Chapter 17 Local And Humoral Control Of Blood Flow

Question 1

What are the tissue needs related to the local tissue blood flow control?

Answer 1

1) Delivery of oxygen and nutrients to the tissues.
2) removal of carbon dioxide and hydrogen ions from the tissue.
3) maintenance of proper concentration of ions in the tissue.
4) Transport of various hormones and other substances into the tissue.

Question 2

What is the blood flow to the brain per minute?

Answer 2

700 ml/min or 14 percentage of the cardiac output

Question 3

What is the blood flow to the heart per minute?

Answer 3

200 ml/ min or 4 % of the cardiac output

Question 4

What is the blood flow to the bronchi?

Answer 4

100 ml / min or 2 percentage of the cardiac output

Question 5

What is the blood flow to the kidneys?

Answer 5

1100 ml/min or 22% of the cardiac output

Question 6

What is the blood flow to the liver per minute?

Answer 6

1350( portal 1050 and Arterial 300) or 27% of the cardiac output.

Question 7

What is the blood flow to the resting skeletal muscle?

Answer 7

750 ml/ min or 15 percentage of the cardiac output.

Question 8

What is the blood flow to the bones ?

Answer 8

250 ml / min or 5% of the cardiac output.

Question 9

What is the blood flow to the skin in cool weather?

Answer 9

300 ml/ min or 6% of the cardiac output

Question 10

What is the blood flow to the thyroid gland?

Answer 10

50 ml/ min or 1% of the cardiac output

Question 11

What is the blood flow to the adrenal gland?

Answer 11

25 ML/ min or 0.5% of the cardiac output.

Question 12

What are the main mechanisms of blood flow control?

Answer 12

Acute control - It is achieved by rapid vasoconstriction or vasodilation of the arterioles, metarterioles, and precapillary sphincter.

Long-term control - This comes about as a result of an increase or decrease in the physical size and number of blood vessels supplying the tissue.

Question 13

How does carbon monoxide poisoning affect oxygen delivery?

Answer 13

It inhibits the ability of the hemoglobin to transport oxygen.

Question 14

How does cyanide poisoning affect oxygen delivery?

Answer 14

It inhibits the ability of the tissues to use oxygen

Question 15

How does cerbera odollam cause death?

Answer 15

It’s content cerberin is a digoxin type cardenolide and cardiac glycoside which inhibits calcium channels in the heart and incur severe sinus bradycardia and arrhythmias. The cerberin is hard to detect in autopsy specimen.

Question 16

What are the factors that modulate acute local blood flow?

Answer 16

1) increase in tissue metabolism increases local blood flow.
2) Reduced tissue oxygen availability increases tissue blood flow.

Question 17

What is the basis of vasodilator theory for acute local blood flow regulation?

Answer 17

The vasodilator theory says the greater the rate of metabolism, or the lesser the O2 availability or other nutrients availability, the greater the formation of vasodilator substances in the tissue cells such as adenosine, adenosine phosphate compounds, histamine, potassium ions, and hydrogen ions. These vasodilator substances exert paracrine effect on the vascular smooth muscles of precapillary sphincter, metarterioles and arterioles.

Question 18

What causes the vasodilators: adenosine and lactic acid containing hydrogen ions release into the microcirculation?

Answer 18

Reduction in oxygen availability to meet the metabolic demands of the tissue.

Question 19

Coronary ischemia causes the release of what vasodilator?

Answer 19

Adenosine

Question 20

What is the definition of vasomotion?

Answer 20

It is the cyclical opening and closing of the metarterioles and precapillary sphincters are called vasomotion. The vasomotion frequency is directly proportional to the metabolic need of the tissue.

Question 21

What is the effect of beriberi on tissue perfusion?

Answer 21

Beriberi caused by the deficiency of thiamine, riboflavin or Niacin will impair oxygen induced phosphorylation necessary for ATP production. This will reduce the contractility of the smooth muscles of metarterioles and precapillary sphincters at the tissues across the body leasing to generalized hypermia.

Question 22

What is reactive hyperemia?

Answer 22

It is a transient increase in local blood flow due to local occlusion of blood flow for > 1 min.

Question 23

What is autoregulation of blood flow?

Answer 23

When there is an increase in blood pressure the blood flow concomitantly increases. However, within less than a min the blood flow returns to normal in the face of persistent elevation of the blood pressure. This phenomenon is called autoregulation of blood flow.

Question 24

Between the arterial pressure of 70 and 175 mmHg, what is the increase in blood flow?

