Cardiovascular System Flashcards
Describe the structure of the pericardium?
Parietal pericardium- strong outer fibrous layer
Intrapericardial space- lubricating fluid
Visceral pericardium- inner serosal layer
What is the fibrous layer of the pericardium attached to? Why?
Sternum and mediastinal portions of the left and right pleurae
Keeps the pericardial sac firmly anchored within the thorax
What structures emerge from the pericardium?
Superiorly: aorta, pulmonary artery, superior vena cava
Inferiorly: inferior vena cava
Why do we need a cardiovascular system?
All cells require oxygen and release carbon dioxide
Diffusion is not efficient over long distances. Rate of diffusion is proportional to square of the distance.
Why doesn’t the left ventricle receive all oxygen and nutrients from the oxygenated blood within its ventricular cavity? Where does it receive its oxygen and nutrients from?
Some cells are supplied with blood directly from the ventricular cavity through tiny vascular channels known as thebesian veins.
There is a large distance from the source of oxygen to some of the cells in its thick muscle wall.
Majority of the left ventricle is supplied with blood from the left coronary artery which branches into the anterior interventricular artery and the circumflex artery
Which arteries branch off the aortic arch?
Brachiocephalic trunk- supplies right upper limb, head and neck
Left common carotid artery- supplies head and neck
Left subclavian artery- supplies left upper limb with some branches to the head and thorax
Describe the location of the heart.
The heart is enclosed in the mediastinum, the medial cavity of the thorax. It extends 12-14cm from the second rib to the fifth intercostal space. It is superior to the diaghragm. It is anterior to the vertebral column and posterior to the sternum. The lungs are lateral to the heart and partially obscure it.
What are the valves in the heart?
Mitral valve- two cusps- between left atrium and left ventricle
Tricuspid valve-three cusps- between right atrium and right ventricle
Aortic valve- semilunar, three cusps- between left ventricle and aorta
Pulmonary valve- semilunar, three cusps- between right ventricle and pulmonary artery
Where are the output vessels of the heart located?
The base of the heart consists of the hearts output vessels; the ascending aorta which leads on to the aortic arch and the pulmonary trunk which splits into the two pulmonary arteries.
What are the different layers of the heart?
Endocardium - layer of endothelial cells lining chambers
Myocardium - thick layer of cardiac muscle cells
Epicardium/ visceral pericardium- layer of connective tissue/adipose tissue through which pass the larger blood vessels and nerves that supply the heart muscle
Where is the fossa ovalis? What is this?
It is a depression in the right atrium of the heart at the level of the interatrial septum. It is the remnant of the opening between the atria in the foetus as blood flow to the lungs and double circulation only begins after birth with the baby’s first breath.
What are trabeculae carnae? Where are they?
Irregular muscle ridges in the heart. They are present in the right and left ventricular walls giving them a spongelike appearance.
What structures prevent the inversion of of the mitral and tricuspid valve cusps during systole?
3 papillary muscles in RV which hold thin string like chordae tendinae which attaches to the edges of the tricuspid valve leaflets
2 papillary muscles in LV which hold thin string like chordae tendinae which attaches to the ended of the mitral valve leaflets
Contraction of the papillary muscles prior to other regions of the ventricle tightens the chordae tendinae and the valve is forced closed.
What controls the opening and closing of the pulmonic and aortic valves?
During relaxation of the ventricles, elastic recoil of the pulmonary arteries forces blood back toward the heart, distending the valve cusps towards one another closing the valve. Therefore, there is slight backflow of blood into the ventricles.
Which vessels enter the atria and where from?
The superior vena cava enters the right atrium superiorly. The inferior vena cava and coronary sinus enter the right atrium inferiorly
The four pulmonary veins enter the left atrium posteriorly.
How is the left side of the heart adapted to the pumping blood at a higher pressure than the right side of the heart?
Structures on the left side of the heart are approximately three times thicker than structures on the right side of the heart.
What do the grooves on the surface of the heart indicate?
Anterior and posterior interventricular grooves (interventricular sulcus)
—> inter ventricular septum
Anterior and posterior atrioventricular grooves (coronary sulcus)
—>boundary between atria and ventricles
Where are impulses in the ventricles first transmitted to and why?
Impulses within the His-Purkinje fibres are transmitted first to the papillary muscles and then throughout the walls of the ventricles so the papillary muscles contract before the ventricles. This coordination prevents the regurgitation of blood through the AV valves.
Where do the right and left coronary arteries originate from and how do they reach the heart?
The root of the aorta just above the aortic valve cusps. The left main coronary artery arises in the left aortic sinus and the the right coronary artery arises in the right aortic sinus. After their origin, these vessels pass anteriorly one on each side of the pulmonary artery.
Describe the position of the atria relative to the ventricles?
The atria are positioned slightly posteriorly and to the right of the ventricles.
What factors affect the rate of diffusion in the cardiovascular system?
Surface area- higher capillary density in metabolically active tissues
Diffusion resistance- nature of the molecule and the barrier (exchange occurs in capillaries), proportional to square root of the distance
Concentration gradient- substance which is used by tissues will have a lower concentration in capillary blood than arterial blood
What factors affect how much lower the concentration of a substance is in the capillary blood than the arterial blood?
Rate of use by the tissue
Rate of blood flow through the capillary bed- the lower the blood flow, the lower the capillary concentration. Blood flow must be high enough to maintain a sufficient concentration gradient and must match the tissues metabolic needs.
How will capillary density and perfusion rate vary between a tissue that is not very metabolically active and a tissue that is very metabolically active?
The tissue that is metabolically active will have:
- a higher capillary density
- greater perfusion rate (greater rate of blood flow)
What is perfusion rate?
The rate of blood flow
Which organs require high, constant flow of blood to them?
Brain
Kidneys
Heart
During exercise, blood flow to which tissues increases?
Heart
Brain
Skeletal muscle
What is the normal rate of blood flow? What can this increase to during exercise?
Normal-5 litres per minute
Exercise-25 litres per minute
What causes cardiac tamponade?
