Factors affecting blood flow Flashcards
1
Q
how does blood flow vary
A
from one organ to another
2
Q
what does blood flow between organs depend on
A
the metabolic demands of each organ system
3
Q
what does blood flow to the lungs align with
A
cardiac output
4
Q
why does blood flow to the lungs align with the cardiac output
A
because all blood must pass through the lungs for oxygenation and removal of carbon dioxide
5
Q
which organ system requires blood flow similar to cardiac output
A
the lungs
6
Q
what increases and decreases the blood flow to specific organs
A
metabolic requirements of the tissues
7
Q
why does blood flow to skeletal muscle increase during exercise
A
greater demand for oxygen
8
Q
why does blood flow to the GI system increase following a meal
A
there is greater demand for oxygen following ingestion of food
9
Q
why are there interorgan blood flow differences
A
as a result of alterations in vascular resistance
10
Q
how can the mechanisms of blood flow regulation be categorised
A
local and hormonal
11
Q
describe local control of blood flow
A
matches blood flow to metabolic requirements of the tissue systems
direct action on the metabolites on arteriolar resistance
12
Q
describe the neural/hormonal control of blood flow
A
action of sympathetic nervous system on vascular smooth muscle
action of vasoactive substances
13
Q
what are some vasoactive substances involved in hormonal control of blood flow
A
- histamine
- bradykinin
- prostoglandins
14
Q
what are the specific needs for blood flow
A
- delivery of oxygen to tissues and nutrients
- removal of carbon dioxide and hydrogen ions
- maintenance of ion concentrations in tissues
- transport of hormones
15
Q
what are the nutrients that blood delivers to tissues
A
glucose
amino acids
fatty acids
16
Q
what are the mechanisms by which intrinsic control of blood flow can occur
A
autoregulation
reactive hyperemia
active hyperemia
17
Q
describe autoregulation
A
maintenance of constant blood flow while arterial pressure changes
18
Q
example of autoregulation
A
if the coronary arterial pressure decreases, there is immediate compensatory vasodilation of coronary arterioles to decrease the coronary vasculature resistance
19
Q
describe active hyperemia
A
blood flow to tissues is proportional to its metabolic activity
increased blood flow when metabolic activity increases
increased arteriolar dilation
20
Q
when would there be an increase in blood flow due to metabolic activity
A
exercising skeletal muscle tissue which increases oxygen consumption
21
Q
describe reactive hyperemia
A
increase in blood flow in response to a prior period of decreased blood flow
22
Q
example of reactive hyperemia
A
following a period of arterial occlusion, oxygen debt accumulates. the longer the arterial occlusion, the greater the oxygen debt and the greater the increase of blood flow above the pre occlusion levels. this continues occurs the oxygen debt is reversed
23
Q
what are the factors that determine resistance to blood flow
A
vessel diameter
vessel length
viscosity of blood
24
Q
how does vessel diameter change
A
with vasoconstriction and vasodilation as a result of contraction and relaxation of vascular smooth muscle
25
what is the vascular smooth muscle
the tunica media
26
how does a small change in vessel diameter affect resistance
there are large changes as a result of even just small changes
27
does viscosity of blood ever really change
no it usually remains within a narrow range
28
what is the exception to the concept that blood viscosity changes
haemocrit
29
what can happen to the blood vessels to lead to changes in resistance
change in their diameter
30
what can cause an increase in blood viscosity
dehydration and immobility
31
what can reduce the risk of increases blood viscosity
hydration
movement
compression socks
32
why does movement decreases changes in normal blood viscosity
it encourages venous return
33
what can a change in blood viscosity lead to
risk of deep vein thrombosis
34
what is vessel resistance directly proportional to (an increase in one will increase the other)
length of the vessel and viscosity of the blood
35
what is vessel resistance inversely proportional to
radius to the fourth power of the vessel
36
describe the equation for the relationship between flow, pressure and resistance
flow = change in pressure over resistance
37
what is poiseuilles equation
Q = r^4 times change in pressure over viscosity times length of the vessel
38
what does poiseuilles equation describe
how flow is related to perfusion pressure, radius, length, and viscosity
39
what does the poiseuilles equation assume
- flow is through a uniform straight pipe
- flow is non pulsatile
- flow is laminar
40
what does it mean to say that flow is laminar
