Lecture 12 Flashcards
Where is our extra blood stored?
Systemic veins - because we have more blood than we need at any given time
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Blood volume and pressure in arteries?
High volume and low blood pressure
What is compliance?
The extent to which a vessel allows deformation in response to an applied force
How are veins able to hold such high volumes of blood?
Structure… Muscular tunica media in veins is thin which makes it easy to change shape and adapt in different conditions - allows compliance.
How is the wall of arteries different to that of veins?
Arteries have thick rigid walls and veins have thin compliant walls.
How is compliance meausred?
Volume over pressure
How does change in pressure affect volume in arteries?
There is almost no change in volume when pressure increases in arteries, this indicates very low compliance
How does change in pressure affect volume in veins?
When pressure is added to the vein, the volume increasing easily making a large change. This indicates good compliance
What does it mean that veins have survival value?
they are able to move blood over to the arteries in emergencies
What is venoconstriction?
Constriction of a vein
What is pooling
Increased pressure in the leg and feet veins, in the upright position venous volume below the heart increases.
How do alves counteract pooling?
By creating individual pockets of blood which allow for smooth unidirectional flow
How does the tissue surround veins also help to prevent pooling?
Muscle tone - It is actively squeezing on the vein which pushes blood upwards and downwards.
How does skeletal muscle help to prevent pooling?
The walls of muscle are not compliant, this supports the vein prevents it from bending out
How does muscle contraction increase venous return to the heart?
Valves superior to the contracting muscle open, allowing blood to move toward the heart. As well as valves inferior to the contracting muscle are forced closed, preventing backflow of blood to capillaries
Give an example of when skeletal muscle contraction effects venous return to the heart?
During exercise when skeletal muscles are used, breathing and heart rate increases.
What is Sterlings Law of the heart?
The more stretched muscle fibres are before a contraction, the stronger the contraction will be
what is the relationship between blood volume stroke volume?
The more blood that is packed into the ventricles before it contracts, the stronger the stroke volume will be.
What is the cellular mechanism of cardiac contraction?
Calcium levels increase
Myosin binds to actin - forms cross bridge
Myosin pulls on actin to shorten sarcomere and generate force
Every Myocyte is activated during each beat
What other way can generate more force?
Stretching the walls of ventricles by increasing blood volume, stretches the cells themselves which will in turn increase stroke volume
