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HN220 > Chapter 14: Cardiovascular System - Blood Vessels > Flashcards

Chapter 14: Cardiovascular System - Blood Vessels Flashcards

1
Q

how does blood flow in the cardiovascular system?

A

a CLOSED system, through the vasculature (circulatory system) which is an elaborate system of pipes (arteries and veins)

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2
Q

2 principles that pertain to blood vessels

A

1) pressure gradients = driving force the pushes the flow of liquid through the pipe (high to low pressure)
2) resistance = the measure of factors that hinder the flow of liquid through a pipe

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3
Q

what is the flow rule?

A
  • flow = pressure gradient (P) / resistance (R)
  • flow is directly proportional to the pressure gradient
  • flow is inversely proportional to the resistance of the pipe
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4
Q

role of pressure gradients in driving blood flow

A
  • ensures that blood flow through the circulatory system/body is maintained
  • the heart creates the pressure gradient for the bulk flow of blood
  • the greater the pressure gradient, the greater the fluid flow (since it is proportional)
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5
Q

how does the heart create a pressure gradient?

A
  • the heart pumps blood into the arteries, which increases the mean arterial pressure
  • this creates a pressure difference between the arteries (high pressure) and veins (low pressure) that drives blood flow
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6
Q

role of resistance in the cardiovascular system

A
  • is a key determinant of blood flow and blood pressure
  • increased resistance = increase in blood pressure
  • increased resistance = decrease in blood pressure
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7
Q

factors affecting resistance in the cardiovascular system

A

1) radius of the vessel (r) - if radius increases = blood flow increases, if radius decreases = blood flow decreases
2) length of vessel (L) - longer vessels = more resistance
3) viscosity of fluid (n) - resistance increases as viscosity increases (depends on concentrations of RBC’s, proteins)

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8
Q

what is total peripheral resistance?

A
  • the combined resistance of all blood vessels in the systemic circuit (the body)
  • the resistance of the vascular network depends on the resistances of all individuals blood vessels (arteries, arterioles, capillaries, venules, and veins) it contains
    –> therefore when some arteries experience increased resistance, it can lead to decreased blood flow not only in those specific arteries but also in the entire network supplied by those arteries
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9
Q

what is Poiseuille’s Law?

A
  • it describes how flow is related to pressure, radius, length, and viscosity.
  • represents the enormous influence that vessel diameter has on the blood flow rate that circulates through the vessels
    –> therefore any changes to the radius of the blood vessels (increase or decrease) will influence FLOW and PRESSURE of blood through the vasculature
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10
Q

what has the greatest impact on resistance within the CV system?

A
  • RADIUS of blood flow
  • vasoconstriction = decreased radius = increased resistance
  • vasodilation = increases radius = decreased resistance
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11
Q

how is resistance related to flow?

A
  • flow through a vessel is inversely proportional to resistance
    –> if resistance increases, flow decreases (if pressure is unchanged)
    –> if resistance decreases, flow increases (if pressure is unchanged)
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12
Q

how are pressure gradients and resistance applied to the systemic circuit?

A

cardiac output (CO) = mean arterial pressure (MAP) / total peripheral resistance (TPR)

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13
Q

role of arteries

A

any vessel that carry blood away from the heart

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14
Q

role of veins

A

any vessel that carry blood to the heart

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15
Q

what is the microcirculation?

A
  • arterioles
  • capillaries
  • venules
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16
Q

arterioles

A

a very small blood vessel that branches off from your artery and carries blood away from your heart to capillaries

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17
Q

venules

A

the smallest veins and receive blood from capillaries and bring to larger veins toward the heart

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18
Q

capillaries

A

form the connection between vessels that carry blood away from the heart (arteries) and the vessels that return blood to the heart (veins), also the site of exchange of fluids and gases

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19
Q

3 layers of blood vessels

A

1) tunica intima (interna)
- composed of endothelial cells and elastic membrane
2) tunica media
- made of smooth muscle (circular and longitudinal arrangement)
3) tunica externa
- made of a mixture of collagen and elastic fibres
- veins may contain some smooth muscle
- helps to anchor the vessel and provide stability

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20
Q

why are arteries referred to as a pressure reservoir? what is the importance?

