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HHP > Systemic Circulation > Flashcards

Systemic Circulation Flashcards

1
Q

Which two circuits go into / out of the heart

A

Pulmonary

Systemic

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2
Q

What are the parts of the peripheral vasculature (organs it supplies) and in order top to bottom as they are arranged in parallel

A
  • lungs

1) brain
2) heart
3) liver and GI tract
4) kidneys
5) skeletal muscle
6) skin
7) skeleton, fat, other tissues

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3
Q

As blood rejoins from different pathways to get back to the heart what implications does this have

A

Implications for resistance to blood flow itself

And pressure within different blood vessels

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4
Q

What happens at rest vs at exercise in peripheral vasculature supply

A
  • %s of blood flow change

- gross quantities of blood (litres/minute) going through each organ changes

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5
Q

What happens to blood flow to the brain during exercise

A
  • decreases from 13-15% of normal blood flow
  • to just 3-4% during exercise

BUT

actual amount of blood going to the brain increases slightly because the brains blood supply has to be maintained if exercising or resting

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6
Q

What happens to blood flow to the liver and GI tract and to the kidneys during exercise

A
  • massive decrease compared to % of normal blood flow (around 45% to them at rest drops to 9% during exercise)
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7
Q

What happens to blood flow to the skeletal muscles and skin during exercise

A
  • usually 25%

- increases to 85% in exercise

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8
Q

Which vessels are in the systemic system

A 
Aorta 
Arteries
Arterioles
Capillaries
Venules 
Veins 
Vena cava
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9
Q

Which vessels are in the pulmonary system

A 
Arteries
Arterioles
Capillaries
Venules
Veins
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10
Q

Which vessels are in the heart

A

Atria

Ventricles

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11
Q

What is the number of great vessels vs numbers for distributing vessels (arteries arterioles capillaries)

And what is this mirrored by

A

Great vessels = very small numbers just 1 or 2

Others = large numbers (increase by 3 orders of magnitude)

Mirrored by total cross sectional area / luminal space (2.8cm^2 in aorta compared to 1357 for all capillaries)

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12
Q

Which vessels have the largest total cross sectional area for luminal space

A

CAPILLARIES

  • even though individual capillaries are tiny there are loads of them
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13
Q

Where is the majority of blood volume at any given moment

A

In venous circulation (67%)

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14
Q

What is the rship between velocity of blood flow and total cross sectional area of vessels

A
  • roughly inversely proportional
  • increase in cross sectional area going into capillaries (as a whole not individual capillaries) is opposed by a decrease in velocity of blood flow
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15
Q

Explain the graphs for total cross sectional area vs velocity of blood flow

A

1) high velocity in aorta
2) velocity decreases rapidly through arterioles
3) velocity at lowest when comes to capillaries
4) velocity increase through venules, veins and vena cava BUT not as rapidly (only to half of level of when in aorta)

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16
Q

What is the rship between cross sectional area and blood volume in each vessel

A

Aorta - area no volume
Arteries - larger volume than area
Arterioles - area no volume

Capillaries - much larger area than volume

Veins - almost the same
Vena cava -area no volume

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17
Q

What are the 3 layers of blood vessels and explain them

A

1) tunica adventitia - outermost layer, made of connective tissue (collagen fibres)
2) tunica media - middle layer, contains smooth muscles + elastin fibres
3) tunica intima - innermost later, layer of endothelium (squamous epithelium)

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18
Q

What are the exceptions to the standard 3 blood vessels layers

A

VERY SMALL VESSELS

Ie capillaries

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19
Q

What is the layer structure In capillaries

A
  • ONLY endothelial layer (effectively tunica intima though not called this) with thin basement membrane of connective tissues surrounding it
  • smaller and simpler than large vessels
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20
Q

What is the structure of elastic arteries (ie aorta and it’s branches)

A
  • large diameter (wide large internal diameter of 4mm)
  • low resistance pathways
  • so can carry large amounts of blood rapidly with little resistance throughout body
  • so blood distributed rapidly and efficiently
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21
Q