Excess fluid building up relatively rapidly in the pericardial space.
The heart becomes compressed due to the inextensible fibrous pericardial layer
Compression of the heart leads to cardiac tamponade
Pressure of the fluid means that the heart cannot fully fill during diastole leading to a smaller stroke volume and smaller cardiac output.
When is pericardiocentesis required?
Fluid from pericardial space to be removed for testing
Fluid from pericardial space to be removed to relieve compression after a cardiac tamponade
Where is the transverse pericardial sinus? What is its relevance?
Posterior to the pulmonary trunk and the ascending aorta, superior to the left atrium and anterior to the superior vena cava.
A clamp can be placed here during a heart lung bypass so that there is no blood leaving the heart without damaging the pericardium. The heart lung bypass machine receives blood from the inferior and superior vena cava, oxygenates the blood and transfers it to the aortic arch.
Where is the oblique sinus?
Small concavity in the pericardium, posterior to the heart bound by pulmonary veins on either side.
What happens if a major coronary artery is blocked?
Myocardial infarction
There is not a very high pressure gradient between the veins and the right atrium. What valves prevent the backflow of blood from the right atrium into the vessels?
Incomplete valves
Inferior vena cava - eustachian valve
Coronary sinus - thebesian ring
Why is mitral stenosis more common than tricuspid stenosis?
The entrance of the left atrium into the left ventricle is smaller than the entrance of the right atrium into the right ventricle.
At what rate should blood flow to the brain be at all times?
750ml per minute
What are the major components of the cardiovascular system?
Heart- pump Arteries - distributing vessels Arterioles - resistance vessels- restricting blood flow to easily perfused areas so that blood can flow to those often vulnerable parts that are not easily perfused Capillaries- exchange vessels Veins - capacitance vessels
What is the role of capacitance vessels? Which blood vessels are capacitance vessels?
Veins store blood (without an increase in pressure) to cope with temporary imbalances between the amount of blood returning to the heart and the amount that is required to pump out. This gives the cardiovascular system the ability to cope with changes in cardiac output.
What is the mediastinum?
The intervening region in the thoracic cavity between the right and left pleural cavities occupied by the lungs.
How do we prevent all of our blood from going to t he most easily perfused areas and how do we allow blood to flow to areas that are difficult to perfuse?
Resistance vessels restrict blood flow to drive supply to areas that are difficult to perfuse.
Explain how resistance and capacitance vessels work together to meet demand during exercise?
In exercise, more blood needs to flow to the heart muscle, skeletal muscle and cardiac muscle
Resistance vessels restrict flow to other organs by constricting and dilate to allow blood to flow to these organs
Cardiac output increases so there is less blood stored in capacitance vessels.
Is the output greater from the right or left hand side of the heart?
Neither- its the same. Any difference would cause oedema.
What is the typical pressure in the left an right ventricle?
Left ventricle
120 systole / 10 diastole
Right ventricle
25 systole/ 4 diastole
What does systole mean?
Contraction and ejection of blood from ventricles
What does diastole mean?
Relaxation and filling of ventricles
At rest, what is the typical stroke volume?
70ml
At rest, what is typical heart rate?
70 beats per minute
What embryonic tissue gives rise to the CVS?
Splanchnic Mesoderm
How do we prevent all blood from going to the most easily perfused areas and how do we allow blood to reach the brain against gravity?
Resistance vessels restrict blood flow to drive supply to hard to perfuse areas
What is the purpose of capacitance vessels?
Enable CVS to vary amount of blood pumped around the body
Why are resistance and capacitance vessels important?
Blood supply must change to meet demand and this is achieved by a balance between blood in these vessels.
What is typical pressure in the left and right atrium?
Left atrium= 8-10 mm Hg
Right atrium = 0-4 mm Hg
What is typical pressure in the aorta and pulmonary artery?
Aorta- 120 systole/ 80 diastole mm Hg
Pulmonary artery- 25 systole/ 10 diastole mm Hg
How is a cardiac action potential different to other action potentials and why is it different?
It is relatively longer because it lasts for the duration of a single contraction (beat) of the heart.
Duration of cardiac action potential = 280 ms
Duration of skeletal muscle action potential = 2-5 ms
During which phase in the cardiac cycle are both the mitral and aortic valves open?
NEVER
When do the mitral and tricuspid valves open at the same time?
ALWAYS
What is the function of the papillary muscles and chordae tendinae?
They prevent inversion of the cusps of the mitral and tricuspid valves.
Which phases of the cardiac cycle occur during systole?
Phase 2: Isovolumetric contraction
Phase 3: Rapid ejection
Phase 4: Reduced ejection
Which phases of the cardiac cycle occur during diastole?
Phase 5: Isovolumetric relaxation
Phase 6: Rapid filling
Phase 7: Reduced filling
Phase 1: Atrial contraction
What is the typical duration of systole at 67 beats per minute
0.35 seconds
What is the typical duration of diastole at 67 beats per minute?
0.55 seconds
As heart rate increases, how does the cardiac cycle change?
Each cardiac cycle is shorter.
Systole stays the same length but diastole shortens.
When does the length of systole change?
NEVER
The mitral/tricuspid valves are open. The aortic and pulmonary valves are closed.
What stages of the cardiac cycle could the heart be in?
Diastole
Phase 6: Rapid filling
Phase 7: Reduced filling
Phase 1: Atrial contraction
The mitral/tricuspid valves and aortic/pulmonary valves are all closed.
Is the heart in systole or diastole?
Could be in systole.
Phase 2: Isovolumetric contraction
Could be in diastole.
Phase 5: Isovolumetric relaxation
When do the mitral/tricuspid valves open?
At what point in the cardiac cycle does this occur?
When pressure in the atria exceeds pressure in the ventricles.
Pressure in the atria gradually rises due to venous return until it exceeds pressure in the ventricles after phase 5-Isovolumetric relaxation.
This marks the beginning of
Phase 6: Rapid filling
What is the A wave?
Atrial pressure rises due to atrial systole during phase 1 (atrial contraction) of the cardiac cycle.
