Cardiovascular System Lecture 7

Question 1

What changes as Arteries become Arterioles?

Answer 1

Blood Pressure:
- pressure drop with distance from heart and resistance encountered.

Total cross-sectional area:
- Significant branching – increasing cross-sectional area – increasing resistance.

Velocity of blood flow:
- Slowing.
- Strong area of resistance regulation.

Manipulation
- vasoconstriction and vasodilation.

Question 2

What nerves/centers supply Arterioles?

Answer 2

Arterioles have a rich supply of sympathetic nerves coming from the vasomotor center; little parasympathetic

Question 3

What is Vasomotor Tone?

Answer 3

arterioles start in a state of partial vasoconstriction (some level of sympathetic all the time)

Question 4

How does Vasoconstriction occur in Arterioles?

Answer 4

Recruit alpha (α) receptors:
smooth muscle contracts/arteriole radius decreases

Question 5

How does Vasodilation occur in Arterioles?

Answer 5

Recruit beta 2 (β2) receptors:
smooth muscle relaxes / arteriole radius increases

Question 6

Force on an Organ

Answer 6

Question 7

How do different Arteriole radii change during exercise?

Answer 7

From rest to strenuous exercise:
- Maintain blood flow in the Brain

Using vasodilation to direct blood to:
- Heart, Skin and Skeletal Muscle

Using vasoconstriction to divert blood
away from:
- Kidneys, Abdominal organs

Question 8

Where are ⍺-receptors more dominant?

Answer 8

⍺-receptors in the skin and kidneys >

Question 9

Where are β2-receptors more dominant?

Answer 9

β2 greater numbers in skeletal muscle, and respiratory passages.

Question 10

What occurs when ⍺-receptors bind?
(neural and hormonal)

Answer 10

• arteriolar vasoconstriction
• increases TPR (Total Peripheral Resistance)
• Neural: vasomotor nerves release norepinephrine and epinephrine.
• Hormonal: secretion of
  angiotensin II / antidiuretic hormone

Question 11

What occurs when β2-receptors bind?
(neural and hormonal)

Answer 11

• arteriolar vasodilation
• decreases TPR (Total Peripheral Resistance)
• Neural: vasomotor nerves release
  nitric oxide and epinephrine.
• Hormonal:
  secretion of atrial natriuretic peptide

Question 12

Which hormone can bind with both alpha and beta2 receptors?

Answer 12

epinephrine
(depends on the quantity of alpha or beta 2 receptors)

Question 13

What causes local Arteriolar vasoconstriction?

Answer 13

stretch arteriole / cold environment.

Question 14

What causes local Arteriolar vasodilation to take place? (5)

Answer 14

• decreased oxygen
• elevated potassium and hydrogen
• elevated osmolarity
• endothelial cell release (nitric oxide, injury cytokines)
• hot environment

Question 15

Would Exercising skin lead to arteriolar vasoconstriction or vasodilation?

Answer 15

exercising skin would involve lots of α receptors, therefore neural or hormonal would lead to arteriolar vasoconstriction

HOWEVER, it is actually arteriolar vasodilation occurring due to local effects

(in some cases, the local effect can be the strongest one)

Question 16

What is Active hyperemia? (3)

Answer 16

1. Active Hyperemia causes increased metabolic activity in an organ
2. This decreases oxygen levels due to higher O2 consumption and increases waste production
3. Arteriolar Vasodilation occurs in response and there is an increased blood flow to the organ

Question 17

What is Flow autoregulation? (3)

Answer 17

1. Flow autoregulation helps maintain a stable blood flow to an organ by decreasing arterial pressure to the organ
2. The decrease in pressure results in a decrease in oxygen and an increase in waste production in the organ
3. In response, arteriolar vasodilation occurs to restore blood flow to normal in the organ.

Question 18

What changes as Arterioles become Capillaries?

Answer 18

Blood Pressure:
* Still decreasing pressure.
* Higher pressure as enter capillaries and lower as exit capillaries.

Total cross-sectional area:
* Maximal branching – maximal cross sectional area – maximal resistance.

Velocity of blood flow:
* Slowest; ideal for exchange.

Question 19

What are the 2 factors in the regulation of Arterioles leading into the Capillaries?

Answer 19

2 factors in the regulation of Arterioles leading into capillaries.
- Vasoconstricted – less capillary blood flow.
- Vasodilated – greater capillary blood flow.

Question 20

What are Precapillary sphincters?

Answer 20

Precapillary sphincters are small muscular rings located at the entrance of capillaries that regulate blood flow into capillary beds

Question 21

How do Precapillary sphincters regulate blood flow into capillary beds?

Answer 21

Constricted
- less capillary bed open
- most blood in metarteriole
- smaller exchange surface area,
- greater diffusion distance.

Relaxed
- more capillary bed open
- greater exchange surface area,
- smaller diffusion distance.

Question 22

What are the 4 Starling Forces?

Answer 22

2 Hydrostatic Pressures
2 Osmotic Pressures

Question 23

Net Filtration Pressure (NFP)

Answer 23

NFP = (P-c + π-if) - (P-if + π-c)

Question 24

What 2 Starling Forces move from Capillaries to Interstitial Fluid?

Answer 24

P-c and π-if

Question 25

What 2 Starling Forces move from Interstitial Fluid to Capillaries?

Answer 25

P-if and π-c

Question 26

When does Filtration take place in the Blood Vessel?

Answer 26

when:
P-c and π-if > P-if and π-c

Net movement from capillaries to interstitial fluid

Question 27

When does Absorption take place in the Blood Vessel?

Answer 27

when:
P-if and π-c > P-c and π-if

Net movement from interstitial fluid to capillaries

Question 28

Capillary Exchange Examples

Answer 28

True at arterial end:
NFP = (35 + 3) – (0 + 28) = +10 (filtration)

True at venous end:
NFP = (15 + 3) – (0 + 28) = –10 (absorption)

Question 29

How does Vasodilation alter blood hydrostatic pressure?

Answer 29

Vasodilation results in higher P-c coming into capillaries
This means :more filtration, less absorption.

Example: (photo below)
increased +15 mmHg
(other values unchanged).

At arterial end:
NFP = (50+3)–(0+28) = +27 filtration (was +10)
At venous end:
NFP = (30+3)–(0+28) = –5 absorption (was -10)

Question 30

How does Vasconstriction alter blood hydrostatic pressure?

Answer 30

Vasoconstriction results in lower P-c coming into capillaries
Therfore, less filtration, more absorption.

Example:
decreased -15 mmHg
(other equation values unchanged).

At arterial end:
NFP = (20+3)–(0+28)= –5 absorption (was +10)

At venous end:
NFP = (0+3) - (0+28)= –25 absorption (was –10