What is the structure of the tunica media in elastic arteries

A
  • large amounts of elastin fibres
  • purpose = stretch, withstand, smooth out large pressure fluctuations (due to pulses of blood coming out of contracting heart)
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22
Q

Describe muscular arteries

A
  • deliver blood to specific organs (ie hepatic artery)

- diameters of 0.3-10mm

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23
Q

What is the structure of the tunica media in muscular arteries

A
  • less elastin fibres and more smooth muscle cells so vessel is less distensible (able to vasoconstrict/stress/stretch and cope with that)
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24
Q

Where are muscular arteries most active

What does this mean

A
  • In vasoconstriction
  • action of vascular smooth muscle cells
  • so able to reduce pressure somewhat
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25
Q

What is the role of arterioles and what is their structure

A
  • carry out much vasoconstriction
  • deliver blood directly to capillary beds
  • small (10um - 0.3mm diameter) and this vessel lumen diameter regulates blood flow to the capillary beds responding to neural stimuli and local chemical influences
  • tunica media almost entirely smooth muscles (little-no elastin)
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26
Q

What is the diameter size of capillaries and what 2 basic types of capillaries exist

A
  • 8-10um

1) continuous capillaries
2) fenestrated capillaries

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27
Q

Describe continuous capillaries

A
  • most common type
  • endothelial cells have tight junctions between them
  • there are narrow intercellular clefts (slice through wall of capillary plasma space)
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28
Q

What does the narrow intracellular clefts in continuous capillaries allow

A
  • limited passage of fluid and small solutes

- between the plasma space inside the vessel lumen and the extracellular and vice versa

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29
Q

Describe fenestrated capillaries

A
  • some endothelial cells in these have oval shaped pores (FENESTRATIONS) which act as wide intercellular gaps
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30
Q

What do the fenestrations in fenestrated capillaries allow

A
  • makes them much more permeable to fluids and small solutes
  • allow much easier passage of small cells (ie WBCs), fluids and other molecules (ie protein)
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31
Q

Where are fenestrated capillaries found most often

A
  • where active absorption of filtrate formation occurs (ie small intestine, kidneys)
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32
Q

Describe capillary beds

A
  • broad structure
  • interwoven branching networks of capillaries
  • TRUE CAPILLARIES are the exchange vessels (10-100 per bed)
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33
Q

What is flow through capillary beds called

A

MICROCIRCULATION

34
Q

What occurs in most capillary beds and when is this more likely

A
  • A VASCULAR SHUNT

- occurs when tissue is inactive or not a large blood flow is needed to a particular area at a given time

35
Q

What is a vascular shunt

A
  • metarteriole (base of vessel running through the centre of the capillary bed) BYPASSES the true capillaries either side of it
  • happens due to stimulation in vascular sphincter muscles which close either side of the metarteriole
  • so significantly reduces blood flow passing out into the capillary bed
36
Q

What happens when a tissue is more active

A
  • vascular sphincter muscles relax
  • more blood can feed into true capillaries (capillary bed) from the metarteriole
  • increase in blood flow passing out into capillary bed
37
Q

What regulates capillary flow

A

PRECAPILLARY SPHINCTER

  • ring of smooth muscle fibres around the neck of the tiny vessels
38
Q

Describe venules

A
  • formed when capillaries come out of capillary bed and unite
  • diameters = 8-100um
  • walls of smaller venules only consist of epithelium so barely distinguishable from capillaries in terms of structure
  • larger venules = sparse tunica media (thin muscular in middle) and tunica adventitia (collagen layer on outside)
39
Q

Describe veins

A
  • have the 3 distinct tunicae
  • thinner walls and larger lumens to their corresponding arteries
  • enables them to accommodate large blood volume
  • valves
40
Q

What type of vessel are veins

A

CAPACITANCE VESSELS

41
Q

Why do veins have valves

A
  • low pressure blood in venous system

- valves ensure blood continues to flow toward the heart (prevent backflow) and does not sit stagnant on the venous side