What is the C wave?
Atrial pressure increases slightly due to closing of the mitral valve during phase 2 (Isovolumetric contraction) of the cardiac cycle.
What is the X descent?
Atrial pressure initially decreases as the atrial base is pulled downward as the ventricle contracts during phase 3 (rapid ejection) of the cardiac cycle.
What is the V wave?
Atrial pressure gradually rises due to continued venous return from the lungs during phase 4 (reduced ejection) of the cardiac cycle.
What is the dicrotic notch?
There is a slight rise in aortic pressure as the aortic valve closes during phase 5 (isovolumetric relaxation) of the cardiac cycle.
What is the Y descent?
Atrial pressure decreases after opening of the mitral valve during phase 6 (rapid filling) of the cardiac cycle.
What is the P wave?
Signifies onset of atrial depolarisation on an electrocardiogram.
What is the QRS complex?
Signifies onset of ventricular depolarisation on an electrocardiogram.
What is the T wave?
Signifies ventricular repolarisation on an electrocardiogram.
Which phase in the cardiac cycle marks the end of systole?
Phase 4: Reduced ejection
Which phase in the cardiac cycle marks the end of diastole?
Phase 1: Atrial contraction
When in the cardiac cycle can S1 be heard?
Beginning of Phase 2- Isovolumetric contraction, as the mitral/tricuspid valves close.
When in the cardiac cycle can S2 be heard?
Beginning of phase 5- isovolumetric relaxation as the mitral/pulmonary valves close.
When in the cardiac cycle can s3 be heard?
During phase 6- rapid ventricular filling. This is usually silent but can sometimes be heard in children and is a sign of pathology in adults.
What proportion of ventricular filling does atrial contraction account for?
10%
Passive filling driven by venous pressure accounts for 90% of the filing of the ventricles.
What is typical end diastolic volume?
120ml
Atrial contraction usually accounts for the final 10% of ventricular filling. Does this value tend to increase or decrease with age?
It increases because venous pressure in the elderly decreases so there is less passive filling of the ventricles.
Which heart sound caused by the opening of valves?
NONE - they are caused by the closing of valves.
Where can S1 be heard at its loudest?
At the apex of the heart
Where can closing of the aortic valve and pulmonary valve be most clearly heard?
Aortic valve- 2nd intercostal space, right sternal edge
Pulmonary valve- 2nd intercostal space, left sternal edge
Where can closing of the tricuspid and mitral valve be heard the clearest?
Tricuspid valve
4th intercostal space, left sternal edge
Mitral valve
5th intercostal space, mid-clavicular line
What is stenosis?
Valve does not open enough. There is an obstruction to blood flow when the valve is usually open.
What is regurgitation?
Valve does not open fully. Back leakage when valve should be closed.
Is abnormal valve function more common in the left or right side of the heart?
Left
What are the common causes of aortic valve stenosis? (3)
Degenerative (senile calcification/fibrosis)
Congenital (bicuspid form of valve)
Chronic rheumatic fever- inflammation - commissural fusion
What are the effects of aortic valve stenosis?
Less blood can get can get through valve.
> increased left ventricle pressure–> LV hypertrophy
> left sided heart failure–> syncope, angina
What are the effects of aortic valve regurgitation?
Blood flows back into left ventricle during diastole
Increases stroke volume
Systolic pressure increases
Diastolic pressure decreases
Bounding pulse (head bobbing, Quinke’s sign- beds of nails flush in colour with each heart beat)
LV hypertrophy
What are the common causes of aortic valve regurgitation? (2)
Aortic root dilation- leaflets pulled apart
Vlavular damage- endocarditis rheumatic fever
What are the common causes of mitral valve stenosis?
99.9% cases caused by rheumatic fever (autoimmune)
Commissural fusion of valve leaflets
Harder for blood to flow from left atria to the left ventricle
What are the common causes of mitral valve regurgitation?
REMEMBER Chordae tendinae and papillary muscles normally prevent prolapse in systole
-Myxomatous degeneration can weaken tissue leading to prolapse
Other causes:
-Damage to papillary muscle after heart attack
-Left sided heart failure leads to LV dilation which can stretch valve
-Rheumatic fever can lead to leaflet fibrosis which disrupts seal formation
How does aortic valve stenosis cause angina?
Less blood can get through the valve. This causes left sided heart failure leading to angina.
What is syncope?
Insufficient blood flow to the CNS
How does aortic valve stenosis cause microangiopathic haemolytic anemia?
Red blood cells are damaged as blood is transported under very high pressure through a very narrow gap.
What type of abnormal valve function results in increased systolic pressure and decreased diastolic pressure?
Aortic valve regurgitation
What sound is characteristic of aortic valve stenosis?
Crescendo-decrescendo murmur
What sound is characteristic of aortic valve regurgitation?
Early decrescendo diastolic murmur
What heart sound is characteristic of mitral valve stenosis?
Snap as valve opens
Diastolic rumble
What sound is characteristic of mitral valve regurgitation?
Holosystolic murmur
What does afterload mean?
The load the heart must eject blood against (roughly equivalent to aortic pressure).
What does preload mean?
Amount the ventricles are stretched (filled) in diastole- related to the end diastolic volume or central venous pressure.
What does total peripheral resistance mean?
Sometimes referred to as systemic vascular resistance- resistance to blood flow offered by all the systemic vasculature
What happens to pressure of blood in a vessel as it encounters resistance?
The pressure that the blood exerts drops as it flows through ‘a resistance’.
Which blood vessels offer the greatest resistance and how can they increase resistance?
Arterioles. Constriction of the arterioles increases resistance.
How does constriction of the arterioles change arterial and venous pressure without a change in cardiac output?
Venous pressure decreases
Arterial pressure increases
What are the effects of dilation of arterioles/pre-capillary sphincters and not changing cardiac output on arterial and venous pressure?
Arterial pressure decreases
Venous pressure increases
What are the effects of increased total peripheral resistance and not changing cardiac output on venous and arterial pressure?
