Lesson 23: Topic 19 - Arterioles and Microcirculation

Question 1

a large component of the arteriole wall is?

Answer 1

smooth muscle

Question 2

are arterioles apart of our macro or microcirculation?

Answer 2

microcirculation
- because they are located within an organ

Question 3

arterioles determines blood flow to what?

Answer 3

individual organs

Question 4

what is the greatest contributors to “total peripheral resistance”?

Answer 4

arterioles, thus important regulators of MAP

Question 5

higher diameter = ____ resistance = ______ flow

Answer 5

lower resistance, greater flow

Question 6

why does pressure drop so much at the level of the arterioles?

Question 7

what is one of the largest regulators of the blood flow through any blood vessel?

Answer 7

pressure gradient / resistance

Question 8

how do we determine resistance?

Answer 8

resistance = 1/radius ^4

Question 9

what increases resistance other than radius?

Answer 9

• tube length
• viscosity of blood

Question 10

if we increase viscosity of blood, how does resistance react?

Answer 10

proportionally
(2x viscosity = 2x resistance)

Question 11

what is the biggest contributor to resistance of a blood vessel?

Answer 11

radius

Question 12

true or false: blood flow to each organ is the same

Answer 12

false, not the same

Question 13

true or false: blood flow to an individual organ can vary over time

Answer 13

true

Question 14

how do we regulate the variable of blood from organ to organ?

Answer 14

• through changing the resistance of the arterioles and changing constriction and dialation

Question 15

in a rested state, where is majority of our blood going?

Answer 15

digestive tract and liver and also the kidneys

Question 16

why are we increasing blood flow to the skin during exercise?

Answer 16

to try and cool the body down

Question 17

why is there no blood flow change in the brain from rest to exercise?

Answer 17

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

Question 18

by how much does skeletal muscles blood supply increase from rest to exercise?

Answer 18

1066%

Question 19

if we increase resistance in a blood vessel that is going to be through?

Answer 19

vasoconstriction (less blood will come through here)

Question 20

if we decrease resistance (increase diameter) in a blood vessel that is going to be through?

Answer 20

vasodilation (more blood will come through here)

Question 21

if we are stressed or have blood less what happens to our blood flow?

Answer 21

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)

Question 22

what is the predominant composition of arterioles?

Answer 22

made of 2 cell types (and connective tissue on the outside)
- endothelial cells (inner layer)
- smooth muscle (outer layer)

Question 23

what is the function of smooth muscle cells in the arterioles?

Answer 23

• maintain shape of blood vessel (structural support)
• set blood vessel diameter… vasoconstriction or vasodilation
• regulate local blood flow within an organ

Question 24

how does a smooth muscle contract?

Answer 24

by actin-myosin crossbridge formation and calcium induced calcium release like cardiac muscle cells

Question 25

how is smooth muscle arranged?

Answer 25

not striated - they have dense bodies that can be thought of as z-lines

Question 26

where is the thick and thin filaments on a smooth muscle?

Answer 26

on the lines between the dense bodies and are anchored by the dense bodies

Question 27

what type of signal causes vasoconstriction in smooth muscle cells?

Answer 27

signals that increase actin-myosin cross bridges

Question 28

what type of signal causes vasodilation in smooth muscle cells?

Answer 28

signals that decrease actin-myosin cross bridges

Question 29

true or false: once you activate smooth muscle, it can stay contracted without further activation

Answer 29

true

Question 30

what is the inner layer of the arteriole?

Answer 30

endothelial cells

Question 31

what is the function of endothelial cells?

Answer 31

- 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

Question 32

what is the vasodilator substance?

Answer 32

nitric oxide

Question 33

what is the vasoconstrictor substance?

Answer 33

endothelin

Question 34

how does nitric oxide (NO) cause relaxation (vasodilation) of smooth muscle?

Answer 34

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

Question 35

how does the endothelial cells produce nitric oxide?

Answer 35

takes L-Arginine, uses enzyme nitric oxide synthase to covert it to nitric oxide

Question 36

how can we control the amount of cyclic GMP that is circulating inside the smooth muscle?

Answer 36

by the enzyme PDE (phosphodiesterase)

Question 37

what does phosphodiesterase do?

Answer 37

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

Question 38

what can cause more cGMP and greater increase in blood flow other than nitric oxide?

Answer 38

1. increased production of cGMP by the enzyme nitroglycerin 2. decreased breakdown of cGMP (Viagra) (inhibit phosphodiesterase)

Question 39

what happens if you increase vasodilation throughout the entire body when you do not need it?

Answer 39

fainting can happen (should be wearing gloves if you want to touch it)

Question 40

why would someone with a heart attack be given nitroglycerin?

Answer 40

to produce increased blood flow

Question 41

what is the enzyme that is activated to form cGMP after NO diffuses into smooth muscle?

Answer 41

guanylate cyclase