Lecture 8-The heart as a pump Flashcards
How do you define the left and right chambers of the heart?
By what they would be from the perspective of the person so opposite to your left and right
Describe the pumping action of the heart..
- Right and left pumps contract simultaneously
- Atria contract first then the ventricles, then have relaxation
- Valves open and close to direct blood flow
What two structures are key to the cellular mechanism of cardiac contraction?
- 2 fibers that run parallel to each other down the length of the cell.
- Thin filament= actin (are the structural element)
- Thick filament= myosin (act as force generator)
-When the myosin head interacts with the actin cross bridges form
How do actin and myosin interactions (cross bridges) cause the contraction of the heart?
- When calcium is released from the sarcoplasmic reticulum, myosin binds to actin to form cross bridges
- When this occurs myosin pulls on actin to shorten the sarcomere and generate force required for contraction of muscles
What happens in regards to actin and myosin interactions in heart relaxation?
- Decrease in cytosolic calcium levels as calcium is pumped back into the sarcoplasmic reticulum.
- Cross bridges are released when ATP binds to myosin thus priming it for the next contraction
- Reduction of force means heart can relax
How many myocytes are involved in heart contraction and relaxation?
All myocytes are involved in every heart beat
If every myocyte is required in each beat already how do we increase force of cardiac contraction?
- Need more interactions between myosin and actin/cross bridges forming.
- To do this we need more calcium to be released from the SR so this is the response to say running
What is the name of the circuit that sends oxygen-rich
blood to the tissues of the body and brings oxygen-poor blood back to the heart?
Systemic circuit
Diastole=
- Relaxation
- Falling pressure
Systole=
- Contraction
- Rising pressure
What is the first stage of the cardiac cycle?
- Two atria contract, ventricles are relaxed
- AV valves open, semilunar valves closed.
This is called the atria systole phase
What is the second stage of the cardiac cycle?
- Atria relax, ventricles contract.
- AV valves shut to prevent back flow, semilunar valves are also shut
This is called the isovolumetric ventricular systole phase
What is the third stage of the cardiac cycle?
- Pressure in ventricles rises beyond the pressure in outflow arteries causing semilunar valves to open
- Result is the ejection of blood
This is called the ventricular ejection phase
What is the forth stage of the cardiac cycle?
- Both valves are shut
- pressure falls
This is called the Isovolumetric ventricular relaxation phase.
What is the fifth and final stage of the cardiac cycle?
- AV valves open
- blood flowing in to ventricles
- Passive filling
This is called the ventricular diastole phase
What does isovolumetric mean in regards to the cardiac cycle?
Same volume
What is meant by systolic and diastolic blood
pressure?
- Systolic= highest point in blood pressure
- Diastolic= lowest point in blood pressure
What is pulse pressure?
The difference between the highest and lowest point in blood pressure (the pressure that has been generated)
What is mean mean blood pressure? Does the heart
spend more time in systole or diastole?
- Mean blood pressure is the average pressure across whole cycle
- Not usually at the mid-point between systolic and diastolic, as the heart spends more time in low pressure (diastolic-filling)
What are systemic and pulmonary pressure?
Which on is typically higher?
- Systemic= pressure in vessels going from the heart out to the body and back
- Pulmonary= pressure in vessels going from heart to lungs and back
-Systemic pressure tends to be high (pumping out to entire body) while pulmonary pressure as just going between heart and lungs is low.
What is hypertension?
High blood pressure, leads to diseases
What is hypotension?
Low blood pressure, as a result it is hard to pump blood to far away parts of the body such as the brain and may lead to fainting and dizziness.
What is haemodynamics?
How blood flows in a single vessel
What is the equation for haemodynamics?
Flow = Pressure Difference / Resistance
Q = DP/R
What does the haemodynamic equation tell us about the resistance of the arteries in the different circuits?
If flow is the same (need the same volume of blood moving through both circuits) and pressure is different, then resistance must also be different to compensate…
- Heart to lungs (pulmonary)= low pressure, low resistance
- out to body (systemic)= high pressure, high resistance
What is the blood left in the ventricles during Isovolumetric ventricular relaxation phase called?
End systolic fraction/volume
