Histology of the Lymphatic System

Question 1

what are the roles of the lymphatic system?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

jugular nodes (tons of other nodes)

tonsils

thoracic duct

thymus gland

spleen

bone marrow

lymphatic vessels

Question 4

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

Answer 4

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

Question 5

what are the subcategories of diffuse lymphatic tissue?

Answer 5

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

Question 6

what are the two stages of lymphocyte development?

Answer 6

1. immature to mature
2. naïve to effector

these two stages occur in sequence

Question 7

what happens during the maturation state of lymphocyte development?

Answer 7

involves the development from immature lymphocytes into mature lymphocytes.

Question 8

what happens during the activation stage of lymphocyte development?

Answer 8

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

Question 9

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

Answer 9

lymphocytes

Question 10

where do B- lymphocytes mature/develop?

Answer 10

bone marrow

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

Question 11

where are B-lymphocytes activated?

Answer 11

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

Question 12

how are mature, naive B-cells activated?

Answer 12

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

Question 13

where are B-cells usually activated?

Answer 13

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

Question 14

where do T-lymphocytes mature?

Answer 14

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

Question 15

where do T-cells get activated?

Answer 15

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

Question 16

how do T-cells get activated?

Answer 16

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

Question 17

what are T cells found in the body?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

what does the thymus look like under a microscope?

Answer 19

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

Question 20

what are trabeculae?

Answer 20

made of connective tissue

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

where do immature T-cells go in the thymus?

Answer 23

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

Question 24

when is the thymus active?

Answer 24

during childhood up to puberty

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

how many T-cells actually undergo full maturation?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

what are Hassall's corpuscles?

Answer 30

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

Question 31

what's the function of Hassall's corpuscles?

Answer 31

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

Question 32

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

Answer 32

lymph nodes, the thymus, and the spleen are encapsulated organs diffuse lymphatic tissue is not encapsulated

Question 33

what is diffuse lymphatic tissue made of?

Answer 33

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

Question 34

where is diffuse lymphatic tissue mostly located?

Answer 34

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

Question 35

what is mucosa?

Answer 35

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

Question 36

what are the two categories of diffuse lymphatic tissue?

Answer 36

1. Skin-associated lymphatic tissue | 2. Mucosa-Associated Lymphatic Tissue (MALT)

Question 37

what are the types of MALT?

Answer 37

MALT = Mucosa-Associated Lymphatic Tissue 1. GALT (we mostly look at this in class) 2. BALT 3. genitourinary system

Question 38

what is GALT?

Answer 38

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

Question 39

what is BALT?

Answer 39

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

Question 40

where is BALT found?

Answer 40

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

Question 41

where is diffuse lymphatic tissue of the genitourinary tract found?

Answer 41

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

Question 42

what is lymph?

Answer 42

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

Question 43

how does lymph form?

Answer 43

lymph originates from extracellular fluid, which is also called interstitial fluid once interstitial fluid enters a lymphatic capillary, it is called lymph

Question 44

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

Answer 44

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

Question 45

what are the two main lymphatic vessels?

Answer 45

1. thoracic duct | 2. lymphatic duct

Question 46

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

Answer 46

the whole left side of the body plus the right leg look at the diagram

Question 47

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

Answer 47

the thorax and up of the right side of the body

Question 48

what is the venous angle?

Answer 48

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

Question 49

where does the thoracic duct drain into?

Answer 49

the left venous angle

Question 50

where does the lymphatic duct drain into?

Answer 50

the right venous angle

Question 51

what is a lymphatic nodule

Answer 51

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

Question 52

where are lymph nodes found?

Answer 52

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

Question 53

what is an edema?

Answer 53

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

Question 54

what do lymph nodes do?

Answer 54

they monitor for foreign substances by filtering lymph ex. antigens or pathogens such as bacteria, viruses and parasites

Question 55

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

Answer 55

infection, cancer radiotherapy fibrosis (scarring) resulting from surgery all could compromise effective flow of lymph through lymph nodes and lymphatic vessels

Question 56

what's the structure of a lymph node?

Answer 56

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

Question 57

where are lymphatic nodules located in lymph nodes?

Answer 57

in the cortex

Question 58

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

Answer 58

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

Question 59

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

Answer 59

medullary cords are closely packed with plasma cells

Question 60

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

Answer 60

they're tortuous, irregularly shaped spaces that allow for the flow of lymph they also house macrophages and reticular cells

Question 61

where are T-cells found in the lymph node?

Answer 61

the paracortex it's the intermediate area between the cortex and medulla T-cells that have traveled from the thymus reside in the paracortex

Question 62

where are B-cells found in the lymph node?

Answer 62

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

Question 63

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

Answer 63

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

Question 64

what is the hilum?

Answer 64

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

Question 65

what are the types of lymphatic nodules?

Answer 65

primary secondary

Question 66

what is a primary lymphatic nodule?

Answer 66

it's a concentration of B-lymphocytes that is organized into a uniform sphere it just looks like a dark purple circle

Question 67

what is a secondary lymphatic nodule?

Answer 67

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

Question 68

what are the parts of a secondary lymphatic nodule?

Answer 68

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

Question 69

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

Answer 69

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

Question 70

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

Answer 70

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

Question 71

what do reticular fibers do?

Answer 71

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

Question 72

what is the stroma?

Answer 72

connective tissue that supports the structure of a lymph node made up of reticular fibers and reticular cells

Question 73

what are reticular cells?

Answer 73

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

Question 74

where are reticular fibers located? what do they do?

Answer 74

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

Question 75

what's the capsule made of?

Answer 75

collagen!!!!

Question 76

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

Answer 76

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

Question 77

what is parenchyma?

Answer 77

functional cells

Question 78

what is the parenchyma of the spleen divided into?

Answer 78

white and red pulp white pulp = immune function red pulp = RBC recycling white pulp is any nodules!! red pulp is everything else

Question 79

what does white pulp of the spleen do?

Answer 79

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

Question 80

where are B-cells located in the spleen?

Answer 80

in the germinal center and mantle of splenic nodules

Question 81

where are T-lymphocytes located in the spleen?

Answer 81

PALs = periartrial lymphatic sheath

Question 82

what is PALS?

Answer 82

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

Question 83

what is a splenic cord?

Answer 83

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

Question 84

what are the subdivisions of red pulp?

Answer 84

1. splenic cords | 2. splenic sinuses

Question 85

what is the splenic sinus?

Answer 85

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.

Question 86

what's the flow of blood through the spleen?

Answer 86

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

Question 87

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

Answer 87

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