42
Q

Which cells are at a consistent level in all vessels

A

ENDOTHELIAL CELLS

43
Q

What is the presence of ELASTIC FIBRES in each vessel

A
  • highly expressed in aorta
  • then progressively less on arterial side (same for collagen fibres on arterial side)
  • none in capillaries or venules
  • present in veins and vena cava but low levels
44
Q

Which vessels only contain endothelial cells

A

True capillaries

Venules

45
Q

List each vessel according to its lumen diameter from biggest to smallest

A 
1- Vena cava (2mm)
2- aorta (12mm)
3- vein (2.5mm)
4- medium artery (2mm)
5- arterioles and precapillary sphincter (both 15um)
7- venules (10um)
8- true capillaries (3um)
46
Q

List each vessel according to its wall thickness from biggest to smallest

A 
1- aorta (2mm)
2- vena cava (1.5mm) 
3- medium artery (1mm)
4- vein (0.5mm)
5- precapillary sphincter (30um)
6- arterioles (20um)
7- venule (2um)
8 - capillaries (1um)
47
Q

What happens with systemic blood pressure as it moves from left ventricle through the systemic circulation to the right atrium

A

Decreases (blood flows along its pressure gradient from high to low)

The closer blood is to the pump (left ventricle, the greater the pressure)

Starts at 130mmHg in left ventricle
Declines steadily through the systemic circulation
Decreases to 3 mmHg in right atrium (once it reaches the heart again)

48
Q

What is fluid driven through

A

Circuit of closed vessels

Operates under pressure

49
Q

When does pressure result

A

When blood flow is opposed by resistance (ie of blood was pumped out of heart into open air it would be very low pressure)

50
Q

Where does the steepest drop in systemic blood pressure occur

A

In the arterioles

  • steepest drop from 90-35
  • they offer greatest resistance to flow
  • pulsatility is eliminated and average pressure reduced at its greatest rate
51
Q

What is blood pressure in the aorta

A

120/80 BP

52
Q

What happens to blood as it progresses through systemic circulation

A
  • gets less pulsation
  • average mean arteriole pressure falls gradually
  • narrowing of blood pressure range and start of reduction in maximum amount of pressure
53
Q

What does arterial blood pressure reflect

A

1) compliance of elastic arteries near heart (their ability to distend (stretch) in response to pressure)
2) volume of blood forced into arteries at particular point in time

54
Q

How does volume of blood forced into arteries vary over the course of the cardiac cycle

A
  • max amounts at beginning of systole
  • none forced out into arteries during diastole
  • BC aortic valve is closed and left ventricle is relaxed
  • result = variation over course of cardiac cycle and arterial blood pressure
  • means blood flow in major arteries is very pulsatile
55
Q

What is systolic pressure (BPs)

A

Highest arterial pressure during systolic phase

120mmHg

56
Q

What is diastolic pressure (BPd)

A

Lowest arterial pressure during diastolic phase

80mmHg

57
Q

What is pulse pressure and give its equation

A

Gap between systolic and diastolic pressure

Pulse pressure equals BPs - BPd

So in general -> 120 - 80 = 40mmHg

58
Q

What is aortic stenosis

A
  • thickening / narrowing of valve
  • so valve doesn’t open as easily / efficiently as normally would
  • with course of arterial blood pressure we see blunting on top of curve
59
Q

What other condition does aortic stenosis cause

A

VENTRICULAR HYPERTROPHY

  • enlargement of the heart
  • due to increased work the left ventricle is doing
60
Q

What is aortic incompetence

A
  • enlargement of the heart as aortic regurgitation
  • valve opens fine during systole but flops backward during diastole
  • so blood leaks backwards into ventricles during diastole

So we still see a peak systolic pressure comparable to what is seen normally
BUT diastolic blood pressure is massively lower (aortic valve should be shut as ventricle relaxes and is filling from the atrium)

61
Q

What is the equation for MAP

A

BPd + (pulse pressure/3)

Typically 80 + (40/3) = 93.3mmHg

62
Q

What process is used clinically to measure blood pressure

A

SPHYGMOMANOMETRY

63
Q

How does SPHYGMOMANOMETRY change the measurement of blood pressure and allow it to be measured

