Flashcards
The Heart as a Pump
Cards in this deck (33)
- 11. Explain how the heart is adapted to supply the pulmonary and systemic circulations. 2. Draw a diagram of the pressure profiles in the left atrium, left ventricle and the aorta for a single cardiac cycle. Label the vertical axis in units of pressure. Indicate the points at which the cardiac valves open and close, and the periods of iso-volumetric contraction and relaxation. 3. Explain the origin and significance of heart sounds 4. Describe Starling’s law of the heart and explain how cardiac output is balanced on the two sides. 5. Explain the concepts of preload and afterload. 6. Note the differences between pulmonary and systemic capillaries. 7. Outline the main processes ensuring adequate venous return to the heartX
- 2Compare the volume of blood in the pulmonary and systemic circulation at any given timeEqual output - otherwise blood would pool in one section
- 3What determines the blood flow to organs in the systemic circulation? Why is pressure higher in the systemic vasculature vs. the pulmonary?1) Constriction of arterioles
2) Pressure has to be kept high in the systemic circulation to ensure organs are adequately perfused. In the pulmonary system the arterial pressure is low because the total peripheral resistance in the pulmonary vascular bed is much lower - only the lungs need to be perfused so there is no need for a higher pressure/distribution. - 4Describe the structure of systemic arteries and pulmonary arteries.1) Medium size, muscular walls
2) Large diameter, thin elastic walls - 5—1) 120/80
2) 100
3) 30
4) 20
5) 10
6) 8
7) 12
8) 15
9) 25/8
10) 25/0
11) 120/0
12) 2
13) 5 - 6Describes Starlings LawVentricular contractile force increases with ventricular filling - i.e. in a healthy heart, whatever the amount of blood that fills it, this will be pumped out - as diameter extends so does force of contraction.
- 7What is preload?Stretch of the ventricles which occurs during diastole - preload id proportional to degree of stretch. As preload increases so does stroke volume and cardiac output (eg during exercise).
- 8What factors contribute to preload?1) End-diastolic fibre length
2) End-diastolic volume
3) End-diastolic pressure
4) Atrial contraction - 9What is thought to be the underlying physiological cause of Starling's Law?Excess overlap of cardiac myosin and actin so that stretching increases the number of functional cross-bridges - n.b. beyond a certain amount of stretch, Starling's law fails and the the force of contraction starts to decrease.
- 10How does Starling's law relate to the output of both ventricles?By Starling's law, averaged over several beats, the two ventricles eject the same volume of blood. This prevents blood pooling in either the pulmonary or systemic systems.
- 11How does Starling's law relate to heart failure? What does heart failure lead to?An enlarged heart is often associated with heart failure - enlarged hearts no longer function via the Starling mechanism so that a larger end-diastolic volume results in a smaller stroke volume. Heart failure can lead to a rise in systemic pressure as the system is unable to effectively remove blood from the venous side.
- 12What is preload proportional to? How is stroke volume calculated? What are the appropriate values in an adult man?1) End-diastolic volume (EDV)
2) EDV-ESV
3) SV= ~70ml, SDV= ~120ml, EDV= ~50ml - 13What is afterload? How is afterload related to cardiac output?The flow impedance (resistance, but this is in a fluctuating system of pressure so impedance is used) of the large arteries/aorta. The greater the impedance of flow the harder the heart has to work. The reciprocal of impedance is compliance - the more compliant an artery the more it stretches and the lower the resistance and the less work which is need to reach a give cardiac output.
- 14What happens to afterload in older people? Why? What else has this effect?1) Afterload increases
2) Increases in collagen (replaces elastin) in arteries. Heart therefore has to work harder.
3) Smoking - 15What is isovolumetric contraction and how does it relate to afterload?1) Muscles tighten/contract but without shortening - builds pressure in the ventricles to open semilunar valves.
2) The greater the afterload the longer the period of isovolumetric contraction which is required, in turn the shorter the period of ejection and consequently a reduced stroke volume and a greater end-systolic volume (residual blood). Increased afterload decreases cardiac output. - 16How does hypertension cause left ventricular hypertrophy?Arterial hypertension causes increased afterload and therefore the heart has to work harder.
