Lesson 25: Topic 21 - Sympathetic Influence on Vasculature

Question 1

how do we regulate increasing blood flow to skeletal muscle when the SNS with systemic controls of the SNS is going to induce vasoconstriction generally throughout our whole entire body

Answer 1

1. activation of b-adrenergic receptors to help counteract the vasoconstriction
2. metabolites override sympathetic vasoconstriction

Question 2

how is skeletal muscle affected during exercise?

Answer 2

a large increase in metabolic activity which increases SNS which causes active hyperemia which induces vasodilation to improve blood flow to skeletal muscle

Question 3

skeletal muscle at rest has 13% of cardiac output, what does it have during exercise?

Answer 3

64% of cardiac output during exercise

Question 4

why is blood flow to the kidneys, liver and digestive tract decreasing during exercise?

Answer 4

because there is no metabolic activity in these organs. so we are not stimulating the vasodilation response so we have increased vasoconstriction
- SNS produces norepinephrine so vasoconstriction occurs and no epinephrine causes a vasodilation effect

Question 5

while blood volume in the brain does not change from rest to exercise, something does change. what is it?

Answer 5

total cardiac output decreases from 13% to 5%

Question 6

why is there no influence of the sympathetic nervous system on blood flow in the brain?

Answer 6

because there is not many alpha adrenergic receptors but also flow auto regulation is what regulates the blood flow in the brain

Question 7

true or false: to the brain we cannot have active hyperemia, but we can INSIDE the brain.

Answer 7

true

Question 8

what is responsible for increasing blood flow to the heart?

Answer 8

reactive hyperemia
- but then active hyperemia can also be activated due to the increase in metabolic activity

Question 9

why does bones cardiac output decrease in exercise from rest?

Answer 9

reduced blood flow because there is no metabolic activity in the bone to counteract the effects of vasoconstriction induced by the SNS

Question 10

if we are stressed, we increase vasoconstriction of the arterioles, that is going to increase total peripheral resistance and then?

Answer 10

that increases MAP

Question 11

what is the consequences of vasoconstricting our arterioles when we are stressed?

Answer 11

• less flow through arterioles to organs which leads to low blood flow in our capillaries
• less blood flow = reduce gas and nutrient exchange
• reduction of blood flow in the capillaries = favour fluid reabsorption more than fluid filtration

Question 12

what does fluid reabsorption mean?

Answer 12

fluid nutrients from the organ that then are going back into the capillary

Question 13

what does fluid filtration mean?

Answer 13

refers to the movement of gases, fluids, nutrients from the capillary to the organ

Question 14

when SNS activity is high due to muscle activity, what happens to the arterioles and pressure?

Answer 14

arterioles are going to vasodilate and cause a low pressure so that will reduce the total peripheral resistance due to the metabolite response which is greater than SNS and override it

Question 15

what happens to MAP when we vasodilate the arterioles? (we are decreasing total peripheral pressure)

Answer 15

it is going to decrease MAP

Question 16

why do we want to vasodilate our arterioles going to skeletal muscle during exercise?

Answer 16

it is going to lead to an increased blood flow to skeletal muscle through our capillaries
- increased gas and nutrient absorption

Question 17

why does blood flow distribution change from organ to organ with exercise?

Answer 17

• no local metabolic activity in an organ will encourage vasoconstriction to that organ
• high metabolic activity in an organ will override increased SNS activity influence (SNS activity causes vasoconstriction so the metabolic activity overrides this in order to vasodilate)
• it depends on whether the organ has flow autoregulation (in the brain, you have flow autoregulation which is going to determine the blood flow distribution to that organ
• it depends on whether the organ has alpha-adrenergic receptors (like in the brain, if you do not have many alpha-adrenergic receptors, you cannot have much vasoconstriction occurring)

Question 18

equation for MAP?

Answer 18

TPR x CO

Question 19

how do we affect TPR?

Answer 19

• we change the diameter of the arteriole (to change resistance)
• viscosity of the blood

Question 20

how do we control arteriole diameter?

Answer 20

• local intrinsic control
• systemic (extrinsic) control

Question 21

what is the major local intrinsic control mechanism affecting blood flow?

Answer 21

local metabolic changing in O2 and other metabolites

Question 22

what is the major systemic (extrinsic) control mechanism affecting blood flow?

Answer 22

sympathetic nervous system and sympathetic nervous activity

Question 23

what are the major control mechanisms affecting blood flow (arteriole diameter)?

Answer 23

metabolic control, local metabolic control, and sympathetic activity

Question 24

what affects the myogenic responses to stretch?

Answer 24

flow auto-regulation

Question 25

what is shear stress?

Answer 25

apart of the local intrinsic control mechanisms - friction of blood flow going through the arteriole

Question 26

what does shear stress do?

Answer 26

when friction is caused because of excessive blood flow going through the arterioles (maybe because of blood doping), it will stimulate the production of nitric oxide to induce vasodilation

Question 27

temperature of skin affects blood flow that is being diverted to the skin, is this local or systemic control?

Answer 27

local intrinsic control

Question 28

heat induces vaso______.

Answer 28

dilation

Question 29

cold will induce vaso______.

