Chapter 17 ( local and humoral control of tissue blood flow.

Question 1

specific needs of tissue for blood flow include…..

Answer 1

Oxygen delivery, other nutrient delivery ( glucose, amino acids, fatty acids), removal of CO2 and hydrogen ions, maintenance of proper concentration of other ions, hormone transport.

Question 2

acute control in pressure

Answer 2

Rapid changes in vasodilation and vasoconstriction

Question 3

Long-term control in pressure

Answer 3

Slow controlled changes over days, weeks, or months. These result from actual increases or decreases in blood vessels supplying the tissues

Question 4

Acute flow regulation when O2 availability changes

Answer 4

When O2 availability goes down as in ( pneumonia, CO2 poisening, high altitude…) the blood flow to the tissue increases

Question 5

Name the 2 theories for regulation of blood flow when either the rate of tissue metabolism changes or availability of O2 changes

Answer 5

Vasodilator theory for acute local blood flow regulation.

Oxygen lack theory for local blood flow.

Question 6

describe the vasodilator theory for acute local blood flow regulation

Answer 6

different compounds cause vasodilation like adenosine, CO2, Adenosine phosphate compounds, histamine, potassium, hyrdogen ions

Question 7

describe the Oxygen lack theory for local blood flow

Answer 7

O2 is needed for constriction. So without O2 the muslces relax and dilate.

Question 8

what is vasomotion

Answer 8

opening and closing of precapillary sphincters and metarterioles which is proportional to the metabolic need of the tissue

Question 9

reactive hyperemia( example of acute metabolic control)

Answer 9

flow is stopped for a few seconds up to an hour and then is unblocked. The flow returns up to 4-7 times the normal and lasts for a few seconds to hours

Question 10

active hyperemia( example of acute metabolic control)

Answer 10

increase metabolism causes cells to devour tissue fluid nutrients rapidly and secrete vasodilator substances

Question 11

Autoregulation

Answer 11

body regulating itself and returning the blood flow back to normal.

Question 12

name the 2 theories for autoregulation

Answer 12

metabolic, myogenic theories

Question 13

metabolic theory

Answer 13

arterial pressure becomes elevated and the excess flow provides too much O2 and other nutrients to the tissues and “washes out” the vasodilators by the tissues. the absence of vasodilators allows the vessel to constrict and return to normal

Question 14

myogenic theory

Answer 14

high arterial pressure stretches the vessel and causes the reactive vascular constriction that reduces the blood flow back to normal. This is initiated by vascular depolarization which rapidly increases calcium which causes the smooth muscle to contract.

Question 15

Nitric oxide

Answer 15

a vasodilator that relaxes vessels. People take these to get more blood to your muscles. It is synthesized from arginine

Question 16

mechanism of long term regulation-

Answer 16

It changes the vascularity of tissues. If metabolism is increased for a prolonged period, vascularity increases ( angiogenesis). There is actual physical reconstruction of the tissue vasculature to meet the needs of the tissues

Question 17

importance of vascular endothelial growth factors in formation of new blood vessels-

Answer 17

examples are VEGF ( vascular endothelial growth factor, fibroblast, growth factor, angiogenin. These have been isolated from a sample of tissue that have inadequate blood supply. These all cause new blood vessels to form ( angiogenesis)

Question 18

valuable characteristic of long term vascular control-

Answer 18

vascularity is determined mainly by the maximum level of blood flow need rather than by average need

Question 19

development of collateral circulation

Answer 19

first stage is dilation of vascular loops that already connect the vessel above the blockage to the vessel below. The new flow is less than ¼ of original flow but it continues to grow to about ½ after a day. After a couple days the flow is usually sufficient to meet the tissues needs ( good example is thrombosis in coronary arteries)

Question 20

Vasoconstrictor agents

Answer 20

norepinephrine and epinephrine. Norepinephrine excites the heart and contracts the veins and arteriole and also excites the adrenal medullae which causes the glands to secrete them into the blood.

Question 21

Angiotensin II

Answer 21

powerful vasoconstrictor

Question 22

Bradykinin-

Answer 22

powerful vasodilator. Causes powerful arteriolar dilation and increased capillary permeability. An injection of 1 microgram can increase blood flow to someones arm as much as sixfold.

Question 23

histamine-

Answer 23

is released when there is damage or inflammation. Its derived from mast cells and basophils in the blood. Powerful vasodilator.

Question 24

name some ions that cause vasoconstriction

Answer 24

calcium, magnesium, or decrease in hydrogen ions

Question 25

name some ions that cause vasodilation

Answer 25

potassium, hydrogen, CO2

Question 26

Do vasodilators & constrictors have a big effect on long term blood flow?

Answer 26

no. Autoregulation prevents this.