Lecture 10: CONTROLLING THE HEART AND BLOOD PRESSURE Flashcards
What does the left ventricle do?
Generate pressure for the systemic circulation
What is the pressure in large systemic arteries?
High
What is the pressure in the systemic circuit linked to?
Ventricular contraction and ejection of blood
Where is the blood pressure pulsatile?
In major arteries (systolic/diastolic)
What is MAP?
Mean arterial pressure
What is mean arterial pressure?
A critically important determinant of blood flow
What is the blood pressure in major arteries?
High
Where is the blood pressure oscillatory?
In major arteries because of blood being ejected from the heart and this nature is reduced in the arterioles, capillaries and venules
Where does blood pressure fall steeply?
Across the arterioles, capillaries and venules
What is the blood pressure in veins?
Very low
Where is there a large difference in pressure?
Between arterial and venous sides
What does the large difference in pressure between arterial and venous sides do?
Create a driving force for blood flow
What does ejection of blood into the arterial system do?
Maintains arterial blood volume and blood pressure
What is the result of blood flowing?
Filling arteries, increasing arterial blood volume and raising arterial pressure
What is the result of blood flowing out?
Drains arteries, decreases arterial blood volume and lowers arterial pressure
What is arterial blood volume and pressure determined by?
Balance between blood flows in and out
What actions happen when blood flows in?
Ventricular contraction and ejection of blood (cardiac output)
What is cardiac output?
Flow of blood out of ventricles into arteries per unit of time
What actions happen when blood flows out?
Capillary flow
What is blood flow out controlled by?
Resistance of the arteries
How can arterial volume and pressure be increased?
Increased cardiac output (increase in flow) and increased resistance (decrease outflow)
What is MAP equal to?
Cardiac output (CO) x Total Peripheral Resistance (TPR)
What is cardiac output determined by?
Stroke volume and heart rate
What is cardiac output equal to?
Stroke volume x Heart rate
What is the units of cardiac output?
L/min
What is the units of stroke volume?
L/beat
What is the units of heart rate?
Beats/min
What is stroke volume also known as?
Contraction strength
What is heart rate also known as?
Contraction speed
What is the stroke volume and heart rate in small animals?
They have small hearts so a low stroke volume and a high heart rate to compensate
What is the stroke volume and heart rate in large animals?
They have large hearts so high stroke volume and a low heart rate to compensate
What is the stroke volume and heart rate in failing hearts?
Decreased stroke volume and increased heart rate to compensate
What happens to stroke volume and heart rate when exercising?
Both increase and so cardiac output therefore also increases
Why is cardiac output variable?
Due to changes in heart rate and/or stroke volume
What is tightly regulated within a narrow range?
Mean arterial pressure
Where is homeostasis of arterial blood pressure coordinated?
Within the brain stem
What maintains homeostasis of arterial blood pressure?
Afferent input and efferent output
Where is afferent input from?
Both the CNS and periphery
Where is efferent output to?
Heart and vessels
What are baroreceptors?
Blood pressure sensors
Where are baroreceptors heavily concentrated?
In the aortic arch and carotid artery
Where in arteries are baroreceptors found?
Embedded in the walls
What type of receptors are baroreceptors?
Stretch receptors
What do baroreceptors do?
Communicate to the brain via signals all the time
What happens when the pace of signal from baroreceptors stays the same?
Blood pressure is stable and no adjustments need to be made
What happens when the pace of the signal from baroreceptors increases?
They have sensed more stretch in the arteries because of the increased blood pressure. Changes will be made
What happens when the pace of the signal from the baroreceptors decreases?
They have sensed less stretch in the arteries because of the decreased blood pressure. Changes will be made
What does the brain use to communicate with the heart?
Sympathetic and parasympathetic systems
What are the nerves used to communicate with the heart?
The vagus nerve and sympathetic cardiac nerves
What system is the vagus nerve part of?
Parasympathetic
What does the vagus nerve do to heart rate?
Decrease it
How doe the vagus nerve decrease heart rate?
It tells the SA node to beat slower and the AV node to pause the blood for longer
What system are the sympathetic cardiac nerves from?
Sympathetic
What does the sympathetic cardiac nerves do?
Increase heart rate and force of contraction
Where do sympathetic cardiac nerves travel?
From the brain, through the spinal cord and exits at the sympathetic trunk ganglion
How do the sympathetic cardiac nerves increase heart rate?
They cause the SA node to beat faster and the AV node to pause the blood for less time
How do the sympathetic nerves increase force of contraction?
They trigger the walls of the ventricles to release more calcium to form more cross bridges and cause stronger contraction, increasing stroke volume and therefore cardiac output.
What happens when the body is tilted upright?
Stroke volume falls as the vessels are working against gravity
Why doesn’t cardiac output fall significantly when the body is tilted, even though stroke volume has?
Because the heart rate increases to compensate
What happens as a result of cardiac output falling slightly?
The mean arterial pressure also drops slightly initially
Why does mean arterial pressure raise again after falling slightly?
Because the total peripheral resistance is increased
