Cardiovascular Flashcards
What is isovolumetric contraction.
Ventricular contraction when all valves are closed. This increases ventricular pressure but as the valves are closed the volume remains unchanged.
What produces the first heart sound?
Closing of the mitral valve.
What causes the mitral valve to close?
When LVp exceeds LAp. Just before ventricular isovolumetric contraction.
Describe systole.
Wave of depolarisation arrives, Ca2+ channels open.
LVp>LAp and the mitral valve closes.
LVp rises, isovolumetric contraction, LVp>aortic p.
Aortic valve opens and ejection begins.
What produces the second heart sound?
Closing of the aortic valve.
Describe diastole.
LVp decreases and there is a phase of reduced ejection. LVp is less than aortic pressure and the aortic valve closes: isovolumetric ventricular relaxation. LVp is less than LAp and mitral valve opens - ventricles fill with blood. Atria contract - atrial booster. LVp > LAp and mitral valve closes.
What is the duration of systole?
0.3s.
What is the duration of diastole?
0.5s.
What is end systolic volume?
The volume of blood remaining in the LV following systole.
Define preload.
The volume of blood in the ventricles just before contraction (EDV).
Define afterload.
The pressure against which the heart must work to eject blood in systole.
Define contractility.
The inherent strength and vigour of the heart’s contraction during systole.
Define elasticity.
Myocardial ability to recover it’s original shape after systolic stress.
Define compliance.
How easily a chamber of the heart expands when it is filled with blood (C=ΔV/ΔP).
Define diastolic distensibility.
The pressure required to fill the ventricle to the same diastolic volume.
Define resistance.
A force that must be overcome to push blood through the circulatory system.
What is the basic principle of Starling’s law of the heart?
Increased EDV = increased SV.
Explain Starling’s law.
The greater the EDV, the greater the sarcomeres are stretched and the more forceful the contraction.
With relation to Starling’s law, what is the effect of an increased venous return?
EDV will increase and so SV increases and so Cardiac output also increases as CO=SVxHR.
Give the equation for stroke volume.
SV=EDV-ESV.
Give the equation for cardiac output.
CO=SVxHR.
Define cardiac output.
The volume of blood each ventricle pumps per unit time.
Give the equation for mean arterial pressure.
MAP = DP + 1/3(SP-DP).
SP - systolic pressure, DP - diastolic pressure
Give the equation for pulse pressure.
PP=SP-DP.
Give the equation for blood pressure.
BP=COxTPR.
What is Poiseuille’s equation?
Q=r^4.
What is Ohm’s law?
F=ΔP/R.
What are the principle vessels of resistance?
Arterioles.
What do arterioles respond to?
Blood pressure changes. Local, neural and hormonal factors.
Name 2 local factors that result in vasoconstriction.
Endothelin, internal BP.
Name 5 local factors that result in vasodilation.
Hypoxia, NO, K+ (accumulate from AP), CO2, H+, adenosine.
What neural factors result in vasoconstriction?
Sympathetic nerves that release noradrenaline.
What neural factors result in vasodilation?
Parasympathetic innervation.
Name 3 hormonal factors that result in vasoconstriction.
Angiotenisn 2, ADH, Adrenaline (binds to alpha-adrenergic receptors in smooth muscle).
Name 2 hormonal factors that result in vasodilation.
Atrial natriuretic peptide, Adrenaline (binds to beta2 receptors).
What is myogenic auto-regulation of blood flow?
An intrinsic mechanism in smooth muscle blood vessels. If BP increases the vessel constricts. This is important in regulating blood flow.
Myogenic auto-regulation of blood flow: What is the response to an increase in BP?
Increased BP will result in vasoconstriction and so blood flow decreases.
Myogenic auto-regulation of blood flow: What is the response to a decrease in BP?
Decreased BP will result in vasodilation and so blood flow increases.
What is hyperaemia?
An increased blood flow to tissues.
What is the cause of active hyperaemia?
When blood flow increases due to an increase in metabolic activity.
