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HemOnc Week 3 > Histology of the Lymphatic System > Flashcards

Histology of the Lymphatic System Flashcards

1
Q

what are the roles of the lymphatic system?

A
  1. Protects the body against foreign pathogens and antigens
  2. Returns lymphatic fluid to the circulatory system
  3. Absorbs fat from the GI tract
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2
Q

what’s the difference between lymphatic system and immune system?

A

lymphatic system is like the battle grounds and the immune system is like the soldiers (WBC)

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3
Q

what are some of the organs and tissues of the lymphatic system?

A

jugular nodes (tons of other nodes)

tonsils

thoracic duct

thymus gland

spleen

bone marrow

lymphatic vessels

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4
Q

what are the three areas where the lymphatic system carries out its immune function?

A
  1. diffuse lymphatic tissue (BALT, GALT, tonsils)
  2. lymph nodes
  3. spleen
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5
Q

what are the subcategories of diffuse lymphatic tissue?

A
  1. BALT = Bronchus-Associated Lymphatic Tissue
  2. GALT = Gastrointestinal- Associated Lymphatic Tissue
  3. Tonsils
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6
Q

what are the two stages of lymphocyte development?

A
  1. immature to mature
  2. naïve to effector

these two stages occur in sequence

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7
Q

what happens during the maturation state of lymphocyte development?

A

involves the development from immature lymphocytes into mature lymphocytes.

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8
Q

what happens during the activation stage of lymphocyte development?

A

requires an encounter with an antigen in order for a lymphocyte to change from inactive or naïve to an active or “effector” lymphocyte

activation is the process in which a lymphocyte becomes capable of producing a specific immune response to a particular antigen or microorganism

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9
Q

what cell does the function of the lymphatic system revolve around?

A

lymphocytes

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10
Q

where do B- lymphocytes mature/develop?

A

bone marrow

even though it is mature, a B-lymphocytes is still naïve, meaning that the B-lymphocyte has not yet encountered an antigen

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11
Q

where are B-lymphocytes activated?

A

B-cells become activated in peripheral lymphatic organs or tissues

even though it is mature in the bone marrow, a B-lymphocytes is still naïve, meaning that the B-lymphocyte has not yet encountered an antigen

mature, naïve B lymphocytes leave the bone marrow via the vascular system and travel to peripheral lymphatic organs, i.e. to the spleen, lymph nodes and diffuse lymphatic tissue, where they are activated into mature, effector B-lymphocytes

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12
Q

how are mature, naive B-cells activated?

A

mature, naïve B lymphocytes are activated by antigens to become mature, “effector” plasma cells or mature, “effector” memory B cells

the site of activation of a mature, naive B into a mature, effector B cell is typically a lymphatic nodule

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13
Q

where are B-cells usually activated?

A

the site of activation of a mature, naive B into a mature, effector B cell is typically a lymphatic nodule

  1. a lymphatic nodule of diffuse lymphatic tissue
  2. a lymphatic nodule of a lymph node
  3. splenic (lymphatic) nodule of the spleen
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14
Q

where do T-lymphocytes mature?

A

they begin their maturation in bone marrow and finish their maturation in the thymus

immature T-lymphocytes leave bone marrow and enter the blood circulation to travel to the thymus, where they develop into mature T-lymphocytes

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15
Q

where do T-cells get activated?

A

mature, naive T-cells become activated into effector T-cells in the peripheral lymphatic organs or issues

mature, naive T lymphocytes leave the thymus and re-enter the bloodstream to travel to diffuse lymphatic tissue, lymph nodes or the spleen

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16
Q

how do T-cells get activated?

A

mature, naive T-lymphocytes do not differentiate into mature, effector T- lymphocytes until after they have encountered an antigen

some T-lymphocytes die without ever encountering an antigen

regardless, T-lymphocytes are prepared for an encounter with an antigen and wait and congregate for this encounter in what is called thymus-dependent areas of the body

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17
Q

what are T cells found in the body?

A
  1. the perimeters of lymphatic nodules of diffuse lymphatic tissue
  2. in the periarterial lymphatic sheath (PALS) of the spleen
  3. in the paracortex of lymph nodes
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18
Q

what’s the difference between where B and T cells get activated?

