Regulation of Mean Arterial Blood Pressure

Question 1

What is Blood Pressure?

Answer 1

the outwards (‘hydrostatic’) pressure exerted by the blood on the blood vessel walls

Question 2

What is Systemic Systolic Arterial BP?

Answer 2

• The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
• Normally <140 mmHg (resting)
• Ideal normal range for under 80s is 90-120mmHg
• top number

s for squeeze

Question 3

What is Systemic Diastolic Arterial BP?

Answer 3

• The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
• Normally <90 mmHg (resting)
• Ideal normal range for under 80s is 60-80mmHg
• bottom number

Question 4

What is Hypertension?

Answer 4

Clinic blood pressure of 140/90 mmHg or higher and a daytime average of 135/85 mmHg or higher

Question 5

What is Pulse Pressure?

Answer 5

• The difference between systolic BP and diastolic BP
• Normally between 30 - 50 mmHg

Question 6

What is Mean arterial blood pressure (MAP)?

Answer 6

• The average arterial blood pressure during a single cardiac cycle
• Normally 70 - 105 mmHg
• Must be regulated in a narrow range
• MAP of at least 60 mmHg is needed to perfuse vital organs
• If MAP is too high, it puts strain on the heart/blood vessels and other organs such as the brain, kidneys and eyes.

Question 6

How to calculate MAP?

Mean arterial blood pressure

Answer 6

• MAP = [(2 x Diastolic) + Systolic] / 3 OR
• MAP = Diastolic + (pulse pressure/3)

Question 7

Why is MAP NOT calculated by obtaining average of systolic and diastolic pressures?

Answer 7

the relaxation (diastolic) portion of the cycle is about twice as long as the contraction (systolic) portion of the cardiac cycle

Question 8

What kind of receptors are the Baroreceptors?

Answer 8

mechanoreceptors as they are sensitive to stretch

Question 9

What is the sensor, control centre and effectors in NC of MAP?

Answer 9

Sensor- Baroreceptors
Control Center- Medulla
Effectors- Heart + Blood Vessels

Question 10

How does changes in MAP alter firing rate?

Answer 10

Firing rate in baroreceptos afferent neurons increases when MAP increases + decreases when MAP decreases

Question 11

How does the medulla recieve and process changes in MAP?

Answer 11

• Nucleus tractus solitarius (NTS) is site of the 1st synapse for all CVS afferents (signals) in the medulla
• NTS integrates and relays information to other regions that control the pathways of the 2 divisions (parasympathetic and sympathetic) of the autonomic (”involuntary”) nerous system to heart and blood vessels.

Question 12

What is Cardiac Output?

CO

Answer 12

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

Question 13

What is Stroke Volume?

SV

Answer 13

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

Question 14

What is Systemic Vascular Resistance?

SVR

Answer 14

the sum of resistance of all vasculature in the systemic circulation

Question 15

What is the relationship between MAP, CO + SVR

Answer 15

MAP = Cardiac Output (CO) x Systemic Vascular Resistance (SVR)

Question 16

What is the relationship between CO, SV + HR?

Answer 16

CO = Stroke Volume (SV) x Heart Rate (HR)

Question 17

How can MAP can be regulated?

Answer 17

as MAP = SV x HR x SVR
regulating HR, SV and SVR

Question 18

How is HR regulated?

Heart Rate

Answer 18

• Heart is an electrically controlled muscular pump which sucks and pumps blood
• Electrical signals controlling heart are generated within the heart itself
• Heart is capable of beating rhythmically in absence of external stimuli (autorythmicity).

Question 19

How is Stroke Volume Regulated?

Answer 19

• SV increases if contractile strength of heart increases
• Autonomic nervous system
• Sympathetic nevres innervate (supply) the ventricular myocardium, and stimulatuon increases the force of contracrtion and increases stroke volume
• the vagus (parasympathic) nerve has little direct effect on ventricular contraction
• Stroke volume is intrinsic through starling’s law of the heart

Question 20

How is Heart Rate modified by The Autonomic (“involuntary”) Nervous System (ANS)?

Answer 20

Parasympathetic Division – stimulation of the vagus nerve (10th cranial nerve) slows the heart rate (bradycardia)
-noradrenaline acts on β1 receptors

Sympathetic Division – stimulation accelerates the heart rate (tachycardia)

Question 21

What are the main resistance vessels?

Answer 21

Arterioles

Question 22

How is SVR Regulated?

systemic vascular resistance

Answer 22

• by vascular smooth muscles
• the ARTERIOLES are the main site of SVR
• Contraction of vascular smooth muscles causes vasoconstriction (increasing SVR and MAP). Relaxation causes vasodilatation (decreasing SVR and MAP)
• The vascular smooth muscles are supplied by SYMPATHETIC nerve fibers. -The neurotransmitter is NORADRENALINE acting on α receptors

Question 23

What is Vasomotor tone?

Answer 23

• Vascular smooth muscles partially constricted at rest (vasomotor tone)
• caused by tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
• Increased sympathetic discharge → vasoconstriction

Question 24

What is the response to Decreased Arterial Blood Pressure?

Answer 24

Question 25

What is the response to Increased Arterial Blood Pressure?

Answer 25