Feedback control in the CVS Flashcards
What is BP?
Outwards (hydrostatic) pressure exerted by the blood on blood vessel walls
What is systemic systolic BP?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts.
Normally <140 mm Hg under resting conditions.
What is systemic diastolic BP?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes.
Normally <90 mm Hg
What is MAP?
average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
Normally 70-105mmHg
How do you estimate MAP?
MAP = [(2x Diastolic) + Systolic] divided by 3
OR
MAP = DBP + 1/3 difference between SBP and DBP
Why must Mean arterial Blood Pressure (MAP) be Regulated Within Narrow Range?
To ensure..
Pressure is high enough to perfuse internal organs including the brain, heart, and kidneys
Pressure is not too high to damage the blood vessels or place an extra strain on the heart
Where are the baroreceptors?
Aortic Arch > signals to medulla via CN X
Carotid Sinus > signals to medulla via CN IX
What kind of receptors are the baroreceptors?
Mechanoreceptors which are sensitive to stretch
Increase the MAP does what to the firing rate of baroreceptors?
Increases firing of baroreceptors
Baroreceptors Send Afferent Impulses to the Cardiovascular Control Centre in the Medulla of the Brainstem. What happens?
- The cardiovascular control centre receives CVS afferent information
* Nucleus tractus solitarius (NTS) is site of 1st synapse for all CVS afferents in the medulla - NTS relays information to other regions in the brain
e. g. medulla, hypothalamus, cerebellum - Generates vagal outflow to heart - relay to nucleus ambiguus in the medulla
- Regulates spinal sympathetic neurones
MAP = …
MAP = CO X TPR
What is CO?
The volume of blood pumped by each ventricle of the heart per minute
CO = …
SV X HR
What is SV?
The volume of blood pumped by each ventricle of the heart per heart beat
What is TPR?
The sum of resistance of all peripheral vasculature in the systemic circulation
How can the MAP be regulated?
By regulating… HR SV and TPR
What is AUTORHYTHMICITY?
Heart is capable of beating rhythmically in the ABSENCE of external stimuli
Describe how the heart rate is modified by the ANS?
Sympathetic - accelerates the HR. Noradrenaline acts on beta 1 receptors
Parasympathetic - (vagus nerve stimulation) decreases the HR. Acetylcholine acts on muscadine receptors.
If the contractile strength of the heart increases what happens to SV?
It increases
What regulates the SV? And how?
ANS
Sympathetic nerves innervate the ventricular myocardium, and stimulation increases the force of contraction and increases Stroke Volume
What are the major resistance vessels?
Arterioles
What is TPR regulated by?
Vascular smooth muscles
Where is the main site of TPR?
arterioles
Contraction of vascular smooth muscle, causing vasoconstriction causes..?
Increase in TPR and MAP