Answer 24

20 to 30% even though the blood pressure increased 150%

Question 25

What are the two competing theories of autoregulation of blood flow?

Answer 25

The metabolic theory and myogenic theory.

Question 26

What is the mechanism of blood flow autoregulation according to metabolic theory?

Answer 26

The metabolic theory states that the transient increase in blood flow in conjunction with increase in blood pressure will cause the delivery of excess oxygen and nutrients to the tissue cells and simultaneously wash away the vasodilator substances released by the cells. This will cause the blood flow to normalize by causing vasoconstriction of metarterioles and precapillary sphincters.

Question 27

What is the mechanism of autoregulation of the blood flow according to the myogenic theory?

Answer 27

The increase in blood pressure within the arterioles causes stretching of the vessel wall, which will cause calcium mediated depolarization and contraction of vascular smooth muscles of the metarterioles and precapillary sphincters leading to vasoconstriction and down regulation of the blood flow.

Question 28

What is the mechanism of the renal autoregulation of the blood flow?

Answer 28

The renal autoregulation of blood flow is mediated by the macula densa, which is a jextaglomerular apparatus located where the distal tubule lies adjacent to the afferent and efferent renal arterioles. When excess glomerular filtration occurs the macula densa sends feedback signal to the renal arterioles which leads to vasoconstriction and normalization of renal plasma filtration.

Question 29

What is the mechanism of autoregulation of blood flow in the brain?

Answer 29

An increase in CO2 or H+ in cerebral tissue will cause vasodilation and wash out of these metabolites.

Question 30

Nitric oxide is a powerful____ released by the endothelium.

Answer 30

Vasodilator

Question 31

Explain the endothelial synthesis of nitric oxide?

Answer 31

It is a lipophilic gas synthesized by the endothelial cells with the help of the enzyme eNOS. eNOS synthesis NO from the amino acid L-argenine and oxygen and by reducing inorganic nitrate.

Question 32

What is the mechanistic factor that cause the NO release from the endothelium?

Answer 32

The sheer stress incurred by the viscous drag of the blood on the surface of the endothelium.

Question 33

Other than sheer stress what else causes the release of nitric oxide from the endothelium?

Answer 33

The release of vasoconstrictor angiotensin 2 which binds to AT1 receptors.

Question 34

What is the effect of impaired nitric oxide synthesis?

Answer 34

It will cause excessive vasoconstriction and worsening of atherosclerosis and chronic hypertension

Question 35

What is the effect of PDE-5 inhibitor?

Answer 35

It increases the availability of NO by preventing the PDE-5 mediated catabolism of cGMP

Question 36

What is the major vasoconstrictor released by the endothelial cells?

Answer 36

Endothelin: a very small amount of endothelin can cause powerful vasoconstriction by binding to ETa and ETb receptors. Endothelin is usually released in response to endothelial injury or chronic hypertension.

Question 37

Long term regulation of blood flow?

Answer 37

It occurs over a period of days to weeks to months. Even if the BP remains high the blood flow will return to normal independent of elevated BP insidiously. The long-term regulatory mechanism will cause angiogenesis of the feeders of the metabolically chronically demanding tissues.

Question 38

What are the mechanisms of long-term regulation of blood flow?

Answer 38

1) tissue angiogenesis
2) chronic lack of oxygen induce angiogenesis.
3) angiogenesis mediated by vascular growth factors such as VEGF, PDGF, angiogenin and hypoxia inducible factors etc.
4) vascularity is regulated by maximum blood flow needs not by average need

Question 39

What is retrolental fibroplasia?

Answer 39

It is a leading cause of blindness in children. When a premature child is put in oxygen tents, the excess oxygen causes degeneration of newly formed retinal vessels. When the child is brought out of the oxygen tent, often reactive explosive excessive hyperplasia occurs which is marked by retinal vessels invagination of vitrious humor leading to blindness.

Question 40

Explain the blood flow regulation by collateral circulation?

Answer 40

When there is an obstruction of a vessel. The small vascular loops around the blocked blood vessels dilate due to metabolic factors within 1 or 2 min. It establishes less than 25% tissue perfusion. However further opening ensues within a day establishing 50% of reperfusion.
The collateral circulation continues to evolve over months. Which will cause normalization of blood flow under resting condition. However, when metabolic demands increases during strenuous exercise this flow through collateral vessels may not be enough to prevent hypoxia.

Question 41

Collateral blood flow in heart attack?