A

B-lymphocytes become activated in lymphatic nodules of diffuse lymphatic tissue, in lymphatic nodules of lymph nodes, and in lymphatic nodules of the spleen (in splenic nodules)

T-lymphocytes become activated nearby, in the perimeter of lymphatic nodules of diffuse lymphatic tissue, in the deep cortex of lymph nodes, and in periarterial lymphatic sheath of the spleen

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19
Q

what does the thymus look like under a microscope?

A
  1. lots of nodules lining the PERIMETER of the cell
  2. capsule made of connective tissue enclosing the thymus at the periphery
  3. trabeculae
  4. lobules with outer cortex and inner medulla
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20
Q

what are trabeculae?

A

made of connective tissue

internal extensions of the capsule that penetrate the thymus, dividing it into incomplete domains called lobules

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21
Q

what is a unique feature of the thymus when looking at it under microscope?

A

each lobule has an outer cortex and an inner medulla and medullae of adjacent lobules are continuous with each other

this arrangement of lobules that are not entirely self-contained, i.e. this “sharing” of medullae, is a unique feature of the thymus

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22
Q

why is the cortex darker than the medulla in the H&E stain of the thymus?

A

cortex appears purple and darker than the medulla in an H&E stain because it houses a higher concentration of T-lymphocytes

majority of T-lymphocytes die in the process of maturation that occurs from cortex to medulla, and a lower concentration of surviving T-lymphocytes that reach the medulla helps to explain why the medulla shows up as pinker and lighter-colored than the cortex

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23
Q

where do immature T-cells go in the thymus?

A

they first arrive in the most superficial regions of the cortex

the majority of T-lymphocytes die in the process of maturation that occurs from cortex to medulla

in the medulla, the few successful T-lymphocytes that survive thymus maturation become mature, naive T-cells and subsequently re-enter the vascular system

once back in the blood circulation, some T-lymphocytes remain in the blood, while many other T- lymphocytes take up residence in thymic-dependent areas of the body

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24
Q

when is the thymus active?

A

during childhood up to puberty

around the time of puberty, it begins to transform into fatty tissue

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25
Q

what are the goals of thymus maturation of T-cells?

A
  1. To produce a population of T lymphocytes that are capable of interacting with MHC I and MHC II receptors of antigen presenting cells of the immune system
  2. To produce a population of T-lymphocytes that will not kill normal, healthy “self” cells, i.e. cells of its own lineage
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26
Q

what kind of selection happens in the cortex when it involves T-cell maturation?

A

positive selection

epithelioreticular cells are involved in positive selection in the thymic cortex

they present antigens to T- lymphocytes using MHC I and MHC II receptors.

positive selection is the process by which only T-lymphocytes that interact with either MHC I or MHC II receptors survive

T-lymphocytes that are unable to interact with MHC I or MHC II receptors undergo apoptosis

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27
Q

what kind of selection happens in the medulla when it involves T-cell maturation?

A

negative selection

T-cells that survive positive selection cross the corticomedullary junction into the medulla, where they then undergo negative selection

negative selection is the process by which T-lymphocytes again interact with MHC I or MHC II receptors of epithelioreticular cells

But this time epithelioreticular cells present self-peptides to T- lymphocytes using these receptors

T- cells that survive are the ones that recognize the self-peptides as belonging to the self and are NOT activated, while T-lymphocytes that are activated by self-peptides undergo apoptosis

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28
Q

how many T-cells actually undergo full maturation?

A

2%

thymic maturation occurs with an attrition rate of approximately 98%

aka about 98% of T-lymphocytes undergo apoptosis after failing either positive or negative selection and are subsequently phagocytized by macrophages

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29
Q

why is the blood-thymus barrier important in T-lymphocyte maturation?

A

it ensures that developing T-lymphocytes do not encounter a foreign antigen during their maturation

this is critical because if a T-lymphocyte encounters a foreign antigen in the thymus and survives, it will categorize this foreign antigen as a self-peptide and it will not transform from a naïve into an effector T- lymphocyte if it re-encounters that antigen after leaving the thymus

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30
Q

what are Hassall’s corpuscles?

A

aka thymus corpuscle because it’s exclusively in the thymus!

it’s a structure that is located only in the medulla of the thymus and nowhere else in the body

comprised of flattened epithelioreticular cells

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31
Q

what’s the function of Hassall’s corpuscles?