Arterial pressure increases
Venous pressure decreases
What are the effects of increasing cardiac output and having no change in total peripheral resistance on venous and arterial pressure?
Arterial pressure increases
Venous pressure decreases
In a clinical setting, does hypertension refer to arterial or venous pressure?
Arterial pressure
How do we facilitate changes in demand for blood without changing arterial or venous pressure?
Tissues require more blood.
Arterioles and pre-capillary sphincters dilate.
Peripheral resistance decreases so more blood flows to these tissues.
To counteract arterial pressure decreasing and venous pressure increasing cardiac output increases as this increases arterial pressure and decreases venous pressure.
Cardiac output increases by intrinsic and extrinsic mechanisms.
How can cardiac ouput be increased?
EXTRINSIC MECHANISMS
Greater activity of sympathetic nervous system:
Increase in heart rate
Increase in stroke volume by increasing contractility (changing the slope of the frank starling curve)
INTRINSIC MECHANISMS
Increase in stroke volume by:
Increased preload- increased end diastolic volume and increased venous pressure
Decreased afterload (aortic impedance) - decreased end systolic volume
Stroke volume is about ____% of normal end diastolic volume.
67%
What is the relationship between venous pressure and filling of the heart?
The greater the venous pressure, the more the heart fills.
When does the ventricle stop filling in a healthy heart?
The ventricle fills until the walls stretch enough to produce an intraventricular pressure equal to venous pressure.
What kind of a curve can be plotted to show the relationship between venous pressure and ventricular pressure?
State the labels of the axis.
Compliance curve
X axis = LV volume (ml)
Y axis = LV pressure (mmHg)
What does a significant increase in venous pressure cause?
In lungs - pulmonary oedema
In peripheries- peripheral oedema
What is typical end diastolic volume and the pressure in the left ventricle when it is this full?
EDV = 120ml Pressure = 10 mm Hg
How would left ventricular hypertrophy affect compliance?
More difficult to stretch
Therefore, decreased compliance.
Pressure increases to a higher value with the same value of end diastolic volume.
What is the difference between ventricular dilation and hypertrophy?
Simple dilatation- the walls do not materially decrease in thickness, but the cavities of the heart are enlarged
Hypertrophic dilatation-the cavities enlarge and the walls increase in thickness.
Atrophic dilatation-the cavities are enlarged and the walls of the heart become thin
Hypertrophy-the walls increase in thickness
How does ventricular dilation affect compliance?
Dilated left ventricles causes increased compliance as the ventricle stretches more. The pressure in the ventricle is lower with the same value of end diastolic volume than in a healthy ventricle.
Is ventricular hypertrophy or dilation more likely to cause an increased end diastolic pressure?
What are the implications of this?
Hypertrophy. Less room for blood. Decreased compliance. As venous pressure increases, LV end-diastolic pressure increases to a greater extent than usual. As LV end-diastolic pressure increases, stroke volume increases up to a certain point after which the actin and myosin filaments are too far apart from one another and stroke volume decreases (Frank-starling law).
Explain how decreased compliance can cause eventual decrease in stroke volume.
Decreased compliance. As venous pressure increases, LV end-diastolic pressure increases to a greater extent than usual. As LV end-diastolic pressure increases, stroke volume increases up to a certain point after which the actin and myosin filaments are too far apart from one another and stroke volume decreases (Frank-starling law).
Explain how increased compliance can result in decreased stroke volume.
Increased compliance. More room for blood. As venous pressure increases, LV end-diastolic pressure increases to a lesser extent than usual. Decreased end-diastolic pressure results in a lower stroke volume due to less stretching of the actin and myosin filaments. (Frank-starling law).
Explain the Frank-Starling law of the heart.
Increasing venous return in diastole, increases LV end diastolic pressure and causes an increase in stroke volume up to a certain point.
What are the axis on a starling curve.
X axis = left ventricular end diastolic pressure/ left ventricular volume/ venous pressure
Y axis = stroke volume
Why is the Frank-starling curve steeper in cardiac muscle than skeletal muscle?
In both cardiac and skeletal muscle, an increased sarcomere length decreases overlap between the actin and myosin filaments and increased the force of contraction.
In cardiac muscle, there is also an increase in calcium sensitivity as the muscle fibres are stretched.
How does Starling’s law of the heart ensure that both sides of the heart pump maintain the same output?
As stroke volume on the right side of the heart increases, venous pressure to the left side of the heart increases so stroke volume on the left side of the heart increases…
Why is it important that cardiac output of both sides of the heart is the same?
More blood pumped to lungs than returns to the heart—> pulmonary oedema
More blood pumped to the peripheries than returns to the heart—> peripheral oedema
What causes increased arterial pressure?
Increased peripheral resistance
What effect does hypertension have on stroke volume?
Increased afterload decreases stroke volume as the heart has to pump out against a higher pressure.
Caused by increased peripheral resistance which decreases venous pressure causing a decrease in stroke volume. Cardiac output decreases.
Eventually causes left ventricle hypertrophy as ventricle has to contract against a high pressure.
What factors determining cardiac ouput are controlled by the autonomic nervous system?
Contractility
Heart rate
Explain what happens to cardiac output after eating a meal.
Vasodilation in the gut Peripheral resistance decreases Arterial pressure decreases Venous pressure increases Stroke volume increases so cardiac output increases
The fall in arterial pressure suppresses the parasympathetic nervous system and stimulates the sympathetic nervous system.
Heart rate increases
Contractility increases
Cardiac output increases
Cardiac output increases
Increases arterial pressure
Decreases venous pressure
Returns system back to normal
Explain what happens to cardiac output when you stand up.
Venous pooling
Venous pressure decreases.
Decreased stroke volume. Decreased cardiac output.
Arterial pressure decreases
Why can’t venous pooling be rectified by intrinsic mechanisms?
What happens instead?
Both venous and arterial pressures are lowered
Intrinsic mechanisms would normally increase peripheral resistance to increase arterial pressure and decrease venous pressure.
This would further decrease venous pressure.
Therefore, the autonomic nervous system is involved with the baroreceptor reflex. This increased heart rate and increases total peripheral resistance so that arterial pressure increases and venous pressure does not fall further.
