Cvs 2 Flashcards
How do you calculate cardiac output?
HR x SV
What allows a valve to remain open?
When the flow of blood is going in the direction that the valve allows. The direction of blood flow is determined by the pressure gradient.
Describe the change in pressure in the ventricle
Ventricular pressure steadily increases in diastole due to the flow of blood from the atria this decreases as the ventriclar pressure equals the atrial pressure. In systole the pressure in the atria increases upon contraction forcing a slight of more blood into the ventricle. The ventricle then contracts iso-volumetrically but as soon as the pressure in the ventricle exceeds that in the aorta then volume of the ventricle goes down.
What can cause sound abnormalities in the heart?
Murmurs arise due to stenosis or valve incompetence. Stenosis is where a valve cannot allow the normal amount of blood through due to narrowing incompetence is where blood travels back through the valve, this is known as regurgitation. Additionally extra heart sounds can be generated by other atypical blood flows.
Describe how the action potential spreads across the heart
It starts at the SAN and spreads out across the atria finishing at the AVN. This causes atrial contraction. Then the impulse is held in the AVN for 120ms after which it travels down the bundles of his in the IV septum. It then travels out across the endocardium trough the myocardium and then finally up towards the AV valves. The heart relaxes in the reverse of contraction (from the outside in).
Describe the venous drainage of the heart
On right small cardiac draining into the posterior coronary sinus. On the left is the great cardiac vein which merges with the marginal and becomes the coronary sinus which communicates with the posterior vein.
Describe the formation of the primitive heart tube
Cephalocaudal folding brings the cardiac centre central in the embryo and lateral folding causes the 2 cardial tubes to fuse together forming the primative heart tube.
What are the parts of the primitive heart tube?
Sinus venosus, atria, ventricle, bulbus cordis, truncus arteriosis, Aortic roots.
Describe the developement of the sinus venosus and the atria.
To start with the L and R sinus venosus are of equal size however the L receeds and R enlarges resulting in the coronary sinus and the Vena cava forming respectively. The RA forms from the best part of the atria, the LA has a small contribution from the atria however the majority of its tissue is due to the pulmonary arteries which is envelops as it grows.
How does the transverse coronary sinus develop?
Due to the folding of the primitive tube. This occurs due to the pericardium being of finite space and so as the tube grows it bends in the middle allowing it to fill the space better. The upper half folds ventral, caudal and to the right. and the sinus venosus moves dorsal, cranial and to the left.
What is the significance of the ligamentum arteriosa?
Remnant of the ductus arteriosus.
Allows blood to flow from the pulmonary artery to the aorta in the embryo circulation. Most blood passes into the left atria via the foramen ovale however a small amount passes into the RV and so this must be removed hence the presence of the ductus arteriosus.
Describe how path of the recurrent larygeal nerve and explain the reason for the asymmetry in its paths.
Left loops around the sup clavian and the right around the ductus arteriosis (from anterior to posterior). This is due to the manner that the great vessels develop. in the embryo there is a remodelling of the major vessels so that the series of arches is disrupted. on the right 3 becomes the corotid 4 becomes the sub clavian on the left 3 is also the corotid however 7 forms the sub clav. the ductus arteriosus forms the 6th arch on the left however on the right this diconnects so it doesnt impede the recurrent laryngeal nerve.
What dictates the degree of contraction that the smooth muscle undergo in the aterioles?
sympathetic stimulation to a degree however the biggest affect on vasoconstriction/vasodilation is the presence of cellular products of metabolism (H+, K+ adenosine, CO2).
What dictates venous pressure?
proportional to volume. and volume is proportional to (volume in/volume out). Volume in is controlled by degree of muscle pumping, the affects of gravity and the volume of return from the capillaires. The degree of volume out is based on cardiac output.
Why is there always a degree of vasomotor tone in resistance vessels?
allows the vessel to change the degree of resistance that the blood experiences based on varying demand. If there is no vasomotor tone then there cant be a decrease in PR.
What is reactive hyperaemia?
Occulusion of blood to tissue for a period of time. Then when the blood returns it increases the degree of flow. This is due to the build up of metabolites that have built up in the vessles resulting in vasodilation.
How can average BP be measured?
diastolic + Pulse pressure/3
What is pulse pressure?
The difference between the systolic and diastolic blood pressures
Why is it essential that arteries are stretchy?
This allows blood to flow during diastole. It also decreases resistance for increased blood flow. This is due to there being an increase in radius of vessel. They have elastic recoil that moves the blood during the diastolic period.
What is mitral stenosis? and what does it result in? what are the common causes of?
Mitral stenosis is where the mitral valve is unable to open as fully as in normal. This results in it being harder for blood to flow from the LA to the LV. Consequences of mitral valve stenosis include atrial stretching and resultant arythmias, less blood flowing through the valve leading to pulmonary oedema and also pulmonary hypertension. The resultant hypertension means that a greater amount of pressure is required to overcome the increased resistance and so leads to RV hypertrophy.
