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Microanatomy > MA5 - Blood and Lymphatic Vessels > Flashcards

MA5 - Blood and Lymphatic Vessels Flashcards

1
Q

Describe the organization of blood vessels.

A

blood vessels comprise closed circulatory system

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2
Q

Describe the difference between the left and right sides of the heart in the context of circulation.

A

right side = pulmonary circulation between heart and lungs

left side = systemic circulation between heart and peripheral tissue

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3
Q

What is the function of lympathic vessels?

A

return excess tissue fluid from tissues to blood

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4
Q

Describe how the pressure and rate of blood flow changes while progressing from arteries to capillaries.

A

both pressure and rate of flow drop

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5
Q

Differentiate between elastic arteries and other arterial structures in terms of primary composition.

A

elastic arteries = elastic substance predominates

muscular arteries/small arteries/arterioles = smooth muscle predominates

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6
Q

Which structure regulates the amount of blood entering capillaries?

A

arterioles

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7
Q

Where is total blood vessel area highest?

A

capillary beds

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8
Q

Where is vessel permeability highest?

A

capillary beds

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9
Q

Through which structure do white blood cells migrate to reach tissues?

A

postcapillary venules

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10
Q

What are the three layers of arterial/venous walls?

A

tunica intima

tunica media

tunica adventitia

[from innermost to outermost]

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11
Q

Define tunica intima. (2)

A

innermost layer

includes endothelial lining

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12
Q

Define tunica media. (2)

A

middle layer

rich in smooth muscle (vascular smooth muscle)

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13
Q

Define tunica adventitia. (2)

A

outermost layer

connective tissue layer that provides support

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14
Q

What are the components of the tunica intima? (4)

A

endothelium

basal lamina of endothelium

subendothelial connective tissue [in larger arteries]

internal elastic lamina

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15
Q

Describe the endothelium of the tunica intima.

A

single layer of squamous epithelial cells

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16
Q

Describe the composition of the subendothelial connective tissue in the tunica intima of larger arteries. (7)

A

non-contractile smooth muscle cells

macrophages

lymphocytes

mast cells

type I/III collagen

elastic fibers

ground substance

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17
Q

What is the internal elastic lamina?

A

component of tunica intima that is a fenestrated lamina (layer) of elastin

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18
Q

Where is the internal elastic lamina visible?

A

visible in arteries and larger veins

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19
Q

The internal elastic lamina is synthesized by what cells?

A

synthesized by smooth muscle cells and endothelial cells of tunica intima and tunica media

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20
Q

Generally speaking, what is the function of the tunica media?

A

resists pressure within vessel

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21
Q

What are the components of the tunica media?

A

circular smooth muscle

fenestrated elastic laminae [in elastic arteries]

external elastic lamina

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22
Q

Describe the circular smooth muscle found in the tunica media.

A

circumferentially organized in extracellular matrix of fibers and ground substance

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23
Q

What produces the fibers and ground substance found in the tunica media?

A

vascular smooth muscle cells

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24
Q

What is the most prominent feature of the arterial wall?

A

tunica media

[note: tunica media in veins is much smaller, so it is potentially useful to distinguish between arteries and veins]

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25
Q

What is the external elastic lamina?

A

one or more fenestrated elastic laminae near the border of tunica media/tunica adventitia

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26
Q

Most vascular smooth muscle in arteries is found in what layer?

A

tunica media

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27
Q

What are the components of the tunica adventitia? (7)

A

mostly type I collagen

some elastic fibers organized longitudinally

fibroblasts

macrophages

smooth muscle [in large veins only — organized longitudinally]

vasa vasorum

nervi vascularis

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28
Q

What is the function of the tunica adventitia?

A

provides external mechanical support

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29
Q

What is the most prominent feature of the venous wall?

A

tunica adventitia

[note: this is in contrast to the arterial wall, whose most prominent layer is the tunica media]

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30
Q

What synthesizes the elastic fibers and collagen found in the tunica adventitia?

A

fibroblasts

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31
Q

What is the function of macrophages in the tunica adventitia? (2)

A

maintain tissue homeostasis

serve as immune sentinels

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32
Q

(T/F) Smooth muscle is present in all venous structures.