What happens if the baroreceptor reflex and autonomic nervous system do not work during venous pooling?
Postural hypotension
What happens to cardiac output during exercise?
Initially muscle pumping and venoconstriction increases venous pressure and returns more blood to the heart, increasing stroke volume.
Later, decreased total peripheral resistance increases venous pressure further.
Very early response of increased heart rate via decreased parasympathetic drive and increased sympathetic drive.
Increased contractility due to increased sympathetic drive - without this, increased venous pressure alone would move ventricular function to the top part of the Starling curve.
What would happen if only venous return increased during exercise?
What is also increased during exercise to prevent this from occurring?
If only venous return increased, then ventricular function would be shifted to the flat part of the frank starling curve.
Increasing contractility couples with increased venous return to cope to prevent this from occurring.
Why can murmurs be heard during exercise in normal individuals?
Turbulent flow
A murmur is heard in an individual who is at rest. What could this be caused by?
Disturbed flow through a valve due to stenosis
Back flow through an incompetent valve due to regurgitation
Describe the difference between centrifuging unclotted whole blood and clotted whole blood.
Unclotted whole blood
Plasma
Buffy coat
Red blood cells
Clotted whole blood
Serum
Clot
The fluid collected from clotted blood is…
Serum
The fluid collected from unclotted blood is…
Plasma
How can you prevent blood from clotting?
Add an anti-coagulant eg. Heparin
Finish the following equation
Serum = plasma -
Clotting factors
Particularly fibrinogen
Increased total blood viscosity leads to…
Sludging of blood in peripheries. Peripheries feel colder.
What is the most common cause of increased blood viscosity?
Multiple myeloma
Cancer of plasma cells- a malignant clone of plasma cells produces immunoglobulins in large quantities which increases the viscosity of the blood.
What causes increased blood viscosity? (4)
Multiple myeloma- increased plasma cells
Polycythaemia- increased red blood cells
Thrombocythaemia- increased thrombocytes
Leukaemia- increased white blood cells
Why is it clinically useful to measure plasma viscosity?
Minor changes in plasma viscosity can result from raised levels of acute phase proteins (eg. Fibrinogen, complement factors and C-reactive protein). Acute phase proteins increase in response to inflammation. Therefore, minor changes in plasma viscosity can be used to measure the inflammatory response. In recent years, we have been able to measure C-reactive protein (CRP) and this is more commonly used to measure inflammation
What is the difference between turbulent and laminar blood flow?
Turbulent flow- blood flowing in all directions in the vessel and continually mixes within the vessel.
Laminar flow- blood flows in streamlines with each layer of blood remaining the same distance from the wall.
Describe normal blood flow.
Laminar
When is blood flow turbulent?
Increased blood flow and the rate of blood flow becomes too great Blood passes an obstruction in a vessel Blood makes a sharp turn Blood passes over a rough surface Increased resistance to flow
Why might you hear a murmur in anaemic patients?
Limited number of red blood cells.
Heart rate to increase cardiac output so oxygen can be transported around the body quick enough
Results in turbulent flow which can be heard as a murmur
Why might you hear a murmur in a patient with thyrotoxicosis?
Increased T3 and T4
Causes increased sensitivity to catecholamines
Increased chronotropy and inotropy
Turbulent flow
What units is pressure measured in?
Psi (pounds per square inch)
What are the units for blood flow?
Volume per unit time ml/min or l/hour
Give an equation for calculating kinetic energy.
1/2 x m x v squared
M= mass V= velocity
There must be a difference in ____ to feel a pulse.
Pressure
Why can’t a pulse be felt in blood vessels that are not compliant?
Volume does not change in response to pressure.
Describe how flow, pressure, velocity and kinetic energy changes distally and proximally to a stenosis in an artery.
Proximal to the stenosis, flow is less, pressure is greater, velocity is lower and kinetic energy is lower
Distal to the stenosis, flow is less, pressure is less, velocity is higher and kinetic energy is higher
When palpated, what can be felt at a stenosis?
A thrill
Blood vessel vibrates due to the high velocity and kinetic energy.
On auscultation, what can be heard if there stenosis of a peripheral artery/heart valve?
Peripheral artery
Bruit - sounds like a plane taking off
Heart valve
Murmur
What is a stenosis?
Narrowing of a blood vessel
Eventually, what might occur distally to a stenosis in an an artery?
Distal to the stenosis, blood hits the wall of the artery at high velocity and high kinetic energy. This causes a post stenotic dilatation of the blood vessel as the wall of the artery dilates. Bursting of this is an aneurysm.
What causes critical ischaemia?
One stenosis followed by another stenosis.
Distal to the second stenosis, flow is further decreased and may stop flowing completely.
Where is critical ischaemia common?
Legs
Why is it usually difficult to find an elderly persons pulse in the femoral artery?
As people age, arteries often calcify and become less compliant. Volume does not increase in response to an increase in pressure so a pulse cannot be felt.
What are the changes in flow, pressure and velocity when there is greater peripheral resistance?
Flow and pressure decreases
Velocity increases
What are the changes in flow, pressure and velocity when peripheral resistance is decreased?
Flow and pressure increases
Velocity decreases
In an descending aorta pressure tracing, what creates the anacrotic limb?
Systolic uptake
Pressure in the descending aorta increases rapidly during systole as blood is ejected out of the ventricles as they contract and the elastic walls of the aorta stretches.
Peak systolic pressure
This is the highest pressure in the descending aorta.
In a descending aorta pressure tracing, what creates the dicrotic limb?
Systolic decline
Pressure decreases as the ventricles relax and less blood is ejected from the ventricles
Dicrotic notch
The pressure in the aorta exceeds that in the left ventricle and the aortic valve closes. This is the end of systole. There is a slight increase in pressure as blood collects in the aorta.
Diastolic run off
Pressure decreases as blood flows down the aorta and the aortic wall recoils
End diastolic pressure
This is the lowest pressure in the aorta as there is no flow of blood from the ventricles
Give an equation for calculating pulse pressure.
