of the inlet and outlet valves?
Inlet: triscuspid (right) and mitral/bicuspid (left)
Outlet: pulmonary (right) and aortic (left)
What shape is the pathway taken by blood through the ventricles?
What is the ratio of the peak pressure of the LV:RV? Compare this to the ratio of the wall thickness.
How many cusps does the pulmonary valve have?
How are outlet valves sometimes described?
What is the difference between the appearance of the aortic and pulmonary valves?
We would see the openings of the coronary artieries near the aortic valve.
What is the structure of inlet valves?
Cusps are flat flaps with their free edges restrained by cords.
Describe the structure of outlet valves.
Shaped like a small pocket and lack cords.
What happens when the outlet valves are inflated with blood?
They gain strength from the 3D shape.
When are the outlet valves in the open position?
What word do we use to describe the lack of energy required for outlet valve opening and closure?
When is the outlet valve in the closed position? Why does it close?
Ventricular filling - The pressure of blood trying to re-enter the ventricle forces the free edges of the cusps tightly together. The superior lip is then pressed against the neighbouring valve leaflets.
In what direction does the apex of the heart point?
Inferiorly, anteriorly and to the left
What proportion of the mass of the heart lies to the right of the midline of the body?
What is the right border of the heart mainly formed by?
The right atrium
What is the inferior border of the heart mainly formed by?
The right ventricle
What is the left border of the heart mainly formed by?
The left ventricle
What is the heart enclosed in?
A double walled bag - pericardium
What are the inner and outer walls of the pericardium made of?
A single layer of squamous mesothelial cells.
Where are the two walls of the pericardium continuous?
Where the great vessels enter and leave the heart.
What are the names of the two walls that the pericardium is made up of?
Inner: visceral pericardium
Outer: parietal pericardium
What is another name for the visceral pericardium?
What is found within the pericardial space?
What is the purpose of the serous fluid?
Allows the parietal and visceral surfaces to slide without friction as the heart beats.
What are the layers of the pericardium?
What are the layers of the heart wall?
Myocardium (cardiac muscle)
Inside ventricle (blood)
Which layer of the heart wall and the pericardium overlap?
What are the functions of the fibrous skeleton?
Supports and anchors the valve leaflets to the heart wall and acts as electrical insulation.
How fast is the conduction from the SA node to the atrial muscles? What is the result of this?
0.5 m/s (slow)
What occurs when the electrical impulse reaches the AV node? What is the speed of conduction through the AV node?
100 ms delay
How fast is the conduction from the AV bundle to the Purkinje fibres? What is the result of this?
Even contraction of ventricle - systole
How is the right side of the heart different to the left?
It is similar but pressures are much lower.
What are the steps of the cardiac cycle?
Ventricular filling, atrial contraction, isovolumetric ventricular contraction (systole), ventricular ejection, isovolumetric ventricular relaxation
When does ventricular filling begin? What happens during this phase?
Phase commences as pressure in the ventricle drops below that in the atrium. The mitral valve opens quietly and blood enters the ventricle. The ventricle will fill to about 80% of its capacity during this phase. Diastole
Which phase is the longest phase and takes up half the cycle?
What occurs during atrial contraction? What is this stimulated by?
The left atrium contracts to complete the filling of the ventricle. Stimulated by SA node
Why is the atrial pressure small?
1) Muscle layer is thin
2) There are no valves where the pulmonary veins enter the atrium and therefore nothing to prevent backflow into the veins.
What happens to our atria as we get older? Does this affect us very much?
Atria flutter instead of contracting. No significant effect because a small amount of blood is topped up in the atria.
What happens during isovolumetric ventricular contraction?
Systole. The ventricle begins to contract. Blood within it lifts backwards towards the atrium and the mitral valve closes. Ventricular pressure is still below that in the aorta so the aortic valve remains closed.
What is the first heart sound caused by?
When the blood within the ventricle lifts backwards towards the atrium and the mitral valve closes during isovolumetric ventricular contraction.
During what phases is the ventricle isolated from the rest of the circulation for a brief period, with its inlet and outlet valves closed?
During isovolumetric ventricular contraction (systole) and relaxation
What is the first heart sound called?
Compare the pressure differences between the atria, ventricles, and arteries during ventricular contraction.
Atrial pressure is less than ventricle pressure (increasing), which is less that arterial pressure.
