Cardiovascular System (S1-6) Flashcards
S1: Intro To CVS + Histology Of The Heart S2: The Heart As A Pump S3: Congenital Heart Defects S4: Cellular And Molecular Events In The CVS / The ANS And The CVS S5: Pressure, Flow And Resistance / The Peripheral Circulation S6: Control Of Cardiac Output / Response Of Whole System
Why do we need a cardiovascular system? (S1)
We have many cells (to the order of 10^14), many of which are far from the source of O2 and nutrients. Diffusion alone cannot efficiently exchange O2 and nutrients around the body. It is too slow. A cardiovascular system, which comprises of gas exchange and a circulatory system, allows us to have efficient exchange.
What does blood transport around the body? (S1)
O2, metabolic substrates, CO2 and waste products.
Where does diffusion between blood and tissues take place? (S1)
At the capillaries
What is the composition of capillaries? (S1)
They have one layer of endothelial cells - simple squamous epithelium - surrounded by basal lamina
At the capillaries, what does O2 and CO2 diffuse through? What do other molecules such as glucose, lactate and amino acids, which are hydrophillic, diffuse through? (S1)
O2 and CO2 diffuse through the lipid bilayer.
Larger molecules diffuse through small, aqueous pores between endothelial cells, in the membranes.
What factors affect the rate of diffusion? (S1)
The area, diffusion ‘resistance’, concentration gradient.
How does area affect the rate of diffusion? What is area like with regards to capillaries? (S1)
The rate of diffusion depends on the area available for exchange; the more available, the quicker diffusion will be.
Area available for exchange between capillaries and tissues are very large, although it depends on capillary density. A more metabolically active tissue will have more capillaries.
What three factors affect diffusion resistance? (S1)
It depends on the nature of the molecule (lipophilic/hydrophilic, size), nature of the barrier (eg pore size and number of pores for hydrophillic substances) and the path length. The path length depends on capillary density and the path is shortest in the most active tissues. Diffusion resistance is mostly low.
What is the rate of blood flow known as? (S1)
The perfusion rate.
How much blood flow does the brain, heart and kidneys need? (S1)
Brain: 0.5 (constant flow); Heart: 0.9 to 3.6 (increases during exercise); Kidneys: 3.5 (constant flow). All units are ml.min-1.g-1
Something different…
How much roughly do the brain, heart and kidneys weigh if flow l.min-1 is 0.75 (brain), 0.3 to 1.2 (at rest and pumping to its maximum capacity; the heart) and 1.2 (kidneys)?
Brain: 1.5kg (probably an over-estimate); Heart: 0.3kg; Kidneys: 0.3kg
When is blood flow to skeletal muscle high? And to the gut?
Skeletal muscle: during exercise (can go from 1 l.min-1 to up to 16 l.min-1)
The gut: high after a large meal (1.4 lmin-1 at rest, can increase to 2.4 l.min-1
How much blood flows to the body’s tissues in a minute at rest? (S1)
5 l.min-1
What proportion does the brain, heart and kidneys make up of the total blood flow around the body (at rest)? (S1)
0.45
How much blood flows to the skin in a minute - does this ever change? (S1)
0.2 litres. No.
What is the maximum blood flow to the body’s tissues in a minute when might this occur? (S1)
24.5 l.min-1 seen during intense exercise.
What are the components of the cardiovascular system? (S1)
Pump: the heart;
Distribution system: vessels & blood;
Exchange mechanism: capillaries;
Flow control: arterioles and precapillary sphincters.
Why is the brain harder to perfuse than the kidneys? (S1)
Due to gravity’s effects.
What must be added to regulate blood flow? (S1)
Resistance reduces the ease with which some regions are perfused in order to direct blood flow to the more difficult regions to perfuse.
Which vessels can increase resistance (in doing so regulating blood flow)? (S1)
Arterioles. Precapillary spinchters will also play a part in regulating blood flow.
How can veins control the total flow in the system? (S1)
Veins have thin walls which can easily distend or collapse enabling them to act as a variable reservoir for blood. This capacitance of the veins provides the temporary store… This process requires a temporary store of blood which can be returned to the heart at a different rate.
How is blood distributed in the cardiovascular system? (S1)
65% in the veins, 20% heart & lungs, 10% arteries & arterioles, 5% capillaries
How much blood will a large man contain? (S1)
6 litres.
