Local Control of Blood Flow

Question 1

What are the two pathways that regulate the dual control of peripheral blood flow?

Answer 1

Extrinsic and Intrinsic

Question 2

What is the primary means of extrinsic control of peripheral blood flow?

Answer 2

Nervous system (and humorally as well)

Question 3

What are examples of pharmacologic stimuli that cause contraction of vascular smooth muscle?

Answer 3

Catecholamines.
Endothelin.
Serotonin.
Angiotensin II.
Vasopressin

Question 4

What are examples of pharmacologic stimuli that cause relaxation of vascular smooth muscle?

Answer 4

Histamine.
Adenosine.
Nitric Oxide (NO).
Carbon Dioxide.
Potassium
Hydrogen ion.
Prostaglandins.
Acetylcholine.
Bradykinin.

Question 5

How does the metabolic mechanism work?

Answer 5

Any intervention that results in an inadequate oxygen (nutrient) supply for the metabolic requirements of the tissues results in the formation of vasodilator substances which increase blood flow to the tissues.

Question 6

What two things can cause relaxation of smooth muscle at the precapillary sphincter?

Answer 6

Lack of oxygen.

Formation of vasodilators via tissue metabolites and ions.

Question 7

Dfine active hyperemia:

Answer 7

Increase in organ blood flow that is associated with an increased metabolic activity of that organ. Supply must equal demand.

Question 8

Define reactive hyperemia:

Answer 8

Transient increase in organ blood flow that is associated with the period of time that that organ (or area of tissues) has become ischemic.

Question 9

What is an example of reactive hyperemia in the clinical setting?

Answer 9

Tourniquet use for ortho cases

Question 10

What might reactive hyperemia after tourniquet release do to the patient’s vital signs?

Answer 10

Increased Heart rate.
Increased ETCO2.
Hypotension.

Question 11

What is typically the maximum time for tourniquet use for an ortho case?

Answer 11

2 hours

Question 12

Would you normally see hypotension or hypertension while tourniquet in on during surgery?

Answer 12

Likely you will see hypertension.

(same volume, less space= more pressure)

Question 13

What is autoregulation as an intrinsic control of local blood flow?

Answer 13

Intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure.

Question 14

What are two possible explanations for autoregulation?

Answer 14

Myogenic Mechanism.

Metabolic mechanism

Question 15

What is the theory behind myogenic mechanism of autoregulation?

Answer 15

When a lumen of a blood vessel is suddenly expanded, the smooth muscles respond by contracting in order to restore the vessel diameter and resistance.

Question 16

What is the proposed mechanism by which smooth muscles contract in response to blood vessel expansion?

Answer 16

Stretch of vascular smooth muscle causes activation of membrane calcium channels.

Question 17

What MAP is minimal requirement to maintain CBF?

Answer 17

MAP 55-60

Question 18

What role does the endothelium play in microcirculation?

Answer 18

Plays an active role in regulating the micrcocirculation through substances that elicit contraction or relaxation of the vascular smooth muscle.

Question 19

List the 4 (3 main) vasoactive substances released by the endothelium.

Answer 19

1. Nitric Oxide (most important)
2. Prostacyclin.
3. Endothelin.
4. Endothelial-derived hyperpolarizing factor (EDHF)

Question 20

Does smooth muscle become dilated or constricted via the endothelin pathway?

Answer 20

Contracted/Constricted

Question 21

Does smooth muscle become vasodilatedor constricted via Nitric oxide pathway?

Answer 21

Vasodilated/antiproliferation.

Question 22

Does smooth muscle become dilated or constricted via Prostacyclin pathway?

Answer 22

Vasodilated/antiproliferation.

Question 23

What is antiproliferation?

Answer 23

Inhibiting or stopping cellular growth. In terms of blood vessels, antiproliferation is the inhibition of growing the smooth muscle

Question 24

What are two examples of endothelial substances that cause antiproliferation?

Answer 24

Nitric oxide and Prostacyclin.

Question 25

What is the half life of Nitric Oxide?

Answer 25

Approx 6 seconds

Question 26

Why is the half life of nitric oxide so short?

Answer 26

Due to rapid oxidation into nitrite and nitrate. Also due to binding to hemoglobin

Question 27

Biochemically speaking, what does Nitric Oxide do in the body?

Answer 27

Increases cGMP concentration which produces relaxation by decreasing cytosolic free calcium.

Question 28

What 7 things stimulate NO production?

Answer 28

``` Shearing forces acting on the endeothelium. Angotensin II. Acetylcholine. Bradykinin. Histamine. Insulin. Substance P. ```

Question 29

In addition to a potent vasodilator, Nitric oxide also provides what other functions in CV system?

Answer 29

Inhibition of platelet adhesion. Antiproliferative. Free radical scavenger.

Question 30

How does Nitric Oxide improve RV performance?

Answer 30

Decrease PVR. Decrease Pulm artery pressure. Which decreases right ventricular afterload. Afterload goes down=RV performance gets better

Question 31

How does Nitric oxide effect V/Q relations?

Answer 31

Inhaled nitric oxide is delivered only to ventilated alveoli. This improves V/Q relations by vasodilating capillaries and improving blood flow to areas participating in gas exchange.

Question 32

What are two things that stop inhaled NO from having fully systemic effects?

Answer 32

Bind to Hgb. | Oxidizes into nitrites and nitrates.

Question 33

What does prostcyclin do to the blood vessel smooth muscle?

Answer 33

Strong vasodilator. | Inhibits platelet adhesion to the vascular endothelium.

Question 34

What does endothelin do to vessels?

Answer 34

Potent vasoconstrictor. Increased inotropy/chrontropy. Releases atrial natriuretic peptide. In heart failure, contributes to calcium overload and hypertrophy (proliferative qualities)

Question 35

Which endoethelially secreted substance is implicated in pathogenesis of hypertension, vasospasm, heart failure, and pulmonary hypertension?

Answer 35

Endothelin.

Question 36

What happens when there is damage to endothelium?

Answer 36

Decrease NO and Prostacyclin. | Increased endothelin production.

Question 37

What symptoms/complications does endothelial cell damage lead to?

Answer 37

Vasoconstriction. Vasospasm. Thrombosis

Question 38

How is acute increase in blood flow regulation different from long-term blood flow regulation?

Answer 38

Acute increase in blood pressure will substantially increase flow through vessels; however, long-term regulation develops in the period of hours/days/weeks post acute regulation. At this point, even increase blood pressure will only flow the normal amount

Question 39

What is angiogenesis?

Answer 39

A key mechanism for long-term local blood flow regulation is to change the amount of vascularity of the tissues. For instance, if the metabolism in a tissue is increased for a prolonged period, vascularity increases.

Question 40

Who has experiences collateral circulation?

Answer 40

By age 60, most people have at least one branch of coronary vessel closure, but do not notice because of collateral blood vessels.

Question 41

What happens in a more acute event when collateral vessels are unable to form quick enough following a blockage?

Answer 41

Coronary insufficiency, serious heart attack, death.