What happens during ventricular ejection?
Systole continues, but now ventricular pressure exceeds aortic pressure and the aortic valve cusps open quietly. Blood leaves the ventricle.
Why does the pressure in the ventricle and aorta continue to rise steeply during ventricular ejection until later.
Blood is ejected into the aorta faster than it can run-off into the distributing arteries. Later in the phase, the rate of ejection falls below the rate of run-off and aortic and ventricular pressures level-off and then begin to decrease.
What happens during isovolumetric ventricular relaxation?
The ventricle relaxes. As it does so, ventricular pressure drops suddenly, flow reverses in the aorta and the aortic valve closes as blood tries to reenter the ventricle.
What causes the second heart sound?
When flow reverses in the aorta and the aortic valve closes as blood tries to re-enter the ventricle during ventricular relaxation.
What is the name of the second heart sound?
Why is the dub sound higher pitched than the lub sound?
The valve closes over a smaller hole.
How long do ventricular contraction and releaxation last for?
Compare the pressure between the atria, ventricles and arteries during ventricular relaxation.
Atrial pressure is less that ventricular pressure (decreasing), which is less than arterial pressure
Why are there two dub sounds?
Aortic valve closes just before the pulmonary. Blood tries to return into the LV faster than to the RV.
What is the conduction pathway of the heart?
SA node -> Atrial muscle -> AV node -> AV bundle -> Purkinje fibres
What are elastic arteries? What do they do during systole and diastole? What does this result in?
Very large arteries which have elastic walls. They expand during systole to store the bolus of blood leaving the ventricle. During diastole, they push blood out into the arterial tree by elastic recoil.They smooth out the pulsatile flow of blood leaving the ventricles.
What is the structure of elastic arteries?
Many thin sheets of elastin in the middle tunic.
What is the size of elastic arteries?
What is the size of muscular arteries?
Pencil -> pin
What are the functions of muscular arteries?
Distribute blood around the body at high pressure (and lungs at medium pressure).
How is rate of blood flow adjusted by muscular arteries?
By using smooth muscle to vary the radius of the vessel.
What is flow proportional to in the muscular arteries? What does this imply?
The fourth power of radius
A small change in radius has a large effect on flow rate.
What is the structure of muscular arteries?
Many layers of circular smooth muscle wrapped around the vessel in the middle tunic.
What are the three layers of muscular artery walls?
Tunica interna (intima)
What is the size of arterioles?
What is the function of arterioles?
Controls blood flow into capillary beds.
What is special about arteriole walls?
They have a thicker muscular wall relative to their size than any other blood vessel.
Where are arterioles found in the body?
In the circulation where the greatest pressure drop occurs, where there is the greatest resistance to flow.
What does the degree of constriction of arterioles throughout the body determine?
Total peripheral resistance, which in turn affects mean arterial blood pressure.
What is the structure of arterioles?
Between one to three layers of circular smooth muscle wrapped around the vessel in the middle tunic.
What do arteries often travel alongside?
Their companion veins.
What are the differences between artery and vein walls?
Arteries have much bigger walls but a smaller lumen.
How large are capillaries?
Size of a red blood cell
What are the functions of capillaries to the thinness of their walls?
Allows exchange of gases, nutrients and wastes between blood and the surrounding tissue fluid.
Is blood flow fast or slow through capillaries? What does this allow for?
Allows time for exchange to occur
Capillaries are ______ vessels. ______ escapes but not ___ ______ _____.
Red blood cells
How is most of the lost plasma immediately recovered?
Due to the osmotic gradient
What is the structure of capillaries?
Diameter just wide enough to admit one RBC. Capillary walls is a single layer of endothelium with an external basement membrane.
What is not present in capillary walls?
Smooth muscle (so no ability to adjust diameter)
What is another name for tissue fluid?
What drives tissue fluid out of capillaries?
What type of tissue are WBC's?
What are venules?
Low-pressure vessels which drain capillary beds.
Where do white blood cells leave the blood circulation? When do they leave? What do they then do?
During infection and inflammation
To attack bacteria in the tissue alongside.
Compare the structures of small and large venules?
Small venules: endothelium, connective tissue.
Larger venules: endothelium, connective tissue, single layer of smooth muscle.
What is the function of veins?
