Week 4: Blood pressure

Question 1

What is the primary function of the CVS control center?

Answer 1

To maintain a high bloop pressure in the arteries to ensure all tissues and organs recieve a good blood supply.

Question 2

How is regulation of cardiac output monitored? (formular)

Answer 2

CO = HR x SV

Question 3

How can we calculate MAP?

Answer 3

MAP = CO x TPR

Question 4

How are variations in BP regulated?

Answer 4

By baroreceptor mechanisms

Question 5

What are stretch receptors? where are they found in relation to the Cardiovascular system?

Answer 5

Stretch receptors are modified muscle cells that are found in the walls of the blood vessels and in the heart itself and they work to effectively measure pressure and volume.

Question 6

What are baroreceptors and where are they found? what are the two main ones?

Answer 6

Baroreceptors are high pressure receptors of stretch, they are situated on a direct route between the heart and the brain which is very useful for monitoring blood pressure.

They measure the stretch due to blood pressure in arterial walls

The two main ones are the aortic arch and the carotid sinus.

Question 7

Explain the baroreceptor reflex in response to an increase in BP as a negative feedback loop using this template with key codes:

Answer 7

Question 8

What are low pressure receptors? where are they found?

Answer 8

These nerves fire when there is an increase in stretch (volume) of the right atrium. They are located in the walls of the atria and great venous vessels.

Question 9

What is the bainbridge reflex?

Answer 9

An increase in HR due to an increase in venous pressure due to a increase in blood volume detected bu the low pressure recptors in the atria.

Question 10

Why would it be important to have an increase of blood flow to the skin during exercise?

Answer 10

We need to excrete excess heat through sweat.

Question 11

What is an arteriole?

Answer 11

A small artery that delivers blood to capillaries

Question 12

How is the structure of arteiroles related to how it is controlled to the SNS?

Answer 12

Arterioles contain a thick layer of smooth muscle that is richly innervated by the SNS. The smooth muscle is also very sensitive to many local chemical changes (circulating hormones).

Question 13

What is vasomotor tone?

Answer 13

The partial constriction that a vessel requires so that it does not collapse during regular activity.

Question 14

What are the major resistance vessels of the CVS? why is this?

Answer 14

Arterioles:

• Are able to convert pulsatile flow coming from the aorta to smooth flow for the capilaries
• Cause the MAP decrease on average from 93mmHg (Thick end of arteriolar system) to 37mmHg (by the time of arrival to capillaries)

Question 15

What are the two categories of control for arteriolar smooth muscle contractility?

Answer 15

Intrisic controls:

• Important in matching blood flow to the metabolic needs of the tissue in which they occur

Extrinsic controls:

• Important in MAP regulation

Question 16

What type of influencers do intrisic controls regulate?

Answer 16

Chemical:

• Local metabolic changes
• Histamine release

Physical Influences:

• Temperature
• Myogenic Responses to stretch

Question 17

What is active hyperaemia?

Answer 17

Active hyperemia is the increase in organ blood flow (hyperemia) that is associated with increased metabolic activity of an organ or tissue.

Question 18

What does histamine do in relation to blood flow?

Answer 18

Mast cells release Histamine in response to allergic reactions or damage to a tissue and the histamine causes vasodilation allowing for more blood flow to the designated area so that leukocytes can do their thing.

Question 19

What happens during active hyperaemia? (pathway)

Answer 19

Increased tissue metabolism causes an increase of metabolic vasodilators into ECF. This causes the arterioles to vasodilate which decreases resistance allowing for more blood flow. The increase in blood flow allows for an increase in oxygen and nutrient supply to tissues.

Question 20

What happens during reactive hyperaemia? (pathway)

Answer 20

The decrease in tissue blood flow due to an occlusion causes metabolic vasodilators to accumulate in ECF which causes the arterioles to REACT by dilating and therfore allowing for some blood to pass the occlusion util the occlusion is cleared. This will result in a decreased resistance causing an increase in blood flow. As the vasodilators wash away, the arterioles constrict and blood flow returns to normal.

Question 21

What is Norepinephrine (NE)? what receptor does it bind to? what is its main role? and what innervates it?

Answer 21

NE is a vasodilator, that binds to alpha receptors. The baroreceptor reflex is responsible for the inatiation of this vasodilator that is innervated by the sympathetic neurons.