A

its function is unknown

but is thought to release interleukins involved with maturation of T-lymphocytes

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32
Q

what parts of the lymphatic system are encapsulated and which aren’t?

A

lymph nodes, the thymus, and the spleen are encapsulated organs

diffuse lymphatic tissue is not encapsulated

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33
Q

what is diffuse lymphatic tissue made of?

A

consists of a collection of lymphocytes, plasma cells, neutrophils, macrophages and antigen-presenting cells

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34
Q

where is diffuse lymphatic tissue mostly located?

A

it’s concentrated in areas where microorganisms attempt to gain access into the body, i.e. in the skin and in mucosa

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35
Q

what is mucosa?

A

the pink inner lining of the gastrointestinal, respiratory and urogenital tracts

it’s the innermost layer and thus the first layer in contact with pathogens

36
Q

what are the two categories of diffuse lymphatic tissue?

A
  1. Skin-associated lymphatic tissue

2. Mucosa-Associated Lymphatic Tissue (MALT)

37
Q

what are the types of MALT?

A

MALT = Mucosa-Associated Lymphatic Tissue

  1. GALT (we mostly look at this in class)
  2. BALT
  3. genitourinary system
38
Q

what is GALT?

A

GALT = Gastrointestinal-associated lymphatic tissue

GALT is a type of mucosa-associated lymphatic tissue (MALT)

it’s diffuse lymphatic tissue that is located in the mucosa of
the gastrointestinal tract

this type of diffuse lymphatic tissue fully extends from the oral cavity to the anal
canal

39
Q

what is BALT?

A

BALT = Bronchus-Associated Lymphatic Tissue

BALT is a type of mucosa-associated lymphatic tissue (MALT)

it’s a diffuse lymphatic tissue that is located in the mucosa of the
respiratory tract

some of its location overlaps with that of GALT, i.e. in the pharynx through which both food, water and air pass

40
Q

where is BALT found?

A

BALT = Bronchus-Associated Lymphatic Tissue

it’s found along the entire length of the respiratory tract and not only at the level of bronchi

it’s located in the larynx, trachea, in bronchioles and small respiratory airways as well

41
Q

where is diffuse lymphatic tissue of the genitourinary tract found?

A

in the mucosa of genitourinary system

ex. in the mucosae of the reproductive organs, bladder and urethra.

42
Q

what is lymph?

A

a type of bodily fluid that travels in lymphatic vessels and through lymph nodes

43
Q

how does lymph form?

A

lymph originates from extracellular fluid, which is also called interstitial fluid

once interstitial fluid enters a lymphatic capillary, it is called lymph

44
Q

what’s the general flow of lymph through a lymph node?

A

lymph initiates at lymphatic capillaries, flows through lymph nodes and terminates at the venous angles

  1. after being absorbed from interstitium into lymphatic capillaries, lymph travels through afferent lymphatic vessels, through a lymph node and then through efferent lymphatic vessels
  2. next, multiple efferent lymphatic vessels converge to form two main lymphatic vessels: lymphatic duct and thoracic duct
  3. the thoracic duct, after receiving lymph from multiple smaller lymphatic vessels, travels from the thorax to the left side of the neck and drains into the left venous angle

the lymphatic duct collects at the base of the right side of the neck and drains into the right venous angle

lymph re-enters the blood circulation via the venous system at the left and right venous angles

45
Q

what are the two main lymphatic vessels?

A
  1. thoracic duct

2. lymphatic duct

46
Q

what parts of the body is interstitial fluid drained by the thoracic duct?

A

the whole left side of the body plus the right leg

look at the diagram

47
Q

what parts of the body is interstitial fluid drained by the lymphatic duct?

A

the thorax and up of the right side of the body

48
Q

what is the venous angle?

A

there are two veins that meet in the neck on both the right and left sides, in a symmetrical fashion

these two veins are called the subclavian veins and internal jugular veins

the venous angle is the term used to mark the specific location where these two veins meet on each side of the neck

49
Q

where does the thoracic duct drain into?

A

the left venous angle

50
Q

where does the lymphatic duct drain into?