Drain blood back to the atria, except portal veins which drain blood to another capillary bed.
Describe the walls of veins.
Thin and soft. They stretch easily (compliant) Similar to a muscular artery but much thinner walled for their size. Have much less muscle and connective tissue.
A small change in venous blood pressure results in a ________ change in venous volume.
What do veins act as?
A reservoir which stores blood.
What percentage of blood volume occurs in systemic veins and venules?
What percentage of blood volume occurs in systemic arteries and arterioles?
Why are there valves in larger veins?
They prevent backflow. As muscles alongside the vein alternately contract and relax during walking, the system acts as a venous pump which returns blood to the atrium.
Where do coronary arteries arise from?
From the aorta just downstream from the aortic valve
What do muscle coronary arteries supply?
Supply the muscle of the heart (myocardium)
When does significant obstruction to blood flow through a coronary artery occur?
When it is narrowed to about 20% of its normal cross section by atheroma.
What is ischaemia?
When the myocardium supplied by the diseased coronary artery runs low on oxygen (especially during exercise).
What is angina?
What does severe ischaemia result in?
Infarction (death) of a local area of the myocardium.
What are anastomoses?
How can the heart adjust to ischaemia?
Anastomoses between small penetrating branches of the main coronary arteries widen slowly so that an ischaemic area of muscle can be supplied by a distant artery.
What is deoxygenated blood from the myocardium drained by?
Where do cardiac veins return blood to?
What is meant by idiopathic?
The cause of dilated cardiomyopathy is _________, but is probably a _______ __________ in many cases?
What are infected muscle fibres attacked by? What happens after they are attacked?
Many die, others are left weakened and slow to contract. Makes muscle fibres longer.
What is meant by dilated cardiomyopathy?
Heart muscle disease
Which ventricle is most affected in dilated cardiomyopathy?
Left ventricle most affected because of high pressure. It dilates - chamber enlarged, wall thickness normal or slightly increased.
What happens to the fibrous ring supporting mitral valve during dilated cardiomyopathy? How does this cause mitral regurgitation
It stretches so that mitral valve flaps no longer meet during systole, causing mitral regurgitation.
After LV dilatation, what happens to the ratio of wall thickness between the left and right ventricle?
Remains the same at 3:1
What is the dilatation of the ventricle due to? What happens during systole?
The lengthening of cardiac muscle fibres.
During systole, blood regurgitates from the left ventricle to the left atrium.
What is the Law of LaPlace?
Pressure is inversely proportional to radius
What is the dilatation of the left ventricle known as?
Which heart sound is affected by mitral regurgitation?
The first heart sound is longer
What is different about the mitral regurgitation cardiac cycle?
Lower max pressure reached by ventricles
Greater pressure reached by atrium as ventricles filled.
What happens to the ventricle between S1 and S2?
What happens to the ventricle between S2 and S1?
Why does a problem on the left (systemic) side of the heart cause symptoms in the right (pulmonary) circuit?
To maintain CO, LV must pump a greater volume. In order to fill the ventricle, LA works harder, so LA pressure increases. Pulmonary venous pressure increases, pulmonary capillary pressure increases, and this leads to increased capillary leakage.
What are the consequences of increased capillary leakage?
Lungs get heavier, wetter, and more rigid. Breathing requires more muscular work. This is called Dyspnoea.
What is Dyspnoea?
Discomfort during breathing, consciousness of laboured breathing.
What is the cycle of mitral regurgitation?
LV dilatation -> Mitral valve ring stretches -> Increased mitral regurgitation -> Volume load on LV -> LV dilatation
How can mitral regurgitation be treated?
Valve replacement or heart replacement
What function does the heart serve?
To supply based on demand
What does the cardiac cycle include?
All events associated with one heart beat, forcing areas of high pressure to low pressure.
Which receptors can notify the body that demand will increase?
Proprioreceptors which detect movement.
What is the equation for cardiac output?
CO = heart rate x stroke volume
What units is heart rate measured in?
Beats per minute
What units is stroke volume measured in?
What is stroke volume?
The volume of blood ejected in one cycle of the heart.
What is the average stroke volume of humans?
What is meant by cardiac output?
The volume of blood ejected into the aorta by the left ventricle per minute
What are the units of cardiac output?
mL per minute
What is cardiac output at rest?
