I. Control Of Bf By Tissues: Local Mechanisms

Front 1

What are the 2 main determinants of how blood flow is regulated by the tissues?

Back 1

Supply and demand.
If demand is increased, supply will increase until no longer needed, and vice versa.

Front 2

What regulates supply of bloodflow to tissues?

Back 2

Resistance

Front 3

What 3 tissue types have very high bloodflow per mass?

Back 3

Kidneys
Adrenals
Thyroid

Front 4

What 3 tissues have intermediary bloodflow per mass?

Back 4

-Brain
-Heart
-Liver

Front 5

What 3 tissues have relatively low bloodflow per mass?

Back 5

Inactive muscle
Bone
Skin

Front 6

How does an increased metabolic rate affect blood flow?

Back 6

It causes BF to increase, but not to the same extent that you would expect; rather 1/2

Front 7

Why doesn't bloodflow increase as much as you would expect during increased metabolism?

Back 7

Because hemoglobin has other mechanisms for increasing O2 delivery without the global bloodflow needing to increase that much.

Front 8

What are the 2 main tissue changes that will cause bloodflow to increase?

Back 8

1. Metabolic rate
2. Blood O2 saturation (Po2)

Front 9

What structures are responsible for local changes in vascular flow to tissues?

Back 9

-Metaarteriole smooth muscle
-Precapillary sphincters

Front 10

What is it called when metabolism regulates bloodflow?

Back 10

Metabolic Autoregulation

Front 11

What are the 2 theories of Metabolic Autoregulation?

Back 11

1. Vasodilator substances
2. Oxygen deficit

Front 12

What substances are capable of vasodilating blood vessels? (6)

Back 12

-Adenosine
-CO2
-H+ and Lactic acid
-Histamine and K+

Front 13

What are the steps in Metabolic Autoregulation Vasodilator Substance Theory?

Back 13

1. Increase metabolic rate
2. Release vasodilators
3. Decrease Arteriole Resistance and precap sphincters
4. Increase blood flow

Front 14

What type of feedback is metabolic autoregulation?

Back 14

Negative - either of the theories.

Front 15

What are the steps in Metabolic Autoregulation Vasodilator Oxygen deficit Theory?

Back 15

1. Increase metabolic rate
2. Dcrease Tissue O2 conc.
3. Decrease Arteriole resistance
4. Increase blood flow

Front 16

2 Special examples of metabolic control of local blood flow:

Back 16

1. Functional hyperemia
2. Reactive hyperemia

Front 17

What type of autoregulation is seen in Functional Hyperemia?

Back 17

Vasodilator substance release

Front 18

What is Functional Hyperemia?

Back 18

Active hyperemia - exercise induced - increase in BF due to build up of metabolites (vasodilator substances).

Front 19

What is Reactive Hyperemia? What type of autoregulation?

Back 19

The excess of tissue bloodflow following occlusion or decreased O2 concentration.

Front 20

How does the responsive flow increase differ between Functional Hyperemia and Reactive hyperemia?

Back 20

Reactive shows an OVERSHOOT in response proportional to the length of time of occlusion.

Front 21

Why is the ability for muscle to change its resistance a good thing?

Back 21

Because it allows bloodflow to remain constant over a wide range of arterial pressure.

Front 22

What if the arteriole resistance could not change?

Back 22

BF would just increase directly ppl to Pressure increase and skyrocket.

Front 23

What is the change in muscle resistance called?

Back 23

Myogenic autoregulation

Front 24

What happens to myogenic autoregulation in the longterm?

Back 24

It keeps bloodflow constant over an even WIDER range of BPs by muscular remodeling.

Front 25

What type of feedback is myogenic autoregulation?

Back 25

Positive feedback

Front 26

How does Myogenic autoregulation compare to Metabolic?

Back 26

-Less precise - not a sensor of changes in metabolism
-Positive vs Negative feedback - more dangerous

Front 27

What are 2 results of decreasing Resistance at the Precapillary Sphincter?

Back 27

1. Release of vasodilator substances
2. Shear stress

Front 28

What is the effect of Shear stress on endothelial cells?

Back 28

They produce Nitric Oxide

Front 29

What does NO do?

Back 29

Vasodilates large vessels PROXIMAL to the precapillary sphincter to increase BF more

Front 30

What is NO produced from?

Back 30

Arginine

Front 31

What enzyme converts Arg into NO?

Back 31

NOS - nitric oxide synthase

Front 32

What is the action of NO?

Back 32

-Activates Guanylyl cyclase
-Activates cGMP formation
-cGMP causes vasodilation

Front 33

What happens to myogenic autoregulation in the long term?

Back 33

It stretches out to keep BF constant even in extremely high BP.

Front 34

How do vessels keep BF low even in high arterial pressure if R can't change anymore?

Back 34

By remodeling the vessel wall - hypertrophy.

Front 35

What law is exhibited by vascular remodeling?

Back 35

Laplace's law:
T = Pr/M
M (muscle thickness) increases to keep Wall Tension from going too high.

Front 36

What is the drawback to vascular remodeling?

Back 36

It increases resistance which makes BP increase even more - a vicious cycle.

Front 37

What is the 4th way to regulate bloodflow at the local level?

Back 37

Angiogenesis

Front 38

What are 3 important angiogenic factors?

Back 38

VEGF
FGF
Angiogenin

Front 39

What induces angiogenic factors?

Back 39

Shear stress or oxygen decrease

Front 40

What do angiogenic factors do?

Back 40

Act on the basement membrane to induce sprouting of endothelial cords.