it is smooth
41
when can velocity of flow be considered the same across the tube
when the flow has negligible resistance
42
what happens to the velocity of flow as viscosity increases
it increases to a maximum at the centre of the tube
43
do veins have a large or small cross sectional area
large
44
how are venous valves orientated
toward the heart
45
why are venous valves orientated toward the heart
to maintain blood flow in one direction
46
what is venous return to the heart aided by
the action of working skeletal muscles intermittently contracting to compress the veins
47
what happens to intrathoracic pressure during exercise
it becomes more negative because there are more frequent respirations that increase the pressure gradient between abdominal and thoracic veins
48
what is in control of the sympathetic activation of venous return
noradrenaline
49
how does noradrenaline play a role in venous return
sympathetic activation which constricts the veins and increases venous return to the heart
50
what is preload
venous return to the right ventricle
51
what happens when there is an increase in preload
the heart will have to work harder to pump the blood out and this can be a problem in coronary artery disease and heart failure
52
what is angina
coronary artery disease
53
what is coronary circulation
this is circulation that facilitates the perfusion of the myocardium
maintains high basal rate of oxygen supply to cardiac muscle
54
what is skeletal muscle adapted for
meeting the metabolic demands of skeletal muscle during exercise
55
what is the function of cerebral circulation
regulation to maintain cerebral perfusion
56
what name is given to the blood vessels that supply the heart
coronary arteries
57
how much of resting cardiac output is provided to the heart through coronary circulation
5%
58
what is blood supply to the myocardium derived from
right and left coronary arteries
59
where do the coronary arteries originate on the heart
at the root of the aorta behind the cusps of the aortic valve
60
what supplies the right ventricle and atrium
the right coronary arteries
61
what supplies the left ventricle and atrium
the left coronary arteries
62
what are the branches of the left coronary artery
left circumflex artery
anterior descending artery
63
what does the left circumflex artery supply
the left atrium and ventricle
64
what does the anterior descending artery supply
the interventricular spetum and a portion of the right and left ventricles
65
which branch of the left coronary arteries descends to the apex
the anterior descending artery
66
what do coronary arteries branch into
segments dividing into capillary networks that facilitate oxygen diffusion into cardiac myocytes that have a high ATP requirement
67
what are the epicardial veins
venules that the blood drains into following coronary circulation
68
what do the epicardial veins collect into
coronary sinus
69
what does the coronary sinus do
collect the blood from the epicardial veins to empty blood into the right atrium
70
what is another name for the epicardial veins
the coronary veins
71
what are thebesian veins
vascular channels on the heart that drain deoxygenated blood from the capillary network in the ventricular wall directly into the cardiac chambers
72
what is the coronary blood flow at rest
70-80 ml/min/100g
73
when does perfusion of the myocardium from the coronary arteries occur
during early diastole
74
do relaxed ventricles compress the arteries
no
75
what constricts the blood vessels
contraction of the myocardium
76
what proportion of left coronary blood flow occurs during diastole
80%
77
what is coronary blood flow during exercise
300-400ml/min/100g
78
what can increase the number of arterioles and capillaries
exercise training
79
why does ventricular mass increase with exercise training
to meet the physiological demands of prolonged exercise training
80
what is meant by athletic heart
this is a physiological adaptation of structural and functional remodelling in response to exercise training
81
what is the difference between exercise induced hypertrophy and pathological hypertrophy
the cellular mechanisms
82
what are some pathological causes of cardiac hypertrophy
valve heart disease
cardiac myopathy
83
how does muscle circulation change during exercises and what is the reason for this
it increases to increase oxygen and glucose delivery to match the increase in work
84
how can the relationship between blood flow and exercise intensity be described
coupled
85
what is the vascular resistance of skeletal muscle a major influence of
total peripheral resistance
86
what regulates blood flow at rest
sympathetic innervation
87
what regulates blood flow during exercise
local control mechanisms
88