4-7 litres per minute
What is cardiac output also equal to? What does this imply?
Total blood volume
So, per minute, total blood volume is ejected. Thus the heart is a high-flowing system. Allows rapid filtering of blood.
What percentage of the cardiac output does the kidney get at rest?
What is meant by venous return?
The volume of blood returning to the heart from the vasculature every minute and is linked to cardiac output.
What is meant by cardiac reserve?
The maximum ability to supply. It refers to the difference between the resting rate at which the heart pumps blood and the max capacity for pumping blood.
What can proprioreceptors detect? What do they do?
Movement. Tell the body that demand will increase.
What occurs during heart failure?
Ability to increase cardiac output is reduced. Demand of tissues remains the same but supply is reduced. Cardiac reserve decreases.
What 3 things is stroke volume affected by?
1) Preload stretch
3) After load
What is meant by preload stretch?
Stretch on the left ventricle before it contracts
What is another word for contractility?
What is meant by contractility?
Forcefulness of contractility
What is another word for heart rate?
What ions have an excitatory or inhibitory effect on contractility?
What is meant by after load?
Pressure the heart has to work against for LV to eject blood into the aorta.
What is the Frank-Starling Law?
An increase in filling pressure leads to both an increase in end diastolic value and an increase in the subsequent stroke volume. This response can be explained by the ability of the cardiac muscle to respond to increased stretch with a more forceful contraction. Thus the energy of the contraction of the ventricle is a function of the initial length of the muscle fibers comprising its walls.
What gives rise to blood pressure?
What are the two mechanisms by which the stroke volume is regulated?
1) Intrinsic regulation of the forc e of contraction governed by the degree of stretch of the myocardial fibre at the end of diastole.
2) Extrinsic regulation, which is determined by the activity of the autonomic nervous system and the circulating level of various hormones.
What is a consequence of Starling's Law?
The heart automatically adjusts its output to match its venous return.
What determines blood pressure?
What is the pumping action of the heart achieved by?
The mechanical work of the myocardium.
What must happen for mechanical work to be performed?
A load must be moved through a distance.
For a 3D system, what is work equal to?
The change in pressure times the change in volume, so that the work performed by the heart each time it beats is given by the area of the pressure-volume curve for ventricular contraction. - Stroke Work
Why is it necessary to construct a graph of ventricular pressure against volume to determine the stroke work accurately?
Ventricular pressure varies during the ejection phase of the cardiac cycle.
Why does the pressure fall at first while the ventricle is filling? What happens after this?
Due to the suction effects of the relaxing muscle.
Later, it starts to rise passively as volume increases.
What gives rise to the first steep rise in the pressure volume graph?
The pressure rises steeply, but since the aortic valve is closed, there is no change in volume. This is isovolumetric contraction.
What happens after volumetric contraction with regard to the pressure-volume graph?
Aortic valve opens and blood is ejected from the ventricle.
What happens after ejection with regard to the pressure-volume graph?
The valve closes again and isovolumetric relaxation occurs.
What often causes stroke volume to increase?
The presence of a positive inotropic agent. The agent promotes the influx of Ca2+ during cardiac action potentials, which strengthens the force of the subsequent muscle fibre contraction (contractility).
What often causes the stroke volume to decrease?
Negative inotropic agent. The agent promotes the influx of K+, which reduces the contractility.
What is meant by ejection fraction?
The percentage of blood pumped out of a filled ventricle during each cycle. There is always a volume of blood that remains in the lungs.
What can damage to the SA node result in?
What is the SA node? What does it exhibit?
What is excitation initiated by?
Specialised cells in the SA node.
Where is the SA node found?
It lies close to the point of entry of the great veins into the right atrium.
What happens after excitation?
A wave of depolarisation is conducted throughout the myocardium.
What does an ECG measure?
The electrical activity being produced by the heart.
What value of voltage is produced by the electrical activity of the heart?
Why is the electrical activity of the heart able to spread throughout the body?
Because water is an electrical conductor and the body is made up of mostly water.
What is electrical activity controlling?
Contractile activity: Making sure fibres contract at the right time.
What is ventricular arythmia
Lack of rhythmicity in the coordinated contraction.
How can arythmia be reverted?
Giving the person a shock using defibrillators.
What happens in atrial arythmia?
Atria are not contracting in a coordinated fashion.