Pulse pressure = peak systolic pressure - end diastolic pressure
In an average person, what is the value of pulse pressure?
120 - 80 = 40 mm Hg
How do we measure blood pressure?
Sphygomanometer
How can mean arterial pressure be estimated?
Diastolic pressure + 1/3 pulse pressure
In an average person, what is the value of mean arterial pressure?
80 + 13 = 93 mm Hg
What are the implications of mean arterial pressure being below 70 mm g?
Organ perfusion is impaired
When measuring blood pressure, how can you make the reading as accurate as possible?
Cuff must go around at least 80% of the arm.
An undersized cuff can give a false reading of blood pressure.
What can affect the accuracy of a blood pressure reading?
The height at which blood pressure is measured due to the effect of gravity. Venous and arterial pressure is greater at a lower height when standing up.
The size of the cuff. An undersized cuff can give a false reading of blood pressure.
What is retrograde flow?
Retrograde flow is when the blood bounces back slightly. It can occur in the arterial system and is greatest when peripheral resistance is high.
What is the effect of peripheral resistance on retrograde flow?
Greater peripheral resistance—> greater retrograde flow
What determines the volume of a pulse?
- The force with which the left ventricle is able to eject the blood into the arterial system to develop a normal shock wave.
Weaker force —> reduced pulse volume—> thready pulse - Pulse pressure. This is the major determinant of how strong the pulse is.
Greater pulse pressure—> increased pulse volume—> bounding pulse
Pulse pressure= peak systolic pressure - end diastolic pressure
What is a thready pulse?
Pulse volume is lower than usual
What are the causes of a thready pulse?
LV failure
Aortic valve stenosis
Hypovolaemia (severe dehydration/bleeding)
Why does bradycardia produce a bounding pulse?
Bradycardia- greater amount of time spent in diastole than usual. End diastolic pressure reaches a smaller value than normal. Pulse pressure increases and pulse volume increases
Why does low peripheral resistance cause a bounding pulse?
Low peripheral resistance caused by vasodilation- diastolic run off occurs more quickly as blood rushes out of the aorta to the peripheries. End diastolic pressure reaches a smaller value within the same period of time. Pulse pressure increases and pulse volume increases
What are the common causes of congenital heart defects? (3)
Genetic
Downs, turner’s syndrome, marfan’s syndrome
Environmental
Teratogenicity from drugs, alcohol etc.
Maternal infections
Rubella, toxoplasmosis etc.
Give the approximate percentage saturation of haemoglobin in the different chambers of the heart.
Left atrium- 99% Left ventricle- 99% Aorta- 99% Right atrium- 67% Right ventricle- 67% Pulmonary arteries- 67%
Give the average pressures in the different chambers of the heart
Right atrium- 0-4mmHg Right ventricle- 25/3 mmHg Pulmonary arteries- 25/10mmHg Left atrium - 8-10 mmHg Left ventricle- 120/7mmHg Aorta-120/80mmHg
What is a shunt?
A communication between two sides of the circulation.
What is cyanosis?
Bluish discolouration skin, nail beds and mucous membranes due to unsaturated haemoglobin entering the systemic circulation
When does the cardiogenic field appear and why?
In the 3rd week of development because nutrient and gas exchange needs of the rapidly growing embryo can no longer be met by diffusion alone so the developing cardiovascular system is formed to deliver these substances over long distances.
How is the primitive heart tube formed?
The endocardial tubes are brought together during embryonic folding and fuse in the midline.
Describe the primitive heart tube.
Cranial end
Aortic roots (2 vessel outlet) Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus (4 vessel inlet)
Caudal end
What is the truncus arteriosus destined to be?
The roots and proximal portions of the pulmonary trunk and aorta
What is the bulbus cord is destined to be?
Part of the right ventricle
What is the primitive ventricle destined to be?
The left ventricle
What is the primitive atrium destined to be?
Most of the right atrium and some of the right ventricle
What is the cardiogenic field?
A zone within the mesoderm consisting of blood pools and tiny vessels. There is a space which will be the pericardial cavity.
What is the sinus venosus destined to be?
Right atrium
What happens during looping of the primitive heart tube?
The tube elongates.
It runs out of room.
Twists and folds up placing the inflow cranially and dorsally to the outflow.
From which structures in the primitive heart tube is the right atrium developed from?
Most of the primitive atrium
Sinus venosus
This recieves venous drainage from the body (venue cavae) and the heart (coronary sinus)
From which structures in the primitive heart tube does the left atrium develop from?
A small portion of the primitive atrium
Absorbs proximal parts of pulmonary veins
Receives oxygenated blood from the lungs
What explains why an adults left atrium has a smooth inner surface whereas their right atrium has a rough inner surface?
The left atrium mainly develops from proximal parts of the pulmonary veins which has a smooth inner surface whereas the right atrium mainly develops from the primitive atrium which has a rough inner surface.
What ensures the heart occupies fully the pericardial sac?
Looping in the fourth week of embryonic development
What is the difference between adult and foetal circulation?
There is a double circulation in series in an adult but in a foetus, the lungs do not work so there is no requirement for this double circulation.
Oxygenation and removal of carbon dioxide occurs at the placenta for a foetus.
Shunts are required to maintain foetal life but these must be reversible at birth
What shunts are present in a foetal circulation and what is the purpose of these?
Ductus venosus- between inferior vena cava and the liver to prevent all blood entering the liver
Ductus arteriosus- between the aorta and pulmonary trunk which is right to left to ensure all highly oxygenated blood is pumped to the foetus
Foramen ovale-between the atria which is right to left to ensure that blood enters the left atria and hence the left ventricle so that blood can enter the systemic circulation
In which vessel is the most oxygenated blood in a foetus?
The inferior vena cava which comes from the placenta
How do the shunts close when a baby is born?
Ductus venosus-physiological closure
Placental support is removed
Ductus arteriosus
Ductus arteriosus undergoes a muscular spasm and closes
Ductus venosus and ductus arteriosus become fibrotic and close.