How much surface area does the capillaries have for exchange? (S1)
About 600m^2.
What do arteries do? (S1)
They are blood vessels that carry blood away from the heart to the capillary beds.
Which three major arterial trunks arise from the arch of the aorta? (S1)
The brachiocephalic artery, common carotid artery and the left subclavian artery.
In the abdominal cavity the aorta terminates by bifurcating into the… (S1)
Left and right common iliac arteries in the pelvis.
What does left ventricle contraction cause blood pressure in the aorta to rise to? (S1)
Approx. 120 mm Hg. The walls of the aorta will stretch (as well as other elastic arteries).
What happens during diastole? (S1)
The aortic semilunar valve closes and the walls of the aorta recoil. This maintains the pressure on the blood and moves it towards the smaller vessels.
What does aortic pressure drop to during diastole? (S1)
70-80 mm Hg.
What three types (from widest to narrowest) are arteries classified into? (S1)
Elastic conducting arteries (which will have more elastic fibres), muscular distributing arteries (which have more smooth muscle fibres) and arterioles.
What is the diameter of arteries and arterioles controlled by? (S1)
The autonomic nervous system.
What do the arterioles branch into before reaching the capillaries? (S1)
Metarterioles.
What are the three layers of the walls of the arteries and veins called (starting from nearest to the lumen)? (S1)
Tunica intima, tunica media and tunica adventita.
Why might elastic arteries appear yellow? (S1)
This may be the case if there is abundant elastin. It will normally be seen in the fresh state.
Outline the main features of each layer of the elastic arteries. (S1)
Tunica intima: Endothelial cells; narrow subendothelium of connective tissue with discontinuous internal elastic lamina.
TUNICA MEDIA: 40-70 fenestrated elastic membranes, with smooth muscle cells and collagen between these lamellae.
Tunica adventitia: Layer of fibroelastic connective tissue containing vasa vasorum, lymphatic vessels and nerve fibres.
What are vasa vasorum? (S1)
Vasa vasorum are a network of small blood vessels that supply the walls of large blood vessels.
Outline the main features of each layer of the muscular arteries. (S1)
Tunica intima: Endothelium, subendothelial layer, thick internal elastic lamina.
TUNICA MEDIA: 40 layers of smooth muscle cells (connected by gap junctions for coordinated contraction). Prominent external elastic lamina.
Tunica adventitia: THIN layer of fibroelastic tissue containing vasa vasorum, lymphatic vessels and nerve fibres.
What are end arteries and where might they be found in the body? (S1)
End arteries are terminal arteries supplying all or most of the blood to a body part without significant collateral circulation. The coronary artery, splenic and renal arteries as well as the central artery to the retina are all end arteries.
What is the issue if end arteries are occluded? (S1)
End arteries branch without the development of channels connecting with other arteries. This means if they are occluded there will be insufficient blood supply to the dependent tissue.
When is an artery considered an arteriole? (S1)
When it has a diameter less than 0.1mm.
Outline the main features of each layer of the arterioles. (S1)
Tunica intima: layer of endothelial cells and very thin layer of subendothelial connective tissue.
TUNICA MEDIA: only one to three layers of smooth muscle, although in small arterioles the tunica media is composed of a single smooth muscle cell that encircles the endothelial cells.
Tunica adventitia: scant
Define a metarteriole. (S1)
It is an artery that supplies blood to capillary beds.
How do metarterioles differ from arterioles? (S1)
The smooth muscle layer is not continuous in metarterioles. Rather, the individual muscle cells are spaced apart and each encircles the endothelium of a capillary; this is known as the precapillary sphincter. Each muscle cell acts as a spinchter, upon contraction, controlling blood flow into the capillary bed.
During strenuous exercise how is blood flow to skeletal muscles increased? How would this differ after eating a hearty meal? (S1)
Dilation of arterioles to skeletal muscle, and constriction of arterioles to the intestine. The reverse is true for a large meal.
How wide are the narrowest arterioles? How much wider than an ordinary capillary is this? (S1)
30um. 3-4 times.
What are the three types of capillaries and where are they found? (S1)
Continuous: found in nervous, muscle and connective tissues, exocrine glands and the lungs.
