Module 6: Section 3

Question 1

Arteriole walls

Answer 1

• Similar in structure to arteries but lack the high content of collagen and elastin in their connective tissues
• Much smaller in size compared to arteries

Question 2

Arteriolar resistance

Answer 2

• Also called total peripheral resistance
• Not a constant value as arterioles are dynamic in the regulation of their radius

Question 3

2 reasons for adjustment of the arteriolar radius

Answer 3

1. To distribute cardiac output to various organs depending upon the body’s needs
2. To help regulate arterial blood pressure

Question 4

To distribute cardiac output to various organs depending upon the body’s needs

Answer 4

• At rest, more blood is needed in the digestive system
• Arterioles supplying the digestive system will increase their radius to lower resistance and increase blood flow
• During exercise, arterioles will decrease their radius to decrease blood supply and allow blood to go to other organs
• Process is called shunting

Question 5

To help regulate arterial blood pressure

Answer 5

If necessary to increase blood pressure, arterioles can decrease their radius, increasing resistance and increasing arterial blood pressure

Question 6

How total cardiac output is related to MAP - Pressure Gradient (ΔP)

Answer 6

• Represents pressure gradient for the entire body
• MAP is 93 mmHg
• Blood returning to the heart is 0 mmHg
• ΔP=93 mmHg

Question 7

How total cardiac output is related to MAP - Resistance (R)

Answer 7

• Represents the summation of all the resistance of the systemic peripheral vessels
• Called total peripheral resistance (TPR) and represents resistance at the level of the arterioles as they contribute the greatest to resistance

Question 8

How total cardiac output is related to MAP - Flow (F)

Answer 8

Represents total cardiac output

Question 9

Vasoconstriction

Answer 9

When the smooth muscle contracts, the radius of the arteriole becomes smaller

Question 10

Vasodilation

Answer 10

Smooth muscle relaxes and the radius increases

Question 11

Vascular tone

Answer 11

• Smooth muscle in the walls of the arterioles is generally in a state of partial contraction called vascular tone
• Important as it allows the arterioles to either constrict or dilate as necessary

Question 12

Intrinsic control chemical influences

Answer 12

Generally local metabolic changes and histamine

Question 13

Intrinsic control - vascular tone

Answer 13

• Also called local controls as they occur within the organs themselves to regulate their own blood supply
• Can be either chemical or physical in nature and are important in regulating the distribution of cardiac output

Question 14

Intrinsic control physical influences

Answer 14

Chemical responses to shear stress and the myogenic response to stretch

Question 15

Extrinsic control - vascular tone

Answer 15

• Refers to all of the non-local or metabolic factors that affect vasodilation and vasoconstriction
• Includes both neural and hormonal inputs
• Important in regulating blood pressure

Question 16

Metabolic changes that result in vasodilation - Intrinsic control

Answer 16

• Decreased oxygen
• Increase carbon dioxide
• Increased acid
• Adenosine release
• Increased potassium
• Increased osmolarity
• Prostaglandin release

Question 17

Decreased oxygen

Answer 17

Result of increased oxidative metabolism

Question 18

Increased carbon dioxide

Answer 18

Due to increased oxidative metabolism

Question 19

Increased acid

Answer 19

Comes from carbonic acid produced during carbon dioxide production and lactic acid produced from anaerobic metabolism

Question 20

Adenosine release

Answer 20

Adenosine can be released from increased metabolic activity or deprivation of oxygen

Question 21

Increased potassium

Answer 21

Occur in very active muscles if the rate of action potentials exceeds the ability of the Na+/K_ pump to restore normal concentration gradients

Question 22

Increased osmolarity

Answer 22

High metabolically active tissues releases osmotically active particles

Question 23

Prostaglandin release

Answer 23

Local chemical messengers derived from the fatty acid chains in the plasma membrane of cells

Question 24

How do local chemical influences work?