what are the local vasodilators that work to increase blood flow to skeletal muscle during exercise
lactact
adenosine
potassium ions
89
what is the muscle capillary density adapted for
muscle function
90
what does alpha one adrenoreceptor activation cause
vasoconstriction
91
which form of vasoconstriction is the most usual in the body
alpha one induced
92
how does vasoconstriction work
it decreases resistance to increase blood flow
93
what does beta two adrenoreceptor activation lead to
vasodilation
94
how does vasodilation work
decreased resistance, increased blood flow
95
which hormone causes vasodilation during stress or exercise
adrenaline released from the adrenal gland
96
during exercise, do all capillaries vasodilate
no, there is tonic sympathetic vasoconstriction that continues to feed the arteries and proximal resistance vessels, which prevents excessive decrease in the total peripheral resistance
97
what couples blood flow to exercise intensity
the metabolic vasodilation
98
what accounts for half of vascular resistance
cerebral arteries
99
which arteries enter the cranial cavity to supply the brain
the basilar and internal carotid arteries
100
what forms the circle of willis
the anastomosation of the basilar and internal carotid arteries once they enter the cranial cavity
101
describe cerebral autoregulation
- cerebral resistance vessels dilate to maintain perfusion when arterial blood pressure falls.
- the cerebral blood flow will steeply decline at a blood pressure lower than 60mmHg
102
what happens if the there is hypotension to the brain
mental confusion and syncope
103
what is syncope
loss of consciousness
104
what are the cerebral resistance vessels sensitive to
local hypoxia and arterial carbon dioxide
105
what is hypercapnia
too much carbon dioxide
106
what does hypercapnia cause
cerebral vasodilation, which is mediated by endothelial nitric oxide
107
what does hypocapnia cause
cerebral vasoconstriction, leading to hyperventiculation, reducing cerebral perfusion
108
what is the symptom of cerebral perfusion
dizziness
109
what does local hypoxia lead to
cerebral vasodilation
110
what does systemic hypoxia stimulate
ventilation
111
what are some circulations in the body with specialised local control
- pulmonary circulation
- skin circulation
- renal circulation
112
describe the arrangements of blood components in a capillary following centrifugation
- red blood cells are at the bottom
- buffy coat containing leukocytes
- plasma at the top
113
what does local control of blood flow allow
matching of flow to metabolic demands
114
what does autoregulation allow
maintenance to constant blood flow to tissue systems despite changes in arterial pressure
115
why does reactive hyperaemia occur
due to occlusion of the vessel lumen which leads to greater blood flow due to accumulation of blood
116
what can cause occlusion of the blood vessel lumen
atherosclerotic plaque
117
why is blood flow not smooth
there are different factors that can make blood flow turbulent
118
where in the blood vessels is blood flow fastest and why
in the centre as there is resistance against the blood flow in the vessel wall
119
describe the importance of venous valves
there is no pulsatile pushing or compliance to push the blood flow, so there can be tendency of blood to backflow if there were not these valves to maintain the blood flow in the one direction
120
what aids preload
skeletal muscle contraction
121
what constricts the veins to help push blood back toward the heart
sympathetic activation
122
what is starlings mechanism
greater preload stretches the myocardial cells leading to increased contractility
123
how do coronary arteries profuse cardiomyocytes
they branch to become arterioles and capillaries
124
how many mils of blood per minute are involved in coronary circulation
70-80
125
what is angiogenesis
formation of new capillaries from existing blood vessels
126
what is an angioplasty
a procedure used to widen the coronary arteries that are blocked or narrowed
127
what is an angiogram
an x ray photograph of blood or lymph vessels to check for blockages to reduce risk of infarction
128
can the myocardium be profused during systole
no
129
why is capillary density adapted to muscle function
to increase or decrease the metabolic demands of the muscle groups engaged in activity
130
what does tonic vasoconstriction mean
it is a slow and graded physiological response
131
what is the specialised circulation of skin related to
temperature regulation
132
why was the level of haematocrit in the blood samples of the lab lower than the suggested range
there is species variation in the haematocrit layers
133
what must be maintained to maintian the profusion of vital systems
cardiac output
