Lecture 8 Flashcards
Which chamber of the heart pressurises systemic circulation? What are the two parts to the pulsatile nature?
The left ventricle. The pressure can be systolic (highest pressure) or diastolic (lowest pressure).
How is the driving force for blood created? By which point has the oscillatory behaviour of blood pressure stopped?
The driving force is created by the large difference in pressure between the arterial and venous sides of the blood flow by the capillaries the pulsatile nature of blood pressure has almost stopped.
What is blood pressure maintained by? What is the equation?
The blood flow in (caused by ventricular contraction leading to ejection of blood, this is known as cardiac output) and the blood flow out (this is controlled by the resistance of the arteries). The balance between these two forces determines the pressure.
mean arterial pressure = cardiac output x total peripheral resistance.
What is cardiac output determined by? (equation?)
Cardiac output = stroke volume (L/beat) x heart rate (beats/min).
How can we determine stroke volume?
Compare the blood left in the ventricles at the end of systole with the end of diastole.
What determinants of cardiac output can change?
Both the heart rate and the stroke volume can change.
Why is it important for total peripheral resistance to change if cardiac output changes? How is this coordinated?
Mean arterial pressure is maintained tightly within a narrow range and because mean arterial pressure = cardiac output x total peripheral resistance the resistance must go down.
The brain recieves an afferent signal from periphery baroreceptors about the pressure, if the pressure is too high the brain will send out an efferent signal to the heart and blood vessels to reduce the resistance.
Where are the main concentrations of baroreceptors?
the aortic arch and the left and right interior carotid.
What nerve path increases cardiac output? Which decreases it? Where do they synapse? Why does the more synapse containing one contain more?
Where do they both come from?
The parasympathetic slows the heart and synapses on the SA and AV (increasing gap between SA signal and pulse) nodes. It travels down the vagus nerve from the medulla oblongatta
The sympathetic speeds up the heart and synapses with the SA and AV (decreasing gap between SA signal and pulse) node as well as several other points along the heart wall. This is important as it is important to get the heart beating very quickly if the sympathetic nervous system is acting. This travels from the medulla oblongata to the thoracic spinal cord and then to the sympathetic chain ganglia before travelling to the heart.
What occurs to blood return when laid down horizontally? What changes to compensate?
You get a greater return of blood to the heart because your body no longer has to fight gravity, this increases stroke volume and hence cardiac output. When we stand up the heart increases heart rate and vascular resistand to keep mean arterial pressure the same.
What structure can also help move blood around sometimes?
Skeletal muscle when activated.
