Blood pressure and regulation

Question 1

What is Blood Pressure?

Answer 1

This is the force exerted by the molecules in the blood on the walls of the blood vessel

Force = Pressure/ Area

Thus, this is the amount of pressure exerted on a particular area of the vessel.

Question 2

How does flow relate to pressure and resistance?

Answer 2

Flow = Change in Pressure/ Resistance

Flow is directly proportional to the change in pressure because as the pressure increases then blood flow increases and as the pressure decreases the blood flow decreases

Flow is inversely proportional to the resistance because as the resistance increases the blood flow decreases and as the resistance decreases the flow of blood will increase.

Question 3

What is systolic pressure?

Answer 3

This is the pressure within the artery due to the force create from the heart contraction or a heart beat

A blood pressure of 120 mmHg means that as the heart beats or contracts the blood pressure within the artery will shoot up to 120mmHg

Question 4

What is diastolic pressure?

Answer 4

This is the pressure between heartbeats or contractions.

It is created as the blood backflow into the ventricles as pressure drops due to ventricular relaxation

Question 5

Why does the blood pressure drop significantly from arteries to arterioles?

Answer 5

Overall the flow rate of the blood is decreased by the narrow openings of the arteries which create high resistance.

The highest pressure drop is experienced over a largest resistor

Pressure is inversely proportional to Resistance

ie. More pressure means that the blood is flowing with less resistance

This pressure drop is because individually the arterioles are smaller than arteries and blood flow becomes harder with a smaller diameter.

Smaller radius = higher resistance

Higher resistance = Lower pressure

There are also fewer of them in parallel (less cross-sectional area)

Question 6

Why is is it important that the arterioles slow down the flow of blood?

Answer 6

The blood from the arterioles enters the capillaries which are just a cell thick and are not meant to withstand high pressure.

The decrease in the diameter of the arteriole creates a high enough resistance to lower the pressure and flow of blood going into the capillary beds so the pressure is high enough to force gases, water, and molecules into the surrounding tissue but not high enough to burst the vessel.

Question 7

Which vessels in the body have the lowest flow rate and greatest cross-sectional area?

Answer 7

Capillaries

The cross-sectional area is the diameter of all the capillaries in the body added up, because there are so many capillaries the cross-sectional area is greater than that of arteries.

Q = Area x Velocity

Flow = Pressure/ Resistance

Also, because they are tiny vessels the resistance to blood flow will be high causing a low velocity.

Question 8

What is resistance dependent on?

Answer 8

Poiseuille’s law

Resistance is dependent on the length of the vessel, the radius of the vessel, and the viscosity (how thick or thin a liquid is)

Resistance = 8Lŋ/ pi x (radius)⁴

Question 9

What is the determinant of blood viscosity?

Answer 9

The higher the concentration of the blood cells, proteins, and molecules in the blood and the lower the amount of actual fluid or water can cause the viscosity or thickness of the blood to increase or become thicker.

Question 10

What is Total Pressure Resistance?

Answer 10

This is the combined resistance across all the blood vessels within the circulatory system.

This is important because if the resistance in one vessel increases through vasoconstriction, this can cause an overall increase throughout the system. Vice versa

i.e. the arterioles to cause a massive increase in resistance

Question 11

What is the Cardiac output?

Answer 11

Cardiac Output = Stroke Volume x Heart Rate

This is the volume/ amount of blood flowing out of the heart each minute or with each heart beat

Question 12

What does compliance mean?

Answer 12

This is how easy it is to stretch or distend a vessel

i.e. Patient compliance with their treatment is how easily or readily they do what they are told (Will the vessel(patient) stretch if made to stretch)

Question 13

What does low compliance mean?

Answer 13

You have to apply a high-pressure for there to be a little expansion in the vessel

For example, due to the thick walls of arteries, they can withstand high pressure and only have a small change in volume (distension or stretch)

Question 14

What does low compliance mean?

Answer 14

When you apply a high pressure to the vessel it have a big increase in the volume or distention

ie. Because the walls of the veins are so thin when blood flows into it the walls will stretch so as much blood as possible can enter.

Question 15

Why is it important that the arteries have low compliance?

Answer 15

The arteries are responsible for maintaining blood pressure throughout the system after the blood has left the heart under high pressure.

When the blood enters the arteries it stretches slightly due to the elastic fibers storing that elastic potential energy, but once the ventricle has finished contracting the smooth muscle and elastic fibers will recoil (passively) and use that energy stored to propel the blood through the vessel (blood flow).

The ability to store the pressure and recoil means that although the artery has low compliance because it will stretch a little bit and return to its normal shape.

Question 16

What does it mean that the arteries are Pressure reservoirs?

Answer 16

Arteries have thick walls with a lot of elastic fibers which makes the walls stiff and stretchy. When the blood passes through the arteries the pressure causes the vessels to stretch slightly during systole or when the ventricles fill the artery with blood and recoil using the stored elastic pressure to propel the blood forward.

Question 17

Why are veins called blood reservoirs?

Answer 17

Veins have thin walls with very little smooth muscle and fewer elastic fibers than arteries which means that when they are stretched they cannot recoil so they remain distended.

The increase in volume means that there is a decrease in pressure allowing for a lot of blood to be stored in the veins.

More blood entering the veins = higher Venous return

Question 18

What is the site at which resistance to blood flow is regulated?

Answer 18

Arterioles

Question 19

How is blood pressure or arterial pressure measured?