Fenestrated: in parts of gut, endocrine glands and renal glomerulus. There are small holes across thin parts of the endothelium, bridged by a thin diaphragm (except in the renal glomerulus).
Discontinuous (sinusoidal): seen in liver, spleen and bone marrow. They have a larger diameter (30-40um) and slower blood flow.
What is angiogenesis? (S1)
The development of new blood vessels from pre-existing vessels.
What is the diameter of postcapillary venules? Are they more or less permeable than capillaries? (S1)
10-30um, they are more permeable than capillaries.
Why does fluid tend to drain into postcapillary venules? What is the exception? (S1)
This is due to the pressure being lower in them than that of capillaries and surrounding tissue. When there is an inflammatory response operating fluid and leukocytes emigrate. These venules are the preferred location for emigration of leukocytes from the blood.
What is the diameter of venules? (S1)
50um and they can increase to 1mm.
Outline the main features of each layer of the vein. (S1)
Small and medium-sized veins have:
Tunica intima: thin
Tunica media: 2 or 3 layers of smooth muscle
Tunica adventitia: well developed
Large veins have diameters >10mm
Tunica intima: thicker
Tunica media: not prominent but have circularly arranged smooth muscle
Tunica adventitia: well-developed logitudinally orientated smooth muscle
Why might the superficial veins of the legs have a well-defined muscular wall? (S1)
Possibly to resist distension caused by gravity.
What are venae comitantes? What does the pulsing of the artery promote? (S1)
They are the deep paired veins that, in certain anatomical positions, accompany one of the smaller arteries on each side of the artery. The three vessels are wrapped together in one sheath. The pulsing of the artery promotes venous return within the adjacent, parallel, paired veins.
What are some examples of arteries that have venae comitantes? (S1)
The brachial, ulnar and tibial arteries.
What are some examples of large veins? (S1)
Vena cavae, pulmonary, portal, renal, internal jugular, iliac, and azygous veins.
What is the mitral valve between? (S2)
The left atria and the left ventricle. It is sometimes known as the bicuspid valve.
What is the tricuspid valve between? (S2)
The right atria and the right ventricle.
What does the action potential cause (in relation to the concentration of ions within the cell)? (S2)
It causes intracellular calcium to rise.
How long is an action potential? (S2)
A single contraction lasts 280ms.
What are action potentials triggered by? (S2)
The spread of excitation from cell to cell.
What is the contraction period referred to as?
And the relaxation period? (S2)
Systole
Diastole
What do pacemakers do? (S2)
They generate one action potential at a regular interval.
How often does the sino-atrial node generate an action potential at rest? (S2)
About once a second.
How long does ventricular systole last for? (S2)
280ms
How long does ventricular diastole last for? (S2)
At rest, it will last for 700ms before the next systole.
When does the mitral valve open? When does it close? (S2)
It opens when atrial pressure exceeds intraventricular pressure i.e. early diastole and closes at a point in ventricular systole, when ventricular pressure exceeds atrial pressure and back flow of blood causes the valves to close shut.
When does the aortic valve open? When does it close? (S2)
It opens in systole, after the ventricles contract so that intra-ventricular pressure exceeds aortic pressure. It closes when aortic pressure exceeds ventricular pressure - this is towards the end of systole - and blood flows backwards shutting the valve.
How is ventricular muscle organised in order to facilitate the pumping of blood? (S2)
Ventricular muscle is organised into figure of eight bands. These squeeze the ventricular chamber forcefully in the most effective way to allow ejection through the outflow valve.
How does the contraction of the ventricle ensure back flow of blood is reduced? (S2)
The apex of the heart contracts first and relaxes last to reduce back flow of blood.
What is the main difference between the right and the left heart? (S2)
The left side has a thicker myocardium and so must pump blood around the body and therefore harder, than just around the lungs.
What is the origin of the first heart sound? (S2)
As the atrioventricular valves close oscillations are induced in a variety of structures, producing a mixed sound with a crescendo-descendo quality – ‘lup’
What is the origin of the second heart sound? (S2)
As the semi-lunar valves close oscillations are induced in other structures, including the column of blood in the arteries. This produces the sound of shorter duration, higher frequency and lower intensity than the first – ‘dup’
Why may a 3rd or even 4th sound be heard? (S2)
A 3rd sound may be heard early in diastole and a 4th may be heard during atrial contraction.