A
  • due to the thickness and elasticity of arterial walls, they provide stiffness and the ability to expand/contract as blood pressure rises and falls
  • when arterial walls expand due to increased blood volume (during systole), the elastin fibers in the arterial walls act like a spring and stretch. the elastic force is stored so that when no blood is entering during diastole, the walls passively recoil inward and propel blood forward
  • this allows them to ensure a continual, smooth flow of blood through the vasculature even though the heart is not pumping (diastole)
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21
Q

what arterial compliance?

A

refers to the ability of a blood vessel to stretch and expand in response to pressure change

  • low compliance = the vessel is less stretchable = will experience a significant increase in pressure with a small increase in volume
  • high compliance = the vessel can easily stretch and expand = the vessel can accommodate larger changes in volume with minimal changes to pressure
    –> compliance is low in blood vessels that are less elastic, such as large arteries
    –> compliance is high in more elastic vessels, such as small veins
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22
Q

How does the compliance of arteries contribute to their function as a pressure reservoir?

A
  • low compliance = better pressure reservoir
  • this is because these vessels do not readily expand (don’t stretch much) when blood fills the artery into them during systole
  • instead, they store the pressure generated by the heart’s contractions
  • the stored pressure is then gradually released during diastole (heart relaxation) as the walls recoil and exert pressure on the blood to maintain a steady flow of blood through the arteries.
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23
Q

what happens to blood pressure in a low compliance vessel?

A
  • in a vessel with low compliance (an artery), since it is less elastic and can’t expand as easily, it cannot accomodate a large increase in blood volume
  • when there is more blood in a smaller space, the pressure increases = increase blood pressure
    –> when a heart ejects blood into the arteries during systole and causes the vessels the expand, the resulting rise in pressure is greater than if arteries compliance was higher
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24
Q

what is arterial blood pressure?

A

the pressure within the aorta

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25
Q

what is blood pressure?

A
  • the force blood exerts on the arterial wall
  • systolic BP = peak blood pressure when the heart is contracting
  • diastolic BP = lowest blood pressure when the heart is relaxing
  • measured as systolic over diastolic (SP/DP)
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26
Q

how do arterioles affect blood flow?

A
  • arterioles provide the greatest resistance to blood flow (60%)
  • it causes the largest pressure drop in the vasculature (goes from 90mmHg to 40mmHg) due to their small radius causing resistance
  • this is due to the fact arterioles contain smooth muscles (can contract and relax) therefore changing the radius of the vessel = causing resistance
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27
Q

how do arterioles vary their resistance?

A
  • is regulated by the changes in arteriole radius
  • depends on arterial tone = if their smooth muscle is contracted or relaxed
    –> vasoconstriction = decreased radius = increased resistance
    –> vasodilation = increased radius = decreased resistance
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28
Q

2 key functions of arterioles

A

1) controlling blood flow to individual capillary beds (intrinsic control)
2) regulating mean arterial pressure (extrinsic control)

29
Q

intrinsic control of blood flow

A
  • regulation and distribution of blood flow to organs is based on metabolic need
  • is regulated by varying resistance of blood vessels via vasodilation or vasoconstriction of arteriole smooth muscle

organ blood flow = mean arterial pressure / organ resistance

30
Q

4 intrinsic factors that affect radius

A
  • changes in metabolic activity (active hyperemia, reactive hyperemia)
  • changes in blood flow
  • stretch of arteriole smooth muscle
  • local chemical messengers
31
Q

how does metabolic activity affect blood flow

A
  • arteriole smooth muscle either contracts or relaxes based on whether concentrations of O2, CO2, K+ or H+ in ECF rise or fall
  • increased metabolic activity = vasodilation
  • decreased metabolic activity = vasoconstriction
32
Q

what occurs at steady-state?

A
  • O2 is delivered as fast as it is consumed
  • CO2 is removed as fast as it is produced
    –> this changes when metabolic activity increases
33
Q

what occurs in active hyperemia?

