Incomplete Cardiovascular System Flashcards
How wide and long are ventricular cells?
100um long and 15um wide.
How far apart are T-tubules
2uM apart, lying alongside each Z-line of every myofibril.
How does an action potential cause excitation of cardiac muscle?
1) T-tubules experience depolarisation. L-type Ca channels open allowing Ca2+ to enter the cell
2) Ca2+ binds to the SR Ca release channels (Ryanodine receptors) on the sarcoplasmic reticulum
3) Ca2+ leaves the sarcoplasmic reticulum and causes contraction
4) CaATPase protein on sarcoplasmic reticulum pumps Ca2+ back onto sarcoplasmic reticulum
5) Na/Ca exchanger pumps Ca2+ outside cell
What underpins the relationship between muscle length and amount of force?
- Increase in active force produced by actin-myosin interactions
- increase of passive force produced by elastic element of the muscle
How does cardiac muscle relate to skeletal muscle in terms of compliance?
Cardiac muscle is less compliant than skeletal muscle.
When does cardiac muscle do isometric and isotonic contraction?
Isometric when pressure in both ventricles increase.
Isotonic is where blood is ejected from both ventricles.
What effect does increasing the pre-load have on a muscle?
Increases force of the muscle as it produces more passive force.
What effect does increasing the after-load have on a muscle?
Decreases force, as decreases the amount the muscle is able to shorten
What are the in-vivo correlates of pre-load and after-load?
Pre-load: around of blood that fills the ventricles.
After-load: the load against which the left ventricle ejects blood after the opening of the aortic valve.
What are the measures of cardiac pre-load and after-load?
Pre-load: end-diastolic pressure/volume, right atrial pressure
After-load: diastolic material blood pressure
What is starling’s law?
Increased diastolic fibre length increases ventricular contraction
What two factors explain starling’s law?
- Changes in number of cross-bridges
- Changes in Ca sensitivity of myofilament. Two theories for this: (A) Troponin C changes conformation as sarcomere length increases; (B) spacing between myosin and actin filaments decreases forming strong-binding cross-bridges.
What is stroke work?
Work done by the heart to eject blood under pressure into the aorta and pulmonary trunk. = SV x Pressure
What is the Law of Laplace?
When pressure within a cylinder is held constant, the tension of its walls increases with increasing radius.
How is the Law of Laplace applied to the ventricles?
Radius of curvature of the left-ventriclar wall is less than right-ventricle, allowing the left-ventricle to generate higher pressures with similar wall stress.
How is the heard beat divided and further divided?
Diastole (ventricular relaxation during which the ventricles fill with blood):
- Isovolumetric ventricular relaxation
- rapid filling of ventricles
- late, slow filling
- begin of atrial systole
Systole (ventricular contraction when blood is pumped into arteries):
- Isovolumic ventricular contraction
- Ventricular ejection
How is stroke volume calculated?
End-diastolic volume - End-systolic volume
What is the Ejection fraction?
SV / End-diastolic volume. Normally 65%
How do the pressure changes in the right side of the heart compare to those in the left side of the heart?
Follows same patterns except quantitatively lower.
Describe the points on a pressure-volume loop.
X1 marks the beginning of isovolumic contraction. The volume of the ventricles are high, but pressure is low. Pressure then shoots up to X2.
X2 to X3 represents ejection, as pressure increases and then decreases back to X2 level, while volume decreases.
X4 is isovolumic relaxation, as X4 to X1 represents ventricular filling and atrial systole.
How can SV be calculated by a pressure-volume loop?
X1 represents end-diastolic pressure while X3 represents end-systolic pressure.
How can the pressure-volume loops be changed?
Increasing pre-load widens PV loop. Increasing after load lengthens PV loop but flattens the loop as it decreases stroke volume (as less active force shortening can occur).
Increasing contractility will make the whole PV loop larger, increasing cardiac output.
How is Cardiac Output calculated?
CO = Stroke Volume x Heart Rate
Explain the origins of the heart sounds
S1 (lub) is due to closure of AV valves.
S2 (dub) is due to the closure of arctic and pulmonary valves.
S3 can signify turbulent ventricular filling.
S4 can be due to severe hypertension or mitral incompetence.