A

False. Smooth muscle is only present in large veins, and if it is present, is organized longitudinally.

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33
Q

What is the vasa vasorum?

A

plexus of blood vessels that supplies the outer aspects of larger blood vessels (both large veins and arteries)

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34
Q

In which layer of the arterial/venous wall is the vasa vasorum found?

A

usually most abundant in tunica adventitia near the border with the tunica media, but can penetrate into the tunica media

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35
Q

What is the nervi vascularis?

A

plexus of autonomic nerves at border of tunica media and tunica adventitia that regulates contraction of smooth muscle of the tunica media

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36
Q

Where is the nervi vascularis found?

A

border of media/adventitia only in arteries and arterioles

[tip: nervi vascularis is for contraction, and only arteries and arterioles contract]

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37
Q

What kinds of junctions are present in the endothelial cells of blood vessels?

A

zonula adherens

zonula occludens

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38
Q

Describe how endothelial cells can regulate blood pressure and vascular tone.

A

endothelial cells produce paracrine factors that regulate smooth muscle contraction (and therefore regulate blood pressure/vascular tone) — e.g. nitric oxide

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39
Q

Describe the role of endothelial cells in leukocyte extravasation.

A

local inflammation increases expression of adhesion
receptors for leukocytes on luminal surface of endothelial cells

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40
Q

Describe the role of endothelial cells in regulating blood coagulation.

A

endothelial cells release factors that modulate platelet function + clot formation/dissolution

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41
Q

(T/F) Endothelial cells of blood vessels are capable of division.

A

True. They are capable of proliferation.

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42
Q

Endothelial cells are the result of differentiation from

A

vascular stem cells

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43
Q

What stimulates stem cells for the endothelium to proliferate and differentiate?

A

vascular endothelial growth factor (VEGF)

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44
Q

What is vascular endothelial growth factor (VEGF)?

A

growth factor released by hypoxic tissues (wound healing, recovery from ischemia) to promote angiogenesis

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45
Q

What are pericytes?

A

support cells for capillaries and postcapillary venules

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46
Q

List the features of pericytes. (2)

A

have contractile functions required for blood flow

required for angiogenesis

47
Q

How do pericytes change in response to wound repair?

A

pericytes differentiate into myofibroblasts during wound repair

48
Q

Where are pericytes found?

A

bound to/encapsulated by basal lamina of endothelium of tunica intima

49
Q

What structure helps prevent/reduce spontaneous ruptures in capillaries and venules?

A

pericytes

50
Q

Define vasculogenesis.

A

de novo generation of vessels through migration/proliferation of angioblasts, the endothelial cell precursors

51
Q

How does vasculogenesis differ from angiogenesis?

A

vasculogenesis does not require connection to pre-existing vasculature to generate new vessels (build first, then connect)

52
Q

What are the two types of angiogenesis?

A

sprouting angiogenesis

splitting angiogenesis

53
Q

Describe the steps of sprouting angiogenesis. (6)

A

low O2 tension → VGEF production → endothelial cell proliferation → closed-end tubes → closed-end tubes fuse → new vessel

54
Q

What is sprouting angiogenesis?

A

new vessels sprout from existing vessels

55
Q

What is splitting angiogenesis?

A

splitting of existing vessels

56
Q

Describe the steps of splitting angiogenesis.

A

endothelial cells on opposite sides of capillary form contact → existing junctions become leaky → bone marrow-derived myofibroblasts enter → myofibroblasts + pericytes separate connection into two vessels

57
Q

Differentiate between vasculogenesis and angiogenesis in the context of embryonic development.

A

vasculogenesis occurs frequently during embryonic development

angiogenesis is a post-embryonic process

58
Q

Order the arterial structures in terms of diameter, from largest to smallest.

A

elastic arteries > muscular arteries > small arteries > arterioles

59
Q

What is the first structure to receive blood from the heart?

A

elastic arteries

60
Q

Describe the features of elastic arteries.

