Lesson 25: Topic 21 - Sympathetic Influence on Vasculature Flashcards
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
- activation of b-adrenergic receptors to help counteract the vasoconstriction
- metabolites override sympathetic vasoconstriction
how is skeletal muscle affected during exercise?
a large increase in metabolic activity which increases SNS which causes active hyperemia which induces vasodilation to improve blood flow to skeletal muscle
skeletal muscle at rest has 13% of cardiac output, what does it have during exercise?
64% of cardiac output during exercise
why is blood flow to the kidneys, liver and digestive tract decreasing during exercise?
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
while blood volume in the brain does not change from rest to exercise, something does change. what is it?
total cardiac output decreases from 13% to 5%
why is there no influence of the sympathetic nervous system on blood flow in the brain?
because there is not many alpha adrenergic receptors but also flow auto regulation is what regulates the blood flow in the brain
true or false: to the brain we cannot have active hyperemia, but we can INSIDE the brain.
true
what is responsible for increasing blood flow to the heart?
reactive hyperemia
- but then active hyperemia can also be activated due to the increase in metabolic activity
why does bones cardiac output decrease in exercise from rest?
reduced blood flow because there is no metabolic activity in the bone to counteract the effects of vasoconstriction induced by the SNS
if we are stressed, we increase vasoconstriction of the arterioles, that is going to increase total peripheral resistance and then?
that increases MAP
what is the consequences of vasoconstricting our arterioles when we are stressed?
- 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
what does fluid reabsorption mean?
fluid nutrients from the organ that then are going back into the capillary
what does fluid filtration mean?
refers to the movement of gases, fluids, nutrients from the capillary to the organ
when SNS activity is high due to muscle activity, what happens to the arterioles and pressure?
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
what happens to MAP when we vasodilate the arterioles? (we are decreasing total peripheral pressure)
it is going to decrease MAP
why do we want to vasodilate our arterioles going to skeletal muscle during exercise?
it is going to lead to an increased blood flow to skeletal muscle through our capillaries
- increased gas and nutrient absorption
why does blood flow distribution change from organ to organ with exercise?
- 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)
equation for MAP?
TPR x CO
how do we affect TPR?
- we change the diameter of the arteriole (to change resistance)
- viscosity of the blood
how do we control arteriole diameter?
- local intrinsic control
- systemic (extrinsic) control
what is the major local intrinsic control mechanism affecting blood flow?
local metabolic changing in O2 and other metabolites
what is the major systemic (extrinsic) control mechanism affecting blood flow?
sympathetic nervous system and sympathetic nervous activity
what are the major control mechanisms affecting blood flow (arteriole diameter)?
metabolic control, local metabolic control, and sympathetic activity
what affects the myogenic responses to stretch?
flow auto-regulation
what is shear stress?
apart of the local intrinsic control mechanisms
- friction of blood flow going through the arteriole
what does shear stress do?
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
temperature of skin affects blood flow that is being diverted to the skin, is this local or systemic control?
local intrinsic control
heat induces vaso______.
dilation
cold will induce vaso______.
constriction
when histamine is released, what does it initiate? this is because of what type of blood flow control mechanism?
it initiates an inflammatory response. histamine release is because of the local intrinsic local control of blood flow
histamine release is because of?
an injury or allergy response
- it initiates an inflammatory response to produce blood flow in that area
epinephrine and norepinephrine is apart of which type of blood flow control mechanism?
extrinsic control
what is important in regulating the activation of alpha and beta adrenergic receptors?
epinephrine and norepinephrine
what hormones are produced by the kidneys that has the purpose of regulating fluid balance?
vasopressin and angiotensin II
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?
increase. apart of the extrinsic control mechanism
what are capillaries?
they connect to the smallest terminal end of the arteriole, become the capillaries and then become and empty their blood into the venules
what are capillaries composed of?
a single layer of endothelial cells
what is the primary purpose of the capillaries?
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
what is the pressure range of capillaries (mmHg)?
15/20 - 40
what is the pressure range of the large arteries similar to?
blood pressure range: 80-120
why do we have low pressure in the capillaries but not too low?
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
other than moving blood throughout the vascular system, what else is a pressure gradient important for in the blood?
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
does high pressure favour filtration or absorption?
filtration
does low pressure favour filtration or absorption?
absorption
a capillary that is inside skeletal muscle, what is the diamater?
about 5 micrometers
what is the approximate diameter of an RBC?
about 5 micrometers (it touches the sides of the capillaries)
the capillary is so thin that it can only move how many RBC at a time in a given space?
one
what ensures a very efficient exchange of oxygen being carried by an RBC through a capillary into the nearby tissue?
that only ONE RBC can fit in a given space in a capillary at a time
what makes the diffusion distance short in a capillary?
their thin walls
- thin walled = short diffusion distance
- this is important to efficiently exchange gases, fluids, and nutrients into the tissue that needs it
what is our blood flow rate in L/min at rest?
5L/min always
where is cross section area going to be the greatest?
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
where is blood flow velocity the lowest?
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)
what is the equation for velocity?
distance/time
ie. mm/sec
what is flows equation?
volume/time
ie. ml/sec or L/min
OR
- cross-sectional area x velocity
= cm2 x mm/sec
= should equation 5L/min
true or false: capillaries have a short diffusion distance
true
true or false: blood pressure is typically less than 15mm Hg
false
when exchange happens between the capillary wall and tissues, what does the substance go through?
substances must pass through the capillary wall, through interstitial fluid, to the tissue cells and metabolic waste products go through in the reverse direction
true or false: the gas and nutrient exchange across the capillary wall requires a diffusion gradient.
true
movement of substances across the capillary does what with regards to the endothelial cell?
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
true or false: lipid-soluble substances (like O2 and CO2) pass through the endothelial cell membrane anywhere
yes
how does small water soluble substances (glucose, amino acids, sodium, potassium) move from capillary to tissue?
pass through capillary only at cell-to-cell junctions (pores between the endothelial cells)
how is large water soluble substances (proteins) moved across the capillary?
moved through vesicular transport through endothelial cells
- transported across endothelial cells by vesicular transport
how is large plasma proteins (like albumin) moved across the capillary?
they hardly ever leave the plasma
true or false: the capillary dictates what can and cannot move out of the capillary
true
- ex. large plasma proteins like albumin cannot move through the capillary