Answer 29

constriction

Question 30

when histamine is released, what does it initiate? this is because of what type of blood flow control mechanism?

Answer 30

it initiates an inflammatory response. histamine release is because of the local intrinsic local control of blood flow

Question 31

histamine release is because of?

Answer 31

an injury or allergy response - it initiates an inflammatory response to produce blood flow in that area

Question 32

epinephrine and norepinephrine is apart of which type of blood flow control mechanism?

Answer 32

extrinsic control

Question 33

what is important in regulating the activation of alpha and beta adrenergic receptors?

Answer 33

epinephrine and norepinephrine

Question 34

what hormones are produced by the kidneys that has the purpose of regulating fluid balance?

Answer 34

vasopressin and angiotensin II

Question 35

is it in the increase or decrease of vasopressin and angiotensin II that induces a vasoconstriction response? what type of blood flow control mechanism is this related to?

Answer 35

increase. apart of the extrinsic control mechanism

Question 36

what are capillaries?

Answer 36

they connect to the smallest terminal end of the arteriole, become the capillaries and then become and empty their blood into the venules

Question 37

what are capillaries composed of?

Answer 37

a single layer of endothelial cells

Question 38

what is the primary purpose of the capillaries?

Answer 38

it is a very thin layer of cells because we want an efficient gas exchange - it is the primary sit of gas, nutrient, waste and water exchange

Question 39

what is the pressure range of capillaries (mmHg)?

Answer 39

15/20 - 40

Question 40

what is the pressure range of the large arteries similar to?

Answer 40

blood pressure range: 80-120

Question 41

why do we have low pressure in the capillaries but not too low?

Answer 41

because it still needs a high enough pressure to get into the veins and it cannot do that without a pressure gradient - in order to continue to move blood flow through the vascular system, we need to have a pressure gradient

Question 42

other than moving blood throughout the vascular system, what else is a pressure gradient important for in the blood?

Answer 42

also very important to dictating the exchange of nutrients. the direction of the exchange of nutrients found the capillary into the tissue in the organ

Question 43

does high pressure favour filtration or absorption?

Answer 43

filtration

Question 44

does low pressure favour filtration or absorption?

Answer 44

absorption

Question 45

a capillary that is inside skeletal muscle, what is the diamater?

Answer 45

about 5 micrometers

Question 46

what is the approximate diameter of an RBC?

Answer 46

about 5 micrometers (it touches the sides of the capillaries)

Question 47

the capillary is so thin that it can only move how many RBC at a time in a given space?

Answer 47

one

Question 48

what ensures a very efficient exchange of oxygen being carried by an RBC through a capillary into the nearby tissue?

Answer 48

that only ONE RBC can fit in a given space in a capillary at a time

Question 49

what makes the diffusion distance short in a capillary?

Answer 49

their thin walls - thin walled = short diffusion distance - this is important to efficiently exchange gases, fluids, and nutrients into the tissue that needs it

Question 50

what is our blood flow rate in L/min at rest?

Answer 50

5L/min always

Question 51

where is cross section area going to be the greatest?

Answer 51

at the level of the capillaries - this is because all the branching takes up the most space in a small section, where in arteries or arterioles, there isn't as much space taken up in a section because there is a large surface area for exchange

Question 52

where is blood flow velocity the lowest?

Answer 52

at the level of the capillaries - as we continue to branch out the vasculature, our blood flow is going to drop until it is very low (0.5mm/sec, not 0mm/sec)

Question 53

what is the equation for velocity?

Answer 53

distance/time ie. mm/sec

Question 54

what is flows equation?

Answer 54

volume/time ie. ml/sec or L/min OR - cross-sectional area x velocity = cm2 x mm/sec = should equation 5L/min

Question 55

true or false: capillaries have a short diffusion distance

Answer 55

true

Question 56

true or false: blood pressure is typically less than 15mm Hg

Answer 56

false

Question 57

when exchange happens between the capillary wall and tissues, what does the substance go through?

Answer 57

substances must pass through the capillary wall, through interstitial fluid, to the tissue cells and metabolic waste products go through in the reverse direction

Question 58

true or false: the gas and nutrient exchange across the capillary wall requires a diffusion gradient.

Answer 58

true

Question 59

movement of substances across the capillary does what with regards to the endothelial cell?

Answer 59

depending on the type of substance, it either moves through the endothelial cell, between the endothelial cell or does not move at all through the endothelial cell

Question 60

true or false: lipid-soluble substances (like O2 and CO2) pass through the endothelial cell membrane anywhere

Answer 60

yes

Question 61

how does small water soluble substances (glucose, amino acids, sodium, potassium) move from capillary to tissue?

Answer 61

pass through capillary only at cell-to-cell junctions (pores between the endothelial cells)

Question 62

how is large water soluble substances (proteins) moved across the capillary?

Answer 62

moved through vesicular transport through endothelial cells - transported across endothelial cells by vesicular transport

Question 63

how is large plasma proteins (like albumin) moved across the capillary?

Answer 63

they hardly ever leave the plasma

Question 64

true or false: the capillary dictates what can and cannot move out of the capillary

Answer 64

true - ex. large plasma proteins like albumin cannot move through the capillary