*Physiology 3 (lecture 5) Flashcards
What detects deviations in the MAP?
Baroreceptors
Where is the cardiovascular control system?
Medulla
What are the effectors of MAP?
Heart
Blood vessels
What changes can the heart make that results in a change in the MAP? (2)
Heart rate
Stroke volume
What change can the blood vessels make that results in a change in MAP?
Total peripheral resistance
What type of feedback system is the control of blood pressure/
Negative
What is blood pressure?
The outward hydrostatic pressure exerted by the blood on blood vessel walls
What is the systemic blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts (normally less than 140mmHg)
What is the systemic diastolic pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes (normally less than 90mmHg)
What is mean arterial blood pressure?
The average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
Equations for MAP? (3)
Map = [(2 X Diastolic) = systolic] / 3 MAP = DBP + 1/3 difference between SBP and DBP MAP = CO x TPR MAP = SV X HR X TPR
what is the pulse pressure?
The difference between SBP and DBP
What is the normal arterial blood pressure?
Less than 140 systolic
Less than 90 diastolic
What is the normal range of mean arterial blood pressure?
75 - 105mmHg
What MAP is need, at least, to perfuse the coronary arteries, brain and kidneys?
At least 60mmHg
Why must MAP be regulated within narrow limits?
To ensure pressure is high enough to perfuse internal organs including the brain, heart and kidneys and pressure is not too high to damage the blood vessels or place an extra strain on the heart
Where are the baroreceptors located?
Aortic arch
Carotid sinus
What nerves do the carotid baroreceptors signal to the medulla via?
CN IX
What nerves do the aortic baroreceptors signal to the medulla via?
CN X
What type of receptors are the baroreceptors?
What are they sensitive to?
Mechanoreceptors
Stretch
Firing of the baroreceptors afferent nerves due to increased arterial pressure?
Increased (and vice versa)
What is the site of the 1st synapse for all CVS afferents in the medulla?
What happens after this in order to change MAP?
Nucleus tractus solitarius (NTS relays information to to other regions in the brain e.g. medulla, hypothalamus, cerebellum)
Generates vagal outflow to heart
Regulates spinal sympathetic neurones
What is the total peripheral resistance?
The sum of resistance of all peripheral vasculature in the systemic circulation
How does the sympathetic nervous system accelerate the heart rate?
Through noradrenaline acting on B1 receptors
How does the parasympathetic nervous system slow down the heart rate?
Through the vagus which releases acetylcholine acting on muscarinic receptors
What causes the stroke volume to increase?
If the contractile strength of the heart is increased
What causes the contractile strength of the heart to increase and hence stroke volume?
Sympathetic innervation of the ventricular myocardium which increases the force of contraction and hence the stroke volume
Does the vagus nerve have any effect on ventricular contraction?
No - it does not have a significant impact on stroke volume
What mechanism intrinsically controls the stroke volume?
the Frank-Starling mechanism -that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart
What are the major resistance vessels?
The arterioles
What regulates the TPR?
Vascular smooth muscles (mainly in the arterioles)
State of the vascular smooth muscles at rest?
Partially constricted - vasomotor tone
What type of nerves supply the vascular smooth muscles?
Sympathetics (noradrenaline acting on alpha receptors)
No significant parasympathetic innervation
What causes the vasomotor tone?
Tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline)
What happens to baroreceptors firing if high blood pressure is sustained?
It is decreased