A
  • blood flow increases in response to increased metabolic activity
    –> O2 is consumed faster than it is delivered
    –> CO2 is produced faster than it is removed
  • in response to low O2 and high CO2, vasodilation occurs to increase blood flow in order to deliver more oxygen and remove CO2 byproduct
34
Q

what occurs in reactive hyperemia?

A
  • increased blood flow in response to a a blockage or reduction in blood flow to a tissue
    –> O2 concentration decreases
    –> CO2 concentration increases
  • in response, vasodilation and a decrease in resistance occurs which allows for more blood to flow
  • this increases oxygen delivery and CO2 removal
  • when the blockage is released, there is a higher than normal blood flow to the area until excess metabolites are removed and tissue oxygen concentration is back to normal
35
Q

extrinsic control of blood flow

A
  • regulation and distribution of blood flow to organs is based the control of mean arterial pressure (MAP)
36
Q

how does mean arterial pressure influence blood flow to individual organs and the entire systemic circuit?

A
  • blood flow to individual organs is determined by a pressure difference caused by MAP
  • MAP serves as the driving force for blood flow through the systemic circulation because it provides the pressure gradient necessary to propel blood through the systemic circuit
  • arterioles regulating blood flow to tissues/ organs by adjusting their diameter in response to changes in mean arterial pressure (MAP)
    –> increase in MAP = more blood flow to organs so it triggers vasoconstriction to regulate bloood flow
    –> decrease in MAP = decreases blood flow to organs so it triggers vasodilation to increase blood flow
37
Q

what 2 factors affect mean arterial pressure?

A

1) neural mechanisms
2) hormones can
–> affect arteriolar resistance and arteriolar radius = impact MAP

38
Q

how do hormones affect MAP?

A
  • hormones regulate arteriolar resistance by causing vasoconstriction or vasodilation = increases MAP

1) vasopressin (ADH) is secreted by the posterior pituitary gland, promotes vasoconstriction and increases blood pressure
2) angiotensin II is present in the plasma, and promotes vasoconstriction, increasing BP and MAP
3) epinephrine primarily acts as a vasoconstrictor during fight-or-flight
4) noprepinephrine promotes vasoconstriction by binding α1 adrenergic receptors
5) atrial natriuretic peptide promotes vasodilation

39
Q

how do neural mechanisms affect MAP?

A

neural mechanisms by the autonomic nervous system (ANS) regulate both cardiac output and peripheral resistance
- SNS increases cardiac output (high HR) and causes vasoconstriction of arterioles = increase MAP
- PNS decreases cardiac output (low HR) = low MAP (the PNS doesn’t innervate blood vessels so it cannot constrict/dilate)
- baroreceptors (pressure) and chemoreceptors (O2, CO2, and pH levels) sense changes and can increased SNS activity and decreased PNS activity = resulting in vasoconstriction and increased heart rate = raise blood pressure

40
Q

what is the arterial baroreceptor reflex?

A
  • a reflex that keeps your blood pressure steady when you experience something that raises or lowers it
  • a negative feedback loop that maintains homeostasis
41
Q

how does the arterial baroreceptor reflex work?

A
  • baroreceptors are stretch sensitive mechanoreceptors and consistently monitor pressure to the brain (carotid artery) and to the body (aortic artery)
    –> if blood pressure increases = more stretch = causes increase in frequency of action potential firing
    –> if blood pressure decreases = less stretch = causes decrease in frequency of action potential firing
  • the afferent signals from baroreceptors are sent to the cardiovascular control centre (CVCC) in the brainstem which generates efferent signals to the ANS regulate blood pressure via PNS and SNS
    –> if BP high –> increased parasympathetic activity = vasodilation = decreases heart rate = decrease blood pressure back to normal
    –> if BP low –> increased sympathetic activity = vasoconstriction = increased heart rate = increased blood pressure back to normal
42
Q

why is regulation of MAP so critical?