How does the regulation of flow through the pulmonary circulation differ to the systemic?
Supply driven instead of demand led.
What are the 2 blood supplies to the lung?
Pulmonary for gaseous exchange and bronchial circulation for supplying the lung tissue with oxygen and metabolites.
Why is the resistance of the pulmonary circulation low?
Due to the cappilaires being arranged in parallel, large lumens and spare smooth muscle of arterioles.
What is the typical time for blood to flow through the pulmonary circulation? what is the minimum for 100% saturation of HB? Why is there this apparent redundancy?
1 second, 0.3 seconds, allows an increase in flow thorough the lungs without reducing the oxygen saturation preventing cyanosis.
what are the pressures in the heart chambers?
RA: 0-8mmHG
RV: 15-30/4-12mmHG
LA: 1-10mmHg
LV: 100-140/1-10mmHg
How is gaseous exchange optomised in the lungs?
Decreasing diffusion distances, increasing surface area and increasing cappillary density.
What is the VQ ratio?
A ratio between air supplied and blood supplied to the alveoli. This tends to be maintained at 0.8 although it tends to be higher at the apex and lowest at the base.
How can the VQ change in disease?
Higher means more air then blood ratio. This can occur in pulmonary embolism for example. it will decrease when there is less air able to get to the tissue. This could be because of increased lung fluid such as in pulomonary oedema or in infections.
Describe septation of the heart. (atria, ventricle and outflow tract)
First Dorsal ventral divide forms in the AV canal.
Endochondral cushions from neural crest cells form causing the divide.
Then atrial septation. First septum primum which gives rise to the ostium primum which gets progressively smaller and vanishes. As it goes the ostium secundum forms in the septum primum. Septum secundum begins to grow in a horse shoe shape downwards. This forms the foramen ovale.
This is a R–>L shunt in the embryo.
Then the Ventricle undergoes septation. Upgrowth of muscle and a membranous section forms the septum.
Spetation of the outflow tract spirals as the endochondral cushions are staggered.
What is the role of the ductus venousus?
Allows placenta blood supply to bypass liver.
Describe the coronary arteries
–A.I.V
–D
L –C
–M
--S.A.N R --Marginal --A.V.N -- P.I.V
Describe the venous return from the heart
Great cardiac vein travels up the AIV groove and then follows the path of the circumflex artery. Middle cardiac vein joins and it becomes the coronay sinus. From the R side the small cardiac vein joins the coronary sinus.
What factors influence the flow of fluid through tubes?
Flow= velocity x area. Flow=pressure/resistance. Area=Pi x r^2 Friction Pouisellus law Reynold number of fluid i.e laminar vs chaotic viscosity of fluid.
Define flow
The volume of fluid that passes through a particular area in a given period of time (litres x area/ time)= flow
Define velocity
Change in displacement per unit time. (ms^-1)
What is laminar flow? How does it compare to chaotic fluid flow?
When a fluid flow is unidirectional and in “tidy” concentric layers without any loss of uniformity in all layers of the fluid.
Chaotic is where the fluid is tumbling in a non-uniform manner that gives rise to the breakdown of the concentric layers of fluid. Chaos is a predictable behavior that has a specific starting value that any deviation in this value will lead to a deviation in the end result i.e the two slightly different initial values will give rise to progressively divergent functions.
Describe the consequences of pousielles law
flow is equal to the radius to the power 4 multiplied by Pi, and the pressure divided by 8 times the dynamic viscosity of the fluid and length. Flow can be increased by decreasing... -length of tube -decrease viscosity and increasing... -radius -pressure
Define resistance
A measurement of how hard it is to push a flow through a section of a circuit.
How many joules are required to overcome the resistance per unit time ( JS^-1)
What affect flow resistance in blood vessels?
Smooth muscle and pericytes contracting. This is regulated by the SNS and also the presence of metabolites in the blood. like ATP, NO, adenosine, H+ and K+.
How do resistors get summated?
in parallel using a 1/Rsum=1/Ra + 1/Rb
in series through simple addition.
How does pressure change across the circulation?
Pressure will drop across the system due to the expenditure of energy to overcome resistance.
How does flow change across the circulation?
Flow depends on CO. But it should be constant if CO is so. This is due to a decrease in blood velocity when the number of vessels increases just like the arterioles and capillaries.
How does vessel stretchy-ness feature in flow and pressure?
Resistance will decrease as radius increases.
so a stretching of arteries in systole allows an increase in blood flow.
The stretching allows blood to flow in diastole as the pressure remains high due to the deforming of the elastic on the large elastic arteries.
How do vessels show capacitance?
When they can act as momentary blood stores.
Arteries store blood during the influx during systole
Veins store blood allowing for a variable CO.
What is the significance of the concentric layers of fluid in laminar flow?