- 17What is inotropy? How does it affect stroke volume?1) Force of contraction
2) Reduces residual volume and therefore increases stroke volume - 18What are the 6 factors which can increase contractility?1) Increased blood calcium
2) Beta agonists
3) Drugs which increase calcium entry into cardiac muscle
4) Insulin
5) Glucagon
6) Cardiac glycosides - 19Where are there not valves in the heart?Between the right atria and the vena cava and the left atria and the pulmonary veins - i.e. not in the venous return system
- 20What is the function of the chordae tendineae and the papillary muscles?Hold the heart valves closed during systole (contract just before the ventricles do).
- 21How many phases are there in ventricular systole?2 - in the first phases the AV valves close but there is not enough ventricular pressure to open the semilunar valves. In the second phase the semilunar valves open.
- 22What process is mainly responsible for ventricular filling? When is a problem with the other contributing factor noticeable?1) Elastic recoil of the ventricles
2) Atrial systole - atrial fibrillation (noticeable by the absence of a P wave) is only generally noticeable when an individual is exercising and cardiac output must significantly increase. Atrial fibrillation results in a shortened ventricular diastole due to the increased heart rate. Therefore stroke volume is decreased. - 23What is responsible for the heart sounds?1) S1 - 'Lubb' - closing of atrial valves
2) S2- 'Dubb' - opening of the semilunar valves - 24When do the mitral and aortic valves open?Mitral opens when the pressure in the ventricle is greater than that in the atria (just after atrial systole). There is then a period of isovolumetric contraction until the pressure in the ventricle is greater than that in the aorta which forces the aortic valve open (around 80mmHg). There is then a period of ejection, then less ejection, then the aortic valve closes and the pressure drops resulting in isovolumetric diastole. Once the pressure drops to less than that of the atria (~15mmHg) the mitral valve opens again. There is then a period of rapid ventricular filling followed by reduced ventricular filling (diastole) and then atrial contraction.
- 25What is S3? Who is S3 common in? Why does it occur?1) Low pitched sound which can be heard 1/3 of the way through diastole, relates to a period of rapid ventricular filling.
2) Many young adults and children or in adults who have a heart disease
3) In healthy conditions it occurs due to the presence of turbulent flow - in older adults it can be due to damaged heart valves. - 26What is S4? What ar S3 and S4 sometimes called? How would they be further investigated?1) Low pitched sound which occurs immediately before S1, turbulent ventricular flow which occurs during diastolic filling.
2) Gallops - both are associated with diastolic filling, rhythmic sounds.
3) Phonocardiogram - 27What is the jugular venous pulse/why does it occur?There are no valves between the right atrium and the vena cava and the left atrium and the pulmonary veins - this is because the pressure in these systems is so low that a valve would actually increase resistance. But because of this when the atria contract there is some backflow which can be felt as a weak pulse - the jugular venous pulse.
- 28—a) The pressure due to the contraction of the aorta before the AV closes
c) The pressure due to the closure of AV valves as they bulge back into the atria
v) The pressure due to venous filling when the tricuspid valve is close.
- 29How does the JVP relate to heart failure?JVP is very small/non-existent in healthy individuals - if there is right side heart failure this will increase the JVP.
- 30What are the three contributing factors to venous return?1) One-way valves in the veins
2) Muscular pumps - as the muscles contract this forces blood back towards the heart
3) Thoracoabdominal pump - on inspiration the pressure in the thoracic cavity (veins in the abdomen are compressed) causes blood to be pulled into the inferior vena cava. During expiration blood is forced into the atrium (veins in the thorax are squeezed) - 31Why is damage to the venous drainage generally less important than restoring arterial supply? How much of the blood is in the venous system?1) Veins have many anastomoses which enables many parallel pathways for blood to return to the heart.
2) ~80% - 32—Draw from memory
- 33—X
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