BP Control

Question 1

Pulse Pressure

Answer 1

Systolic BP - Diastolic BP

Question 2

How to calculate mean arterial pressure

Answer 2

Diastolic BP + (Pulse Pressure)/3

heart spends more time in systole than diastole which is why pp is divided by 3

Question 3

Factors affecting Systolic BP

Answer 3

Stroke Volume - Increased SV, increased SBP

Aortic Elasticity - Decreased elasticity, increased SBP

Question 4

Factors affecting diastolic BP

Answer 4

Peripheral resistance - Increase PR, increase DBP

Aortic elasticity - Decrease elasticity, decrease DBP

Heart Rate - Decrease HR, decrease DBP

Question 5

How does aging of the aorta cause hypertension in the elderly

Answer 5

Normally, the elastic aorta takes up kinetic energy from blood during systole & dampens rise in BP

During aging though, the aorta loses elasticity, causing systolic hypertension

Question 6

Formula for Mean Arterial BP (MAP)

Answer 6

Cardiac Output x Total Peripheral Resistance

Question 7

Typical MAP, Cardiac Output and Total Peripheral Resistance in Systemic Circulation

Answer 7

MAP - 100mmHg
Cardiac Output - 5 L/min
TPR - 20 Units (mmHg/L/min)

Question 8

Typical MAP, Cardiac Output and Total Peripheral Resistance in Pulmonary Circulation

Answer 8

MAP - 10mmHg
Cardiac Output - 5 L/min
TPR - 2 Units (mmHg/L/min)

Question 9

Mechanisms that support control of arterial BP

Answer 9

Pressure Sensors (in circulation) - Afferent Input

Integration centres (in CNS)

Effector Mechanisms (via ANS) - Efferent Output

Question 10

Arterial Baroreceptors - What are they, Where, What do they do/how

Answer 10

High Pressure BP Sensors

In walls of carotid arteries & aortic arch

They detect an increase in stretch of vessels, increasing afferent nerve discharge via IX and X (vagus) cranial nerves

Question 11

Effector Mechanisms to Control BP via ANS in heart

Answer 11

Parasympathetic - ACh, Muscarinic Receptors; decrease HR

Sympathetic - NA, B1 Adrenoceptors; Increase HR & StV

Question 12

Effect of SNS on arteries

Answer 12

Sympathetic nervous system activates a2 adrenoceptors causing vasoconstriction, increasing resistance and thus BP

Question 13

Low Pressure Baroreceptors - Where, What do they do/how

Answer 13

Located in pulmonary vasculature, Atrial-vena caval junctions, ventricular walls

‘volume receptors’ of the heart

Increase in transmural pressure increases afferent nerve discharge - vagus

Question 14

What are the groups of neurons in the medulla that play a role in BP control

Answer 14

The caudal depressors only a role in highly elevated BP

**FOCUS ON MIDDLE ROW

Question 15

How do the following values changes when going from a supine to standing position to maintain BP:
HR
Stroke Volume
Cardiac Output
Total Peripheral Resistance

Answer 15

Question 16

Discuss the neuronal/nervous changes that occur when arterial BP drops

Answer 16

Baroreceptors reduce afferent nerve discharge. This reduces vagal nerve activity (PNS). This decreases tonic inhibition at pressor area and increase in SNS activity

Heart Rate & StV increase along with cardiac output (B1) as result
Peripheral resistance increases (a1 adrenoceptors activated)

BP returns to normal

Question 17

Discuss the neuronal/nervous changes that occur when arterial BP increases

Answer 17

Afferent nerve discharge increases; this increases vagal activitys (PNS) and decreases SNS activity

Depressor is activated & pressor’s inhibition is increased

These systems work to reduce heart rate & StV and thus cardiac output (B1)

Peripheral resistance is thus reduced (a1 adrenoceptors)

All this reduces BP to normal