Chapter 17 ( local and humoral control of tissue blood flow. Flashcards
specific needs of tissue for blood flow include…..
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.
acute control in pressure
Rapid changes in vasodilation and vasoconstriction
Long-term control in pressure
Slow controlled changes over days, weeks, or months. These result from actual increases or decreases in blood vessels supplying the tissues
Acute flow regulation when O2 availability changes
When O2 availability goes down as in ( pneumonia, CO2 poisening, high altitude…) the blood flow to the tissue increases
Name the 2 theories for regulation of blood flow when either the rate of tissue metabolism changes or availability of O2 changes
Vasodilator theory for acute local blood flow regulation.
Oxygen lack theory for local blood flow.
describe the vasodilator theory for acute local blood flow regulation
different compounds cause vasodilation like adenosine, CO2, Adenosine phosphate compounds, histamine, potassium, hyrdogen ions
describe the Oxygen lack theory for local blood flow
O2 is needed for constriction. So without O2 the muslces relax and dilate.
what is vasomotion
opening and closing of precapillary sphincters and metarterioles which is proportional to the metabolic need of the tissue
reactive hyperemia( example of acute metabolic control)
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
active hyperemia( example of acute metabolic control)
increase metabolism causes cells to devour tissue fluid nutrients rapidly and secrete vasodilator substances
Autoregulation
body regulating itself and returning the blood flow back to normal.
name the 2 theories for autoregulation
metabolic, myogenic theories
metabolic theory
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
myogenic theory
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.
Nitric oxide
a vasodilator that relaxes vessels. People take these to get more blood to your muscles. It is synthesized from arginine
mechanism of long term regulation-
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
importance of vascular endothelial growth factors in formation of new blood vessels-
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)
valuable characteristic of long term vascular control-
vascularity is determined mainly by the maximum level of blood flow need rather than by average need
development of collateral circulation
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)
Vasoconstrictor agents
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.
Angiotensin II
powerful vasoconstrictor
Bradykinin-
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.
histamine-
is released when there is damage or inflammation. Its derived from mast cells and basophils in the blood. Powerful vasodilator.
name some ions that cause vasoconstriction
calcium, magnesium, or decrease in hydrogen ions
