Negative Feedback Control in Cardiovascular System Flashcards
What is blood pressure
Outward hydrostatic pressure exerted by the blood on blood vessel walls
What is Systemic systolic arterial blood pressure
Pressure exerted by blood on walls of the aorta and systemic arteries when heart contracts
What is Systemic diastolic arterial blood pressure
Pressure exerted by the blood on walls of the aorta and systemic arteries when heart relaxes
What is the normal range of systolic arterial blood pressure
90-120 mmHg
What is the normal range of diastolic arterial blood pressure
60-80mmHg
What is hypertension
Clinical blood pressure of 140/90mmHg or higher & Day time average of 135/85mmHg or higher
What is pulse pressure
Difference between systolic and diastolic blood pressures
-Normally between 30-50mmHg
What is mean arterial blood pressure (MAP)
Average arterial blood pressure during a single cardiac cycle - Contraction and relaxation of heart
Why is Mean arterial blood pressure NOT obtained by averaging systolic and diastolic pressures
As in normal cardiac cycle,
- Diastolic portion is TWICE as long as systolic portion
How is mean arterial blood pressure (MAP) calculated
By using formula:
MAP= [(2x diastolic) + Systolic] /3
What is MAP of 120mmHg systolic and 80mmHg diastolic
MAP= [(2x80) + 120] /3
MAP= (280) /3
MAP= 93.3 mmHg
What is the normal range of mean arterial blood pressure
70-105mmHg
- MAP of at least 60 needed to perfuse vital organs (Brain, heart and kidneys)
Why must Mean arterial blood pressure be regulated within narrow window
- Pressure must be high enough to perfuse vital organs like brain, heart and kidneys
BUT
-Not too high that damage to blood vessels occurs or places extra strain on organs
What is the mechanism of baroreceptor reflex in short-term regulation of MAP
Negative feedback control
What is the sensor of detecting MAP variable
baroreceptors
What is the control centre being informed by baroreceptor (the sensor) in MAP
Medulla (The Cardiovascular control centre)
What is the effector that’s sent instructions from medulla (control centre)
- Heart
- Blood vessels
What do effectors in negative feedback control do
Bring about a compensatory response to restore the regulated variable to desired range
Where are the baroreceptors
Aortic arch= Aortic baroreceptors
Each carotid sinus= Carotid baroreceptors
How do baroreceptor signals reach the medulla
Carotid baroreceptors signals via 9th cranial nerve to medulla
Aortic baroreceptors signals via 10th cranial nerve to medulla
What kind of receptors are baroreceptors
Mechanoreceptors which are sensitive to stretch
What does increasing MAP cause the firing rate in baroreceptors afferent neurons
Increases
What does decreasing MAP cause the firing rate in baroreceptors afferent neurons
Decreases
What impulses are sent from baroreceptors to cardiovascular control centre
Afferent impulses sent to CV control centre in medulla of the brainstem
(Means they carry information from sensory receptors of the skin and other organs to the central nervous system)
What is the Cardiac Output (CO)
Volume of blood pumped by each ventricle of the heart per minute
What is stroke volume (SV)
Volume of blood pumped by each ventricle of the heart per heart beat
How is Cardiac Output calculated
CO= Stroke volume x Heart rate
What is systemic vascular resistance (SVR)
Sum of resistance of all vasculature in systemic circulation
How is MAP calculated using Systemic vascular resistance (SVR)
- MAP= Cardiac output x systemic vascular resistance
- MAP= stroke volume x Heart rate x systemic vascular resistance
What 3 factors mean MAP can be regulated by regulating:
- Heart rate
- Stroke volume
- Systemic vascular resistance
Heart is electrically controlled, where are the electrical signals generated
Within the heart itself
What is auto rhythmicity
Heart is capable of beating rhythmically in the ABSENCE of external stimuli
What system modifies heart rate
Autonomic (involuntary) Nervous System ANS
What does the sympathetic division of Autonomic nervous system do
Stimulation accelerates the heart rate (Tachycardia)
-noradrenaline acts on Beta1 receptors
What does the parasympathetic division of Autonomic nervous system do
Stimulates the vagus nerve (10th cranial nerve) slowing the heart rate (bradycardia)
-acetylcholine acts on muscarinic M2 receptors
What system modifies stroke volume
Autonomic nervous system
How does autonomic nervous system regulate stroke volume
SV increases if contractile strength of heart is increased
Sympathetic nerves innervate the ventricular myocardium, and stimulation increases the force of contraction therefore increases SV
What are the major resistance vessels in systemic vascular resistance
Arterioles
What regulates systemic vascular resistance
Vascular smooth muscles
What does contraction of vascular smooth muscles do to SVR and MAP
Increases SVR and MAP
-DUE to vasoconstriction
What does relaxation of vascular smooth muscles do to SVR and MAP
Decreases SVR and MAP
-Due to vasodilation
What supplies vascular smooth muscle
Sympathetic nerve fibres- neurotransmitter is noradrenaline acting on alpha receptors
What is Vasomotor tone
Vascular smooth muscles are partially constricted at rest
What is vasomotor tone caused by
Tonic discharge of sympathetic nerves resulting in continuous noradrenaline release
What increases vasomotor tone
Increases sympathetic discharge, resulting in vasoconstriction
What decreases vasomotor tone
Decreases sympathetic discharge, resulting in vasodilation
