Short term control of blood pressure

Question 1

what is the equation for mean arterial pressure

Answer 1

MAP = CO x TPR Mean arterial pressure = cardiac output x total peripheral resistance

Question 2

what is the driving force pushing blood through the circulation

Answer 2

Mean arterial pressure

Question 3

If your mean arterial pressure is too low what can this cause?

Answer 3

fainting - syncope

Question 4

If your mean arterial pressure is too high what can this cause?

Answer 4

hypertension

Question 5

what are the 2 sets of baroreceptors called

Answer 5

aortic arch baroreceptors and carotid sinus baroreceptors - both stretch receptors

Question 6

which nerve do the carotid sinus baroreceptor signals travel up? and where do they synapse

Answer 6

Glossopharyngeal nerve. They synapse in group of cells within the medullary cardiovacular centres

Question 7

which nerve do the aortic arch baroreceptor signals travel up? and where do they synapse

Answer 7

vagus nerve

medulla

Question 8

what other things input into the medullary cardiovascular centres? (4)

Answer 8

• Cardiopulmonary baroreceptors
• Central chemoreceptors
• Chemoreceptors in muscle Joint receptors
• Higher centres

Question 9

In what 2 different ways can the sympathetic system work to increase blood pressure

Answer 9

venoconstriction- constrict veins to squeeze blood back to the heart. This increases the end diastolic volume and the preload. Also then increases the systolic volume and blood pressure arteriolar constriction- because arterioles are resistance vessels, if you make them constrict you will increase resistance to blood flow and increase blood pressure

Question 10

Describe the parasympathetic response to baroreceptor signal returning to the heart

Answer 10

parasympathetic travels back down the vagus nerve. It releases acetylcholine which acts on muscarinic receptors on pacemaker cells in the sinoatrial node. This causes them to depolarise to threshold later - bradychardia

Question 11

Describe the sympathetic response to baroreceptor signal returning to the heart

Answer 11

sympathetic nerves release noradrenaline that acts on beta 1 receptors in the heart. Pacemaker cells depolarise to threshold sooner so you get tachycardia.

Question 12

what happens every time you stimulate sympathetic nerves other than the release of noradrenaline?

Answer 12

adrenaline is released from the adrenal medulla - binds to beta 1 receptors too and increases heart rate.

Question 13

Describe how noradrenaline acts on myocardial cells in the ventricles.

Answer 13

noradrenaline acts on beta 1 receptors on myocardial cells in the ventricles which increases the amount of Ca2+ coming in for the AP and increases the amount of Ca2+ being released from stores. More cross bridges are formed and this leads to increased contractivity

Question 14

Apart from the heart, what else does the sympathetic response act on that will cause an increase in blood pressure?

Answer 14

veins and arterioles

Question 15

What is the negative feedback system called that maintains blood pressure homeostasis?

Answer 15

‘arterial’ baroreflex

Question 16

what can happen if the mean arterial pressure is too high

Answer 16

long term problems because the thin/fine vessels in the capillaries can get damaged by high blood pressure and over time as this damage progresses it can lead to heart disease etc

Question 17

what is a sinus

Answer 17

a cavity

Question 18

what are the two arteries that travel up through the neck from the heart called

Answer 18

L+R common carotid arteries

Question 19

what happens when blood flows through vessels/aorta?

Answer 19

the vessel wall is stretched and as it stretches baroreceptors detect this. The receptors then send signals to the brain to let it know what is happening in the vessel.

Question 20

Name 2 situations where the arterial baroreflex would come into effect

Answer 20

posture- standing up from sitting or lying down valsalva manoeuvre

Question 21

Define the Valsalva manoeuvre?

Answer 21

it is a breathing technique forced expiration against a closed glottis

Question 22

Describe 2 real life situations using the Valsalva manoeuvre

Answer 22

• when unblocking your ears- closing your mouth and holding your nose and trying to force air out of your ears
• whilst constipated - must be in sitting position on toilet - strain to help evacuate the bowel by inhaling, closing the glottis and increasing thoracic pressure to force stuff out

Question 23

How does the Valsalva manoeuvre affect the heart?

Answer 23

it stops blood flow returning to the heart due to increased thoracic pressure (no longer the pressure gradient that is required to push venous blood back to the heart)

in summary:- decreased venous return increased thoracic pressure decreased EDV, SV, CO, MAP

Question 24

why does increased thoracic pressure prevent venous return to the heart?

Answer 24

both the pulmonary vessels and aorta are constricted. When this pressure is released venous blood can once more return to the chest and the heart and cardiac output begins to increase.

Question 25

describe the reflex response against the Valsalva manoeuvre

Answer 25

once the mean arterial pressure decreses the arterial baroreceptors detect this drop in BP and start the process of increasing sympathetic tone/activity so increased cardiac output and increased TPR (constrict peripheral arterioles so BP increases) Decrease in thoracic pressure causes the aorta to expand again and venous return is restored so SV increases.

Question 26

what happens if you reduce filling and preload?

Answer 26

there is a fall in cardiac output by the Frank-Starling mechanism

Question 27

what happens when you stand up after sitting or lying down?

Answer 27

increase in hydrostatic pressure causes pooling of blood in the veins/venules of the feet or legs this is turn causes a decrease in:- vocal resonance, EDV, preload, stroke volume, cardiac output, MAP because of this there is a decreased baroreceptor firing rate as the aorta is less stretched due to decreased CO and SV but the decrease in BP then stimulates sympathetic activity

Question 28

what are the 2 reflex responses to the drop in blood pressure that occurs whilst standing?

Answer 28

decreased vagal tone - ie prevent activation of parasympathetic and in turn this causes increased HR and CO

increase sympathetic tone

• 1. act on pacemaker cells and increase HR and CO
• 2. act on myocardium which increases contractility, SV and CO.
• 3. Stimulate sympathetic nerves in smooth muscle around veins so increase venoconstriction, venous return, EDV, SV, CO
• 4. arteriolar constriction occurs which increases TPR, this causes increase in blood pressure