The heart has an inherent ______ _______ like ability.
What is the inherent rate of the heart?
What is the inherent ability of the heart due to?
SA node - special group of cells with an autorhythmicity.
If the SA node is damaged, what can replace it?
The AV node
How does ht ewave of depolarisation travel through the heart?
It sweeps over the surface of the heart, reaching different parts at different times and thus causing contraction at different times.
What do we measure using an ECG?
The wave front of electrical acitivity sweeping across the heart surface.
What do we record using an ECG?
The way the electrical activity is getting to different parts of the heart.
Why are different ECG's slightly different?
Electrodes are placed on different spots. This takes a picture of one angle of the heart. The different pictures taken by the leads shows different parts of the heart.
What do the letters on an ECG refer to?
Different stages of the cardiac cycle
What does the P wave stand for?
Relates to the wavefront activating and causing depolarisation of the atria
What does the Q wave represent?
Depolarisation of ventricles
What does the T wave represent?
Repolarisation of ventricles to get ready for the next cycle.
What gives rise to the QRS complex?
Depolarisation of ventricular contractile fibers produces the QRS complex.
What does an enlargement of the P wave indicate?
Enlargement of the atria. Higher preload
What does enlargement of the R wave indicate?
Enlargement of ventricles
What happens in heart failure?
There is more stretch on the wall. There may be a portion that is damaged. Other myocytes respond to heart failure by enlargement. Unlike other muscles, which get larger when exercised, heart muscles get larger in a non-beneficial way (hypertrophy).
The electrical activity moves through the heart on a _________
The build up of plaque in coronary vessels can lead to what?
Causes a blockage, reducing the diameter and resulting in transient ischaemia which can lead to angina (the pain associated with the lack of blood supply).
What is angiography?
Injecting a dye into the vessels and looking at it with an xray to detect blockages.
What are some ways to treat blocked vessels?
Bypass using leg vein
Describe the action potential of a ventricular contractile fiber.
1) Initially, negative resting membrane potential. Rapid depolarisation due to Na+ inflow when voltage-gated fast Na+ channels open.
2) Plateau (maintained depolarisation) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open. Cannot have another heartbeat during this refractory period.
3) Repolarisation due to closure of Ca2+ channels and K+ outflow when additional voltage-gated K+ channels open.
Compare the heart rate of a human dog, rabbit and rat. Now compare their blood pressures.
Human: 60 bpm
dog: 90 bpm
Rabbit: 150 bpm
Blood pressure is pretty much the same in every mammalian species. However, rats have a much smaller, so to generate the same pressure, they must beat much faster.
What is the intrinsic rate of the SA node? Why is our resting heart rate different?
It is driven by the autonomic nervous system
What are the two branches of the autonomic nervous system?
Parasympathetic and sympathetic
Where do parasympathetic nerves start?
In the brain stem
What is meant by the auto part of autonomic nervous system? What does this mean for control of the heart rate?
Not under conscious control. Cannot control your heart rate.
Where is the medulla situated? What does it control?
At the back of the brain under the cerebellum.
Critical region involved in cardiovascular and respiratory control.
What is the vagus nerve? What does it come alongside?
A group of cells in the medulla form a nerve axon (parasympathetic) which is called the vagus. Comes down alongside the carotid artery.
How thick is the vagus nerve?
4-5mm in diameter
Where does the vagus nerve lead to? What does it release there and what effect does this have on the heart rate?
The SA node and releases the neurotransmitter acetylcholine. This then decreases heart rate.
Why is the resting heart rate lower than the intrinsic rate of the SA node?
The vagus nerve reduces heart rate by releasing acetylcholine when nerve impulses are sent in the autonomic nervous system.
What is the effect of exercise on vagal activity?
The proprioreceptors which sense movement in joints sends signals to the medulla which decreases vagal activity, which leads to an increase in heart.
What type of relationship exists between vagal activity and heart rate?
What is the predominant role of the vagus? What may be another role of the vagus?
Regulating heart rate. May have minor role on stroke volume.
What is another factor that can cause an increase in heart rate?
The central nervous system and cardiovascular system work together to ensure that you have the ___________________________________
Optimum heart rate for the current situation
Where do sympathetic nerves travel?
Go down the spinal cord and then goes out at different segments. Some of the segments go to the coronary vessels and myocardium of the heart.