A

thick tunica intima

thick tunica media with elastic laminae interspersed among smooth muscle

thick adventitia w/ vasa vasorum

61
Q

Describe the features of muscular arteries. (4)

A

thin intima

well-defined internal elastic lamina

many layers of smooth muscle cells

adventitia w/ collagen fibers

62
Q

Describe the features of small arteries. (2)

A

branches of muscular arteries

up to 10 layers of smooth muscle in tunica media

63
Q

How do you differentiate between arterioles, capillaries, venules, muscular venules, and small veins in section?

A

arterioles = lumen 1-2 RBCs wide + media w/ 1-2 layers of smooth muscle

capillaries = lumen 1 RBC wide but no media

venules = lumen 2-4 RBCs wide but no media

muscular venules = lumen >4 RBCs wide + media w/ 1-2 layers of smooth muscle but no tunica adventitia

small veins = lumen >4 RBCs wide + definitve media and adventitia

64
Q

What are metarterioles?

A

branches of arterioles (and metarterioles themselves branch into capillaries)

65
Q

Describe the role of metarterioles in blood flow from the arteriole to the capillary.

A

precapillary sphincter (rings of smooth muscle) located where capillary branches from metarteriole

if sphincter open → blood flows through

if sphincter closed → blood flows through thoroughfare channel connecting metarteriole to venule (bypass capillary)

66
Q

Blood pressure is a combination of what two factors?

A

cardiac output

total peripheral resistance

67
Q

Peripheral resistance is regulated by (3)

A

local factors (nitric oxide)

systemic factors (epinephrine)

autonomic innervation (nervi vascularis)

68
Q

Through which structure do hormones of endocrine glands enter the circulation?

A

capillaries

69
Q

Describe the composition of capillaries.

A

layer of endothelial cells

basal lamina

pericytes

70
Q

What are the three types of capillaries?

A

continuous

fenestrated

discontinuous (a.k.a. sinusoid)

71
Q

Of the three types of capillaries, which is most common?

A

continuous capillaries

72
Q

What junctions are present in continuous capillaries?

A

leaky zonula occludens (important for paracellular movement of nutrients, waste)

73
Q

The leaky zonula occludens junctions between endothelial cells found in continuous capillaries permit the passage of

A

small molecules (nutrients, waste)

**but not protein

74
Q

Describe how fluid moves on the arterial side of the capillary bed.

A

on arterial side, hydrostatic pressure > colloidal pressure, so fluid leaves the arterial side, allowing for delivery of nutrients/O2 to tissue

75
Q

Describe how fluid moves on the venous side of the capillary bed.

A

on venous side, colloidal pressure > hydrostatic pressure so fluid enters venous side, allowing for removal of waste products from tissue

76
Q

The leaky zonula occludens junctions in continuous capillaries permit the passage of small molecules but not protein. How does protein cross endothelial cells?

A

proteins and lipoproteins cross by transcytosis via numerous caveolae and pinocytotic vesicles

77
Q

Most continuous capillaries have leaky zonula occludens junctions, but there are some exceptions. What are the exceptions?

A

capillaries of nervous system and thymic cortex have very tight zonula occludens (i.e. not leaky) and therefore do not permit any movement via paracellular pathway

78
Q

What are the characteristics of fenestrated capillaries?

A

presence of 50-100 nm fenestrations (holes in endothelium) that allow small molecules and proteins to pass through

79
Q

Fenestration in capillaries commonly replaces what transport mechanism?

A

fenestration commonly replaces transcytosis (and fenestration increases protein flux by ~100 fold)

80
Q

In fenestrated capillaries, how does the basal lamina modulate protein flux?

A

basal lamina repels negatively charged proteins

81
Q

Give three examples of tissues/organs in which fenestrated capillaries would be found.

A

endocrine glands

kidney

liver

82
Q

Describe the features of discontinuous/sinusoid capillaries. (4)

A

gaps between endothelial cells for protein flux

discontinuous basal lamina

fast rate of exchange

conform to underlying parenchyma

83
Q

Which of the three types of capillaries have the fastest rate of exchange?

A

discontinuous/sinusoid — the fast rate of exchange means there is reduced ability to regulate protein movement

84
Q

Describe the features of venules.

A

continuous basal lamina

pericytes

no smooth muscle

85
Q

Describe the role of junctions in venules.