There is a change in volume from Vmax in the center to zero at the edge. The higher flow rate in the center results in the cells in the blood travelling there so RBCs travel faster then the plasma at the peripheral.
What are the observable markers of chaotic blood flow?
Noise
Decrease in velocity
Higher resistance
Thrombosis.
What is the effect of a drop in blood pressure on resistance vessels?
The will close completely as a degree of basal pressure is required to oppose the resistance.
Describe reactive hypernemia
Occlusion of tissue of blood that leads to an increase in metabolites used and more waste products excreted into the blood vessels.
When the blood is allowed to return there is a transient increase in flow. This is due to the decrease in resistance due to the products of metabolism resulting in vasodilation of the smooth muscle in the vessels.
How does the heart exhibit demand led supply?
An increase in HR–> higher flow, all products of metabolism washed away.
This leads to an increase in TPR
Leads to a drop in venous return
Leads to a drop in Vp
stroke volume is dependent on Vp so CO will return to how it was before.
This demonstrates that blood flow is only going to tissues as demand dictates.
What determines venous pressure?
Venous pressure is due to venous volume. Blood in:
- Low TPR
- High tissue demand for metabolites
- Muscle pumping
How is cardiac output calculated?
stroke volume x HR
Describe the various mechanisms that can give rise to arrythmias
Extra conduction pathways (wolff parkinson white), damage to various parts of the heart due to hypoxia/trauma/infection/congenital defects. leading to a disruption in the normal conducting pathways.
These could be uni-directional and none conducting regions of heart tissue that can give rise to re-entry loops, early depolarisations can arise due to action potentials taking a long period of time. This is commonly due to Long QT which can arise from being very healthy in athletic heart syndrome.
Stretch and required growth of tissue in stress results in pathways being deranged from normal.
What are the plausible causes of congenital heart disease?
toxins (alcohol and cocaine)
infection (rubella, toxoplasmosis)
genetics (trisomy 21 and marfans)
Describe aortic coarction
Narrowing of the aorta typically below the subclavian, if not then disruption to rate and rythym. Individual will develop LV hypertrophy as a result and premature congestive heart failure without treatment.
Describe dextro-transposition of the great vessels
The Aorta goes to the body from the RV so bypasses the lungs: this is not compatible with life after the ductus arteriosus has been closed. Treatment is surgical correction and prostoglandin to keep the ductus arteriosus open.
Describe hypoplastic left heart syndrome
LV underdeveloped. Baby kept alive only until the ductus ateriosus is closed.
Describe pulmonary atresia
Poor pulmonary flow resulting in no oxygen getting to tissue around the systemic circulation. Treatment will be surgical and the giving of prostaglandin.
Describe tetraology of fallot
- overriding aorta
- ventricular septal defect
- pulmonary stenosis
- RV hypertrophy
describe tricuspid atresia
Absence of the RAV connection so oft hypoplastic RV and an inibility to pump blood through the pulmonary circulation.
Describe univentricular heart
Only one ventricle develops.
Can be due to lack of septum developement.
RA can be isomerised resulting in 2 SAN.
Describe total anomolous pulomonary venous drainage
The 4 pulmonary veins fail to join the LA like in normal physiology.
Results in no blood going through the left side of the heart.
Not compatible with life.
What is cyanosis? what must be present for this to occur?
cyanosis is the presence of deoxy blood in the systemic circulation
Due to a R–>L shunt at any level.
What can cause a L–> R shunt?
Atrial septal defect
Ventricular septal defect
patent foramen ovale and pulmonary stenosis.
What nerves are PSNS?
s2–>4 and cranial 10, 9, 7 and 3
What nerves are SNS?
T1–>L2
Describe the action of the vagus nerve on the heart
Provides the parasympathetic control. Innervates the SAN and increases the time taken for each depolarisation.
Also due to activated Kach channels there is a greater degree of hyperpolarisation so threshold takes longer to be achieved.
Role in the vasovagal response, sinus arrythmia/bainbridge reflex and in the dive response.
How is the rate of SAN action potential up or down regulated?
Based on the levels of cAMP in the SAN cells.
. If upregualted by cAMP directly.
What is the sympathetic effect on heart contraction?
PKA phophorylates delayed rectifier. and also phospholabam.
If this is high then more PKA activated causing more L type Vocc action through phophorylation
-increased force of contraction, increased conducting velocity and increased heart rate.
How is blood pressure regulated?
Through baroreceptors in the blood vessels.
These are found in the corotid sinus and arch of the aorta. They provide feedback to the brain’s cardiac centre as to whether there needs to be an increase of decrease in CO. Also there is the bainbridge/ sinus arrythmia which is due to the pressures in the right atria and lungs respectively.
What is the role of the ANS?
homeostasis of the subconscious basal requirements of the body.
What is the action of the PSNS on cardiac contraction?
Decreases the rate of contraction but has no effect on the force of contraction as no innervation to the ventricle.