How does sympathetic activity affect the heart?
Increases the heart rate and stroke volume and thus increases cardiac output. Contractility and inotropy
What inputs does the sympathetic nervous system receive?
Proprioreceptors, oxygen levels, temperature, blood pressure, blood volume
What is excitation of the heart initiated by? What occurs after this?
Specialised cells in the sinoatrial node. A wave of depolarisation is then conducted throughout the myocardium.
Where is the sinoatrial node found?
It lies close to the point of entry of the great veins into the right atrium.
Is the resting potential of the SA node stable or unstable?
What does the membrane potential between successive action potentials show? What happens when threshold is reached?
A progressive depolarisation
An action potential is triggered to initiate a heartbeat.
Do the myocytes of the atria, ventricles, and conducting system have action potentials with the same or different characteristics? Describe similarities and differences.
Although they cary in duration, they all show a fast initial upstroke followed by a plateau phase of depolarisation prior to repolarisation.
What is the plateau phase of cardiac muscle contraction due to?
The inward movement of calcium ions.
What does the calcium influx that occurs during the plateau phase of the action potential ensure?
That the action potential lasts almost as long as the contraction of the cell. Because the muscle is refractory both during and shortly after the passage of the action potential, the long plateau phase ensures the unidirectional excitation of the myocardium.
When does repolarisation of the myocardial cells occur?
When the voltage dependent calcium channels inactivate.
Describe a typical ECG and how it correlates with atrial and ventricular systole.
1) P wave: depolarisation of atrial contractile fibers
2) Flat region: atrial systole (contraction)
3) QRS complex: Depolarisation of ventricular contractile fibers produces QRS complex.
4) Flat region: ventricular systole (contraction)
5) T wave: repolarisation of ventricular contractile fibres
6) Flat region: ventricular diastole (relaxation)
What gives rise to the P-Q interval, the S-T segment and the Q-T interval?
P-Q interval: Beginning of P wave and the flat region after it.
S-T segment: Flat region between QRS complex and T wave.
Q-T interval: The beginning of the QRS complex to the end of the T wave.
What are the two inputs to the cardiovascular center in the brain? Give examples for each.
From higher brain centers: cerebral cortex, limbic system, and hypothalamus.
From sensory receptors: proprioreceptors ( Monitor movements), chemoreceptors (monitor blood chemistry), baroreceptors (monitor blood pressure).
What are the two outputs of the cardiovascular (CV) center and give examples of how it affects the heart.
1) Cardiac accelerator nerves (sympathetic)
- Increased rate of spontaneous depolarisation in SA node (and AV node), which increases heart rate.
- Increased contractility of atria and ventricles, which increases stroke volume.
2) Vagus (X) nerves (parasympathetic)
- Decreased rate of spontaneous depolarisation in SA node (and AV node), which decreases heart rate.
Describe the factors that increase stroke volume.
- Increased preload
- Increased contractility
- Decreased afterload
How can preload be increased? What are the consequences?
- Increase end-diastolic volume (stretches the heart).
- Within limits, cardiac muscle fibres contract more forcefully with stretching (Frank-Starling law)
How can contractility be increased? What are the consequences of this?
- Positive inotropic agents such as increased sympathetic stimulation: catecholamines, glucagon, or thyroid hormones in the blood lead to increased Ca2+ in extracellular fluid.
- These agents increase force of contraction at all physiological levels of stretch.
How can afterload be decreased? What are the consequences of this?
- Decreased arterial blood pressure during diastole.
- Semilunar valves open sooner when blood pressure in aorta and pulmonary artery is lower.
Describe the factors that increase heart rate.
Nervous sustem : Cardiovascular center in medulla oblongata receives input from cerebral cortex, limbic system, proprioreceptors, baroreceptors, and chemoreceptors. Leads to increased sympathetic and decreased parasympathetic stimulation.
Chemicals: catecholamine or thyroid hormones in the blood moderate increase in extracellular Ca2+
Other: Infants and senior citizens, females, low physical fitness, increased body temperature.
The pressure the LV has to work against in order to eject blood into the aorta
What is another name for blood pressure?
What is arterial pressure?
The pressure in the arteries
What causes arterial pressure?
The heart pushing against the aortic valve.
What do the two numbers used to describe blood pressure relate to?