A

junctions become leaky in response to inflammatory mediators such as histamine

86
Q

Describe the relationship between venules and leukocytes.

A

venules are the sites where leukocytes bind (margination) and extravasate (diapedesis) out of blood circulation

87
Q

Differentiate between muscular venules, small veins, and medium veins.

A

muscular venules = receive blood from postcapillary venules

small veins = receive blood from muscular venules

medium veins = receive blood from small veins

88
Q

How are muscular venules, small veins, and medium veins similar in section?

A

all have 1-2 layers of smooth muscle in media

89
Q

Describe the characteristics of large veins.

A

2-15 layers of smooth muscle in media

thin intima

thin media

thick adventitia

longitudinally-oriented smooth muscle in adventitia

90
Q

Large veins are also called

A

hanging veins

91
Q

What are valves?

A

paired, thin flaps of tunica intima that project into lumen of vessel

92
Q

Valves are reinforced by

A

elastic fibers

collagen fibrils

93
Q

Describe the function of valves.

A

flip back and close lumen to prevent backflow away from heart

94
Q

(T/F) The lymphatic system is bidirectional.

A

False. The lymphatic system is unidirectional.

95
Q

What is the function of the lymphatic system?

A

removes excess fluid from tissues

96
Q

Describe the order of structures in the lymphatic system. (4)

A

fluid goes through lymphatic capillaries → collecting vessels → lymphatic ducts → subclavian veins

97
Q

Describe the characteristics of lymphatic capillaries. (4)

A

discontinuous endothelium

discontinuous basement membrane

lack pericytes

anchoring microfibrils

98
Q

Describe the function of anchoring microfibrils in lymphatic capillaries. (2)

A

maintain openness of capillaries

tissue swelling pulls on microfibrils to help open gaps between endothelial cells to facilitate intravasation of fluid

99
Q

Describe the characteristics of collecting vessels. (4)

A

have colloidal material

thin walls compared to lumen size

valves to prevent backflow of lymph

small amount of spiraling muscle

100
Q

What is the function of spiraling muscle in collecting vessels/thoracic duct?

A

contractions of spiraling muscle drive lymph toward lymphatic ducts

101
Q

Describe the characteristics of the thoracic duct. (3)

A

3-layered wall structure

spiraling smooth muscle in media

thick adventitia compared to media/intima

102
Q

Describe how atherosclerosis arises.

A

buildup of lipid (from VLDL, LDL) in tunica intima that can result in fatty plaque

103
Q

Describe the resulting events when lipids build up in the intima of arteries. (9)

A

macrophages and SMCs modify/phagocytose LDL → macrophages converted into foam cells → foam cells die → resulting hypoxia promotes angiogenesis → weakening of vessel wall → expansion of necrotic core → plaque rupture → thrombosis → infarction

104
Q

How do lipids gain access to the intima of an artery in the first place?

A

transcytosis

leaky tight junctions weakened by oscillatory blood flow

105
Q

What causes aneurysms?

A

weakining of tunicae in wall, allowing bulge/balloon to extend from vessel

106
Q

(T/F) Aneurysms are restricted to arteries.

A

False. They can occur in any vessel, but are most common in arteries.

107
Q

What are three risk factors for aneurysms?

A

atherosclerosis

smoking

diabetes

108
Q

What causes hypertension?

A

increased systemic resistance at level of small arteries and especially arterioles

109
Q

Why is hypertension a significant risk factor for heart failure?

A

hypertension promotes ventricular hypertrophy (stiffens ventricular wall through vibrosis) which disrupts connections between cardiomyocytes and leads to arrhythmias

110
Q

Describe how aging leads to changes in large/medium arteries.

A

aging causes diameter of large/medium arteries to increase

makes walls thicker/stiffer (more type I collagen replacing elastic laminae)

111
Q

Describe how aging leads to changes in small arteries/arterioles.

A

become more tortuous (twisty)

112
Q

Describe how aging leads to changes in all arteries.

A

walls have dimished compliance → higher systolic BP

113
Q

Describe the relationship between aging and nitric oxide. (3)

A

aging → reduction in nitric oxide → BP rises to compensate

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