A
  • crucial for homeostasis, normal organ function, overall health

if MAP < normal
- hypotension
- inadequate blood flow to tissues (especially the brain)

if MAP > normal
- hypertension
- is a stressor for heart and blood vessels

43
Q

what are capillaries?

A

the primary site where exchange of nutrients and waste products occur between blood and tissue

44
Q

anatomy of capillaries

A
  • the smallest blood vessels
  • have a small diameter
  • very thin walls consisting of a single layer of endothelial cells
    –> the small diameter and width provide a short diffusion distance between blood and interstitial fluid
45
Q

2 classes of capillaries

A

1) continuous capillaries
2) fenestrated capillaries

46
Q

continuous capillaries

A
  • the most common type
  • found mostly in muscles, lungs, adipose tissue and the brain
  • made of endothelial cells that are joined together by tight junctions that provides narrow spaces between cells
  • are highly permeable to small water-soluble molecules that pass through the intercellular cleft (big substances wouldn’t fit)
  • permeable to lipid-soluble molecules that move through the endothelial cells
47
Q

fenestrated capillaries

A
  • made of endothelial cells that have large gaps between neighbouring cells, forming pores (fenestrations)
  • allows for diffusion of proteins, and sometimes blood cells
  • located in kidneys, intestine and endocrine glands
48
Q

what does a capillary bed consist of?

A

1) a vascular shunt (metarteriole)
- metarteriole = intermediate of arteriole and capillaries
- serves as a bypass channel through capillaries that directly connects arterioles to venules
2) true capillaries
- where the actual exchange of gases, nutrients, and waste products occurs
3) precapillary sphincter
- smooth muscle that surrounds the root of each capillary at each arteriole end
- act as valves to regulate blood flow into capillary beds by constricting or relaxing.

49
Q

2 purposes of movement across capillary walls

A

1) exchange of material between blood and cells
2) normal distribution of extracellular fluid

50
Q

mechanisms of exchange across capillary walls

A

based on a molecules size, solubility and location:
1) diffusion (most common)
- direction of diffusion depends on the electrochemical gradient
- nutrients/oxygen move from blood to tissue
- waste products and carbon dioxide move from tissue to blood

2) transcytosis
- large proteins are selectively transported by endothelial that engulf them in the plasma via endocytosis to the interstitial fluid

3) mediated transport
- occurs in the brain

4) bulk flow
- the movement of fluid across a capillary wall based on pressure gradients

51
Q

lipophilic vs lipophobic

A

–> lipophilic = small, lipid soluble solute diffuse across endothelial cell membrane
–> lipophobic = small, water soluble solute diffuse via through pores/channels

52
Q

filtration vs absorption

A
  • filtration = when fluid moves out of capillary bed/blood into the interstitial fluid
  • absorption = when fluid moves into the capillary bed/blood from the interstitial fluid
53
Q

what forces are required for bulk flow?

A

the forces that drive the movement of fluid into and out of capillaries are called Starling forces.

1) capillary hydrostatic pressure = pressure of fluid inside the capillary (FILTRATION)
2) interstitial fluid hydrostatic pressure = pressure of fluid outside the capillary (ABSORPTION)
3) capillary osmotic pressure = presence of non- permeating solutes inside the capillary (ABSORPTION)
4) interstitial fluid osmotic pressure = presence of non-permeating solutes outside the capillary (FILTRATION)

54
Q

hydrostatic vs osmotic pressure

A
  • hydrostatic pressure forces fluid out of the capillary
  • osmotic pressure draws fluid back in.
55
Q

hydrostatic pressures

A
  • when a hydrostatic pressure exists across a capillary wall, the pressure tends to move water across the wall.
    –> the capillary hydrostatic pressure favours filtration = drives fluid out of the capillary and into the interstitial space
    –> the interstitial fluid hydrostatic pressure favors absorption = movement of fluid from the interstitial space into the capillary
56
Q

osmotic pressures

A
  • water tends to flow from the side where the solute concentration is lower to the side where the solute concentration is higher
    –> the capillary osmotic pressure = draw fluid from the interstitial fluid into the capillary
    –> the interstitial fluid osmotic pressure = draw fluid out of the capillary and into the interstitial fluid
57
Q

what is net filtration pressure?

