Lecture 16: Local Control of Blood FLow

Question 1

what 3 things regulate arteriolar diameter

Answer 1

local, auto-regulatory control
autonomic fiber release of nitric oxide
sympathetic NS (like Epi)

Question 2

what is metabolic theory (active hyperemia)

Answer 2

local metabolic factors can increase blood flow to active muscles

tissue supply of oxygen matches the tissue demand for oxygen

Question 3

what is myogenic response (flow autoregulation)

Answer 3

arteriolar smooth muscle responds to changes in arteriolar blood pressure

this protects fragile capillaries when arteriolar pressure gets too high

Question 4

ventilation-perfusion coupling occurs when

Answer 4

poorly ventilated lung segments vasoconstrict
(hypoxia causes vasoconstriction)

Question 5

what factors cause vasodilation –> active hyperemia in skeletal muscle

Answer 5

decrease in O2 levels in tissue
increased CO2 levels in tissue
decreased tissue pH
increased tissue temperature
K+ levels

Question 6

chemical signals that result in vasodilation

Answer 6

• CO2
• K+ ions
• Adenosine
• Lactic acid
• nitric oxide
• Thromboxane
• prostacyclin
• histamine
  -bradykinin

Question 7

chemical signals that result in vasoconstriction

Answer 7

O2
endothelin-1

Question 8

why are negative feedback loops w/in capillary beds so important?

Answer 8

b/c if capillary beds were to remain dilated it messes with the pressure gradient and therefore blood flow

Question 9

what is active hyperemia?

Answer 9

blood flow response to increased tissue metabolic activity

Question 10

what is reactive hyperemia?

Answer 10

blood flow response to a blood flow occlusion that causes the build up of waste products and an inability to deliver oxygen and nutrients

Question 11

explain why blood flow through the coronary arteries is not consistent

Answer 11

blood flow through the coronary arteries increases during diastole and decreases during systole

• during diastole, vessels are NOT compressed so blood flow increases
• during systole, vessels are compressed so blood flow is reduced

Question 12

explain nitric oxides role in adaptation to animals living at high altitude

Answer 12

O2 partial pressure is low at high altitudes and can cause chronic poor ventilation / pulmonary hypoxia

• big horn sheep & lama have chronically elevated production of nitric oxide (vasodilator)

Question 13

what condition has the strongest control of arterial diameter

Answer 13

hpoxia

Question 14

what does hypoxia lead to in lungs?

Answer 14

hypoxia in the lungs causes vasoconstriction of pulmonary arteries

Question 15

what does hypoxia lead to in skeletal muscle?

Answer 15

vasodilation

Question 16

active hyperemia in skeletal muscle causes what

Answer 16

vasodilation

Question 17

what is active hyperemia?

Answer 17

blood flow response to an increase in tissue metabolic activity

Question 18

what is reactive hyperemia?

Answer 18

blood flow in response to flow occlusion

Question 19

what are local controls of blood flow

Answer 19

CO2, O2, pH

Question 20

what is metabolic theory

Answer 20

local metabolic factors can cause increased blood flow to active muscles

the tissue supply of O2 matches the tissue demand for O2

Question 21

explain ventilation-perfusion coupling

Answer 21

poorly ventilated lung segments vasoconstrict

Question 22

what are myogenic responses (flow autoregulation)

Answer 22

arteriolar smooth muscles responds to changes in arteriolar BP

Question 23

what is epinephrines’ effect on blood flow

Answer 23

epinephrine causes vasodilation via B2 adrenergic receptors, causing relaxation of smooth muscle at arterioles and skeletal muscle

Question 24

what is angiotensin II effect on blood flow

Answer 24

angiostensin II is a potent vasoconstrictor, it acts on smooth muscle of arterioles

gets synthesized when BP is low
increases aldosterone synthesis

Question 25

what is vasopressins (ADH/AVP) effect on blood flow

Answer 25

vasopressin is a peptide released from the posterior pituitary
- arteriolar vasoconstrictor
- released when plasma osmolarity or BP is low
- increases the reabsorption of water in kidney

Question 26

what is the CV response to aerobic exercise

Answer 26

an increased demand for O2 rich blood & nutrients in muscle

increased need to remove CO2
- this demand is met in part by an increased CO but also by redirecting blood flow

Question 27

why is blood flow redirected 4 fold times to the skin during exercise?

Answer 27

thermoregulation

Question 28

what are the 2 psychogenic responses?

Answer 28

defense alarm reaction (fight or flight) and vasovagal syncope

Question 29

what occurs during the defense-alarm reaction

Answer 29

the baroreceptor reflex is reset (there is a change in setpoint) in order to maintain higher BP

increased sympathetic
- causes Epi and NE release
- causes ADH + Angiotensin II
- ↑ HR, ↑SV, ↑BP
- vasoconstriction of non-critical organs
- vasodilation of coronary vessels and working skeletal muscle

Question 30

what occurs during vasovagal syncope

Answer 30

• the opposite of the defense alarm reaction
• occurs when an emotional state overrides the typical response of baroreceptors
• results in fainting or playing dead

Question 31

explain the regulation of arteriolar diameter via the sympathetic NS

Answer 31

• decreased parasympathetic innervation to the heart
  - ↑ HR, ↑CO
• ↑Sympathetic activity
  - SA node ↑HR, contractile cells ↑SV
  - Vasomotor fibers to veins and arterioles ↑TPR
  -all this results in an ↑MAP

Question 32

what are the 3 main hormonal controls of arteriolar diameter?

Answer 32

epinephrine (vasodilation, B2 receptors)
Angiotensin II (vasoconstriction)
Vasopressin (ADH/AVP) - vasoconstriction