Answer 41

When there is an occlusion of the main coronary artery, there will be rapid collateral circulation opening around the occluded vessel. If the time window is not enough to open up these collateral vessels Severe coronary insufficiency can occur and the attack will evolve to serious heart attack

Question 42

What is inward eutrophic remodeling?

Answer 42

It is the remodeling of vascular smooth muscles and endothelial cells of the small vessels in response to consistent increase in blood pressure. They remodel in proportion to the small lumen diameter over a period of days to months with no change in the total cross sectional area of the vascular wall.

Question 43

What is hypertrophic remodeling of the vascular wall?

Answer 43

In large vessel that doesn’t constrict in response to increased chronic pressure on the vascular wall. The vascular wall smooth muscles and the endothelium will undergo outward hypertrophic remodeling that results in an increase in the cross-sectional area of vascular wall. The thickness of the wall and stiffness increase by the deposition of additional extracellular matrix proteins like the collagen and fibrinectin. This hypertrophic stiffening is the wholemark of chronic hypertension.

Question 44

What are the effects of increased intravascular pressure or blood flow on vascular remodeling?

Answer 44

The chronic increase in blood pressure: increases vascular wall tension which causes vascular wall hypertrophy and thickness in particular in large vessels.

The chronic increase in blood flow rate and sheer stress caused by the viscous drag of the blood will cause outward remodeling and increase in lumenal diameter to accommodate increased blood flow

Question 45

What is humoral control of the circulation?

Answer 45

It is the control of circulation by the hormones and other substances released locally by the tissues and endocrine glands that have paracrine and autocrine effect on the circulatory system.

Question 46

What are the vasoconstrictor substances?

Answer 46

Norepinephrine and the epinephrine: released by the sympathetic nerve endings locally and the adrenal medullae systemically.
Angiotensin 2: It is a powerful vasoconstrictor one millionth of a gram can cause strong arterioler constriction. It causes an increase in generalized peripheral resistance by pan arterioler constriction and retention of sodium and water by reducing GFR.
Vasopressin- It is the most potent vasoconstrictor produced in the hypothalamus and released into the blood by the neurophypophysis. It acts by increasing blood volume by increasing renal tubular water reabsorption.

Question 47

What are the vasodilators involved in humoral control of the blood circulation ?

Answer 47

Bradykinin and histamine

Question 48

What are kinins ?

Answer 48

The kinins are small polypeptide vasodilators formed in the blood and tissue of some organs. They are catabolized by proteolytic enzymes from alpha 2 -globulins in the plasma fluid.

Question 49

How is bradykinin formed?

Answer 49

When there is maceration of the blood or inflammation of the tissue or chemical or physical insult occurs the proteolytic enzymes Kallikrein gets activated and it stimulates the alpha 2 -globulins to release a kinin called kallidin, which is converted by tissue enzymes to bradykinin.

Question 50

How is bradykinin catabolized?

Answer 50

It is degraded within a few minutes from the formation by the enzyme carboxypeptidase or converting enzyme.

Question 51

What catabolizes the activated Kallikrein enzyme?

Answer 51

Kallikrein inhibitor

Question 52

How does bradykinin affect tissue perfusion?

Answer 52

It causes powerful arterioler dilation and increased capillary permeability

Question 53

How do kinins cause edema?

Answer 53

The kinins in particular bradykinin increases capillary blood flow, transmembrane permiability by increasing capillary pore size leading to edema

Question 54

What causes release of histamine?

Answer 54

The tissue damage, inflammation or allergic reaction causes the mast cells in the damaged tissue and basophils in the blood to release histamine. It is a powerful vasodilator like the bradykinin which can significantly increase capillary porosity and cause edema

Question 55

How does calcium ions cause vasoconstriction?

Answer 55

It causes vascular smooth muscle contraction to incur vasoconstriction

Question 56

How does potassium ions cause vasodilation?

Answer 56

Potassium ions inhibits vascular smooth muscle contraction leading to vasodilation

Question 57

What is the effect of magnesium on vascular smooth muscle contractility?

Answer 57

Magnesium is a powerful vascular smooth muscle contraction inhibition, it causes vasodilation

Question 58

An increase in H+ causes ____ and decrease in H+ causes _____.

Answer 58

Vasodilation and vasoconstriction

Question 59

Effect of carbon dioxide on arterioler contractility?

Answer 59

Increase in carbon dioxide causes vasodilation in the brain and most tissues. The carbon dioxide acting on the brain vasomotor center can cause sympathetically mediated systemic vasoconstriction.