Question 22

What is epinephrine? What receptor does it bind to? where is it produced? and what does it act on?

Answer 22

Epinephrine is an extrinsicly controlled vasodilator, it binds to beta receptors to increase blood flow to skeletal muscle, heart, liver etc. It is made by the adrenal medulla.

Question 23

How is increased blood volume compensated? (pathway)

Answer 23

Increased blood volume leads to increased blood pressure which triggers a fast and a slow response;

• Fast response: Compensation by CVS in the forms of vasodilation and decreased cardiac output will lower pressure
• Slow response: Compensation by kidneys through means of excretion of fluid in urine to essentially decrease the blood volume eventually resulting in a decreased BP

Question 24

How can we physically influence blood flow to an area?

Answer 24

1. With temperature:
   - We can use a heat pack to cause vasodilation
   - Ice pack for vasoconstriction
2. With stretching:
   - Supposedly arteriolar smooth muscle responds to being passively stretched by myogenically increasing its tone, thereby acting to resist the initial passive stretch (e.g. before sport etc)

Question 25

What is physiologically happening: I use an ellastic band to cut off circulation to my finger causing it to become discouloured. I take the elastic band off and my finger turns bright red.

Answer 25

Essentially there was an occlusion/stoppage of blood flow to the tip of my finger, upon removal a myogenic response to relaxation occured. Because the blood flow was heavily restricted, upon removal of the elastic band the blood flow to the tip of my finger became higher than normal and caused it to go bright red.

Question 26

What does the vasomotor center do?

Answer 26

The vasomotor center (VMC) is a portion of the medulla oblongata that, together with the cardiovascular center and respiratory center, regulates blood pressure through processes of vasoconstriction and vasodilation of the smooth muscle in arterioles.

Question 27

what is the main catecholamine responsible for arteriol diameter? how does it work?

Answer 27

Norepinephrine is released passively to acheive tonic activity, however during times of excitation (more frequent AP's) more epinephrine is released onto alpha receptors on arterioles causing vasoconstriction. When the signal rate of excitation decreases (less AP's) very little amounts of epinephrine are released causing the arteriole to vasodilate.

Question 28

What is vasomotor tone?

Answer 28

The normal situation where the SNS maintains an appropriate driving pressure throughout the body by passively constricting arterioles. NOTE: - there is no significant parasympathetic input

Question 29

How is vasodilation in arterioles caused?

Answer 29

A decrease of SNS stimulation below tonic level.

Question 30

What do the terms intrinsic and extrinsic controls mean when reffering to vessel diameter?

Answer 30

extrinsic factorsare those that originate from outside of the organ or tissue in which the blood vessel is located (whole body), and intrinsic factors are those that originate from the vessel itself or the surrounding tissue (organ itself)

Question 31

How does adrenaline work as a vasoconstrictor and vasodilator during a fight or flight response?

Answer 31

During a fight or flight response, circulating adrenaline will bind to alpha receptors; causing vasoconstriction in non-essential organs, where as adrenaline will cause vasodilation to vessels with beta 2 receptors which will open up blood flow to fight or flight organs.

Question 32

How MAP regulated?

Answer 32

It is accomplished by controlling CO, TPR and blood volume.

Question 33

What are the 3 types of rapid systems in arterial pressure regulation?

Answer 33

1. Baroreceptor feedback system 2. Chemoreceptor mechanism 3. CNS Ischaemic mechanism

Question 34

what are the 3 intermediate systems in arterial pressure regulation?

Answer 34

1. Hormonal mechanisms for rapid control of MAP 2. stress/relaxation changes in the vascelature 3. fluid shifts between tissues and the circulation to reajust blood volume

Question 35

what is the longterm control system in arterial pressure regulation?

Answer 35

This is the renal, body fluid pressure system involving the RAA and aldosterone secretion by the adrenal medulla. It brings about the return of normal MAP by it controlled retention of body fluid.

Question 36

how do baroreceptors work to change MAP?

Answer 36

Baroreceptors in the carotid sinus and aortic arch are sensitive to MAP and PP. When BP falls receptor firing rate decreases and when BP rises; receptor firing rate increases. These signals are sent to the CCC in the medulla and the CCC will alter the ratio between PNS and SNS output.

Question 37

Explain what happens when you go from lying down to standing up; How do postural changes affect MAP?

