Central Control of Peripheral Circulation

Question 1

What triggers vascular smooth muscle contraction?

Answer 1

1. Passive stretching of VSM cells
2. Depolarization of VSM membranes
3. VSM receptor specific signal transduction responses to norepi, epi, angiotensin II, endothelin I…etc.

Question 2

What different mechanisms determine the level of intracellular calcium?

Answer 2

Question 3

What six things determine degree of vascular smooth muscle contraction?

Answer 3

1. Degree of sympathetic innervation
2. Basal rate of sympathetic activity
3. Relative number of α1 and β2 adrenergic VSM receptors
4. Level of circulating hormones
5. Level of locally produced metabolic factors
6. Level of arterial pressure (impacts strech mediated voltage-gated calcium channels)

Question 4

How does norepinephrine modulate intracellular calcium of vascular smooth muscle?

Answer 4

Norepi binds to α1 receptors - activating Gq proteins and pohspholipase C

Phospholipase C produces DAG and IP₃

IP₃ activates the ryanodine receptor in the SR causing and increase in intracellular Ca²⁺ which binds to calmodulin and activates myosin light chain kinase

DAG activates PKC which also leads to myosin light chain phosphorylation (causing VSM contraction)

Question 5

What hormones cause VSM contraction through IP₃-gated Ca²⁺ channel activation?

Answer 5

1. Endothelin
2. Angiotensin II
3. Vasopressin (ADH)

Question 6

How does TXA cause VSM contraction?

Answer 6

TXA binds to receptors in smooth muscle cells that directly activate calcium channels on the membrane and produce VSM contraction

Question 7

What is the integration center for the carotid baroreceptors?

Answer 7

The nucleus tractus solitarius (NTS)

Question 8

Where are the sensory fiber terminals for baroreceptors located?

Answer 8

In the adventitial layer of the carotid sinus and aortic arch

Question 9

Baroreceptors in the carotid sinus send afferent fibers to the nucleus tractus solitarius via what nerve?

Answer 9

The sinus nerve of Hering (branch of glossopharyngeal nerve - CN IX)

Question 10

Baroreceptors in the aortic arch send afferent fibers to the nucleus tractus solitarius via what nerve?

Answer 10

The vagus nerve (CN X)

Question 11

Which baroreceptor is the most sensitive?

Answer 11

The carotid sinus - threshold pressure of ~60 mmHg and responds to pressures between 60-180 mmHg

Question 12

How does decreased afferent input to the nucleus tractus solitarius affect the heart and blood vessels?

Answer 12

The sympathetic efferent activity to the heart and blood vessels is increased

Question 13

Increased BP activates excitatory interneurons directed from the nucleus tractus solitarius to what?

Answer 13

To the dorsal motor nucleus and the nucleus ambiguous

From dorsal motor nucleus and nucleus abmiguous, increased parasympathetic activity is directed to the heart, which acts to decrease heart rate

Question 14

Increased BP activates inhibitory interneurons directed from the nucleus tractus solitarius to what?

Answer 14

To the C1 and A1 region of the vasomotor area of the medulla - inhibits sympathetic activity to the heart and blood vessels

Question 15

What is the net effect of a reduction in parasympathetic activity and a reduction of inhibitory activity directed to the vasomotor area of the medulla?

Answer 15

Decrease in parasympathetic directed to the heart and an increase in sympathetic activity to the heart and blood vessels

Question 16

What areas of the heart receive parasympathetic innervation

Answer 16

SA/AV nodes and atria - receive vagal innervation

Parasympathetic innervation of ventricles is minimal

Question 17

Baroreceptor response to decrease in arterial BP

Figure

Answer 17

Question 18

How is intra-thoracic pressure respond during the Valsalva maneuver?

Answer 18

Increases from ~-5 cm H₂ to +35-30 cm H₂

Question 19

How is baroreceptor function assessed by the Valsalva maneuver?

Answer 19

By taking the ratio of the highest and lowest HR obtained during phase II and phase IV, respectively