Cardiovascular Physiology Part D: Blood Circulation

Question 1

What is blood flow?

Answer 1

volume of blood flowing through any tissue/min (ml/min.)

Question 2

Equation for blood flow?

Answer 2

Flow = change in pressure / resistance

Question 3

What does resistance depend on?

Answer 3

1. vessel length
2. blood viscosity
3. radius of arterioles controlled by smooth muscle innervated by SNS
   - vasodilation and vasoconstriction

Question 4

Vasodilation

Answer 4

1. ⇑ radius ∴ ⇓ R, ⇑ F

2. opposite of constriction

Question 5

Vasoconstriction

Answer 5

1. ⇓ radius ∴ ⇑ R, ⇓ F
2. P in artery ⇑ (backs up)
3. P in organ ⇓ (less blood flows into organ capillaries)

Question 6

1. If vasoconstriction/dilation is local or
2. If vasoconstriction/dilation is systemic,
   what happens to BP?

Answer 6

1. no observable change in systemic (arterial) BP

2. systemic BP will change

Question 7

Intrinsic regulation control of vasoconstriction/dilation:

Myogenic Regulation

Answer 7

1. when smooth muscle is stretched, it contracts ∴ if ⇑ systemic bp ⇒ arterioles constrict
   
   • e.g. on standing ⇒ high arterial bp in feet (gravity) ∴ arterioles constrict ⇒ ⇓ flow into capillaries
   • e.g. on standing ⇒ low arterial bp in brain (gravity) ∴ arterioles dilate ⇒ ⇑ flow into capillaries

Question 8

Intrinsic regulation control of vasoconstriction/dilation:

Metabolic Regulation

Answer 8

1. blood levels of ⇓ O2, ⇑ CO2, ⇓ pH (⇑ metabolism in organ) - endothelial cells + hemoglobin release nitric oxide ⇒ vasodilation ⇒ ⇑ blood flow to organ
2. if ⇑ O2, pH ⇑, CO2 ⇓ (= low metabolism) - endothelial cells release endothelins ⇒ vasoconstriction ⇒ ⇓ blood flow to organ

Question 9

Extrinsic regulation control of vasoconstriction/dilation:
Neural Regulation (SNS)

Answer 9

1. arteriolar vasocon. (except in brain - intrinsic regulation only)
2. vasodilation due to ⇓ SNS signals (only important PSNS effect = dilation of arterioles of penis/clitoris)
3. also venoconstriction (vein constriction)

Question 10

Extrinsic regulation control of vasoconstriction/dilation:

Hormonal Regulation

Answer 10

1. epinephrine
   
   • vasoconstriction - skin, viscera - reinforces SNS
   • vasodilation - heart, skeletal muscle, liver - opposes SNS
2. other hormones
   
   • angiotensin II, ADH – vasoconstriction
   • histamine – vasodilation