Answer 24

• These factors trigger the endothelial cells lining the vessels to release chemical messengers that target the smooth muscle cells
• Ex of this is nitric oxide

Question 25

Note about endothelial cells

Answer 25

- Also release constricting chemicals - Endothelia is a very potent vasoconstrictor

Question 26

Histamine

Answer 26

- A chemical that can cause vasodilation which is not related to metabolic activity of the tissue - When a tissue is damaged or there is an allergic reaction histamine is released - Acts as a paracrine molecule - Causes relaxation of smooth muscle cells which result in vasodilation - Can be seen as rides or swelling to the area

Question 27

Intrinsic control - 3 principle physical influences

Answer 27

1. Temperature 2. Shear stress 3. Myogenic response to stretch

Question 28

Temperature - local physical influence

Answer 28

- Applying heat to an area causes vasodilation and increases blood flow - Applying cold to an area causes vasoconstriction and reduces blood flow

Question 29

Shear stress - local physical influence

Answer 29

- Blood cells flowing through the vessels cause friction (shear stress) on the endothelial cells lining the vessels - When shear stress increases, endothelial cells release nitric oxide (NO), which causes vasodilation

Question 30

Myogenic response to stretch - local physical influence

Answer 30

- When smooth muscle cells are passively stretched they have a myogenic response that causes vasoconstriction to oppose the stretch, to maintain lumen diameter - If there is less stretch to smooth muscle, muscle cells respond by relaxing resulting in vasodilation

Question 31

Chemical and physical influences working together - increase

Answer 31

- When the cuff is initially inflated, the cuff pressure becomes high enough to compress the brachial artery and stop blood flow to the lower arm - This causes profound vasodilation in the lower arm due to myogenic causes (decreased pressure) and chemical influences (decrease in oxygen and increase in carbon dioxide and acids)

Question 32

Chemical and physical influences working together - decrease

Answer 32

- If cuff pressure is suddenly decreased, blood flow to the lower arm is much higher than normal as the arterioles are widely dilated - Purpose is to rapidly restore the local chemical balances - Followed by an increase in vascular tone

Question 33

Extrinsic control - neural input

Answer 33

- Sympathetic nervous system innervates arteriolar smooth muscle - Neural regulation of arteriolar tone is achieved by sympathetic activity

Question 34

What does increasing sympathetic activity do? - neural input

Answer 34

Increases arteriolar tone

Question 35

What does decreasing sympathetic activity do? - neural input

Answer 35

Decreases arteriolar tone

Question 36

Where does neural regulation of arteriolar tone occur?

Answer 36

- Does not occur in single organs - Is a generalized response that affects all arterioles - Changing sympathetic activity globally affects arteriolar resistance and can regulate blood pressure

Question 37

Sympathetic activity and norepinephrine

Answer 37

- Sympathetic nerve ending on smooth muscle release norepinephrine - Norepinephrine binds to a1-adrenergic receptors, which results in increased calcium entry into smooth muscle cells and causes arteriolar contraction

Question 38

Where does sympathetic activity and norepinephrine not occur?

Answer 38

- In the brain - Arterioles in the brain do not have a1-adrenergic receptors and therefore do not respond to changes in sympathetic activity - Blood flow to the brain must remain constant, it is under local or metabolic control

Question 39

Mean arterial pressure (MAP) formula

Answer 39

=Total peripheral resistance (TPR) x cardiac output (CO)

Question 40

Sympathetic Control and Pressure Gradient

Answer 40

- To maintain blood flow to tissues and organs, the pressure gradient must be maintained - increasing sympathetic activity increases arteriolar tone and resistance, which raises mean arterial pressure - decreasing sympathetic activity lowers pressure if it becomes too high

Question 41

Can local control override the sympathetic system?

Answer 41

Under some conditions in organs, local control is a stronger influence than sympathetic inputs

Question 42

Can local control override the sympathetic system? - riding a bike example

Answer 42

- When riding a bike, the increased activity in the skeletal muscles of your legs creates a strong response to increase blood supply - Metabolic influences are stronger than sympathetic activity and arteriolar dilation will occur

Question 43

What is vasopressin also called?

Answer 43

Antidiuretic hormone (ADH)

Question 44

Vasopressin and Angiotensin II

Answer 44

- Roles as vasoconstrictors - Crucial in times of massive blood loss (ex: haemorrhage) - These compounds are released to help maintain blood pressure despite the decreased volume