Feedback control in the CVS

Question 1

What is BP?

Answer 1

Outwards (hydrostatic) pressure exerted by the blood on blood vessel walls

Question 2

What is systemic systolic BP?

Answer 2

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.

Question 3

What is systemic diastolic BP?

Answer 3

The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes.
Normally <90 mm Hg

Question 4

What is MAP?

Answer 4

average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
Normally 70-105mmHg

Question 5

How do you estimate MAP?

Answer 5

MAP = [(2x Diastolic) + Systolic] divided by 3
OR
MAP = DBP + 1/3 difference between SBP and DBP

Question 6

Why must Mean arterial Blood Pressure (MAP) be Regulated Within Narrow Range?

Answer 6

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

Question 7

Where are the baroreceptors?

Answer 7

Aortic Arch > signals to medulla via CN X

Carotid Sinus > signals to medulla via CN IX

Question 8

What kind of receptors are the baroreceptors?

Answer 8

Mechanoreceptors which are sensitive to stretch

Question 9

Increase the MAP does what to the firing rate of baroreceptors?

Answer 9

Increases firing of baroreceptors

Question 10

Baroreceptors Send Afferent Impulses to the Cardiovascular Control Centre in the Medulla of the Brainstem. What happens?

Answer 10

1. The cardiovascular control centre receives CVS afferent information
   * Nucleus tractus solitarius (NTS) is site of 1st synapse for all CVS afferents in the medulla
2. NTS relays information to other regions in the brain
   e. g. medulla, hypothalamus, cerebellum
3. Generates vagal outflow to heart - relay to nucleus ambiguus in the medulla
4. Regulates spinal sympathetic neurones

Question 11

MAP = …

Answer 11

MAP = CO X TPR

Question 12

What is CO?

Answer 12

The volume of blood pumped by each ventricle of the heart per minute

Question 13

CO = …

Answer 13

SV X HR

Question 14

What is SV?

Answer 14

The volume of blood pumped by each ventricle of the heart per heart beat

Question 15

What is TPR?

Answer 15

The sum of resistance of all peripheral vasculature in the systemic circulation

Question 16

How can the MAP be regulated?

Answer 16

By regulating… HR SV and TPR

Question 17

What is AUTORHYTHMICITY?

Answer 17

Heart is capable of beating rhythmically in the ABSENCE of external stimuli

Question 18

Describe how the heart rate is modified by the ANS?

Answer 18

Sympathetic - accelerates the HR. Noradrenaline acts on beta 1 receptors

Parasympathetic - (vagus nerve stimulation) decreases the HR. Acetylcholine acts on muscadine receptors.

Question 19

If the contractile strength of the heart increases what happens to SV?

Answer 19

It increases

Question 20

What regulates the SV? And how?

Answer 20

ANS
Sympathetic nerves innervate the ventricular myocardium, and stimulation increases the force of contraction and increases Stroke Volume

Question 21

What are the major resistance vessels?

Answer 21

Arterioles

Question 22

What is TPR regulated by?

Answer 22

Vascular smooth muscles

Question 23

Where is the main site of TPR?

Answer 23

arterioles

Question 24

Contraction of vascular smooth muscle, causing vasoconstriction causes..?

Answer 24

Increase in TPR and MAP

Question 25

What are the vascular smooth muscles supplied by?

Answer 25

Sympathetic nerve fibres.

Neurotransmitter is noradrenaline acting on alpha receptors

Question 26

Describe vasomotor tone?

Answer 26

Vascular smooth muscles are partially constricted at rest.

Question 27

What is the vasomotor tone caused by?

Answer 27

tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline

Question 28

Increasing sympathetic discharger will do what to the vasomotor tone?

Answer 28

Increase the vasomotor tone resulting in vasoconstriction, increasing TPR and MAP

Question 29

Decreasing sympathetic discharger will do what to the vasomotor tone?

Answer 29

Decrease the vasomotor tone resulting in vasodilation, decreasing TPR and MAP

Question 30

What happens with baroreceptor firing is high blood pressure is sustained?

Answer 30

Baroreceptors “re-set” - they will fire again only if there is an acute change in MAP above the new higher steady state level. So they cannot supply info about prevailing steady state BP.