Lesson 23: Topic 19 - Arterioles and Microcirculation Flashcards
a large component of the arteriole wall is?
smooth muscle
are arterioles apart of our macro or microcirculation?
microcirculation
- because they are located within an organ
arterioles determines blood flow to what?
individual organs
what is the greatest contributors to “total peripheral resistance”?
arterioles, thus important regulators of MAP
higher diameter = ____ resistance = ______ flow
lower resistance, greater flow
why does pressure drop so much at the level of the arterioles?
what is one of the largest regulators of the blood flow through any blood vessel?
pressure gradient / resistance
how do we determine resistance?
resistance = 1/radius ^4
what increases resistance other than radius?
- tube length
- viscosity of blood
if we increase viscosity of blood, how does resistance react?
proportionally
(2x viscosity = 2x resistance)
what is the biggest contributor to resistance of a blood vessel?
radius
true or false: blood flow to each organ is the same
false, not the same
true or false: blood flow to an individual organ can vary over time
true
how do we regulate the variable of blood from organ to organ?
- through changing the resistance of the arterioles and changing constriction and dialation
in a rested state, where is majority of our blood going?
digestive tract and liver and also the kidneys
why are we increasing blood flow to the skin during exercise?
to try and cool the body down
why is there no blood flow change in the brain from rest to exercise?
blood flow is not increasing to the brain because the brain is in a restricted space and increased blood flow would make it expand but it cannot.
- also to protect it from damage and in order to absorb nutrients and oxygen, the blood flow needs to be slow for proper absorption so it has its own regulation
by how much does skeletal muscles blood supply increase from rest to exercise?
1066%
if we increase resistance in a blood vessel that is going to be through?
vasoconstriction (less blood will come through here)
if we decrease resistance (increase diameter) in a blood vessel that is going to be through?
vasodilation (more blood will come through here)
if we are stressed or have blood less what happens to our blood flow?
vasoconstriction response in some areas and we lose blood blow in that area. (for blood loss this is good so we do not lose so much blood)
what is the predominant composition of arterioles?
made of 2 cell types (and connective tissue on the outside)
- endothelial cells (inner layer)
- smooth muscle (outer layer)
what is the function of smooth muscle cells in the arterioles?
- maintain shape of blood vessel (structural support)
- set blood vessel diameter… vasoconstriction or vasodilation
- regulate local blood flow within an organ
how does a smooth muscle contract?
by actin-myosin crossbridge formation and calcium induced calcium release like cardiac muscle cells
how is smooth muscle arranged?
not striated
- they have dense bodies that can be thought of as z-lines
where is the thick and thin filaments on a smooth muscle?
on the lines between the dense bodies and are anchored by the dense bodies
what type of signal causes vasoconstriction in smooth muscle cells?
signals that increase actin-myosin cross bridges
what type of signal causes vasodilation in smooth muscle cells?
signals that decrease actin-myosin cross bridges
true or false: once you activate smooth muscle, it can stay contracted without further activation
true
what is the inner layer of the arteriole?
endothelial cells
what is the function of endothelial cells?
- they line the heart and blood vessels
- they prevent blood cell and platelet adherence (thrombosis)
- they control the exchange of fluid and nutrients in capillaries
- they secrete vasodilator (nitric oxide) and vasoconstrictor (endothelin) substances
what is the vasodilator substance?
nitric oxide
what is the vasoconstrictor substance?
endothelin
how does nitric oxide (NO) cause relaxation (vasodilation) of smooth muscle?
nitric oxide that was produced in the endothelial diffuses from the endothelial cell to the smooth muscle and activates guanylate cyclase (an enzyme) which then converts GTP into cyclic GMP (cGMP) which is responsible for the relaxation of the smooth muscle –> vasodilation –> decreased resistance and increased blood flow
how does the endothelial cells produce nitric oxide?
takes L-Arginine, uses enzyme nitric oxide synthase to covert it to nitric oxide
how can we control the amount of cyclic GMP that is circulating inside the smooth muscle?
by the enzyme PDE (phosphodiesterase)
what does phosphodiesterase do?
breaks down cGMP into GMP in order to reduce the concentration of cGMP to try and produce a cGMP concentration and reduce its affects on increasing blood flow
what can cause more cGMP and greater increase in blood flow other than nitric oxide?
- increased production of cGMP by the enzyme nitroglycerin
- decreased breakdown of cGMP (Viagra) (inhibit phosphodiesterase)
what happens if you increase vasodilation throughout the entire body when you do not need it?
fainting can happen (should be wearing gloves if you want to touch it)
why would someone with a heart attack be given nitroglycerin?
to produce increased blood flow
what is the enzyme that is activated to form cGMP after NO diffuses into smooth muscle?
guanylate cyclase