A

the right venous angle

51
Q

what is a lymphatic nodule

A

a lymphatic nodule is smaller than a lymph node and is located inside a lymph node

there are usually multiple lymphatic nodules within a single lymph node

lymphatic nodules are found not only in lymph nodes but also in diffuse lymphatic tissue and in the spleen

52
Q

where are lymph nodes found?

A

they’re optimally situated subcutaneously and near the respiratory, gastrointestinal and genitourinary tracts to facilitate encounter with foreign substances

but lymph nodes are all over your body

53
Q

what is an edema?

A

an abnormal accumulation of interstitial fluid

increased amounts of lymph in lymphatic vessels prevents interstitial fluid from seeping into lymphatic capillaries, resulting in buildup of interstitial fluid or edema

54
Q

what do lymph nodes do?

A

they monitor for foreign substances by filtering lymph

ex. antigens or pathogens such as bacteria, viruses and parasites

55
Q

what could negatively effect the flow of lymph through the lymph nodes?

A

infection, cancer

radiotherapy

fibrosis (scarring) resulting from surgery

all could compromise effective flow of lymph through lymph nodes and lymphatic vessels

56
Q

what’s the structure of a lymph node?

A

go look at the diagram honestly

an external capsule surrounds a lymph node and extends into the substance of the lymph node as trabeculae

trabecular sinuses are spaces on both sides of each trabecula that allow for flow of lymph

right underneath the capsule there is a space called the subcapsular sinus, which allows for flow of lymph

each lymph node has an outer cortex and inner medulla

57
Q

where are lymphatic nodules located in lymph nodes?

A

in the cortex

58
Q

what’s the medulla of a lymph node made of?

A

medullary cords and medullary sinuses

medullary cords are closely packed with plasma cells

medullary sinuses are tortuous, irregularly shaped spaces that allow for the flow of lymph and that also house macrophages and reticular cells

59
Q

what are the medullary cords of the lymph node medulla made of?

A

medullary cords are closely packed with plasma cells

60
Q

what are the medullary sinuses of the lymph node medulla made of?

A

they’re tortuous, irregularly shaped spaces that allow for the flow of lymph

they also house macrophages and reticular cells

61
Q

where are T-cells found in the lymph node?

A

the paracortex

it’s the intermediate area between the cortex and medulla

T-cells that have traveled from the thymus reside in the paracortex

62
Q

where are B-cells found in the lymph node?

A

the cortex and medulla

B-lymphocytes from bone marrow reside primarily in lymphatic nodules of the cortex as well as in medullary cords

63
Q

what are the steps of the flow of lymph through a lymph node?

A
  1. Lymph originates when interstitial fluid first enters the lymphatic vascular network at lymphatic capillaries. Lymphatic capillaries are tributaries for afferent lymphatic vessels
  2. Multiple afferent lymphatic vessels bring lymph to a lymph node’s convex surface
  3. Lymph travels to subcapsular sinuses
  4. Lymph in subcapsular sinuses drains into trabecular sinuses
  5. Trabecular sinuses reach medullary sinuses of the medulla. As lymph in the medulla percolates through medullary
    sinuses, macrophages and reticular cells in the medullary cords sift through the lymph on the lookout for antigens
  6. Multiple medullary sinuses converge together to drain lymph into a single efferent lymphatic vessel that exits the
    lymph node. The efferent lymphatic vessel then usually becomes one of the afferent lymphatic vessels of another lymph node located downstream. All lymph flows through at least one lymph node before returning to the blood circulation at the venous angles in the base of the neck
64
Q

what is the hilum?

A

a structure of the lymph node

the space through which the efferent lymphatic vessel travels, as well as a the lymph node’s blood supply

sometimes it appears as an “indented” area of the lymph node

65
Q

what are the types of lymphatic nodules?

A

primary

secondary

66
Q

what is a primary lymphatic nodule?

A

it’s a concentration of B-lymphocytes that is organized into a uniform sphere

it just looks like a dark purple circle

67
Q

what is a secondary lymphatic nodule?

A

a collection of B-cells that looks like a circular mass

looks like a circle with a white/lighter center and a darker outer purple layer

its central, lighter area is called the germinal center and its surrounding, darker rim is called the mantle

68
Q

what are the parts of a secondary lymphatic nodule?

A

the central, lighter area is called the germinal center – houses naive B-cells

the surrounding, darker rim is called the mantle – houses effector B-cells

69
Q

what’s the relationship between primary and secondary lymphatic nodules?