Systolic over diastolic
What is the incidence of hypertension in NZ?
What blood pressure is used to define hypertension?
140 over 90
What is the impact of having high blood pressure on the heart and on blood vessels?
- Makes the heart have to work harder because the afterload is higher so there is a decrease in efficiency. Over a number of years, heart failure will occur and the ejection fraction will decline. Breathlessness and venous congestion will result.
- Tortuosity, bends and plaque buildup can occur in small vessels. These are weak points that hypertension can cause bursts in (stroke)
Is the increase in heart muscle size beneficial?
What are the risk factors for hypertension?
Smoking, alcohol, overweight, no exercise as well as genetic factors.
What is happening when a cuff is placed on the arm when measuring blood pressure? What is listened for?
Occluding all blood flow into and out of the arm so there is zero blood supply.
When a small amount of blood is allowed to flow when the valve is just released, turbulent flow can be heard. This gives the systolic value. The valve is wound down until silence is heard. This is because flow in tubes that is laminar (non-turbulent) is silent. This is the diastolic value.
What is the majority of the 5 L of blood in the body situated?
The major veins
When we are measuring pressure with a cuff, what are we measuring?
The pressure in the arteries
Does blood pressure change when we exercise?
Yes, but to a small extent.
What do we see happening to the pressure and pulsatility when we move from the arteries to the arterioles? Why?
A big reduction in pressure. The pulsatility of the wave decreases. This is because they don't have as much connective tissue and a good amount of smooth muscle, which contracts.
What do the arterioles act as?
A shock absorber or dampening force
How does the smooth muscle affect the arterioles? How does this affect the pressure?
Changes the radius of the blood vessel, which affects the resistance. (Inverse square law)
Reduces the pressure.
What is the approximate pressure in the capillaries?
What happens to the blood pressure in the arterial end of capillaries? Why?
Pressure falls because substances leak out.
When we get to the venules, what is the blood pressure and what happens there?
We reabsorb the waste products.
What can pressure in the superior vena cava reach?
Does flow rate change despite the change in pressure?
Flow in = Flow out
What does blood pressure drive?
Is the pressure across mammalian species the same? What is the exception?
What substances cause negative forceful filtration in the capillaries? Does it vary across the capillary bed?
Substances that are not easily filtered due to their molecular weight. They only pass through special secretory process and therefore restrain other things from being pushed out. This is the same across the capillary bed.
What opposes the blood hydrostatic pressure? What contributes to it?
Blood colloid osmotic pressure
Contributed to by substances that cannot be easily filtered.
What is the interstitial hydrostatic pressure in most regions of the body? Where is it different?
What is the pressure that drives filtration?
Net filtration pressure: 10mmHg
What is the system that drains most of the interstitial fluid?
In the venous end of the capillary, what is the same and different about the pressure?
All pressure values are the same except for the blood hydrostatic pressure, which goes from 35 to 16 mmHg.
What is the pressure in the venule end compared to the arterial end of the capillary? What does this serve to do?
-9 in the venule end vs +10 in the arterial end.
This sucks substances back into the capillary.
If blood pressure stays low for a very long period of time?
A lower net filtration pressure. Stuff is not being pushed out so cells are not getting the nutrients and oxygen for normal metabolism to occur.
What occurs when the pressure goes up? When can this occur?
More filtration due to increase of net filtration pressure.
Standing still for a long time: great hydrostatic pressure in the ankles and feet, leads to higher force driving fluid out of capillaries. Less net reabsorption occurs. This leads to a edema (swollen ankles) occurring.
What vessels provide the major resistance to flow?
What is total peripheral resistance (TPR)?
The sum of all the resistances provided by all the vessels around the body.
What equation relates blood pressure, cardiac output, and total peripheral resistance?
Blood pressure = Cardiac output x Total peripheral resistance
Why doesn't pressure in the arterial system go to zero?
Because we have peripheral resistance
How do we regulate total peripheral resistance?
By regulating the diameter of arterioles. Vasoconstriction or vasodilation.
E.g. hot day leads to vasodilation of arterioles.
How is the vascular supply to different organs arranged?
What does this mean for the pressure entering each organ?
What would be the result if they were arranged in series?
All organs receive the same pressure going into them. This is useful for exchange.
The organ at the end would receive very little pressure.