Answer 37

Upon standing MAP to head and upper part of body tends to fall. Baroreceptors detect this change in lowered pressure in the carotid sinus and aortic arch and elicit an immediate response causing a strong sympathetic discharge to minimise the decrease in MAP, but because of the effect of gravity the veins between the heart and feet will preferentially increase their volume rather than returning the blood to the heart, this causes a reduced CO (cause very little blood is re entering circulation) and therefor we get a fall in MAP.

Question 38

"Baroreceptors are transient" explain what this means? give an example.

Answer 38

They addapt themselves within 1-2 days of whatever pressure level they are exposed to: if for any reason a person went from having a BP of 100mmHg to 200mmHg in a day. over the next day or two the baroreceptors would reduce their rate of firing as they get used to the pressure change.

Question 39

How do atrial and pulmonary arteriole low pressure receptors work? what is unique about the atrial receptors?

Answer 39

They rely on volume of blood to stretch the walls of the atria and pulmonary arteries to cause a response which will inhibit the vasomotor centre and thus reflexly decrease BP. In addition the atraial receptors can also paly a role in controlling the blood volume via the hypothalamus through having it decrease stimulation of ADH therefor resulting in a decreased volume eventually as the heart will excrete the excess fluid as urine.

Question 40

What do the carotid and aortic chemoreceptors do in response to a fall in BP?

Answer 40

Because the lungs are extremely dependant on the heart: When the chemoreceptors detect an increase in CO₂ and and decrease in O₂ the heart can basically signal the respiratory system to become more efficient. They also have an affect on their own CVS aswell in that they can work to excite the vasomotor center to increase BP.

Question 41

What is the CNS ischaemic response?

Answer 41

Ischaemia = tissues starving of oxygen = tissues dying This happens when blood flow to the vasomotor centre in the lower brain stem becomes extremely low so in response the vasomotor center and the cardioaccelaratory neurons become strongly excited as a "last ditch effort" to try and bring the tissues oxygen. They do this by raising the BP abnormally high to about 270mmHg for up to 10 mins. This response is only triggered when MAP falls excedingly low (around 20mmHg).

Question 42

how do catecholamines work work to intermediately control MAP?

Answer 42

- Circulate to all parts of the body in blood - Produced in adrenal medulla - stimulate the heart and constrict most blood vessels including veins - they are activated for about 1-3 minutes before being deactivated.

Question 43

How does vasopressin (ADH) work?`

Answer 43

When MAP is low the hypothalamus secretes large ammounts of ADH which is a powerful vasoconstrictor. In high concentrations ADH also helps to increase blood volume through the means of increasing fluid retention in the kidneys

Question 44

How does the renin-angiotensin mechanism work?

Answer 44

- Angiotensin II is a powerful vasoconstrictor - It stimulate the adrenal glands to release aldosterone which can increase salt and water retention in the kidneys which will subsequently increase blood volume and thereby indirectly increase BP

Question 45

What is the stretch relaxation system?

Answer 45

When pressure in the blood vessels become too high, they become stretched. If this is maintained for long periods of time the pressure in the vessels will eventually fall to normal. Can act as an immediate-term pressure "buffer" to accomodate for changes in pressure and volume.

Question 46

what is the main physiology behind the capillary fluid shift mechanism?

Answer 46

If the cappillary pressure falls too low: - starlings law of the capillaries dictates that net fluid reabsorption into the capillaries will occur If the cappillary pressure gets too high: - fluid will be absorbed by the tissues from the cappillaries

Question 47

Explain how the renal-body fluid mechanism works to regulate a longterm increase in MAP?

Answer 47

MAP rises; - The increase in pressure directly causes the kidney output of water and salt to increase resulting in a pressure diuresis and pressure naturesis. This causes a decrease in ECF volume and decreased blood volume with the decreased blood volume resulting in the increase in BP to come back to normal. (the reversed process happens with low MAP)

Question 48

What is the difference between arteriosclerosis and atherosclerosis?

Answer 48

Arteriosclerosis: - Hardening of the artery walls; Muscle and elestic tissue is replaced y fibrous tissue and calcified plaques. Artherosclerosis: - a type of arteriosclerosis where narrowing of arteries occurs to fibrofatty plaque build up - Causes: hyperlippidaemia