Answer 19

Sphygmomanometer is used to measure blood pressure

1. A blood pressure cuff is placed around the arm surrounding the brachial artery.
2. The cuff is pumped up to about 120mmHg which is the normal maximum blood pressure.
3. When the blood flow can no longer be heard through the artery that means the pressure within the cuff is greater than that of the artery.
4. Pressure within the cuff will be released and once the first pulse or turbulent flow is heard this is the systolic pressure
5. When the last pulse is heard that is called the diastolic pressure

Question 20

What are Korotaff sounds?

Answer 20

The sound turbulent blood makes as it passes through a compressed blood vessel.

Question 21

When do the Korotaff sounds disappear?

Answer 21

They disappear once the blood vessel becomes uncompressed and laminar flow ensues.

This happens in diastole

Question 22

What are the intrinsic factors that can affect blood flow to arteries?

Answer 22

Regulation of blood flow based on the need of the tissue or organ

The metabolic products and needs of the cells such as CO2 and O2 can affect whether or not the arterioles vasoconstrict or vasodilate

Regulated by varying the resistance in the arteriole which changes the resistance and blood flow into the capillary beds.

Question 23

What changes occur in the blood vessels due to increased metabolic activity?

Answer 23

Active hyperemia → increased blood flow in response to increased metabolic activity

1. Metabolic rate increases
2. Oxygen is used up fast and Carbon dioxide is produced fast
3. This triggers the smooth muscle in the arterioles to vasodilate allowing more CO2 gases to diffuse into the blood and increasing the flow rate of the blood to the lungs for oxygenation.
4. As the vessel dilates the resistance ⇓⇓ and the pressure and flow rate ⇑⇑ increases oxygen supply to the tissues and increases carbon dioxide removal from tissues
5. Higher O2 levels and lower CO2 levels act as negative feedback so the smooth muscle stops dilating

Question 24

What is reactive hyperemia?

Answer 24

This is increased blood flow in response to the previous reduction in blood flow.

May occur during Fight or flight where the blood is shunted from the GI tract or bladder towards the skeletal muscles where they may be needed to supply sugar and oxygen to escape danger.

After the danger is passed the blood flow needs to be returned to normal to prevent tissue death.

Question 25

Describe the changes that occur in reactive hyperemia.

Answer 25

1. Blood flow is low due to the vasoconstriction (⇡Resistance ⇣Blood flow)
2. The Oxygen supply becomes low and the [CO2] is high in the tissues
3. In response the smooth muscles in the arterioles vasodilate to increase the blood flow to the tissues and ⇑ oxygen delivery while ⇑ carbon dioxide uptake and removal.
4. Once [O2] is high and [CO2] is low this will act as a negative feedback for the smooth muscles to stop vasodilating

Question 26

What is the myogenic response to increased blood flow to organs?

Answer 26

Change in vascular pressure in response to stretching of the blood vessels in the absence of external factors.

This allows for the autoregulation of blood flow as too much stretch due to blood flow triggers vasoconstriction.

Question 27

How does myogenic autoregulation of blood flow occur?

Answer 27

1. Increased perfusion pressure increases blood flow and pressure in arterioles
2. Increased pressure in arteriole stretches arteriole wall
3. Stretch of vascular smooth muscle induces contraction of vascular smooth muscle—inherent property of smooth muscle
4. Vasoconstriction decreases blood flow
5. Once restricted this will act as negative feedback to prevent the blood vessel from completely occluding.

Question 28

What is perfusion pressure?

Answer 28

This is the pressure caused by the delivery of blood to an organ

Question 29

What is Mean Arterial Pressure?

Answer 29

This is the average of systolic and diastolic pressure. It decreases as you get further away from the heart.

Question 30

What receptors do the skeletal and cardiac muscles have on them?

Answer 30

Alpha and Beta 2 receptors

Question 31

What adrenergic hormone binds to both alpha and beta receptors based on its concentration?

Answer 31

Epinephrine binds to both receptors

It will bind to beta receptors first at lower concentrations because it has a high affinity for the receptor

It will bind to alpha receptors second at higher concentrations because it has a lower affinity for epinephrine

Question 32

What effect will epinephrine bound to a Beta receptor have on a vessel?

Answer 32

Vasodilation

Question 33

What effect will epinephrine have if both alpha and beta receptors are bound?

Answer 33

It depends on which receptor dominates as the receptors have different responses when bound. If alpha receptors are higher in number this would cause overall vasoconstriction.

Question 34

Where has the highest concentration of alpha receptors?

Answer 34

The Gastrointestinal tract because it has to constrict in order to move the food along.

Question 35

Does the parasympathetic system innervate the arteriolar smooth muscle?

Answer 35

No

Only in the external genitalia → vasodilation → pudendal nerve

Question 36

What is Vasopressin and what secretes it?

Answer 36

Vasopressin or Antidiuretic hormone is secreted by the posterior pituitary gland

Question 37

What does Vasopressin do?

Answer 37

Given to raise blood pressure

Promotes vasoconstriction in most tissues resulting in increased TPR and Mean Arterial Pressure (blood pressure)

Question 38

What is angiotensin II?

Answer 38

This is a hormone released by the kidneys which cause vasoconstriction

⇑⇑⇑ TPR ⇑⇑⇑MAP

Question 39

How is angiotensin II made?

Answer 39

It is derived from angiotensinogen which is cleaved by renin into angiotensin I

Angiotensin-converting enzyme present on the inner surface of certain blood vessels converts it to angiotensin II.