Cardiovascular System Lecture 7 Flashcards
What changes as Arteries become Arterioles?
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.
What nerves/centers supply Arterioles?
Arterioles have a rich supply of sympathetic nerves coming from the vasomotor center; little parasympathetic
What is Vasomotor Tone?
arterioles start in a state of partial vasoconstriction (some level of sympathetic all the time)
How does Vasoconstriction occur in Arterioles?
Recruit alpha (α) receptors:
smooth muscle contracts/arteriole radius decreases
How does Vasodilation occur in Arterioles?
Recruit beta 2 (β2) receptors:
smooth muscle relaxes / arteriole radius increases
Force on an Organ
How do different Arteriole radii change during exercise?
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
Where are ⍺-receptors more dominant?
⍺-receptors in the skin and kidneys >
Where are β2-receptors more dominant?
β2 greater numbers in skeletal muscle, and respiratory passages.
What occurs when ⍺-receptors bind?
(neural and hormonal)
- arteriolar vasoconstriction
- increases TPR (Total Peripheral Resistance)
- Neural: vasomotor nerves release norepinephrine and epinephrine.
- Hormonal: secretion of
angiotensin II / antidiuretic hormone
What occurs when β2-receptors bind?
(neural and hormonal)
- arteriolar vasodilation
- decreases TPR (Total Peripheral Resistance)
- Neural: vasomotor nerves release
nitric oxide and epinephrine. - Hormonal:
secretion of atrial natriuretic peptide
Which hormone can bind with both alpha and beta2 receptors?
epinephrine
(depends on the quantity of alpha or beta 2 receptors)
What causes local Arteriolar vasoconstriction?
stretch arteriole / cold environment.
What causes local Arteriolar vasodilation to take place? (5)
- decreased oxygen
- elevated potassium and hydrogen
- elevated osmolarity
- endothelial cell release (nitric oxide, injury cytokines)
- hot environment
Would Exercising skin lead to arteriolar vasoconstriction or vasodilation?
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)
What is Active hyperemia? (3)
- Active Hyperemia causes increased metabolic activity in an organ
- This decreases oxygen levels due to higher O2 consumption and increases waste production
- Arteriolar Vasodilation occurs in response and there is an increased blood flow to the organ
What is Flow autoregulation? (3)
- Flow autoregulation helps maintain a stable blood flow to an organ by decreasing arterial pressure to the organ
- The decrease in pressure results in a decrease in oxygen and an increase in waste production in the organ
- In response, arteriolar vasodilation occurs to restore blood flow to normal in the organ.
What changes as Arterioles become Capillaries?
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.
What are the 2 factors in the regulation of Arterioles leading into the Capillaries?
2 factors in the regulation of Arterioles leading into capillaries.
- Vasoconstricted – less capillary blood flow.
- Vasodilated – greater capillary blood flow.
What are Precapillary sphincters?
Precapillary sphincters are small muscular rings located at the entrance of capillaries that regulate blood flow into capillary beds
How do Precapillary sphincters regulate blood flow into capillary beds?
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.
What are the 4 Starling Forces?
2 Hydrostatic Pressures
2 Osmotic Pressures
Net Filtration Pressure (NFP)
NFP = (P-c + π-if) - (P-if + π-c)
What 2 Starling Forces move from Capillaries to Interstitial Fluid?
P-c and π-if
What 2 Starling Forces move from Interstitial Fluid to Capillaries?
P-if and π-c
When does Filtration take place in the Blood Vessel?
when:
P-c and π-if > P-if and π-c
Net movement from capillaries to interstitial fluid
When does Absorption take place in the Blood Vessel?
when:
P-if and π-c > P-c and π-if
Net movement from interstitial fluid to capillaries
Capillary Exchange Examples
True at arterial end:
NFP = (35 + 3) – (0 + 28) = +10 (filtration)
True at venous end:
NFP = (15 + 3) – (0 + 28) = –10 (absorption)
How does Vasodilation alter blood hydrostatic pressure?
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)
How does Vasconstriction alter blood hydrostatic pressure?
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