Foramen ovale-mechanical closure
Left atrial pressure increases
Septum primum closes firmly against septum secondum
Which aortic arches in the foetus form the arch of the aorta and the pulmonary artery?
Arch 4 LHS = arch of the aorta
Arch 6 RHS = pulmonary artery
How many aortic arches are there in a foetus?
6
Which nerve loops around the aortic arch?
Left recurrent laryngeal nerve
How does the atrial septal wall form?
Neural crest cells migrate into the developing heart making a shaft of tissue called endocardial cushions.
Endocardial tissues create a crescent shaped wedge down the roof of the atria towards the atrioventricular canal called the septum primum. The hole is the Ostium primum which allows right to left shunt.
Septum secundum forms and the foramen ovale forms.
This forms a right to left shunt.
Why is atrial septal defect common?
There is a complex process in producing the atrial septum. Atrial septal defect can arise due to problems in forming either septum primum or septum secondum.
What are the two components of the ventricular septum?
Muscular
Membranous
Why does inadequate formation of endocardial cushions or endocardial cushions in the incorrect place cause ventricular septal defect?
The muscular portion of the septum which forms the majority of the septum grows upwards towards the fused endocardial cushions.
What is the interventricular foramen and how is it closed?
The interventricular foramen is the gap formed when the muscular portion of the septum grows upwards towards the endocardial cushions.
This is closed by the membranous portion of the interventricular septum formed by connective tissue derived from endocardial cushions to fill the gap.
Describe septation of outflow tracts.
Endocardial cushions appear in the truncus arteriosus.
As they grow towards each other, they twist around each other to form a spiral septum.
This connects the left ventricle to the aorta and connects the right ventricle to the pulmonary trunk
What is transposition of the great arteries?
The aorta arises from the right ventricle.
The pulmonary trunk arises from the left ventricle.
What is tetralogy of fallot?
Large ventricular septal defect
Overriding aorta
Right ventricular outflow tract obstruction (pulmonary stenosis)
Right ventricular hypertrophy
Why are neural crest cells important?
They migrate to from the endocardial cushions which are the foundation of atrial septation, ventricular septation and septation of the outflow tracts.
How can alcohol affect the development of a foetus?
Low concentrations of alcohol can kill or damage these cells
What type of shunting does tetralogy of fallot cause?
Right to left shunting
What causes coarctation of the aorta?
Narrowing of the aortic lumen in the region of the former ductus arteriosus.
What is eisenmenger syndrome?
The condition of severe pulmonary vascular obstruction that results from chronic left to right shunting through a congenital heart defect. The elevated pulmonary vascular resistance causes reversal of the original shunt and systemic cyanosis.
When can patent foramen ovale cause a problem?
Takes on significance if the right atrial pressure becomes elevated (due to pulmonary hypertension or right heart failure) leading to right to left shunting since the higher left atrial pressure causes functional closure of the flap valve.
Coarctation of the aorta affects blood flow to some regions of the body. Which regions of the body are and are not affected?
Because vessels to the head and upper limbs usually emerge proximal to the coarctation, the blood supply to these regions is not compromised.
However, blood flow to the rest of the body is reduced.
If no shunt existence, would transposition of the great arteries be compatable with life?
Compatible with life in uterus because flow through ductus arteriosus and foramen ovale allows communication between the two circulations.
After birth, without any intervention, TGA is not compatable with life because oxygenated blood does not reach systemic tissues.
On examination, what is noticeable about the femoral pulse of patients with coarctation of the aorta?
Femoral pulses are weak and delayed.
An elevated blood pressure in the upper body is common.
Give some examples of acyanotic congenital heart defects.
Left to right shunts: Atrial septal defect (ASD) Patent foramen ovale (PFO) Ventricular septal defect (VSD) Patent ductus arteriosus (PDA) Obstructive lesions: Aortic stenosis (Hypoplasia) Pulmonary stenosis (Valve, outflow, branch) Coarctation of the aorta Mitral stenosis
Give some examples of cyanotic congenital heart defects.
Complex, right to left shunts Tetralogy of Fallot Tricuspid Atresia Transposition of the great arteries Hypoplastic left heart
What is hypoplastic left heart?
Left ventricle and ascending aorta fail to develop properly.
What influences the course of the recurrent laryngeal nerves?
Caudal shift of the development heart and expansion of the developing neck region
The need for a foetal shunt between the pulmonary trunk and aorta
What is the difference between the upstroke in an action potential in cardiomyocytes and pacemaker cells?
Cardiomyocytes = Na+ influx via the opening of fast type Na+ channels due to depolarisation.
Pacemaker cells = Ca2+ influx via the opening of L-type Ca2+ channels due to depolarisation.
What is the difference between the Na+ channels involved in an action potential in cardiomyocytes and pacemaker cells?
Cardiomyocytes
Fast type Na+ channels-responsible for upstroke in AP
Pacemaker cells
Slow type Na+ channels- responsible for ‘pacemaker potential’
What is pacemaker potential?
Slow Na+ channels slowly open and the resting membrane potential depolarises steadily from its most negative value of -60mV in pacemaker cells.
They activate more with hyperpolarisation.
What is the main difference between the shape of an action potential in a pacemaker cell and in a cardiomyocyte?
Plateau phase in cardiomyocytes
Ca2+ influx and K+ outflux
Describe how movement of ions changes in a cardiac action potential in cardiomyocytes.
Phase 0 –> Na+ influx
Phase 1 –> transient K+ efflux
Phase 2 –> Ca2+ influx and K+ efflux
Phase 3 –> K+ efflux
Describe how movement of ions changes in a cardiac action potential in pacemaker cells.
Slow Na+ influx
Fast Ca2+ influx
K+ outflux
Slow voltage gated Na+ channels are activated by depolarisation.
True or false
False
Activated by hyperpolarisation
They are HCN channels
Hyperpolarisation activated cyclic nucleotide gated channels
Which region of the heart depolarises fastest?
SA node- therefore, this sets the rhythm
Where are pacemaker cells found?
