Controlling the heart and blood pressure Flashcards
How does the left ventricle generate pressure for systemic circulation?
High pressure in the large systemic arteries is linked to ventricular contraction and ejection of blood. Pulsatile in major arteries (systolic/diastolic). Mean arterial blood pressure (MAP) is a critically important determinant of blood flow
Blood pressure throughout systemic circulation
Blood pressure high in major arteries. Blood pressure falls steeply across the arterioles, capillaries and venules. Blood pressure is very low in veins. Large difference in pressure between arterial and venous sides (creates driving force for blood flow)
How does blood flow in a single vessel?
Flow through a blood system depends on pressure difference - big pressure difference = more flow
Flow also depends inversely on resistance - how tight the pipes are (harder to get flow through narrower vessels)
Q = ∆P/R
∆P is the mean arterial pressure (MAP)
Q = flow (gone in)
R = resistance (drain out)
MAP = cardiac output x total peripheral resistance
Blood flow in arterial system:
Fills arteries, increases arterial blood volume, raises arterial pressure i.e. ventricular contraction, ejection of blood, cardiac output
Blood flow out of arterial system:
Drains arteries, decreases arterial blood volume, lowers arterial pressure i.e. capillary flow, controlled by resistance of arteries
What is arterial blood volume and pressure determined by?
Arterial blood volume and pressure are determined by balance between blood flows in and out. Increase cardiac output (increase inflow), increase resistance (decrease outflow), increase arterial volume and pressure
MAP = CO x TPR (cardiac output x total peripheral resistance)
How is cardiac output determined?
Cardiac output is determined by how fast the heart is pumping (heart rate) determined by contraction rate and how big the ejections of blood are (stroke volume) determined by contraction strength
CO = SV x HR
Healthy heart vs failing heart Cardiac Outputs
Typically in a human your heart beats 60-80 times per minute and a healthy SV is about 70ml per beat. So your CO is around 5L per minute (same as the amount of blood volume in human body)
In a failing heart the heart rate increases to 120-130 beats per minute and SV is 40ml/beat (heart rate is increased to balance low SV to maintain CO)
How is homeostasis of arterial blood pressure maintained?
Mean arterial pressure is tightly regulated - narrow range
Coordinated within the brainstem - afferent input from both the CNS and periphery. Efferent output to heart and vessels
What are baroreceptors?
Baroreceptors are found in the periphery and are blood pressure sensors. They’re located in the arch of the aorta and in the carotid artery (where most of the blood goes)
They send afferent input (feedback) to the brain about whether the blood pressure is adequate or not and are tonically active which varies with blood pressure
What is the brake output in neural control of cardiac output?
Occurs when blood pressure is too high need to reduce things back. Vagus nerve feeds down into the heart into the SA node and AV node, parasympathetic process which slows heart rate down hence reduces blood pressure
What is the accelerate output in neural control of cardiac output?
Occurs when blood pressure is too low hence system needs to be ‘lifted’. Need to increase cardiac output hence increase SV and HR, blood pressure will increase, sympathetic cardiac nerves increase heart rate and force of contractions