What is a heart murmur? (S2)
The turbulent flow of blood.
What are the two types of murmur? (S2)
Stenosis, incompetence or regurgitation
What is stenosis? (S2)
There is a narrowed valve, normally due to calcification - (in the case of aortic stenosis it could be due to acute rheumatic fever).
What is incompetance of a valve? (S2)
It is where a valve does not close properly and so there is back flow of blood.
When do murmurs occur? (S2)
When blood flow is at its highest, e.g. aortic stenosis produces a murmur in the rapid ejection phase.
What is cardiac output? (S2)
Cardiac output is stroke volume times heart rate. The stroke volume is the amount of blood one ventricle of the heart ejects with each beat.
Outline the entirety of the cardiac cycle (starting from early diastole)! (S2)
INFLOW VALVES OPEN
In early diastole, the ventricular mass relaxes.
The intraventricular pressure falls below atrial pressure = inflow valves opening.
RAPID FILLING PHASE
The atria, having been distended by continuous venous return from throughout the preceding systole, so initially blood is forced rapidly from the atria into the ventricles – the ‘rapid filling’ phase.
SLOWER FILLING OF VENTRICLES
Filling of the ventricles continues through diastole, at a steadily decreasing rate until the intra-ventricular pressure has risen to match atrial pressure. At low heart rates, ventricles are more or less full before the next systole begins.
ATRIAL SYSTOLE
Atrial systole forces a small extra amount of blood into the ventricles. After a delay of about 100-150ms the ventricles begin to contract.
CLOSING OF INFLOW VALVES
As intraventricular pressure rises, blood tends to flow the wrong way through the Mitral valve, producing turbulence that closes the valve forcibly.
OUTFLOW VALVES OPEN
Ventricles then contract isovolumetrically; intraventricular pressure rises rapidly until it exceeds the diastolic pressure of the pressure in the arteries, when the outflow (Aortic/Pulmonary) valves open.
RAPID EJECTION PERIOD
There is then a rapid ejection period, where both intraventricular and arterial pressure rise to a maximum.
OUTFLOW VALVES CLOSE
Towards the end of systole intraventricular pressure falls and once below the arterial pressure the outflow valves close due to the backflow of blood.
When the intraventricular pressure falls below atrial pressure the whole process starts again.
Explain how the… AV VALVES OPEN, RAPID FILLING PHASE and the SLOWER FILLING OF VENTRICLES. (S2)
In early diastole, the ventricular mass relaxes.
The intraventricular pressure falls below atrial pressure = Tricuspid/Mitral valves opening.
The atria, having been distended by continuous venous return from throughout the preceding systole, so initially blood is forced rapidly from the atria into the ventricles – the ‘rapid filling’ phase.
Filling of the ventricles continues through diastole, at a steadily decreasing rate until the intra-ventricular pressure has risen to match atrial pressure. At low heart rates, ventricles are more or less full before the next systole begins.
What happens after the SLOWER FILLING OF THE VENTRICLES? (S2)
ATRIAL SYSTOLE
Atrial systole forces a small extra amount of blood into the ventricles. After a delay of about 100-150ms the ventricles begin to contract.
Why do the AV VALVES CLOSE? (S2)
CLOSING OF AV VALVES
As intraventricular pressure rises, blood tends to flow the wrong way through the Mitral valve, producing turbulence that closes the valve forcibly.
What happens after ATRIAL SYSTOLE and the INFLOW VALVES CLOSE? What is the RAPID EJECTION PERIOD? (S2)
OUTFLOW VALVES OPEN
Ventricles then contract isovolumetrically; intraventricular pressure rises rapidly until it exceeds the diastolic pressure of the pressure in the arteries, when the outflow (Aortic/Pulmonary) valves open.
RAPID EJECTION PERIOD
There is then a rapid ejection period, where both intraventricular and arterial pressure rise to a maximum.
What happens after the RAPID EJECTION PERIOD? What action leads to the OPENING OF THE INFLOW VALVES? (S2)
OUTFLOW VALVES CLOSE
Towards the end of systole intraventricular pressure falls and once below the arterial pressure the outflow valves close due to the backflow of blood.
When the intraventricular pressure falls below atrial pressure the whole process starts again.