- Increased metabolic activity = decreased O2 and increased metabolites = arteriolar dilation = increased blood flow.
What is the cause of reactive hyperaemia?
When blood flow increases following occlusion to arterial flow.
Describe excitation-contraction coupling.
- Na+ depolarises membrane.
- A small amount of Ca2+ is released from T tubules.
- Ca2+ channels in sarcoplasmic reticulum open.
- Ca2+ flows into cytosol. Cytosolic Ca2+ conc raised.
- Ca2+ binds to troponin C, this pulls tropomyosin and exposes the myosin binding site on actin.
- Cross bridge cycling begins.
- After depolarisation, Ca2+ is returned to SR. K+ outflow = repolarisation.
What effect does myocardial contraction have on the A-band of a sarcomere?
No effect, it stays the same length.
What effect does myocardial contraction have on the I-band and H-zone of a sarcomere?
They get shorter.
Describe actin (thin filament).
A globular protein, single polypeptide. It polymerises with other actin monomers to form a double stranded helix. Together they form F actin.
Describe myosin (thick filament).
2 heavy polypeptide chains and 4 light chains. The myosin heads have 2 binding sites; one for actin and one for ATP.
Describe tropomyosin.
An elongated molecule made of 2 helical peptide chains.
What is the function of troponin I?
Troponin I, together with tropomyosin, inhibits actin and myosin binding.
What is the function of troponin T?
Troponin T binds to tropomyosin.
What is the function of troponin C?
Troponin C has a high affinity for Ca2+. TnC drives away TnI and so allows cross bridge formation.
Name 3 effectors in circulation control.
- Blood vessels - vasoconstrict/dilate and effect TPR.
- The heart - can affect rate or contractility.
- Kidneys - regulates blood volume and fluid balance.
Where are baroreceptors located?
Aortic arch and carotid sinus.
What activates baroreceptors?
Baroreceptors contain stretch receptors that respond to pressure.
Are atrial baroreceptors involved in short-term or long-term regulation of BP?
Short-term. (Cardiopulmonary = long-term).
Where central chemoreceptors located?
In the medulla oblangata.
What do central chemoreceptors respond to?
Changes in pH/(H+).
Increased PaCO2 increases H+ and so decreases pH.
Increased PaCO2 results in vasodilation.
What is the ligamentum teres a remnant of?
The umbilical vein.
What is the ligamentum venosus a remnant of?
The ductus venosus.
Briefly describe foetal circulation.
Maternal circulation - umbilical vein (oxygenated blood) - ductus venosus - IVC - RA - LA/RV - aorta - umbilical artery (deoxygenated blood) - maternal circulation.
What layer of the tri-laminar disc forms the cardiovascular system?
The mesoderm.
What does the first heart field produce?
The left ventricle.
What does the second heart field produce?
The right ventricle, atria and outflow tracts.
What are the 3 stages of heart formation?
- Formation of primitive heart tube.
- Cardiac looping.
- Cardiac septation.
Describe what happens in the formation of the primitive heart tube.
Two endocardial tubes form (day 19). The tubes fuse together and the heart beats (day 22).
Describe what happens in cardiac looping.
Nodes secrete nodal, this circulates to the left due to ciliary movement. Nodal causes a cascade of transcription factors that transduce looping.
Describe what happens in cardiac septation.
Endocardial cushions form. Fuse at mid-line to form atrio-ventricular septum. Muscular ridge in the floor of the primitive ventricle migrates to endocardial cushions forming interventricular septum.
What does the sinus venosus form?
The coronary sinus and RA.
What does the primitive atrium form?
RA and LA.
What does the primitive ventricle form?
Forms most of LV.
What does the bulbus cordis form?
Part of the ventricles.
What does the truncus arteriosus form?
The aorta and pulmonary trunk.
What do the 1st and 2nd aortic arches form?
Minor vessels in the head.
What does the 3rd aortic arch form?
The common carotid arteries.
What does the left and right 4th aortic arch form?
Left - aorta. Right - Right subclavian artery.