What happens to the blood flow to organs (kidneys) when running a marathon?
Reduces by vasoconstrictions.
Exercising muscles require more oxygen so blood vessels supplying skeletal muscles vasodilate.
If we start with 4 L/min of cardiac output, how much goes to each of 4 organs?
What does vasoconstriction occur in?
During vasoconstriciton and vasodilation, does blood pressure change radically?
Why is stability in blood pressure what we are after?
For driving exchange
What do we regulate to maintain blood pressure?
Cardiac output (heart rate and stroke volume) and total peripheral resistance.
Why does blood pressure get higher as we age?
Arterioles get stiffer and less responsive due to less smooth muscle, thicker walls and plaque build up, leading to greater total peripheral resistance.
What does vasoconstriction of peripheral blood vessels due to cold temperatures result in?
Brings in blood flow and reduces heat loss.
What factors lead to vasodilation?
What is the approximate reduciton in blood pressure due to gravity when going from lying to standing?
What is decrease in blood pressure sensed by?
Baroreceptors (pressure receptor) in the arterial system.
Where are baroreceptors found?
Carotid artery divides into the external and internal carotid artery under the jaw and in this region, there is a nerve that travels down and the nerve goes across this region. Blood vessel forms a sinus in this region which is a swelling. This is a baroreceptor afferent nerve which terminates in the artery. Baroreceptors are found in the carotid sinus and arch of the aorta.
What is an afferent nerve?
Takes information from the periphery to CNS.
What are baroreceptors sensitive to?
When blood pressure decreases, for example when we go from lying to standing, what is the response?
Baroreceptors fire less -> CNS -> Decrease in vagal nerve firing -> Increase in heart rate
CNS -> Increase in cardiac sympathetic nervous activity -> Increase in heart rate and stroke volume
CNS -> Increase in sympathetic nerve activity -> Vasoconstriction -> Increase in total peripheral resistance
Increase in CO and TPR leads to increase in BP
Why are arterioles able to respond to blood pressure?
Every arteriole has a sympathetic nerve going to it. This sympathetic innervation changes the diameter.
What is the difference in blood pressure and heart rate/SNA over a 24 hour period?
BP: very little variation
HR + SNA: much variation
What does the cardiovascular system use to stabilise blood pressure?
Heart rate and sympathetic nerve activity
Why does exercise help raise low blood pressure?
Skeletal muscles help pump blood back to the heart.
How often do baroreceptors sense changes in pressure?
Every heart beat
What happens if blood pressure and blood volume decrease due to haemorrhage or blood loss?
Same processes occur as decrease in BP due to do standing from lying, but stronger. Blood flow to kidney reduces profoundly due to vasoconstriction so filtration is curtailed. It is difficult to maintain filtration, and some may need dialysis for extreme cases.
How long does the cardiovascular system take to recover from haemorrhage or blood loss?
Where does the sympathetic nerve activity go to especially? What effect does it have there?
The kidneys: regulates vasoconstriction
What are cardiac pulmonary receptors?
Receptors that are located around the veins as they come back to the heart. Superior and inferior vena cava.
Sense venous pressure.
Is pressure in the veins near the heart high or low? Give an approximate value.
What percentage of blood volume is in the veins?
What senses venous pressure?
Nerve endings in the veins near the heart
Why is venous pressure able to go negative?
Due to the pleural cavity
When central venous pressure decreases, what happens?
Goes to central nervous system -> Increase SNA -> Increase SV and HR -> Increase BP
What is the collective name for the cardiovascular system's attempt to restore blood pressure?
What happens as a result of increased blood volume (e.g. due to drinking a lot of water)?
Increase in central venous pressure (Small - 5 mmHg) -> Sensed by cardiac pulmonary receptors -> Decrease in cardiac sympathetic nerve activity -> decrease heart rate and stroke volume
Also decrease in sympathetic nerve activity of kidney -> Vasodilation -> Increase renal filtration -> Increase urine output
What happens between the nerve endings of the sympathetic nervous system and the smooth muscle of arterioles?
Noradrenaline is released as a neurotransmitter, which acts on alpha receptors to cause vasoconstriction.
How can high blood pressure be treated?
Block the receptors for vasoconstriction to bring down the heart rate and stroke volume.
What is cardiovascular disease?
The name for the group of disorders of the heart and blood vessels