A

secondary lymphatic nodules are derived from primary lymphatic nodules

primary nodules change to secondary nodules as a result of antigenic challenge

the number of secondary lymphatic nodules in a tissue or organ is directly proportional to the number of antigenic challenges

70
Q

what’s the difference between primary and secondary lymphatic nodules?

A

both are spherical aggregates of mature B-lymphocytes

BUT primary lymphatic nodules contain only mature, naïve B-lymphocytes

whereas secondary lymphatic nodules contain not only mature, naïve B- lymphocytes but also mature, effector B-lymphocytes

71
Q

what do reticular fibers do?

A

they create space to allow for movement of lymph while simultaneously providing rigity to prevent collapse of a lymph node

72
Q

what is the stroma?

A

connective tissue that supports the structure of a lymph node

made up of reticular fibers and reticular cells

73
Q

what are reticular cells?

A

they produce reticular fibers that are relatively thin yet strong and create spaces called sinuses that allow for flow of lymph through the lymph node

74
Q

where are reticular fibers located? what do they do?

A

they’re in the stroma and cortex of lymph nodes – they’re also in bone marrow and the spleen

in the stroma they create spaces called sinuses that allow for flow of lymph through the lymph node

in the cortex they create a strong, mesh-like scaffold—a porous infrastructure—that promotes intercellular interactions by allowing for movement of dendritic antigen-presenting cells and macrophages

75
Q

what’s the capsule made of?

A

collagen!!!!

76
Q

how does the structure of the spleen differ from the thymus and lymph node?

A

it has a capsule and trabelulae just like thymus/lymph node

BUT the spleen lacks a cortex and medulla!

instead it’s divided into red and white pulp

77
Q

what is parenchyma?

A

functional cells

78
Q

what is the parenchyma of the spleen divided into?

A

white and red pulp

white pulp = immune function

red pulp = RBC recycling

white pulp is any nodules!! red pulp is everything else

79
Q

what does white pulp of the spleen do?

A

it monitors for antigens

antigen-presenting cells recognize foreign substances that are in the bloodstream and present them to B- and T-lymphocytes, which in turn mount an immune response to the antigen

80
Q

where are B-cells located in the spleen?

A

in the germinal center and mantle of splenic nodules

81
Q

where are T-lymphocytes located in the spleen?

A

PALs = periartrial lymphatic sheath

82
Q

what is PALS?

A

periarterial lymphatic sheath

the periartierial lymphatic sheath is a ring of T-lymphocytes located immediately around a central artery in areas of white pulp

83
Q

what is a splenic cord?

A

it’s part of the red pulp of the spleen

it’s an “open” area within the spleen where red blood cells, white blood cells, platelets and other components of blood are deposited

the splenic cord is “open” in that it lacks an endothelial wall, like the rest of the circulatory system

macrophages within the splenic cord portion of red pulp recognize and phagocytize aged or damaged red blood cells

84
Q

what are the subdivisions of red pulp?

A
  1. splenic cords

2. splenic sinuses

85
Q

what is the splenic sinus?

A

part of the red pulp of the spleen

it’s a small vein with a discontinuous wall that serves as the start of the spleen’s venous drainage

in order to return to the circulatory system, RBCs must enter a splenic sinus

if an erythrocyte is young and pliable enough to pass into the splenic sinus of red pulp, it bypasses the macrophages of the splenic cords aka it does not stay stuck in the splenic cords to be phagocytized by macrophages.

86
Q

what’s the flow of blood through the spleen?

A

go look at the picture

  1. Splenic artery
  2. Capsular artery
  3. Trabecular artery
  4. Central artery
  5. Splenic cord
  6. Splenic sinus
  7. Trabecular vein
  8. Capsular vein
  9. Splenic vein
87
Q

when going through circulation, how to RBC get back into the blood after being filtered by the spleen?

A

to return to the circulation, RBCs must be malleable enough to be able to squeeze through the slits between endothelial cells that line the splenic sinuses

RBCs more 120 days (4 months) old typically lack a cytoskeleton that is pliable enough to re-enter the circulation via the splenic sinuses

sickle cell also reduced RBC flexibility

HemOnc Week 3 (22 decks)

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