A
  • the difference in the filtration pressures and the absorption pressures
  • determines the direction of fluid flow across the wall of a capillary
    –> capillary hydrostatic pressure and interstitial fluid osmotic pressure favour filtration
    –> interstitial fluid hydrostatic pressure and capillary osmotic pressure favour absorption
58
Q

characteristics of veins vs arteries

A
  • veins have larger diameters than arteries
  • vein walls are half as thick as artery walls
  • blood pressure in veins is significantly lower than in arteries
  • veins function as volume reservoirs, arteries function as pressure reservoirs
59
Q

key characteristics of the venous system

A
  • vein walls contain smooth muscle and elastic connective tissues
  • veins have one way valves that permit blood to flow forward but not backwards
  • they function as volume reservoirs and are called “low resistance” vessels because they stretch to accommodate an increased volume of blood
60
Q

why are veins called a volume reservoir?

A
  • they are thin walled and easily stretched, so they have high compliance
  • veins can accommodate a large volume of blood without a big change in blood pressure = good at storing volume
61
Q

4 factors affecting venous pressure

A
  • skeletal muscle pump
  • respiratory pump
  • blood volume
  • venomotor tone
    –> these factors all act to increase venous pressure which consequently increases MAP
62
Q

what does the skeletal muscle pump do?

A

the skeletal muscle pumps helps to maintain venous return by compressing underlying veins in order to increase blood flow back to the heart
- when skeletal muscles contract, they press against veins traveling between them which raises the pressure within the vein
- contraction pressure forces distal valves to close in order to prevent blood from flowing backwards. it also forces proximal valves to open and allow blood to flow toward the heart
- when the muscle relaxes, the pressure drops and allows the distal valves to open and more blood to flow forward. the proximal valves close to prevent blood from flowing away from the heart
- by alternating contracting and relaxing, the muscles act as pumps to drive blood toward the heart
–> this is how exercise helps move blood back to he heart.

63
Q

what is the respiratory pump?

A

a mechanism using a pressure gradient in order to pump blood back to the heart using inspiration and expiration
- during inhalation, thoracic pressure is lowered and abdominal pressure is increased = blood flows from abdominal veins to central veins = more blood flow to the heart
- during exhalation, thoracic pressure increases and abdominal pressure decreases = blood moves forward from from central veins to heart because valves in abdominal veins prevent the backward blood flow

64
Q

how does blood volume affect venous return?

A
  • an increase in blood volume = increase in venous pressure
  • a decrease in blood volume = a decrease in venous pressure
65
Q

what is venomotor tone?

A

the degree of tension exerted by smooth muscle in the walls of veins (dilation or constriction)

66
Q

how does venomotor tone affect venous return?

A
  • smooth muscle in the walls of veins can either contract or relax in response to SNS input
  • typically venomotor tone increases (contracts) and has 3 effects:
    (1) constriction of veins increases venous pressure = forces blood toward the heart = increased venous return and causes increase in stroke volume
    (2) increased wall tension reduces venous compliance (doesn’t stretch) = raise venous pressure and causes increase in stroke volume
67
Q

how does venous pressure affect mean arterial pressure (MAP)?

A

increases in muscle pump activity, respiratory pump activity, increased blood volume and increased venomotor tone all act to raise venous pressure –> increases venous return to heart –> increase stroke volume –> increase cardiac output –> increase in MAP

68
Q

how is blood flow redirected during exercise?

A

uring exercise, there is a redistribution of blood flow to meet the increased metabolic demands of active tissues:
- skeletal muscle receives a significantly greater proportion of blood flow during exercise compared to rest
- the heart receives a higher absolute amount of blood during exercise, its relative proportion of total cardiac output remains relatively constant
- the brain receives a greater absolute amount of blood during exercise, its relative proportion of total cardiac output decreases slightly. it still receives sufficient blood flow to meet its metabolic demands because it brain cannot tolerate compromised blood supply for an extended period

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