SA node and AV node
Do purkinje fibres have a stable resting potential?
No they have slow type Na+ channels that allows Na+ to continuously leak in.
But does not depolarise as fast as SA node
Which regions of the heart have the capacity to set the rhythm of the heart?
Those which do not have a stable resting potential due to continuous influx of Na+ :
SA node
AV node
Purkinje fibres
Describe the terms asystole and fibrillation in terms of electrical activity of the heart.
Asystole- action potentials fail
Fibrillation- electrical activity becomes random
What is normal plasma K+ concentration?
3.5-5.5 mmol/L
What is hyperkalaemia?
> 5.5mmol/L of K+ in the blood
Why cardiac myocytes sensitive to changes in K+ concentration?
Their resting membrane potential is very close to Ek (-90mV)
There are many different kinds of K+ channels
What is hypokalaemia?
<3.4mmol/L of K+ in the blood
Describe the effect of hyperkalaemia on an action potential cardiac myocytes.
EK is less negative
Inactivates some of the voltage gated Na+ channels
Slow upstroke
Narrows action potential
What are the consequences of hyperkalaemia on the heart and what do the extent of the consequences depend upon?
Asystole- the heart can stop because of the slower upstroke of the action potential
May initially get an increase in excitability
Depends on extent of hyperkalaemia and how quickly hyperkalaemia develops
What are the treatments for hyperkalaemia and when should they be given?
Calcium gluconate
Insulin + glucose
These won’t work if the heart has already stopped
Define mild, moderate and severe hyperkalaemia.
Mild hyperkalaemia = 5.5-5.9mmol/L
Moderate hyperkalaemia = 6.0-6.3 mmol/L
Severe hyperkalaemia> 6.5mmol/L
Why can calcium gluconate be given as a treatment for hyperkalaemia?
Calcium makes the heart less excitable because it is a bivalent cation.
Why is glucose given together with insulin in the treatment of hyperkalaemia?
To prevent hypoglycaemia
If you gave insulin alone, this would increase uptake of glucose from the blood and would cause hypoglycaemia.
Insulin increases uptake of K+ into cardiac myocytes
What is the effect of hypokalaemia on action potentials in cardiac myocytes?
Decreased plasma K+ concentration
Allosteric effect reducing the conductance of voltage gated K+ channels so downstroke of AP is slower
Leads to a longer action potential
Early reactivation of some voltage gated Ca2+ channels as some of the membrane repolarises
Leads to early after depolarisations (EADs) and hence oscillations in membrane potential
Ventricular fibrillation
What are the effects of hypokalaemia on the heart?
Oscillations in membrane potential—>Ventricular fibrillation
When is hypokalaemia dangerous?
In patients
- with existing heart problems
- people on anti-arrhythmic drug
Describe excitation-contraction coupling in cardiac cells?
Depolarisation open L-type Ca2+ channels in the T-tubule system
Localised Ca2+ entry opens CICR channels in the sarcoplasmic reticulum
Close link between L-type channels and Ca2+ release channels (but they’re not directly connected)
25% enters across the sarcolemma, 75% released from SR
What happens at a cellular level with the relaxation of cardiac myocytes?
Ca2+ in the cardiac myocytes is returned to resting levels
Most is pumped back into the SR as 75% of Ca2+ came from here, some exits across the membrane
Ca2+ ATPase is activated (high affinity)
Where in the vascular wall are smooth muscle cells found?
Tunica media
Describe excitation contraction coupling in smooth muscle cells.
Opening of voltage gated Ca2+ channels due to depolarisation allows Ca2+ to enter
A1 adrenoreceptors activate and Ca2+ is released from SR via activation of phospholipase C and creation of iP3 which binds to SR
Ca2+ binds to calmodulin. Ca2+ activates myosin light chain kinase which phosphorylates the myosin light chain to permit activation with actin.
DAG stimulates PKC which inhibits myosin light chain phosphatase. This allows sustained vasoconstriction.
Does troponin C have a role in contraction in smooth muscle cells?
No. Ca2+ binds to calmodulin.
This activated myosin light chain kinase
Myosin light chain kinase phosphorylates the myosin light chain to permit interaction with actin
Describe what happens in the cell during relaxation of smooth muscle cells.
Myosin light chain phosphatase dephosphorylates the myosin light chain
How is contraction in smooth muscle cells in arterioles different to contraction in cardiac myocytes?
Ca2+ binds to calmodulin which activates myosin light chain kinase in smooth muscle
Ca2+ binds to troponin C in cardiac muscle
How does the body coordinate its response to exercise and stress?
Autonomic nervous system
How does the autonomic nervous system control the activity of the cardiovascular system?
Can change:
Rate
Force of contraction of heart
Peripheral resistance of blood vessels (arteriolar/venous constriction)
We can divide the autonomic nervous system into sympathetic and parasympathetic branches.
This division is based on….
Anatomical grounds
What is the origin of parasympathetic nerves?
Cranial and sacral origin
What is the origin of sympathetic nerves?
Thoracic and lumbar origin
What is the enteric nervous system?
Network of neurones surrounding GI tract
Normally controlled via sympathetic and parasympathetic fibres
What branch of the nervous system is dominant under basal conditions?
Parasympathetic nervous system
Where are alpha 1 adrenoreceptors found?
Smooth muscle of blood vessels- vasoconstriction
Pupil of eye. Dilation
Sweat glands - increased sweat release
If you activate the sympathetic nervous system, is sympathetic drive to all tissues regulated?
No, sympathetic drives to different tissues is independently regulately
What happens if you denervate a heart?
It beats at a faster rate to about 100 beats per minute because parasympathetic nervous system dominates at rest
At rest, which nerve innervates the heart?
Vagus nerve-10th cranial nerve
What muscarinic and adrenergic receptors are present on the heart?
M2
B1
What influence does the parasympathetic nervous system have on the heart?
Decreases heart rate (negative chronological effect)
Decreases AV node conduction velocity
What influence does the sympathetic nervous system have on the heart?
Increases heart rate (positive chronograph)
Increases force of contraction (positive inotropy)