How prevalent are congenital heart diseases? (S3)
6-8 in a 1000
Which are the most common congenital heart diseases? (S3)
Ventricular septal defect (VSD), followed by atrial septal defect (ASD)
What is an ASD? (S3)
An atrial septal defect is where there is an opening between the two atria, which persists following birth.
Why would ASD eventually lead to heart failure? (S3)
Left atrial pressure > Right atrial pressure, so oxygenated blood flows from the left atria to the right atria. This can mean the right ventricle is overloaded and will lead to failure. The fact no deoxygenated blood mixes with the systemic circulation explains partly why ASD’s are usually asymptomatic until late in adulthood.
Which structure closes postnatally in order to prevent the shunting of blood from right to left, as seen in an ASD? (S3)
Foramen ovale
It exists prenatally to permit blood from right –> left and is designed to close shortly after birth.
Where are the most common sites for ASDs? (S3)
ASDs can occur anywhere along the atrial septum but are most common in the foramen ovale (Ostium secundum ASD). They can also be found at the inferior part of the septum (Ostium primum ASD).
What is a VSD? (S3)
A ventricular septal defect is an opening in the interventricular septum.
Where does a VSD most commonly occur? (S3)
In the membranous portion of the septum, but it can occur anywhere.
Which way does blood flow when there is a VSD? (S3)
Left –> Right … Left ventricular pressure > Right ventricular pressure; blood moves from high to low pressure.
How would a VSD patient typically present? (S3)
With left heart failure, normally presenting as an infant. If untreated, it can lead to inoperable pulmonary hypertension.
Will there be right or left ventricular overload with a VSD and why? (S3)
There would be left ventricular overload.
The blood moves from the left ventricle to the right.
So this means the RV is overloaded initially.
But that ‘extra’ blood goes to the pulmonary circulation and means more blood is flowing into the left heart. The left heart is therefore more prone to fail. More blood is moving through the pulmonary veins. This explains the fact there is pulmonary venous congestion.
What is tetralogy of Fallot? (S3)
It is a group of 4 defects that occur together due to a single developmental defect (specifically the interventricular septum is too far in the anterior and cephalid directions). The 4 defects are: Pulmonary stenosis Right ventricle hypertrophy VSD Over-riding aorta
Is tetralogy of Fallot acyanotic or cyanotic? Why? (S3)
It is cyanotic.
This is because the pressure in the right ventricle is higher due to the pulmonary stenosis. This means blood moves from the right to the left ventricle. Therefore deoxygenated blood moves into the systemic circulation - explaining the cyanosis.
How would a tetralogy of Fallot patient present? (S3)
There are different severities of tetralogy of Fallot. They, and the magnitude of the shunt, depend on the extent of the pulmonary stenosis. Severe cases present in early childhood with cyanotic spells. More mild cases are compatible with adulthood.
What is tricuspid atresia? (S3)
It is the lack of development of the tricuspid valve i,e, the right ventricular inlet.
How can the body ‘get around’ a tricuspid atresia? (S3)
A shunt, so that blood can move from the right to the left can be created. Then blood moves to the lungs via a VSD or a PDA.
What is pulmonary atresia? (S3)
It is the lack of development of the pulmonary valve i.e. the right ventricular outlet.
How can the body ‘get around’ a pulmonary atresia? (S3)
There would be a shunt created between the atria so blood can move from the right to the left. Blood will then flow to the lungs by a PDA.
Is tricuspid atresia acyanotic or cyanotic? What about pulmonary atresia? (S3)
They are both cyanotic.
What is transposition of the great arteries? (S3)
The right ventricle is connected to the aorta and the left ventricle is connected to the pulmonary artery. It is not viable unless the two circuits communicate, i.e. through atrial, ventricular or ductal shunts.
How does transposition of the great arteries usually present? (S3)
As a neonatal emergency, due to reduced pulmonary blood flow.
What is hypoplastic left heart? (S3)
It is where the left ventricle is underdeveloped. This means the mitral and aortic valves are also underdeveloped. Therefore there is a necessity for an ASD (or PFO) and PDA. The right ventricle supports the systemic circulation as the ascending aorta is very small.
How would hypoplastic left heart present? (S3)
As a neonatal emergency, due to reduced pulmonary blood flow. There must be surgical intervention.
How common are Patent Foramen Ovale? (S3)
They may be found in up to 20% of the population.