A

1) distensible air cuff inflated to a pressure about the systolic and diastolic blood pressure
2) artery is occluded so smooth laminar flow of blood through it is interrupted
3) turbulent flow in the compressed artery causes audible vibrations (KOROTKOFF SOUNDS)

64
Q

What happens to pressure when the pressure in the cuff decreases

A
  • when pressure in cuff reaches 120mmHg systolic pressure is the same and sounds begin
  • when pressure in cuff reaches 80mmHg diastolic pressure is the same and sounds end
65
Q

Why is there no sound when pressure in the cuff is higher than peak systolic pressure

A

No blood can get through the vessel (it is completely occluded by pressure in the cuff)

66
Q

How does blood make the korotkoff sounds

A
  • pressure reduced to below systolic bp
  • blood can get through but only when pressure high enough to push vessel open
  • allows blood through (opens during systole)
  • during diastole pressure isn’t enough so vessel closes again
  • so get pulsatile sound of turbulent blood flow in compressed artery (this makes the sound)
67
Q

Why do korotkoff sounds stop when the pressure in the cuff becomes lower than diastolic bp

A
  • background pressure is keeping the vessel open against much lower pressure in cuff
  • smooth laminar blood flow in non compressed artery makes no sounds
68
Q

What happens to blood pressure in the capillaries

A
  • drops as go from arterial end (40mmHg) to venous end (20mmHg) of capillary bed
69
Q

Why is pressure in capillary beds so important

A

1) has to be low or the fragile capillary walls will rupture
2) must be closely controlled to regulate amount of filtration of solute out into the interstitial space surrounding the capillaries in tissues

70
Q

What happens to venous blood pressure

A

Stays steady during the cardiac cycle (no longer pulsatile)

71
Q

What is the pressure gradient across
A) whole venous system
B) whole arterial system

A

A) 20mmHg (goes to essentially 0 over progression through the venous system)
B) 60mmHg

72
Q

Why do we need functional adaptations to promote adequate return of blood through the venous side

A
  • venous blood pressure too low to ensure blood gets back to heart at same rate as is pumped out into systemic arterial system
  • if it were a purely pressure based system it would not be sustainable after a few heart beats
73
Q

What adaptation do we have

A

THE RESPIRATORY PUMP

74
Q

What is the role of the RESPIRATORY PUMP in driving venous return

A

1) inspiration increases abdominal pressure so compresses abdominal veins
2) venous valves prevent backflow so forcing blood towards heart
3) so higher pressure in abdomen means abdominal veins are compressed pushing blood through (only goes in 1 direction - to the heart)
4) inspiration reduces pressure in thoracic cavity so thoracic veins expand aiding movement of blood towards right atrium

75
Q

What factor affects venous return

A

THE SKELETAL MUSCLE PUMP

76
Q

How does THE SKELETAL MUSCLE PUMP affect venous return

A

1) when skeletal muscles contract (especially those in legs) they compress the deep veins propelling blood towards heart
2) bc of valve action backflow is prevented (valves distal to point of compression are closed by backflowing blood)

SO OVERALL… compression of skeletal muscle, pressure higher in veins centre, valve forced shut
Valve shut in one direction, pressure pushes it open so venous blood propelled back towards heart

77
Q

Which veins are mostly compressed by the skeletal muscle pump

A

Deep veins deep within limbs (leg most pertinently)

Superficial veins on surface ARE NOT compressed

78
Q

So what does the circulatory system consist of

A

1) pump (the heart)
2) series of distributing + collecting tubes (blood vessels)
3) extensive system of thin vessels (capillaries)
4) rapid exchange of substances between tissues and blood (O2, CO2, nutrients, waste products)

79
Q

What is found particularly in the great vessels (ie aorta, vena cava)

A

COLLAGEN

80
Q

So during sphygmomanometry what does the appearance of korotkoff sounds represent

A

Systolic blood pressure

81
Q

Where does the greatest drop in blood pressure pulsatility occur

A

IN ELASTIC ARTERIES (aorta, major arteries)

82
Q

What does the skeletal muscle pump prevent

A

Inadequate return of blood to the heart

HHP (10 decks)

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